Extreme Brightness Temperatures and Refractive Substructure in 3C273 with RadioAstron

NASA Astrophysics Data System (ADS)

Johnson, Michael D.; Kovalev, Yuri Y.; Gwinn, Carl R.; Gurvits, Leonid I.; Narayan, Ramesh; Macquart, Jean-Pierre; Jauncey, David L.; Voitsik, Peter A.; Anderson, James M.; Sokolovsky, Kirill V.; Lisakov, Mikhail M.

2016-03-01

Earth-space interferometry with RadioAstron provides the highest direct angular resolution ever achieved in astronomy at any wavelength. RadioAstron detections of the classic quasar 3C 273 on interferometric baselines up to 171,000 km suggest brightness temperatures exceeding expected limits from the “inverse-Compton catastrophe” by two orders of magnitude. We show that at 18 cm, these estimates most likely arise from refractive substructure introduced by scattering in the interstellar medium. We use the scattering properties to estimate an intrinsic brightness temperature of 7× {10}12 {{K}}, which is consistent with expected theoretical limits, but which is ˜15 times lower than estimates that neglect substructure. At 6.2 cm, the substructure influences the measured values appreciably but gives an estimated brightness temperature that is comparable to models that do not account for the substructure. At 1.35 {{cm}}, the substructure does not affect the extremely high inferred brightness temperatures, in excess of {10}13 {{K}}. We also demonstrate that for a source having a Gaussian surface brightness profile, a single long-baseline estimate of refractive substructure determines an absolute minimum brightness temperature, if the scattering properties along a given line of sight are known, and that this minimum accurately approximates the apparent brightness temperature over a wide range of total flux densities.

Adventures in order and chaos : a scientific autobiography

NASA Astrophysics Data System (ADS)

Contopoulos, George

The field of Order and Chaos had a remarkable expansion in the last 50 years. The main reason was the use of computers, and the development of new theoretical methods that we call now 'the theory of chaos'. The author describes this fascinating period in a relaxed and sometimes humorous autobiographical way. He relates his interactions with many people in dynamical astronomy and he quotes several anecdotes from these interactions. He refers also to his experiences when he served in various international positions, such as general secretary of the IAU and chairman of the journal Astronomy and Astrophysics. In recent years the theory of chaos has been extended to new areas, like relativity, cosmology and quantum mechanics and it continues expanding in almost all branches of physics. The book describes many important ideas in this field in a simple way. It refers also to problems of more general interest, like writing papers and giving lectures and the interaction of authors and referees. Finally it gives some useful prospects for the future of dynamical astronomy and related fields. George Contopoulos, PhD U.Athens1953; Professor of Astronomy U.Thessaloniki 1957-75; U.Athens 1975-96; Emeritus 1996-; Member, Academy of Athens 1997-. Visiting Professor Yale U., Harvard U., MIT, Cornell U., U.Chicago, U.Maryland, U. Florida, Florida State U., U. Milan; Res. Associate, Yerkes Obs., Inst.Adv.Study Princeton, Inst.Space Studies, Goddard Flight Center, Columbia U., ESO. Author or Editor of 15 books, and about 250 papers on Galactic Dynamics, Relativity and Celestial Mechanics. Positions held: Gen.Secretary of the IAU; Director General Nat.Obs.of Greece, Pres.Hellenic Astron.Soc.; Nat.Representative of Greece in NATO, etc. Distinctions: Amer. Astron.Soc. Brouwer Prize; U.Chicago, Honorary Doctor's Degree; IAU, Pres. Commission 33 (Galaxy); Member Academia Europaea; Associate Royal Astron. Soc.; Chairman of the European Journal "Astronomy and Astrophysics"; Assoc. Editor of "Cel. Mech. Dyn. Astron."; Over 4500 citations and 300 acknowledgements.

Hydrodynamic simulations of moonlet induced propellers and the size of Blériot

NASA Astrophysics Data System (ADS)

Seiss, Martin; Albers, Nicole; Sremcevic, Miodrag; Schmidt, Jürgen; Salo, Heikki; Hoffmann, Holger; Spahn, Frank

2016-10-01

Small moons embedded in Saturn's rings can cause S-shaped density structures in their close vicinity called propellers. These structures have been predicted on base of a combined model involving gravitational scattering of test particles (creating the structure) and diffusion (smearing out the structure, see Spahn and Sremčević (2000, Astron. Astrophys.) and Sremčević et al. (2002,MNRAS)). The propeller model was confirmed later by N-body simulations, which additionally show the appearance of moonlet wakes adjacent to the S-shaped gaps (Seiß et al., 2005, GRL; Lewis and Stewart, 2009, Astron. J.). It was a great success of the Cassini mission when propellers were detected in the data of the ISS (Tiscareno et al., 2006, Nature; Sremčević et al., 2007, Nature; Tiscareno et al., 2008, Astron. J. and 2010, ApJL) and UVIS (Baillié et al., 2013) instruments.Here we present isothermal hydrodynamic simulations of propellers as a further development of the original model (Spahn and Sremčević, 2000, Astron. Astrophys.) where gravitational scattering and diffusion had to be treated separately. We confirm the correctness of the predicted scaling laws for the radial and azimuthal extent of propellers and show that the analytical solution by Sremčević et al. (2002, MNRAS) can be fitted to the azimuthal profile. Furthermore, we show that this new approach is in a good agreement with N-body simulations performed with parameters suitable for the A-ring. Finally, we present simulation results of the giant propeller Blériot and fit them to optical depth profiles gathered by the UVIS experiment aboard of the spacecraft Cassini. The fits are consistent using 600 m for the Hill radius of the moonlet and 350 cm2/s for the kinematic shear viscosity.

Recursive computation of mutual potential between two polyhedra

NASA Astrophysics Data System (ADS)

Hirabayashi, Masatoshi; Scheeres, Daniel J.

2013-11-01

Recursive computation of mutual potential, force, and torque between two polyhedra is studied. Based on formulations by Werner and Scheeres (Celest Mech Dyn Astron 91:337-349, 2005) and Fahnestock and Scheeres (Celest Mech Dyn Astron 96:317-339, 2006) who applied the Legendre polynomial expansion to gravity interactions and expressed each order term by a shape-dependent part and a shape-independent part, this paper generalizes the computation of each order term, giving recursive relations of the shape-dependent part. To consider the potential, force, and torque, we introduce three tensors. This method is applicable to any multi-body systems. Finally, we implement this recursive computation to simulate the dynamics of a two rigid-body system that consists of two equal-sized parallelepipeds.

PKS 1954-388: RadioAstron Detection on 80,000 km Baselines and Multiwavelength Observations

NASA Astrophysics Data System (ADS)

Edwards, P. G.; Kovalev, Y. Y.; Ojha, R.; An, H.; Bignall, H.; Carpenter, B.; Hovatta, T.; Stevens, J.; Voytsik, P.; Andrianov, A. S.; Dutka, M.; Hase, H.; Horiuchi, S.; Jauncey, D. L.; Kadler, M.; Lisakov, M.; Lovell, J. E. J.; McCallum, J.; Müller, C.; Phillips, C.; Plötz, C.; Quick, J.; Reynolds, C.; Schulz, R.; Sokolovsky, K. V.; Tzioumis, A. K.; Zuga, V.

2017-04-01

We present results from a multiwavelength study of the blazar PKS 1954-388 at radio, UV, X-ray, and gamma-ray energies. A RadioAstron observation at 1.66 GHz in June 2012 resulted in the detection of interferometric fringes on baselines of 6.2 Earth-diameters. This suggests a source frame brightness temperature of greater than 2 × 1012 K, well in excess of both equipartition and inverse Compton limits and implying the existence of Doppler boosting in the core. An 8.4-GHz TANAMI VLBI image, made less than a month after the RadioAstron observations, is consistent with a previously reported superluminal motion for a jet component. Flux density monitoring with the Australia Telescope Compact Array confirms previous evidence for long-term variability that increases with observing frequency. A search for more rapid variability revealed no evidence for significant day-scale flux density variation. The ATCA light-curve reveals a strong radio flare beginning in late 2013, which peaks higher, and earlier, at higher frequencies. Comparison with the Fermi gamma-ray light-curve indicates this followed 9 months after the start of a prolonged gamma-ray high-state-a radio lag comparable to that seen in other blazars. The multiwavelength data are combined to derive a Spectral Energy Distribution, which is fitted by a one-zone synchrotron-self-Compton (SSC) model with the addition of external Compton (EC) emission.

Directly polished lightweight aluminum mirror

NASA Astrophysics Data System (ADS)

ter Horst, Rik; Tromp, Niels; de Haan, Menno; Navarro, Ramon; Venema, Lars; Pragt, Johan

2017-11-01

During the last ten years, Astron has been a major contractor for the design and manufacturing of astronomical instruments for Space- and Earth based observatories, such as VISIR, MIDI, SPIFFI, X-Shooter and MIRI. Driven by the need to reduce the weight of optically ultra-stiff structures, two promising techniques have been developed in the last years: ASTRON Extreme Lightweighting [1][2] for mechanical structures and an improved Polishing Technique for Aluminum Mirrors. Using one single material for both optical components and mechanical structure simplifies the design of a cryogenic instrument significantly, it is very beneficial during instrument test and verification, and makes the instrument insensitive to temperature changes. Aluminum has been the main material used for cryogenic optical instruments, and optical aluminum mirrors are generally diamond turned. The application of a polishable hard top coating like nickel removes excess stray light caused by the groove pattern, but limits the degree of lightweighting of the mirrors due to the bi-metal effect. By directly polishing the aluminum mirror surface, the recent developments at Astron allow for using a non-exotic material for light weighted yet accurate optical mirrors, with a lower surface roughness ( 1nm RMS), higher surface accuracy and reduced light scattering. This paper presents the techniques, obtained results and a global comparison with alternative lightweight mirror solutions. Recent discussions indicate possible extensions of the extreme light weight technology to alternative materials such as Zerodur or Silicon Carbide.

RadioAstron and millimetron space observatories: Multiverse models and the search for life

NASA Astrophysics Data System (ADS)

Kardashev, N. S.

2017-04-01

The transition from the radio to the millimeter and submillimeter ranges is very promising for studies of galactic nuclei, as well as detailed studies of processes related to supermassive black holes, wormholes, and possible manifestations of multi-element Universe (Multiverse) models. This is shown by observations with the largest interferometer available—RadioAstron observatory—that will be used for the scientific program forMillimetron observatory. Observations have also shown the promise of this range for studies of the formation and evolution of planetary systems and searches for manifestations of intelligent life. This is caused by the requirements to use a large amount of condensedmatter and energy in large-scale technological activities. This range can also be used efficiently in the organisation of optimal channels for the transmission of information.

Percepção Astronômica de Alunos do Ensino Médio da Rede Estadual de São Paulo

NASA Astrophysics Data System (ADS)

de Oliveira, E. F.; Voelzke, M. R.; Amaral, L. H.

2005-08-01

Embora a astronomia seja uma das ciências mais antigas da humanidade e muitos dos conceitos astronômicos serem populares, principalmente nesta época de alta globalização do conhecimento por intermédio de eficientes meios de comunicação e de obtenção da informação, notadamente através da internet, observa-se que uma parcela significativa dos estudantes encontra-se à margem dessas informações. O presente trabalho visa analisar o nível de conhecimento básico dos alunos de Ensino Médio da rede estadual da cidade de Suzano quanto aos fenômenos astronômicos que os rodeiam, tais como a sucessão dos dias e das estações do ano, além de questioná-los sobre fatos genéricos tais como: quais são os astros que se encontram mais próximos do planeta Terra, o que vem a ser o Sol, o Big Bang, um ano-luz, uma estrela cadente, a estrela de Bélem e o que ocasionou a extinção dos dinossauros. Para tanto foi elaborado um formulário constando de questões de múltipla escolha, o qual foi aplicado no primeiro colegial noturno da Escola Estadual Batista Renzi. Num espaço amostral de 34 alunos constatou-se que apenas 29,4% compreendiam a sucessão dos dias da semana, que apenas 20,6% explicaram corretamente as estações do ano, que apenas 20,6% tinham idéia de quais são os objetos celestes mais próximos da Terra, em contraposição 67,6% sabiam classificar corretamente o Sol como estrela, 55,9% relacionavam o Big Bang à origem do universo, apenas 20,6% identificavam um ano-luz como unidade de distância, 32,4% reconheciam uma estrela cadente como meteoro, 41,2% consideravam a estrela de Belém como um cometa e 50,0% explicaram corretamente a extinção dos dinossauros. A presente análise será expandida para as demais classes de primeiro colegial, não somente do período noturno, mas também do diurno da Escola Estadual Batista Renzi, bem como o formulário será devidamente ampliado. Já nesta primeira fase nota-se claramente o pequeno discernimento de eventos astronômicos dos alunos e principalmente a grande confusão sobre o significado correto de termos astronômicos populares.

RadioAstron Observations of the Quasar 3C273: A Challenge to the Brightness Temperature Limit

NASA Astrophysics Data System (ADS)

Kovalev, Y. Y.; Kardashev, N. S.; Kellermann, K. I.; Lobanov, A. P.; Johnson, M. D.; Gurvits, L. I.; Voitsik, P. A.; Zensus, J. A.; Anderson, J. M.; Bach, U.; Jauncey, D. L.; Ghigo, F.; Ghosh, T.; Kraus, A.; Kovalev, Yu. A.; Lisakov, M. M.; Petrov, L. Yu.; Romney, J. D.; Salter, C. J.; Sokolovsky, K. V.

2016-03-01

Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of 1011.5 K. Relativistic boosting can increase its observed value, but apparent brightness temperatures much in excess of 1013 K are inaccessible using ground-based very long baseline interferometry (VLBI) at any wavelength. We present observations of the quasar 3C 273, made with the space VLBI mission RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as small as 26 μas (2.7 light months) and brightness temperature in excess of 1013 K. These measurements challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive black holes and require a much higher Doppler factor than what is determined from jet apparent kinematics.

Manufacturing, integration, and test results of the MATISSE cold optics bench

NASA Astrophysics Data System (ADS)

Bettonvil, Felix C. M.; Kroes, G.; Agoćs, T.; van Duin, A.; Elswijk, E.; de Haan, M.; ter Horst, R.; Kragt, J.; Kuindersma, J.; Navarro, R.; Roelfsema, R.; Schuil, M.; Tromp, T.; Venema, L.; van Kessel, F.; Jaskó, A.

2014-07-01

MATISSE is the second-generation mid-infrared interferometric spectrograph and imager for ESO's Very Large Telescope Interferometer (VLTI). NOVA-ASTRON is responsible for the Cold Optics Bench (COB), representing the last part of the optics train where the four beams are re-arranged, spectrally dispersed and combined. The COB consist of two sister units, one for the LM-band, one for the N-band, which were successively completed at NOVA-ASTRON in autumn 2013 and spring 2014. The LM-band COB is under cryogenic test in its cryostat at MPIA/Heidelberg; the N-band COB finished cryogenic tests and has been installed at OCA/Nice for integration together with the Warm Optics. This paper focuses on the manufacturing, integration and test results of the COBs, and gives an overview of the current status.

PKS 1954–388: RadioAstron detection on 80,000 km baselines and multiwavelength observations

DOE PAGES

Edwards, P. G.; Kovalev, Y. Y.; Ojha, R.; ...

2017-04-26

Here, we present results from a multiwavelength study of the blazar PKS 1954–388 at radio, UV, X-ray, and gamma-ray energies. A RadioAstron observation at 1.66 GHz in June 2012 resulted in the detection of interferometric fringes on baselines of 6.2 Earth-diameters. This suggests a source frame brightness temperature of greater than 2 × 10 12 K, well in excess of both equipartition and inverse Compton limits and implying the existence of Doppler boosting in the core. An 8.4-GHz TANAMI VLBI image, made less than a month after the RadioAstron observations, is consistent with a previously reported superluminal motion for amore » jet component. Flux density monitoring with the Australia Telescope Compact Array confirms previous evidence for long-term variability that increases with observing frequency. A search for more rapid variability revealed no evidence for significant day-scale flux density variation. The ATCA light-curve reveals a strong radio flare beginning in late 2013, which peaks higher, and earlier, at higher frequencies. Comparison with the Fermi gamma-ray light-curve indicates this followed ~ 9 months after the start of a prolonged gamma-ray high-state—a radio lag comparable to that seen in other blazars. The multiwavelength data are combined to derive a Spectral Energy Distribution, which is fitted by a one-zone synchrotron-self-Compton (SSC) model with the addition of external Compton (EC) emission.« less

Segundo Catálogo Estelar del Hemisferio Sur con Astrolabio Fotoeléctrico PAII

NASA Astrophysics Data System (ADS)

Manrique, W. T.; Podestá, R. C.; Alonso, E.; Actis, E. V.; Pacheco, A. M.; Bustos, G.; Lizhi, L.; Zezhi, W.; Fanmiao, Z.; Hongqi, W.; Perdomo, R.

Recordamos que entre el Observatorio Astronómico ``Félix Aguilar'', el Observatorio Astronómico de Beijing y el Observatorio Astronómico de La Plata, se ha convenido en desarrollar un Proyecto de Investigación conjunto, para la observación sistemática de estrellas en el Hemisferio Sur, con el objeto de la elaboración de un Catálogo Estelar Global utilizando un Astrolabio Fotoeléctrico PAII del Observatorio de Beijing, que ha sido usado con éxito en la República de China. En este trabajo se presenta el Segundo Catálogo Estelar del Hemisferio Sur, derivado de las observaciones realizadas con el PAII instalado en el OAFA, durante el períiodo Febrero de 1992 a Marzo de 1997. En este lapso se han observado mas de 400000 pasajes estelares, obteniéndose las correcciones Δ α y Δ δ de 5241 estrellas del FK4, FK5, FK5 Ext., SRS, CAMC y GC. Las precisiones medias son del orden de ± 3,2 ms en ascensión recta y ±0."057 en declinación. Rango de magnitudes : 2,0 a 11,5 Rango de declinaciones : -3o a -60o Epoca Media : 1994.9 Se analizan los residuos en función de la magnitud y tipo espectral, correcciones de grupo y frecuencia de distribución Δ α y Δ δ.

Molecular Beam Optical Zeeman Spectroscopy of Vanadium Monoxide, VO

NASA Astrophysics Data System (ADS)

Nguyen, Trung; Zhang, Ruohan; Steimle, Timothy

2016-06-01

Like almost all astronomical studies, exoplanet investigations are observational endeavors that rely primarily on remote spectroscopic sensing to infer the physical properties of planets. Most exoplanet related information is inferred from to temporal variation of luminosity of the parent star. An effective method of monitoring this variation is via Magnetic Doppler Imaging (MDI), which uses optical polarimetry of paramagnetic molecules or atoms. One promising paramagnetic stellar absorption is the near infrared spectrum of VO. With this in mind, we have begun a project to record and analyze the field-free and Zeeman spectrum of the band. A cold (approx. 20 K) beam of VO was probed with a single frequency laser and detected using laser induced fluorescence. The determined spectral parameters will be discussed and compared to those extracted from the analysis of a hot spectrum. Supported by the National Science Foundation under the Grant No. CHE-1265885. O. Kochukhov, N. Rusomarov, J. A. Valenti, H. C. Stempels, F. Snik, M. Rodenhuis, N. Piskunov, V. Makaganiuk, C. U. Keller and C. M. Johns-Krull, Astron. Astrophys. 574 (Pt. 2), A79/71-A79/12 (2015). S. V. Berdyugina, Astron. Soc. Pac. Conf. Ser. 437 (Solar Polarization 6), 219-235 (2011). S. V. Berdyugina, P. A. Braun, D. M. Fluri and S. K. Solanki, Astron. Astrophys. 444 (3), 947-960 (2005). A. S. C. Cheung, P. G. Hajigeorgiou, G. Huang, S. Z. Huang and A. J. Merer, J. Mol. Spectrosc. 163 (2), 443-458 (1994)

Evaluation of Cardiovascular Risk Scores Applied to NASA's Astronant Corps

NASA Technical Reports Server (NTRS)

Jain, I.; Charvat, J. M.; VanBaalen, M.; Lee, L.; Wear, M. L.

2014-01-01

In an effort to improve cardiovascular disease (CVD) risk prediction, this analysis evaluates and compares the applicability of multiple CVD risk scores to the NASA Astronaut Corps which is extremely healthy at selection.

A Influência da Escola e da Mídia na Obtenção dos Conhecimentos Astronômicos

NASA Astrophysics Data System (ADS)

da Cunha, W. S.; Voelzke, M. R.; Amaral, L. H.

2006-08-01

O universo em que vivemos possui segredos jamais imaginados pelo homem, fruto da pequena proporção que ocupamos diante de um cosmos infinito. A astronomia funciona como um instrumento que sacia a sede humana em desvendar esses segredos, estudando as galáxias, quasares, pulsares além da existência de todos os elementos que preenchem o espaço cósmico, o vácuo, não mais vazio como se pensou em outros tempos. A mídia explora esse campo de forma mística e também científica. A difusão adequada e dentro dos padrões educacionais vigentes, de conceitos astronômicos, se faz necessária, devido sua presença nos conteúdos escolares, centros de ciência e na mídia, de modo geral. A reforma do Currículo Básico da Escola Pública da maioria dos Estados brasileiros introduziu conceitos astronômicos desde a pré-escola até o Ensino Médio. Num estudo realizado com 1.032 alunos do Ensino Médio de seis escolas estaduais, revelou-se através da aplicação de um questionário que abordava conheciment os básicos em astronomia, como estes foram adquiridos e qual era a infra-estrutura oferecida pela escola: para 66,2% dos entrevistados o professor já fez alguma apresentação a respeito de astronomia. O presente estudo revelou também que 44,5% dos alunos entrevistados adquiriram seus conhecimentos astronômicos na escola, 28,1% através da televisão e 27,4% afirmaram que seus conhecimentos foram obtidos através de outros tipos de mídia (internet, filmes e revistas). Embora o estudo revele claramente que há certo equilíbrio na forma em que os alunos obtiveram seus conhecimentos astronômicos, a mídia ainda explora e muitas vezes desperta o interesse pela astronomia com assuntos que não fazem parte de nosso cotidiano como, por exemplo, o homem na Lua, os projetos espaciais e a primeira viagem de um astronauta brasileiro no espaço. Porém, em certos casos, a mídia pode promover conhecimentos incompletos ou mesmo equivocados sobre os conceitos que envolvam a astronomia, como por exemplo a propagação do som no vácuo observado na maioria dos filmes de f icção científica ou da existência das estações do ano em função da distância da Terra ao Sol, em conformidade com o questionário aplicado.

Rotational Period Determination for 12 Near-Earth Asteroids

NASA Astrophysics Data System (ADS)

Monteiro, Filipe; Arcoverde, Plicida; Medeiros, Hissa; Rondon, Eduardo; Souza, Roberto; Rodrigues, Tersinha; Lazzaro, Daniela

2018-07-01

Rotational periods for 12 near-Earth asteroids (NEAs) were determined from lightcurves acquired at the Observatório Astronômico do Sertão de Itaparica (MPC Y28, OASI) between May 2016 and 2017 August.

VizieR Online Data Catalog: Identifications of Sonneberg variables (Kinnunen+, 1999-2000)

NASA Astrophysics Data System (ADS)

Kinnunen, T.; Skiff, B. A.

2002-09-01

The list below is a continuation of a series providing accurate positions and identifications for variables appearing on the MVS charts (Hoffmeister, 1957, Mitt. Verdander. Sterne, No. 245). The variables here were first described by Hoffmeister (1949, Astron. Abh. Ergaenzungshefte z.d. Astron. Nach., 12, no. 1, A3) in the difficult-to-find ``Ergaenzungshefte'' to the Astronomische Nachrichten, and are the first group from a collection of some 1440 variables from this publication. Details about the identification procedure and table layout are contained in the first report of our series (Kinnunen & Skiff, 2000IBVS.4862....1K). We are grateful to librarians Antoinette Beiser (Lowell) and Brenda Corbin (U. S. Naval Observatory, Washington) for providing a photocopy of the Hoffmeister survey; ``bibliothecaire extraordinaire'' Suzanne Laloe (Obs. Paris-Meudon) advised on how this obscure journal should be cited. (3 data files).

The la Plata Astronomical Data Center

NASA Astrophysics Data System (ADS)

Marraco, H. G.

1990-11-01

RESUMEN. El Centro de Datos Astron6micos tiene su sede en la Facuitad de Ciencias Astron6micas y Geofisicas d la Universidad Nacional de La Plata y funciona por convenio entre esta facultad y el Centre des Stellaires de la Universite' Louis Pasteur en Estrasburgo (CDS), Francia. La finalidad de este centro es la de proveer a los astr6nomos del area con copias de los alrededor de 500 acumulados y/o preparados por el CDS a la vez que promover la producci6n y/o acumulaci6n de en el rea. Para la realizaci6n de esta tarea se cuenta con el apoyo del Centro Superior para el Procesamiento de la Informaci6n (CESPI) de la UNLP cuyos equipos se describen. Las tareas que se estan realizando incluyen la distribuci6n de SIMBAD a los astr6nomos argentinos y se efectuan ensayos de distribuci6n en linea de CD-ROM TEST DISK del Astronomical Data Center (ADC) de la NASA que contiene los 31 mas solicitados por los astr6nomos de todo el mundo. ABSTRACl The La Plata Astronomical Data Center operates by an agreement between the Facultad de Ciencias Astron6micas y Geofisicas at La Plata University and the Centre des Donnees Stellaires of Louis Pasteur University at Strasbourg (CDS), France. The purpose of the Center is to provide to the area astronomers with copies of the catalogs they need amongst those stored and/or prepared at CDS. At the same time the center will act of the astronomical data produced within its area. K words: DATA ANALYSIS

International mission planning for space Very Long Baseline Interferometry

NASA Technical Reports Server (NTRS)

Ulvestad, James S.

1994-01-01

Two spacecraft dedicated to Very Long Baseline Interferometry (VLBI) will be launched in 1996 and 1997 to make observations using baselines between the space telescopes and many of the world's ground radio telescopes. The Japanese Institute of Space and Astronautical Science (ISAS) will launch VSOP (VLBI Space Observatory Program) in September 1996, while the Russian Astro Space Center (ASC) is scheduled to launch RadioAstron in 1997. Both spacecraft will observe radio sources at frequencies near 1.7, 4.8, and 22 GHz; RadioAstron will also observe at 0.33 GHz. The baselines between space and ground telescopes will provide 3-10 times the resolution available for ground VLBI at the same observing frequencies. Ground tracking stations on four continents will supply the required precise frequency reference to each spacecraft measure the two-way residual phase and Doppler on the ground-space link, and record 128 Megabit/s of VLBI data downlinked from the spacecraft. The spacecraft data are meaningless without cross-correlation against the data from Earth-bound telescopes, which must take place at special-purpose VLBI correlation facilities. Therefore, participation by most of the world's radio observatories is needed to achieve substantial science return from VSOP and RadioAstron. The collaboration of several major space agencies and the ground observatories, which generally follow very different models for allocation of observing time and for routine operations, leads to great complexity in mission planning and in day-to-day operations. This paper describes some of those complications and the strategies being developed to assure productive scientific missions.

Angular Distribution of Gamma-Ray Bursts: An Observational Probe of Cosmological Principle

NASA Astrophysics Data System (ADS)

Mészáros, A.; Balázs, L. G.; Vavrek, R.; Horváth, I.; Bagoly, Z.

The test of the isotropy in the angular distribution of the gamma-ray bursts collected in BATSE Catalog (Meegan C. A. et al., http://www.batse.msfc.nasa.gov/data, 2000) is a test of cosmological principle itself, because the gamma-ray bursts are at cosmological distances. Several articles of the authors study this question (Balázs L. G., Mészáros A., & Horváth I., Astron. Astrophys., 339, 1, 1998; Balázs L. G., Mészáros A., Horváth I., & Vavrek R., Astron. Astrophys. Suppl., 138, 417, 1999; Mészáros A., Bagoly Z., & Vavrek R. Astron. Astrophys., in press, 2000). The final conclusion concerning the validity of isotropy is complicated both by instrumental effects and by the fact that there are three subgroups of gamma-ray bursts ("short", "intermediate", "long"; separation is done with respect to the duration of bursts). The long bursts are surely up to z ≃ 4 (z is the redshift); for the remaining two subclasses the redshifts are unknown. The done tests of isotropy suggest (after the elimination of instrumental effects) the existence of anisotropy for the intermediate subclass on the confidence level > 95%. On the other hand, for the remaining two subclasses the situation is unclear; there is no unambiguous rejection of isotropy for them yet on the higher than 95% confidence level. If the bursts of intermediate subclass are at high z-s (say, at, z > 0.1), then the validity of cosmological principle would be at a serious doubt.

Moonlet induced wakes in planetary rings: Analytical model including eccentric orbits of moon and ring particles

NASA Astrophysics Data System (ADS)

Seiß, M.; Spahn, F.; Schmidt, Jürgen

2010-11-01

Saturn's rings host two known moons, Pan and Daphnis, which are massive enough to clear circumferential gaps in the ring around their orbits. Both moons create wake patterns at the gap edges by gravitational deflection of the ring material (Cuzzi, J.N., Scargle, J.D. [1985]. Astrophys. J. 292, 276-290; Showalter, M.R., Cuzzi, J.N., Marouf, E.A., Esposito, L.W. [1986]. Icarus 66, 297-323). New Cassini observations revealed that these wavy edges deviate from the sinusoidal waveform, which one would expect from a theory that assumes a circular orbit of the perturbing moon and neglects particle interactions. Resonant perturbations of the edges by moons outside the ring system, as well as an eccentric orbit of the embedded moon, may partly explain this behavior (Porco, C.C., and 34 colleagues [2005]. Science 307, 1226-1236; Tiscareno, M.S., Burns, J.A., Hedman, M.M., Spitale, J.N., Porco, C.C., Murray, C.D., and the Cassini Imaging team [2005]. Bull. Am. Astron. Soc. 37, 767; Weiss, J.W., Porco, C.C., Tiscareno, M.S., Burns, J.A., Dones, L. [2005]. Bull. Am. Astron. Soc. 37, 767; Weiss, J.W., Porco, C.C., Tiscareno, M.S. [2009]. Astron. J. 138, 272-286). Here we present an extended non-collisional streamline model which accounts for both effects. We describe the resulting variations of the density structure and the modification of the nonlinearity parameter q. Furthermore, an estimate is given for the applicability of the model. We use the streamwire model introduced by Stewart (Stewart, G.R. [1991]. Icarus 94, 436-450) to plot the perturbed ring density at the gap edges. We apply our model to the Keeler gap edges undulated by Daphnis and to a faint ringlet in the Encke gap close to the orbit of Pan. The modulations of the latter ringlet, induced by the perturbations of Pan (Burns, J.A., Hedman, M.M., Tiscareno, M.S., Nicholson, P.D., Streetman, B.J., Colwell, J.E., Showalter, M.R., Murray, C.D., Cuzzi, J.N., Porco, C.C., and the Cassini ISS team [2005]. Bull. Am. Astron. Soc. 37, 766), can be well described by our analytical model. Our analysis yields a Hill radius of Pan of 17.5 km, which is 9% smaller than the value presented by Porco (Porco, C.C., and 34 colleagues [2005]. Science 307, 1226-1236), but fits well to the radial semi-axis of Pan of 17.4 km. This supports the idea that Pan has filled its Hill sphere with accreted material (Porco, C.C., Thomas, P.C., Weiss, J.W., Richardson, D.C. [2007]. Science 318, 1602-1607). A numerical solution of a streamline is used to estimate the parameters of the Daphnis-Keeler gap system, since the close proximity of the gap edge to the moon induces strong perturbations, not allowing an application of the analytic streamline model. We obtain a Hill radius of 5.1 km for Daphnis, an inner edge variation of 8 km, and an eccentricity for Daphnis of 1.5 × 10 -5. The latter two quantities deviate by a factor of two from values gained by direct observations (Jacobson, R.A., Spitale, J., Porco, C.C., Beurle, K., Cooper, N.J., Evans, M.W., Murray, C.D. [2008]. Astron. J. 135, 261-263; Tiscareno, M.S., Burns, J.A., Hedman, M.M., Spitale, J.N., Porco, C.C., Murray, C.D., and the Cassini Imaging team [2005]. Bull. Am. Astron. Soc. 37, 767), which might be attributed to the neglect of particle interactions and vertical motion in our model.

Effelsberg Monitoring of a Sample of RadioAstron Blazars: Analysis of Intra-Day Variability

NASA Astrophysics Data System (ADS)

Liu, Jun; Bignall, Hayley; Krichbaum, Thomas; Liu, Xiang; Kraus, Alex; Kovalev, Yuri; Sokolovsky, Kirill; Angelakis, Emmanouil; Zensus, J.

2018-04-01

We present the first results of an ongoing intra-day variability (IDV) flux density monitoring program of 107 blazars, which were selected from a sample of RadioAstron space very long baseline interferometry (VLBI) targets. The~IDV observations were performed with the Effelsberg 100-m radio telescope at 4.8\\,GHz, focusing on the statistical properties of IDV in a relatively large sample of compact active galactic nuclei (AGN). We investigated the dependence of rapid ($<$3 day) variability on various source properties through a likelihood approach. We found that the IDV amplitude depends on flux density and that fainter sources vary by about a factor of 3 more than their brighter counterparts. We also found a significant difference in the variability amplitude between inverted- and flat-spectrum radio sources, with the former exhibiting stronger variations. $\\gamma$-ray loud sources were found to vary by up to a factor 4 more than $\\gamma$-ray quiet ones, with 4$\\sigma$ significance. However a galactic latitude dependence was barely observed, which suggests that it is predominantly the intrinsic properties (e.g., angular size, core-dominance) of the blazars that determine how they scintillate, rather than the directional dependence in the interstellar medium (ISM). We showed that the uncertainty in the VLBI brightness temperatures obtained from the space VLBI data of the RadioAstron satellite can be as high as $\\sim$70\\% due to the presence of the rapid flux density variations. Our statistical results support the view that IDV at centimeter wavelengths is predominantly caused by interstellar scintillation (ISS) of the emission from the most compact, core-dominant region in an AGN.

RadioAstron space-ground interferometer at 324 MHz: interstellar plasma in the direction to PSR B1919+21

NASA Astrophysics Data System (ADS)

Smirnova, Tatiana; Andrianov, Andrey; Shishov, Vladimir

We present results obtained from analysis of our observations carried out on the space-ground interferometer RadioAstron at frequency of 324 MHz. Observations were conducted on 04.07.12 with a baseline projection of 60000 km. We used two ground telescopes: GBT and WSRT with the space radio telescope (SRT). Notable visibility amplitudes were detected at all baseline projections. We found that frequency structure of interstellar scintillation for pulsar B1919+21 is defined by angular refraction with refractive angle: θref ≈ 60 mas. Cosmic prism is located near to observer with a distance of about 10 pc. The scattering angle is resolved by cosmic interferometer and θsc is about 1 mas. The temporal structure of scintillation is mainly defined by interstellar plasma of extended media, but frequency structure - by extended media and prism influence. We detected also the influence of ionosphere on a phase variations of interferometer.

The abundance of ammonia in Comet P/Halley derived from ultraviolet spectrophotometry of NH by ASTRON and IUE

NASA Technical Reports Server (NTRS)

Feldman, P. D.; Fournier, K. B.; Grinin, V. P.; Zvereva, A. M.

1993-01-01

From an analysis of the spatial profiles of both the NH and OH UV emissions observed by the ASTRON satellite, the ratio of ammonia-to-water production rates in Comet Halley on April 9, 1986 is derived and found to lie in the range of 0.44-0.94 percent. In order to compare this result with those based on both ground-based and in situ observations made on other dates during the 1985-1986 apparition of the comet, the IUE observational data base for December 1985 and March-April 1986 is used to evaluate the ratio of NH to OH column density in the IUE field of view and thus constrain the long-term behavior of this ratio. The IUE data base indicates that, to within a factor of 2, the ammonia-to-water production rate ratio is the same for a small sample of moderately bright comets observed recently.

Erratum: Erratum to: Realistic interpretation of quantum mechanics and encounter-delayed-choice experiment

NASA Astrophysics Data System (ADS)

Long, GuiLu; Qin, Wei; Yang, Zhe; Li, Jun-Lin

2018-05-01

In our article [1] we made a mistake in citing ref. [32], which is the same as ref. [28]. We now replace ref. [32] with the correct reference "L. Hao, D. Liu, and G. L. Long, Sci. China Phys. Mech. Astron. 53, 1765 (2010)" [2].

Astronomical Observations by Speckle Interferometry.

DTIC Science & Technology

1986-06-12

commonly -been noted [Heintz (101)] that it was Karl *, Schwarzchild who iui 1895 [ Schwarzschild (190)] made the first measure- ments of binary stars...J. Lett 163. Michelson, A A, Pease. F. G. 1921. Ap. 280: L23 J. 53: 249 190. Schwarzschild . K. 1896. Astron. Nadir. 164. Morgan. B. L., lieddoes. 1

Improvement of the orbit of the Spektr-R spacecraft in the RadioAstron mission and required conditions for improvement using a Kalman filter

NASA Astrophysics Data System (ADS)

Zhamkov, A. S.; Zharov, V. E.

2017-05-01

This paper is concerned with improvement of the state vector of the Spektr-R spacecraft of the RadioAstron mission. The state vector includes three coordinates of the position of the spacecraft and three components of its velocity in the Geocentric Celestial Reference System. Improvement of the orbit of the spacecraft is understood as improvement of the state vector. The results are compared with the original orbits determined at the Keldysh Institute of Applied Mathematics (IAM). The paper considers both using the Kalman filter based on a single set of radio-range and Doppler data from ground-based stations and the analysis of conditions that will lead to improvement of the orbit. It has been shown that using three ground-based stations that perform simultaneous measurements the problem is solved completely, even when a poor initial approximation is used. Based on the results, a list of requirements is obtained that will provide more accurate information on the orbit of the Spektr-R spacecraft.

The Observatorio Astronómico Nacional - Tonantzintla: Site Evaluation

NASA Astrophysics Data System (ADS)

Hernández-Toledo, H. M.; Martínez-Vázquez, L. A.; Pani-Cielo, A.

2011-06-01

The objective of this contribution is to present some results of an evaluation on the local conditions at the site that were considered in order to propose that the Observatorio Astronómico Nacional, Tonantzintla, (OAN-Tonantzintla) become a National Facility for Astronomy Education. The evaluation included a quantitative diagnostic (CCD photometry) on the quality of the local sky. The attributes of the 1-m telescope, the current instrumentation and a well planned upgrading that includes new instrumentation is considered at the basis for a successful transition maintaining the attractiveness of the site for astronomy education. A 3-year upgrading program actually in progress at UNAM is providing funding for that purpose. Physics and astronomy programs at college and graduated levels at UNAM will benefit from this, yielding clear connections among astronomy researchers and educators and students at various levels. Although the OAN-Tonantzintla faces the danger of deteriorating its sky conditions, we are maintaining awareness of the night sky characteristics in long-term monitoring campaigns and encouraging the local authorities to find alternative solutions to this problem.

Strong lensing probability in TeVeS (tensor-vector-scalar) theory

NASA Astrophysics Data System (ADS)

Chen, Da-Ming

2008-01-01

We recalculate the strong lensing probability as a function of the image separation in TeVeS (tensor-vector-scalar) cosmology, which is a relativistic version of MOND (MOdified Newtonian Dynamics). The lens is modeled by the Hernquist profile. We assume an open cosmology with Ωb = 0.04 and ΩΛ = 0.5 and three different kinds of interpolating functions. Two different galaxy stellar mass functions (GSMF) are adopted: PHJ (Panter, Heavens and Jimenez 2004 Mon. Not. R. Astron. Soc. 355 764) determined from SDSS data release 1 and Fontana (Fontana et al 2006 Astron. Astrophys. 459 745) from GOODS-MUSIC catalog. We compare our results with both the predicted probabilities for lenses from singular isothermal sphere galaxy halos in LCDM (Lambda cold dark matter) with a Schechter-fit velocity function, and the observational results for the well defined combined sample of the Cosmic Lens All-Sky Survey (CLASS) and Jodrell Bank/Very Large Array Astrometric Survey (JVAS). It turns out that the interpolating function μ(x) = x/(1+x) combined with Fontana GSMF matches the results from CLASS/JVAS quite well.

On the possible relation between the Tunguska bolide and comet Encke

NASA Astrophysics Data System (ADS)

Asher, D. J.; Steel, D. I.

1998-02-01

Almost two decades ago Ľ. Kresák ( Bull. Astron. Inst. Czechoslov.29, 129-134, 1978) suggested that the Tunguska bolide might be a fragment of comet Encke, a hypothesis that Z. Sekanina criticized in a publication a few years later ( Astron. J.88, 1382-1414, 1983). One aspect of the proposed genetic relationship is investigated, namely the required differential orbital precession of the two objects so as to make an impact upon our planet possible for the Tunguska projectile, even though the comet's orbit in the current epoch is far from the condition of Earth intersection. This work was foreshadowed in a previous paper in which it was shown how theoretical meteor radiants may be calculated for objects with orbits similar to 2P/Encke ( Earth, Moon and Planets68, 155-164, 1995). By applying appropriate secular perturbation theory and numerical integration techniques, it is shown that the necessary dispersion can be attained within 10 kyr if the semi-major axes of the orbits differ by ˜0.05 AU, an amount easily achieved even under the presently observed non-gravitational forces of 2P/Encke.

Secondary resonances and the boundary of effective stability of Trojan motions

NASA Astrophysics Data System (ADS)

Páez, Rocío Isabel; Efthymiopoulos, Christos

2018-02-01

One of the most interesting features in the libration domain of co-orbital motions is the existence of secondary resonances. For some combinations of physical parameters, these resonances occupy a large fraction of the domain of stability and rule the dynamics within the stable tadpole region. In this work, we present an application of a recently introduced `basic Hamiltonian model' H_b for Trojan dynamics (Páez and Efthymiopoulos in Celest Mech Dyn Astron 121(2):139, 2015; Páez et al. in Celest Mech Dyn Astron 126:519, 2016): we show that the inner border of the secondary resonance of lowermost order, as defined by H_b, provides a good estimation of the region in phase space for which the orbits remain regular regardless of the orbital parameters of the system. The computation of this boundary is straightforward by combining a resonant normal form calculation in conjunction with an `asymmetric expansion' of the Hamiltonian around the libration points, which speeds up convergence. Applications to the determination of the effective stability domain for exoplanetary Trojans (planet-sized objects or asteroids) which may accompany giant exoplanets are discussed.

Como os Alunos do Ensino Médio da Rede Estadual de São Paulo obtém Conhecimentos Astronômicos?

NASA Astrophysics Data System (ADS)

da Cunha, W. S.; Voelzke, M. R.; Amaral, L. H.

2005-08-01

Atualmente vivencia-se um mundo globalizado onde os computadores e a internet permitiram um acesso rápido e seguro a todo tipo de informação e conhecimento. O presente trabalho visa analisar a maneira pela qual alunos de segundo grau da rede estadual da cidade de São Paulo obtiveram, caso tenham, conhecimentos básicos de astronomia quanto aos fenômenos celestes que os rodeiam, tais como a sucessão dos dias e das estações do ano, além de questioná~los sobre fatos genéricos tais como: o que vem a ser o Sol, o Big Bang, o que ocasionou a extinção dos dinossauros. Para tanto foi elaborado um formulário constando de questões de múltipla escolha, o qual foi aplicado no primeiro colegial diurno da Escola Estadual Guilherme de Almeida. Num espaço amostral de 44 alunos constatou-se que 41% dos alunos adquiriram seus conhecimentos astronômicos na escola e 59% através da mídia em geral. Neste mesmo espaço amostral apenas 11% dos alunos usaram computadores na escola, 41% na residência, 5% no trabalho e 43% não utilizaram. O presente estudo revelou também que para 50% dos alunos o professor jamais utilizou um programa de computador a respeito de astronomia ou fez alguma apresentação sobre o tema. Embora em sua fase inicial este estudo revela claramente que a maioria dos alunos não obtém na escola seus conhecimentos astronômicos, estes provém de fontes não especificamente didático-pedagógicas tais como filmes e revistas populares que não raramente geram conhecimentos incompletos e em muitos casos inclusive falhos.

Forward and inverse modeling for jovian seismology

NASA Astrophysics Data System (ADS)

Jackiewicz, Jason; Nettelmann, Nadine; Marley, Mark; Fortney, Jonathan

2012-08-01

Jupiter is expected to pulsate in a spectrum of acoustic modes and recent re-analysis of a spectroscopic time series has identified a regular pattern in the spacing of the frequencies (Gaulme, P., Schmider, F.-X., Gay, J., Guillot, T., Jacob, C. [2011]. Astron. Astrophys. 531, A104). This exciting result can provide constraints on gross jovian properties and warrants a more in-depth theoretical study of the seismic structure of Jupiter. With current instrumentation, such as the SYMPA instrument (Schmider, F.X. [2007]. Astron. Astrophys. 474, 1073-1080) used for the Gaulme et al. (Gaulme, P., Schmider, F.-X., Gay, J., Guillot, T., Jacob, C. [2011]. Astron. Astrophys. 531, A104) analysis, we assume that, at minimum, a set of global frequencies extending up to angular degree ℓ=25 could be observed. In order to identify which modes would best constraining models of Jupiter's interior and thus help motivate the next generation of observations, we explore the sensitivity of derived parameters to this mode set. Three different models of the jovian interior are computed and the theoretical pulsation spectrum from these models for ℓ⩽25 is obtained. We compute sensitivity kernels and perform linear inversions to infer details of the expected discontinuities in the profiles in the jovian interior. We find that the amplitude of the sound-speed jump of a few percent in the inner/outer envelope boundary seen in two of the applied models should be reasonably inferred with these particular modes. Near the core boundary where models predict large density discontinuities, the location of such features can be accurately measured, while their amplitudes have more uncertainty. These results suggest that this mode set would be sufficient to infer the radial location and strength of expected discontinuities in Jupiter's interior, and place strong constraints on the core size and mass. We encourage new observations to detect these jovian oscillations.

Alfabetización en Astronomía de docentes de Educación Primaria y de Educación Secundaria en La Plata

NASA Astrophysics Data System (ADS)

De Biasi, M. S.; Orellana, R. B.

2014-10-01

La educación de este siglo tiene como uno de sus retos alcanzar la alfabetización cientfica de todos los ciudadanos para que comprendan y tomen decisiones sobre el mundo natural y sus cambios originados por la actividad humana utilizando el conocimiento científico. En esta misión los docentes de los niveles obligatorios de enseñanza juegan un papel clave por su rol de agentes multiplicadores del conocimiento. Se requiere, entonces de una adecuada alfabetización en ciencias de los docentes o, como mínimo, que dominen los temas científicos a enseñar. En el campo de la Astronomía, numerosas investigaciones han señalado que maestros de primaria y estudiantes de profesorados poseen una escasa formación en estos temas (Camino 1995 y 1999, Gangui 2010), que frecuentemente presentan a los alumnos concepciones alternativas o no científicas de los fenómenos astronómicos cotidianos (Kriner 2004, Vega Navarro 2007, Gangui et al 2010); a lo que se suma la presentación confusa o errónea de algunos temas astronómicos en los textos escolares (Kriner 2004). Desde 2011, la Facultad de Ciencias Astronómicas y Geofísicas, UNLP, ofrece un curso de capacitación destinado a fortalecer y actualizar los contenidos académicos y didácticos de los docentes del distrito La Plata utilizando diversas estrategias didácticas. Los contenidos comprenden los temas astronómicos de los diseños curriculares vigentes. La evaluación diagnóstica de los conocimientos previos de los docentes cursantes sobre los contenidos de mayor presencia en los diseños curriculares mostró resultados similares a las investigaciones arriba mencionadas. Referente a los movimientos de la Tierra, en promedio, el 54% poseía conceptos erróneos y el 16% no los sabía; con referencia a la Luna el 56% poseía conceptos erróneos y un 4% no los sabía. Los resultados del curso mostraron que el 95% de los docentes revirtió sus conceptos previos erróneos, que adquirió criterios para la búsqueda de fuentes de información confiables y que el grado de conocimientos disciplinares y didácticos alcanzados por los docentes garantiza el efecto multiplicador de esta propuesta. Esta capacitación fue acreditada con puntaje por el organismo educativo provincial en 2011, 2012 y 2013.

A Reappraising of Cosmography: the Interface Between Astronomical and Geographic Studies. (Breton Title: Releitura do Conceito de Cosmografia: a Interface Entre os Estudos Astronômicos e Geográficos.) Una Relectura del Concepto de Cosmografía: la Interfase Entre los Estudios Astronómicos y Geográficos

NASA Astrophysics Data System (ADS)

Azevedo Sobreira, Paulo Henrique

2012-12-01

The concept of "Cosmography" is in disuse since the 80s of the last century, but the astronomical themes previously discussed in the school subjects of Geography and Cosmography remain in current textbooks. The use of term "Cosmography" was rescued in this research, and the study of its re-signification prompted the appearance of the term Geographic Cosmography. The Geographic Cosmography is a field of studies of the Geography, whose set of knowledge and skills is predominantly scholar. It studies the interface between terrestrial and celestial knowledge, and assigns a geographic significance to them. It examines human and natural relationships with Sidereal Space and its consequences for society and nature. O conceito de "Cosmografia" está em desuso desde os anos 80 do século XX, mas os temas astronômicos anteriormente abordados nas disciplinas escolares de Cosmografia e de Geografia permanecem nos atuais livros didáticos. O uso do termo "Cosmografia" foi resgatado nesta pesquisa e o estudo de sua ressignificação proporcionou o surgimento do termo Cosmografia Geográfica. A Cosmografia Geográfica é um campo de estudos da Geografia, cujo conjunto de conhecimentos e habilidades é predominantemente escolar. Estuda a interface entre os conhecimentos terrestres e os celestes e lhes atribui significância geográfica. Analisa as relações humanas e naturais com o Espaço Sideral e suas consequências para a sociedade e a natureza.

Aunque el concepto de "Cosmografía" no se usa desde la década de los '80 del siglo pasado, los temas astronómicos que se enseñaban anteriormente en las asignaturas escolares de Cosmografía y de Geografía permanecen en los actuales libros didácticos. El uso del término "Cosmografía" fue rescatado en esta investigación y el estudio de su resignificación proporcionó el surgimiento del término Cosmografía Geográfica. La Cosmografía Geográfica es un campo de estudio de la Geografía, donde el conjunto de conocimientos y habilidades es predominantemente escolar. Estudia la interfase entre los conocimientos terrestres y los celestes, dándoles un significado geográfico. Analiza las relaciones humanas y naturales con el Espacio Sideral y sus consecuencias para la sociedad y la naturaleza.

Mesa redonda: Argentina en proyectos globales de investigaciones espaciales y astronómicas. Astronomía óptica en Argentina

NASA Astrophysics Data System (ADS)

Folatelli, G.

2016-08-01

This is a brief summary of the current status of observational astronomy in the optical range in Argentina, as seen by the author. This roundtable presentation aimed at setting off the discussion within the community about the issue of observational facilities and its posible solutions.

Extragalactic Radio Sources: Rapid Variability at 90 GHz.

DTIC Science & Technology

1983-12-15

34 Nature 269, 493-494. 37. Kellermann, K. I. (1974). "Detection of a Strong and Possibly Variable Compact Millimeter Wave Component in Centaurus A...Quasi-periodic Bursts in the Nucleus of Centaurus A at -wavelengths," Mon. Not. R. Astron. Soc. 187, 23P-28P. 40. DuPuy, D., Schmitt, J., McClure, R

Speckle Interferometry at the US Naval Observatory. XIII

DTIC Science & Technology

2007-10-01

18443+3940 ............................. STF 2382 AB 6.394 348.9 2.35 1 0.3 0.06 Mason et al. (2004a) 0.2 0.03 Novakovic & Todorovic (2005) 18443+3940...1952, Bull. Astron. Paris, 16, 263 Novakovic , B., & Todorovic, N. 2005, Circ. d’Inf. 157 Olevic, D. 2002, Circ. d’Inf. 147 Olevic, D., & Cvetkovic, Z

Addendum: 1420 and 408 MHz Continuum Observations of the IC 443/G189.6+3.3 Region[Astron. J. 127, 2277 (2004)

NASA Astrophysics Data System (ADS)

Leahy, D. A.

2004-09-01

A previous spectral index study that noted the region of flat spectral index in the southern part of IC 443 is that of Green (1986). The same region was first noted as a hard X-ray source by Keohane et al. (1997).

Erratum: Substructure in clusters of galaxies and the value of {OMEGA}

NASA Astrophysics Data System (ADS)

Dutta, Suvendra N.

1996-05-01

The paper `Substructure in clusters of galaxies and the value of {OMEGA}' was published in Mon. Not. R. Astron. Soc. 276, 1109- 1115(1995). Unfortunately, the wrong set of figures was inadvertently supplied to the publishers after the paper had been accepted. The correct figures are reproduced below, with the corresponding captions. [See Journal].

Mesa redonda: Argentina en proyectos globales de investigaciones espaciales y astronómicas. Uso científico de la Antena de Espacio Profundo DSA 3

NASA Astrophysics Data System (ADS)

Colazo, M.

2016-08-01

Argentine has 10 percent of the operative time available for the DSA 3 Antenna of the European Space Agency, installed in Malargüe, Mendoza. Here we present the history of the project and the current activities for the scientific use of the antenna.

Effective correlator for RadioAstron project

NASA Astrophysics Data System (ADS)

Sergeev, Sergey

This paper presents the implementation of programme FX-correlator for Very Long Baseline Interferometry, adapted for the project "RadioAstron". Software correlator implemented for heterogeneous computing systems using graphics accelerators. It is shown that for the task interferometry implementation of the graphics hardware has a high efficiency. The host processor of heterogeneous computing system, performs the function of forming the data flow for graphics accelerators, the number of which corresponds to the number of frequency channels. So, for the Radioastron project, such channels is seven. Each accelerator is perform correlation matrix for all bases for a single frequency channel. Initial data is converted to the floating-point format, is correction for the corresponding delay function and computes the entire correlation matrix simultaneously. Calculation of the correlation matrix is performed using the sliding Fourier transform. Thus, thanks to the compliance of a solved problem for architecture graphics accelerators, managed to get a performance for one processor platform Kepler, which corresponds to the performance of this task, the computing cluster platforms Intel on four nodes. This task successfully scaled not only on a large number of graphics accelerators, but also on a large number of nodes with multiple accelerators.

TIPTOPbase: the Iron Project and the Opacity Project Atomic Database

NASA Astrophysics Data System (ADS)

Mendoza, Claudio; Nahar, Sultana; Pradhan, Anil; Seaton, Micheal; Zeippen, Claude

2001-05-01

The Opacity Project, the IRON Project, and the RmaX Network (The Opacity Project Team, Vol.1,2), IOPP, Bristol (1995,1996); Hummer et al., Astron. Astrophys. 279, 298 (1993) are international computational efforts concerned with the production of high quality atomic data for astrophysical applications. Research groups from Canada, France, Germany, UK, USA and Venezuela are involved. Extensive data sets containing accurate energy levels, f-values, A-values, photoionisation cross sections, collision strengths, recombination rates, and opacitites have been computed for cosmically abundant elements using state-of-the-art atomic physics codes. Their volume, completeness and overall accuracy are presently unmatched in the field of laboratory astrophysics. Some of the data sets have been available since 1993 from a public on-line database service referred to as TOPbase (Cunto et al Astron. Astrophys. 275), L5 (1993), ( http://cdsweb.u-strasbg.fr/OP.html at CDS France, and http://heasarc.gsfc.nasa.gov/topbase, at NSAS USA). We are currently involved in a major effort to scale the existing database services to develop a robust platform for the high-profile dissemination of atomic data to the scientific community within the next 12 months. (Partial support from the NSF and NASA is acknowledged.)

Improving geolocation and spatial accuracies with the modular integrated avionics group (MIAG)

NASA Astrophysics Data System (ADS)

Johnson, Einar; Souter, Keith

1996-05-01

The modular integrated avionics group (MIAG) is a single unit approach to combining position, inertial and baro-altitude/air data sensors to provide optimized navigation, guidance and control performance. Lear Astronics Corporation is currently working within the navigation community to upgrade existing MIAG performance with precise GPS positioning mechanization tightly integrated with inertial, baro and other sensors. Among the immediate benefits are the following: (1) accurate target location in dynamic conditions; (2) autonomous launch and recovery using airborne avionics only; (3) precise flight path guidance; and (4) improved aircraft and payload stability information. This paper will focus on the impact of using the MIAG with its multimode navigation accuracies on the UAV targeting mission. Gimbaled electro-optical sensors mounted on a UAV can be used to determine ground coordinates of a target at the center of the field of view by a series of vector rotation and scaling computations. The accuracy of the computed target coordinates is dependent on knowing the UAV position and the UAV-to-target offset computation. Astronics performed a series of simulations to evaluate the effects that the improved angular and position data available from the MIAG have on target coordinate accuracy.

Extended 60 μm Emission from Nearby Mira Variables

NASA Astrophysics Data System (ADS)

Bauer, W. H.; Stencel, R. E.

1993-01-01

Circumstellar dust envelopes around some optically visible late-type stars are so extensive that they are detectable as extended at an arc-minute scale by the IRAS survey observations (Stencel, Pesce and Bauer 1988, Astron. J 95, 141; Hawkins 1990, Astron. Ap. 229, L8). The width of the IRAS scan profiles at 10% of peak intensity is an indicator of source extension. Wyatt and Cahn (1983, Ap. J. 275, 225) presented a sample of 124 Mira variables in the solar neighborhood. Of this sample, 11 Miras which show silicate emission are bright enough at 60 microns for a significant determination of the width of a scan at 10% of peak flux. Individual scans and maps were examined in order to determine whether any observed extension was associated with the central star. Five stars showed significant extension apparently due to mass loss from the central star: R Leo, o Cet, U Ori, R Cas and R Hor. IRAS LRS spectra, point source fluxes and observed extensions of these sources are compared to the predictions of model dust shells which assume steady mass loss. This work was supported in part by NASA grant NAG 5-1213 to Wellesley College.

Strong lensing probability in TeVeS (tensor-vector-scalar) theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen Daming, E-mail: cdm@bao.ac.cn

2008-01-15

We recalculate the strong lensing probability as a function of the image separation in TeVeS (tensor-vector-scalar) cosmology, which is a relativistic version of MOND (MOdified Newtonian Dynamics). The lens is modeled by the Hernquist profile. We assume an open cosmology with {Omega}{sub b} = 0.04 and {Omega}{sub {Lambda}} = 0.5 and three different kinds of interpolating functions. Two different galaxy stellar mass functions (GSMF) are adopted: PHJ (Panter, Heavens and Jimenez 2004 Mon. Not. R. Astron. Soc. 355 764) determined from SDSS data release 1 and Fontana (Fontana et al 2006 Astron. Astrophys. 459 745) from GOODS-MUSIC catalog. We comparemore » our results with both the predicted probabilities for lenses from singular isothermal sphere galaxy halos in LCDM (Lambda cold dark matter) with a Schechter-fit velocity function, and the observational results for the well defined combined sample of the Cosmic Lens All-Sky Survey (CLASS) and Jodrell Bank/Very Large Array Astrometric Survey (JVAS). It turns out that the interpolating function {mu}(x) = x/(1+x) combined with Fontana GSMF matches the results from CLASS/JVAS quite well.« less

Establishing the Empirical Relationship Between Non-Science Majoring Undergraduate Learners' Spatial Thinking Skills and Their Conceptual Astronomy Knowledge. (Spanish Title: Estableciendo Una Relación Empírica Entre el Razonamiento Espacial de los Estudiantes de Graduación de Carreras no Científicas y su Conocimento Conceptual de la Astronomía.) Estabelecendo Uma Relação Empírica Entre o RacioCínio Espacial dos Estudantes de Graduação EM Carreiras Não Científicas e Seu Conhecimento Conceitual da Astronomia

NASA Astrophysics Data System (ADS)

Heyer, Inge; Slater, Stephanie J.; Slater, Timothy F.

2013-12-01

The astronomy education community has tacitly assumed that learning astronomy is a conceptual domain resting upon spatial thinking skills. As a first step to formally identify an empirical relationship, undergraduate students in a non-major introductory astronomy survey class at a mediumsized, Ph.D. granting, mid-western US university were given pre- and post-astronomy conceptual diagnostics and spatial reasoning diagnostics, Instruments used were the "Test Of Astronomy Standards" and "What Do You Know?" Using only fully matched data for analysis, our sample consisted of 86 undergraduate non-science majors. Students' normalized gains for astronomy surveys were low at .26 and .13 respectively. Students' spatial thinking was measured using an instrument designed specifically for this study. Correlations between the astronomy instruments' pre- to post-course gain scores and the spatial assessment instrument show moderate to strong relationships suggesting the relationship between spatial reasoning and astronomy ability can explain about 25% of the variation in student achievement. La comunidad de educación en astronomía ha supuesto de forma tácita que el aprendizaje de la astronomía consiste en un dominio conceptual fundamentado en el razonamiento espacial. Como un primer paso para identificar formalmente una relación empírica entre estas dos cosas, utilizamos como muestra los estudantes de graduación de carreras no científicas de un curso experimental en una universidad norteamericana del medioeste de porte mediano con programa de Doctorado em curso, en el cual estos estudiantes se sometieron a un diagnóstico de razonamiento espacial y conceptos astronómicos antes e después del mismo. Las herramientas utilizadas fueron el Test Of Astronomy Standards (TOAST) y el cuestionario What do you know? Utilizando solo los datos completamente consistentes para este análisis, nuestra muestra consistió en 86 estudantes de graduación. Las mejoras, depués de normalizadas, en el desempeño de los estudiantes en estos dos asuntos foram pequenas, 0.26 e 0.13 respectivamente. El razonamiento espacial de los estudiantes fue medido utilizando un instrumento específico desarrollado para este trabaljo. Las correlaciones entre los resultados de los tests astronómicos y este instrumento específico, antes y después del curso mostraron una relación entre moderada y fuerte, sugiriendo que la relación entre el razonamiento espacial y el conocimiento astronómico puede explicar hasta un 25% de la variación em el desempeño de los estudiantes. A comunidade da educação em astronomia tem suposto de forma implícita que o aprendizado da astronomia consiste em um domínio conceitual fundamentado no raciocínio espacial. Como um primeiro passo para identificar formalmente uma relação empírica entre estas duas coisas, utilizamos como amostra os estudantes de graduação de carreiras não científicas de um curso exploratório em uma universidade norte-americana do meio-oeste de médio porte com programa de Doutorado em andamento, onde estes estudantes foram submetidos a um diagnóstico de raciocino espacial e conceitos astronômicos antes e depois do mesmo. As ferramentas utilizadas foram o Test Of Astronomy Standards (TOAST) e o questionário What do you know? Utilizando somente dados completamente consistentes para esta análise, nossa amostra consistiu de 86 estudantes de graduação. As melhoras, depois de normalizadas, do desempenho dos estudantes nos dois quesitos foram pequenas, 0.26 e 0.13 respectivamente. O raciocínio espacial dos estudantes foi medido utilizando um instrumento específico desenhado para este trabalho. As correlações entre os resultados dos testes astronômicos e este instrumento específico antes e depois do curso mostraram uma relação entre moderada e forte, sugerindo que a relação entre o raciocínio espacial e o conhecimento astronômico pode explicar até um 25% na variação no desempenho dos estudantes.

High energy neutrinos from astrophysical accelerators of cosmic ray nuclei

NASA Astrophysics Data System (ADS)

Anchordoqui, Luis A.; Hooper, Dan; Sarkar, Subir; Taylor, Andrew M.

2008-02-01

Ongoing experimental efforts to detect cosmic sources of high energy neutrinos are guided by the expectation that astrophysical accelerators of cosmic ray protons would also generate neutrinos through interactions with ambient matter and/or photons. However, there will be a reduction in the predicted neutrino flux if cosmic ray sources accelerate not only protons but also significant numbers of heavier nuclei, as is indicated by recent air shower data. We consider plausible extragalactic sources such as active galactic nuclei, gamma ray bursts and starburst galaxies and demand consistency with the observed cosmic ray composition and energy spectrum at Earth after allowing for propagation through intergalactic radiation fields. This allows us to calculate the expected neutrino fluxes from the sources, normalized to the observed cosmic ray spectrum. We find that the likely signals are still within reach of next generation neutrino telescopes such as IceCube.PACS95.85.Ry98.70.Rz98.54.Cm98.54.EpReferencesFor a review, see:F.HalzenD.HooperRep. Prog. Phys.6520021025A.AchterbergIceCube CollaborationPhys. Rev. Lett.972006221101A.AchterbergIceCube CollaborationAstropart. Phys.262006282arXiv:astro-ph/0611063arXiv:astro-ph/0702265V.NiessANTARES CollaborationAIP Conf. Proc.8672006217I.KravchenkoPhys. Rev. D732006082002S.W.BarwickANITA CollaborationPhys. Rev. Lett.962006171101V.Van ElewyckPierre Auger CollaborationAIP Conf. Proc.8092006187For a survey of possible sources and event rates in km3 detectors see e.g.,W.BednarekG.F.BurgioT.MontaruliNew Astron. Rev.4920051M.D.KistlerJ.F.BeacomPhys. Rev. D742006063007A. Kappes, J. Hinton, C. Stegmann, F.A. Aharonian, arXiv:astro-ph/0607286.A.LevinsonE.WaxmanPhys. Rev. Lett.872001171101C.DistefanoD.GuettaE.WaxmanA.LevinsonAstrophys. J.5752002378F.A.AharonianL.A.AnchordoquiD.KhangulyanT.MontaruliJ. Phys. Conf. Ser.392006408J.Alvarez-MunizF.HalzenAstrophys. J.5762002L33F.VissaniAstropart. Phys.262006310F.W.SteckerC.DoneM.H.SalamonP.SommersPhys. Rev. Lett.6619912697(Erratum-ibid. 69 (1992) 2738)F.W.SteckerPhys. Rev. D722005107301A.AtoyanC.D.DermerPhys. Rev. Lett.872001221102L.A.AnchordoquiH.GoldbergF.HalzenT.J.WeilerPhys. Lett. B6002004202E.WaxmanJ.N.BahcallPhys. Rev. Lett.7819972292C.D.DermerA.AtoyanPhys. Rev. Lett.912003071102D.GuettaD.HooperJ.Alvarez-MunizF.HalzenE.ReuveniAstropart. Phys.202004429J.Alvarez-MunizF.HalzenD.W.HooperPhys. Rev. D622000093015A.LoebE.WaxmanJCAP06052006003S. Inoue, G. Sigl, F. Miniati, E. Armengaud, arXiv:astro-ph/0701167.E.WaxmanJ.N.BahcallPhys. Rev. D591999023002Phys. Rev. D642001023002K.MannheimR.J.ProtheroeJ.P.RachenPhys. Rev. D632001023003arXiv:astro-ph/9908031M.AhlersL.A.AnchordoquiH.GoldbergF.HalzenA.RingwaldT.J.WeilerPhys. Rev. D722005023001E.WaxmanAstrophys. J.4521995L1Note that the neutrino spectral shape can deviate from that for protons if the Feynman plateau is not flat in pseudo-rapidity space;L.AnchordoquiH.GoldbergC.NunezPhys. Rev. D712005065014This is in fact suggested by Tevatron data;F.AbeCDF CollaborationPhys. Rev. D4119902330J.G.LearnedS.PakvasaAstropart. Phys.31995267F.HalzenD.SaltzbergPhys. Rev. Lett.8119984305J.F.BeacomN.F.BellD.HooperS.PakvasaT.J.WeilerPhys. Rev. D682003093005(Erratum-ibid. D 72 (2005) 019901)L.A.AnchordoquiH.GoldbergF.HalzenT.J.WeilerPhys. Lett. B593200442L.A.AnchordoquiH.GoldbergF.HalzenT.J.WeilerPhys. Lett. B621200518A.M.HillasAnn. Rev. Astron. Astrophys.221984425For a general discussion on the acceleration time-scale in these sources see, e.g.,D.F.TorresL.A.AnchordoquiRep. Prog. Phys.6720041663M.C.BegelmanB.RudakM.SikoraAstrophys. J.362199038M.J.ChodorowskiA.A.ZdziarskiM.SikoraAstrophys. J.4001992181S.MichalowskiD.AndrewsJ.EickmeyerT.GentileN.MistryR.TalmanK.UenoPhys. Rev. Lett.391977737J.L.PugetF.W.SteckerJ.H.BredekampAstrophys. J.2051976638D.HooperS.SarkarA.M.TaylorAstropart. Phys.272007199The non-thermal energy release in GRBs is much smaller than that output by AGN.P.L.BiermannP.A.StrittmatterAstrophys. J.3221987643R.J.ProtheroeA.P.SzaboPhys. Rev. Lett.6919922885J.P.RachenP.L.BiermannAstron. Astrophys.2721993161J.P.RachenT.StanevP.L.BiermannAstron. Astrophys.2731993377R.C.HartmanEGRET CollaborationAstrophys. J. Suppl.123199979See e.g.,M.PunchNature3581992477D.PetryHEGRA CollaborationAstron. Astrophys.3111996L13P.M.ChadwickAstrophys. J.5131999161C.D.DermerR.SchlickeiserA.MastichiadisAstron. Astrophys.2561992L27S.D.BloomA.P.MarscherAstrophys. J.4611996657K.MannheimAstron. Astrophys.269199367K.MannheimScience2791998684A.DarA.LaorAstrophys. J.4781997L5F.A.AharonianNew Astron.52000377M.BoettcherAstrophys. J.5151999L21C.D.DermerR.SchlickeiserAstrophys. J.4161993458F.W.SteckerPhys. Rev. Lett.2119681016G.J.FishmanC.A.MeeganAnn. Rev. Astron. Astrophys.331995415For a list of papers related to SWIFT, see: http://swift.gsfc.nasa.gov/docs/swift/results/publist/.B.LinkR.I.EpsteinAstrophys. J.4661996764C.A.MeeganNature3551992143M.R.MetzgerNature3871997878See e.g.,T.PiranPhys. Rep.3141999575T.PiranPhys. Rep.3332000529For a recent review of GRB phenomenology, see:P.MeszarosRep. Prog. Phys.6920062259E.WaxmanLect. Notes Phys.5762001122M.MilgromV.UsovAstrophys. J.4491995L37E.WaxmanPhys. Rev. Lett.751995386M.VietriPhys. Rev. Lett.7819974328D.BandAstrophys. J.4131993281F. Halzen, in: K. Oliver (Ed.), Proceedings of the TASI’98, Boulder, 1998, p. 524.J.W.ElbertP.SommersAstrophys. J.4411995151L.A.AnchordoquiG.E.RomeroJ.A.CombiPhys. Rev. D601999103001L.A. Anchordoqui, J.F. Beacom, H. Goldberg, S. Palomares-Ruiz, T.J. Weiler, arXiv:astro-ph/0611580; arXiv:astro-ph/0611581.The factor 9/(4R) results from calculating ∫dr∫dr|r-r|(4πR/3), where r is the position of a star and r is the position of an observer (the position of the reaction), in a region of radius R uniformly filled with sources.D.A.ForbesM.J.WardV.RotaciucM.BlietzR.GenzelS.DrapatzP.P.van der WerfA.KrabbeAstrophys. J.4061993L11P. Chanial, H. Flores, B. Guiderdoni, D. Elbaz, F. Hammer, L. Vigroux, arXiv:astro-ph/0610900.P.O.LagageC.J.CesarskyAstron. Astrophys.1181983223S.P.LaiJ.M.GirartR.CrutcherAstrophys. J.5982003392W.BednarekMon. Not. R. Astron. Soc.3452003847W.BednarekR.J.ProtheroeAstropart. Phys.162002397P.BlasiA.V.OlintoPhys. Rev. D591999023001F.W.SteckerAstropart. Phys.262007398F.W. Stecker, arXiv:astro-ph/0610208.A γ-ray signal from the nearby starburst galaxy NGC253 was reported by the CANGAROO-II Collaboration but their subsequent re-analysis of the data is consistent with the expectation from backgrounds:C.ItohCANGAROO-II CollaborationAstron. Astrophys.3962002L1(Erratum-ibid. 462 (2007) 67)T.A. Thompson, E. Quataert, E. Waxman, A. Loeb, arXiv:astro-ph/0608699.D.J.BirdFly’s Eye CollaborationPhys. Rev. Lett.7119933401D.R.BergmanHiRes CollaborationNucl. Phys. Proc. Suppl.136200440T.Abu-ZayyadHiRes-MIA CollaborationAstrophys. J.5572001686M.NaganoJ. Phys. G181992423V.BerezinskyA.Z.GazizovS.I.GrigorievaPhys. Rev. D742006043005R.U.AbbasiHiRes CollaborationPhys. Rev. Lett.922004151101V.BerezinskyA.Z.GazizovS.I.GrigorievaPhys. Lett. B6122005147V.S.BerezinskyS.I.GrigorievaB.I.HnatykAstropart. Phys.212004617See Fig. 21 in:L.AnchordoquiM.T.DovaA.MariazziT.McCauleyT.PaulS.ReucroftJ.SwainAnn. Phys.3142004145D.AllardE.ParizotE.KhanS.GorielyA.V.OlintoAstron. Astrophys.4432005L29D.AllardE.ParizotA.V.OlintoAstropart. Phys.27200761T.Abu-ZayyadHigh Resolution Fly’s Eye CollaborationAstropart. Phys.232005157P. Sommers, et al., Pierre Auger Collaboration, arXiv:astro-ph/0507150.R.U.AbbasiHiRes CollaborationAstrophys. J.6222005910B.N. Afanasiev, et al., Yakutsk Collaboration, in: M. Nagano (Ed.), Proceedings of the Tokyo Workshop on Techniques for the Study of the Extremely High Energy Cosmic Rays, 1993.J. Knapp, private communication.J.RanftPhys. Rev. D51199564R.S.FletcherT.K.GaisserP.LipariT.StanevPhys. Rev. D5019945710J.EngelT.K.GaisserT.StanevP.LipariPhys. Rev. D4619925013N.N.KalmykovS.S.OstapchenkoA.I.PavlovNucl. Phys. Proc. Suppl.52B19977It is important to stress that the Auger data are still at a preliminary stage and the reconstruction procedures are still to be finalised. However, even allowing for the systematic uncertainties still present, it does appear that at the highest energies fewer events are seen than expected from the AGASA analysis.V.S.BerezinskyG.T.ZatsepinPhys. Lett. B281969423F.W.SteckerAstrophys. J.2281979919R.EngelD.SeckelT.StanevPhys. Rev. D642001093010Z.FodorS.D.KatzA.RingwaldH.TuJCAP03112003015D.De MarcoT.StanevF.W.SteckerPhys. Rev. D732006043003D.HooperA.TaylorS.SarkarAstropart. Phys.23200511M.AveN.BuscaA.V.OlintoA.A.WatsonT.YamamotoAstropart. Phys.23200519A point worth noting at this juncture: If iron nuclei are accelerated to very high energies (much higher than the energy spectrum has been measured), then disintegration can lead to large numbers of protons above the spectrum cutoff. In this case, the resulting cosmogenic neutrino flux is not dramatically suppressed. On the other hand, if iron nuclei are only largely accelerated to around 10eV or less, then the liberated protons will only rarely interact with the CMB to produce pions, hence the cosmogenic neutrino flux will be significantly reduced.

Calibrating the Decline Rate - Peak Luminosity Relation for Type Ia Supernovae

NASA Astrophysics Data System (ADS)

Rust, Bert W.; Pruzhinskaya, Maria V.; Thijsse, Barend J.

2015-08-01

The correlation between peak luminosity and rate of decline in luminosity for Type I supernovae was first studied by B. W. Rust [Ph.D. thesis, Univ. of Illinois (1974) ORNL-4953] and Yu. P. Pskovskii [Sov. Astron., 21 (1977) 675] in the 1970s. Their work was little-noted until Phillips rediscovered the correlation in 1993 [ApJ, 413 (1993) L105] and attempted to derive a calibration relation using a difference quotient approximation Δm15(B) to the decline rate after peak luminosity Mmax(B). Numerical differentiation of data containing measuring errors is a notoriously unstable calculation, but Δm15(B) remains the parameter of choice for most calibration methods developed since 1993. To succeed, it should be computed from good functional fits to the lightcurves, but most workers never exhibit their fits. In the few instances where they have, the fits are not very good. Some of the 9 supernovae in the Phillips study required extinction corrections in their estimates of the Mmax(B), and so were not appropriate for establishing a calibration relation. Although the relative uncertainties in his Δm15(B) estimates were comparable to those in his Mmax(B) estimates, he nevertheless used simple linear regression of the latter on the former, rather than major-axis regression (total least squares) which would have been more appropriate.Here we determine some new calibration relations using a sample of nearby "pure" supernovae suggested by M. V. Pruzhinskaya [Astron. Lett., 37 (2011) 663]. Their parent galaxies are all in the NED collection, with good distance estimates obtained by several different methods. We fit each lightcurve with an optimal regression spline obtained by B. J. Thijsse's spline2 [Comp. in Sci. & Eng., 10 (2008) 49]. The fits, which explain more that 99% of the variance in each case, are better than anything heretofore obtained by stretching "template" lightcurves or fitting combinations of standard lightcurves. We use the fits to compute estimates of Δm15(B) and some other calibration parameters suggested by Pskovskii [Sov. Astron., 28 (1984) 858] and compare their utility for cosmological testing.

Magnetogenesis and magnetothermal equilibria in turbulent galaxy-cluster plasmas

NASA Astrophysics Data System (ADS)

Schekochihin, Alexander

2011-04-01

We do not know the exact mechanism of magnetic field generation in magnetised weakly collisional (or collisionless) turbulent plasma. We do know that large-scale MHD motions in such plasmas are subject to fast small-scale kinetic instabilities (mirror and firehose) triggered (at high beta) by pressure anisotropies and that these anisotropies will always arise in a turbulent plasma. Therefore, standard MHD equations cannot be used to describe the turbulent dynamo. I will argue that the likely scenario in such plasmas is explosively fast growth of magnetic fluctuations to dynamical levels. I will further argue that if an efficient turbulent dynamo is assumed, radiative cooling in such plasmas can be balanced in a thermally stable way by turbulent heating, whose rate is set by the condition that plasma locally remains in a marginal state with respect to the mirror and firehose instabilities. This thermal stability suggests that a cooling catastrophe is not inevitable, although whether this old problem is thus resolved depends on whether a number of assumptions about the nonlinear behaviour of the instabilities, strength of turbulence and efficiency of the dynamo are borne out by first- principles microphysical theory, simulations or plasma experiments.References:A. A. Schekochihin, M. Brueggen, L. Feretti, M. W. Kunz, and L. Rudnick, Space Sci. Rev., in preparation (2011)M. W. Kunz, A. A. Schekochihin, S. C. Cowley, J. J. Binney, and J. S. Sanders, Mon. Not. R. Astron. Soc., in press (2011) [e-print arXiv:1003.2719]M. S. Rosin, A. A. Schekochihin, F. Rincon, and S. C. Cowley, Mon. Not. R. Astron. Soc., in press (2011) [e-print arXiv:1002.4017]A. A. Schekochihin, S. C. Cowley, F. Rincon, and M. S. Rosin, Mon. Not. R. Astron. Soc. 405, 291 (2010) [e-print arXiv:0912.1359]A. A. Schekochihin, S. C. Cowley, R. M. Kulsrud, M. S. Rosin, and T. Heinemann, Phys. Rev. Lett. 100, 081301 (2008) [e-print arXiv:0709.3828]A. A. Schekochihin and S. C. Cowley, Phys. Plasmas 13, 056501 (2006) [e-print astro-ph/0601246]A. A. Schekochihin, S. C. Cowley, R. M. Kulsrud, G. W. Hammett, and P. Sharma, Astrophys. J. 629, 139 (2005) [e-print astro-ph/0501362

The nature of albedo features on Mercury, with maps for the telescopic observer. Part II: The nature of the albedo markings

NASA Astrophysics Data System (ADS)

Graham, D. L.

1995-04-01

Part One of this paper (J. Brit. Astron. Assoc., 105(1), 1995) reviewed the classical telescopic observations of albedo markings on Mercury and reproduced the definitive albedo map to assist visual observers of the planet. In Part Two, an investigation into the relationship between albedo and physiography is conducted, and the significance of the historical observations is discussed.

Proceedings of Colloquium 110 of the International Astronomical Union on Library and Information Services in Astronomy Held in Washington, DC on 26 July- 1 August 1988

DTIC Science & Technology

1989-01-01

executive overview, IBM System Service, Stuttgart. 2. Doyen, P., 1987. Analyse d’opportunite et aspects fonctionnels d’une gestion integree par un systeme...Inst. di Astron. Tucson, AZ 85726-6732 Campus do Vale Citta. Universitaria 90049 Porto Alegre RS Viale A. Doris Mo. Vagiawari Alladi BRAZIL 1-95125

The Universe Observation Center: an educational center devoted to Astronomy in Catalonia

NASA Astrophysics Data System (ADS)

Fernández, D.

The Universe Observation Center (in Catalan language, Centre d'Observació de l'Univers, COU) is located in close proximity to the Montsec Astronomical Observatory (Observatori Astronòmic del Montsec, OAM), in eastern Catalonia (Spain). Both centers comprise the Montsec Astronomical Park (Parc Astronòmic Montsec, PAM), managed by the Consorci del Montsec. Montsec Mountain remains the finest location for astronomical observation in Catalonia, as demonstrated by a site-testing campaign conducted by the Astronomy and Meteorology Department of the University of Barcelona. The COU consists of a Central Building (including a permanent exhibition and three classrooms possessing broadband Internet access), the Telescope Park (two astronomical domes equipped with medium-size telescopes, a coelostat for solar observation, and a portable telescope park), the Eye of Montsec (a digital planetarium and, at the same time, an extremely innovative platform for sky observation) and the Garden of the Universe (a tour of the land surrounding the COU, visiting several areas within it). The COU will offer to the Spanish academic community a host of fascinating and unique activities in the fields of astronomy and geology. The Center is open not only to students (from primary school through university), but also to amateur astronomers, people interested in science and the general public.

Amsterdam-ASTRON radio transient facility and analysis centre: towards a 24 x 7, all-sky monitor for the low-frequency array (LOFAR).

PubMed

Prasad, Peeyush; Wijnholds, Stefan J

2013-06-13

The Amsterdam-ASTRON Radio Transient Facility And Analysis Centre (AARTFAAC) project aims to implement an all-sky monitor (ASM), using the low-frequency array (LOFAR) telescope. It will enable real-time, 24 × 7 monitoring for low-frequency radio transients over most of the sky locally visible to the LOFAR at time scales ranging from seconds to several days, and rapid triggering of follow-up observations with the full LOFAR on detection of potential transient candidates. These requirements pose several implementation challenges: imaging of an all-sky field of view, low latencies of processing, continuous availability and autonomous operation of the ASM. The first of these has already resulted in the correlator for the ASM being the largest in the world in terms of the number of input data streams. We have carried out test observations using existing LOFAR infrastructure, in order to quantify and constrain crucial instrumental design criteria for the ASM. In this study, we present an overview of the AARTFAAC data-processing pipeline and illustrate some of the aforementioned challenges by showing all-sky images obtained from one of the test observations. These results provide quantitative estimates of the capabilities of the instrument.

Study of the Local Horizon. (Spanish Title: Estudio del Horizonte Local.) Estudo do Horizonte Local

NASA Astrophysics Data System (ADS)

Ros, Rosa M.

2009-12-01

The study of the horizon is fundamental to easy the first observations of the students at any education center. A simple model, to be developed in each center, allows to easy the study and comprehension of the rudiments of astronomy. The constructed model is presented in turn as a simple equatorial clock, other models (horizontal and vertical) may be constructed starting from it. El estudio del horizonte es fundamental para poder facilitar las primeras observaciones de los alumnos en un centro educativo. Un simple modelo, que debe realizarse para cada centro, nos permite facilitar el estudio y la comprensión de los primeros rudimentos astronómicos. El modelo construido se presenta a su vez como un sencillo modelo de reloj ecuatorial y a partir de él se pueden construir otros modelos (horizontal y vertical). O estudo do horizonte é fundamental para facilitar as primeiras observações dos alunos num centro educativo. Um modelo simples, que deve ser feito para cada centro, permite facilitar o estudo e a compreensão dos primeiros rudimentos astronômicos. O modelo construído apresenta-se, por sua vez, como um modelo simples de relógio equatorial e a partir dele pode-se construir outros modelos (horizontal e vertical)

RadioAstron Science Program Five Years after Launch: Main Science Results

NASA Astrophysics Data System (ADS)

Kardashev, N. S.; Alakoz, A. V.; Andrianov, A. S.; Artyukhov, M. I.; Baan, W.; Babyshkin, V. E.; Bartel, N.; Bayandina, O. S.; Val'tts, I. E.; Voitsik, P. A.; Vorobyov, A. Z.; Gwinn, C.; Gomez, J. L.; Giovannini, G.; Jauncey, D.; Johnson, M.; Imai, H.; Kovalev, Y. Y.; Kurtz, S. E.; Lisakov, M. M.; Lobanov, A. P.; Molodtsov, V. A.; Novikov, B. S.; Pogodin, A. V.; Popov, M. V.; Privesenzev, A. S.; Rudnitski, A. G.; Rudnitski, G. M.; Savolainen, T.; Smirnova, T. V.; Sobolev, A. M.; Soglasnov, V. A.; Sokolovsky, K. V.; Filippova, E. N.; Khartov, V. V.; Churikova, M. E.; Shirshakov, A. E.; Shishov, V. I.; Edwards, P.

2017-12-01

The RadioAstron ground-space interferometer provides the highest angular resolution achieved now in astronomy. The detection of interferometric fringes from quasars with this angular resolution on baselines of 100-200 thousand km suggests the brightness temperatures which exceed the Compton limit by two orders of magnitude. Polarimetric measurements on ground-space baselines have revealed fine structure testifying to recollimation shocks on scales of 100-250 μas and a helical magnetic field near the base of radio emission in BL Lacertae. Substructure within a the scattering disk of pulsar emission on interferometer baselines (from 60000 to 250000 km) was discovered. This substructure is produced by action of the interstellar interferometer with an effective baseline of about 1 AU and the effective angular resolution of better than 1 μas. Diameters of scattering disks were measured for several pulsars, and distances to diffusing screens were evaluated. The ground-space observations of sources of the maser radiation in lines of water and hydroxyl have shown that the maser sources in star-forming regions remain unresolved on baselines, which considerably exceed the Earth diameter. These very compact and bright features with angular sizes of about 20-60 μas correspond to linear sizes of about 5-10 million km (several solar diameters).

The diffuse neutrino flux from FR-II radio galaxies and blazars: A source property based estimate

NASA Astrophysics Data System (ADS)

Becker, Julia K.; Biermann, Peter L.; Rhode, Wolfgang

2005-05-01

Water and ice Cherenkov telescopes of the present and future aim for the detection of a neutrino signal from extraterrestrial sources at energies Eν > PeV [Woschnagg and AMANDA Collaboration, Astro-ph/0409423, talk at Neutrino 2004; Montaruli, in: Peter W. Gorham, Particle Astrophysics Instrumentation, Proceedings of the SPIE, vol. 4858, 2003, p. 92; IceCube Collaboration, Astropart. Phys. 20 (2004) 507]. Some of the most promising extragalactic sources are active galactic nuclei (AGN). In this paper, the neutrino flux from two kinds of AGN sources will be estimated assuming pγ interactions in the jets of the AGN. The first analyzed sample contains FR-II radio galaxies while the second AGN type examined are blazars. The result is highly dependent on the proton's index of the energy spectrum. To normalize the spectrum, the connection between neutrino and disk luminosity will be used by applying the jet-disk symbiosis model from Falcke and Biermann [Astron. Astrophys. 293 (1995) 665]. The maximum proton energy and thus, also the maximum neutrino energy of the source is connected to its disk luminosity, which was shown by Lovelace [Nature 262 (1976) 649] and was confirmed by Falcke et al. [Astron. Astrophys. 298 (1995) 375].

Ajuste de parámetros libres en teorías de campos camaleones a partir de espectros de nubes moleculares galácticas y experimentos terrestres

NASA Astrophysics Data System (ADS)

Teppa Pannia, F. A.; Landau, S. J.

Resultados recientes, basados en el análisis de espectros moleculares de nubes galácticas a través del método del amoníaco, han arrojado nuevos límites sobre la variación del parámetro adimensional μ=m_e /m_p. Los resultados indican Δ μ/μ = (μ_{obs}-μ_{lab})/μ_{lab}= (2.2± 0.4_{est} ±0.3_{sist}) times 10 ^{-8}, en acuerdo con una variación no nula de dicha cantidad (Levshakov et al. 2010). En este trabajo, motivado por los datos astronómicos, estudiamos la solución lineal del modelo teórico fenomenológico de campo escalar camaleón, presentado por Mota y Shaw (2007), que predice variaciones en μ. Con el fin de cotejar estas predicciones con los resultados observacionales, utilizamos datos de experimentos terrestres que testean violaciones al Principio de Equivalencia para analizar el valor de los parámetros libres presentes en el modelo. El trabajo realizado muestra que la solución estudiada no se puede ajustar a los datos experimentales, sugiriendo que el modelo lineal debe ser descartado para explicar las observaciones astronómicas. FULL TEXT IN SPANISH

Practical Astronomical Activities during Daytime. (Spanish Title: Actividades Astronómicas Prácticas Diurnas.) Atividades Astronômicas Práticas Diurnas

NASA Astrophysics Data System (ADS)

Jackson, Eric

2009-12-01

These daytime astronomy activities arose from research done in New Zealand by a group of teachers and astronomers into the problems of teaching astronomy. This showed that it was generally regarded as a difficult subject to take, traditionally relying on books, films and models. The fortunate may have had a visit to an observatory or planetarium, the adventurous may have attempted an outdoor evening viewing session, which sometimes had weather-related difficulties. The problem of not having many 'hands-on' activities, the feelings of inadequate knowledge, the felt need for astronomical equipment and expertise become too daunting for many teachers to do the subject justice. If astronomy was to be taught then a way around these difficulties needed to be found. Our group, working with teachers and children using the constructivism teaching approach, found that the principles of astronomy could be discovered during the day when the students are at school. Working co-operatively they measured and recorded observations of their shadows caused by the motions and interactions of the nearest star, the Sun (Sol), and our planet, Earth. Because children were involved so personally they were much more interested in the results of the study. Astronomy became enthralling and challenging for both teacher and class after applying their daytime experiences to night time viewing at home and reporting back to class. Estas actividades astronómicas diurnas surgieron de una investigación hecha en NuevaZelandia por un grupo de maestros y astrónomos sobre los problemas de la enseñanza de la Astronomía. Este trabajo mostró que la Astronomía es generalmente considerada una disciplina difícil de enseñar, y tradicionalmente basada en libros, filmes y modelos. Los más afortunados pueden haber efectuado alguna visita a un observatorio o planetario, y los más aventajados pueden tal vez haber intentado una sesión de observación nocturna, las cuales sufren a veces de dificultades relacionadas al mal tiempo. El problema de no tener suficientes actividades prácticas, la sensación de poseer conocimientos inadecuados, la necesidad de disponer de equipamiento astronómico y experiencia suelen ser demasiado intimidantes para que los profesores introduzcan la materia en sus clases. Si la Astronomía iba a ser introducida, entonces era preciso encontrar una forma de resolver estas dificultades. Nuestro grupo, trabajando con maestros y alumnos dentro de un marco constructivista, encontró que los principios de la Astronomía pueden ser descubiertos durante el día, en cuanto los alumnos están en la escuela. Trabajando de forma cooperativa los alumnos midieron y registraron observaciones de sus propias sombras causadas por los movimientos de la estrella más próxima, el Sol, y nuestro planeta Tierra. Debido a que los alumnos se involucraran tan personalmente en las actividades, estuvieron mucho más interesados en los resultados del estudio. La Astronomía pasó a ser un desafío para el maestro y sus alumnos cuando aplicaron sus experiencias diurnas a la observación nocturna desde sus casas, reportada después en clase. Estas atividades astronômicas diurnas surgiram de uma investigação feita na Nova Zelândia por um grupo de professores e astrônomos a respeito dos problemas do ensino da Astronomia. Este trabalho mostrou que a Astronomia é geralmente considerada uma disciplina difícil de ensinar, tradicionalmente baseada em livros, filmes e modelos. Os mais afortunados podem ter feito alguma visita a um observatório ou planetário, e os mais avançados podem talvez ter tentado uma sessão de observação noturna, as quais sofrem às vezes de dificuldades relacionadas ao tempo. O problema de não dispor de suficientes atividades práticas, a sensação de possuir conhecimentos inadequados, a necessidade de dispor de equipamento astronômico e experiência tem sido, em geral, demasiado intimidante para que os professores introduzam a matéria nas suas aulas. Se a Astronomia ia ser introduzida, então era preciso encontrar uma forma de resolver essas dificuldades. Nosso grupo, trabalhando com professores e alunos numa abordagem construtivista, encontrou que os princípios da Astronomia podem ser descobertos durante o dia, enquanto os alunos estão na escola. Trabalhando de forma cooperativa os alunos mediram e registraram observações de suas próprias sombras causadas pelos movimentos da estrela mais próxima, o Sol, e nosso planeta Terra. Devido ao fato de os alunos se envolverem muito pessoalmente nas atividades, eles ficaram muito mais interessados nos resultados do estudo. A Astronomia passou a ser um desafio para o professor e seus alunos quando aplicaram suas experiências diurnas à observação noturna desde suas casas, relatada depois em sala de aula.

Essays on Eclipses, Transits and Occultations as Teaching Tools in the Introductory Astronomy College Course. (Spanish Title: Ensayos sobre Eclipses, Tránsitos y Ocultaciones Como Herramientas de Enseñanza en el Curso Universitario Introductorio a la Astronomía.) Ensaios sobre Eclipses, Trânsitos e Ocultações Como Ferramentas de Ensino em um Curso Universitário Introdutório de Astromomia

NASA Astrophysics Data System (ADS)

Dcruz, Noella L.

2014-07-01

We occasionally include projects in our learner-centered introductory astronomy college course to enable non-science major students explore some astronomical concepts in more detail than otherwise. Such projects also highlight ongoing or upcoming astronomical events. We hope that students will feel more interested in astronomy through projects tied to astronomical events. In Spring 2012, we offered short essays focused on eclipses, transits and occultations to promote the rare transit of Venus that occurred on June 5th, 2012. We asked students to write two short essays from three that were offered. The essays contained descriptive and conceptual parts. They were meant to serve as teaching tools. 62% of 106 essays from 55 students earned A, B or C grades. 21% of 47 feedback survey respondents felt the essays increased their interest in astronomy. 49% of respondents felt that the essays were not educationally beneficial and should not be offered again. The most common written response to our survey indicated that students need more guidance and better preparation in writing successful essays. Since students found the conceptual parts of the essays difficult, in the future we will provide relevant activities prior to essay deadlines to help students create successful essays. Ocasionalmente, incluimos proyectos en nuestro curso de introducción a la astronomía universitario centrado en el alumno para permitir que los estudiantes de carreras no científicas exploren algunos conceptos astronómicos en más detalle que lo habitual. Estos proyectos también ponen en relevancia eventos astronómicos en curso o futuros. Esperamos que los estudiantes se sientan más interesados en la astronomía a través de proyectos vinculados a eventos astronómicos. En el período de primavera de 2012 (EUA), propusimos breves ensayos centrados en los eclipses, tránsitos y ocultaciones para promover el raro tránsito de Venus que se produjo el 5 de junio de 2012. Le pedimos a los estudiantes que escribieran dos ensayos cortos de tres que se proponían. Los ensayos contenían partes descriptivas y conceptuales. Los mismos estaban destinados a servir como herramientas de enseñanza. 62% de los 106 ensayos de 55 estudiantes obtuvo grados A, B o C. 21% de los 47 encuestados que respondieron al cuestionario posterior consideró que los ensayos aumentaron su interés por la astronomía. 49% de los encuestados consideró que los ensayos no eran educacionalmente útiles y que no deben ser propuestos de nuevo. Las respuestas escritas más comunes a nuestra encuesta indicaran que los estudiantes necesitan más orientación y una mejor preparación en la redacción de ensayos exitosos. Dado que los estudiantes encontraron las piezas conceptuales de los ensayos difíciles, en el futuro vamos a ofrecer actividades pertinentes antes de los plazos de redacción para ayudar a los estudiantes a crear ensayos de mayor calidad. Nós ocasionalmente incluímos projetos em nosso curso universitário introdutório centrado no aluno para permitir aos estudantes que pertencem às carreiras não científicas explorar alguns conceitos astronômicos em mais detalhes do que o normal. Tais projetos também enfatizam eventos astronômicos em curso ou futuros. Esperamos que os alunos se sintam mais interessados na astronomia através de projetos ligados a eventos astronômicos. No termo de Primavera de 2012 (EUA), propomos ensaios curtos focados em eclipses, trânsitos e ocultações para promover o raro trânsito de Vênus que ocorreu no dia 5 de junho de 2012. Pedimos aos alunos que escrevessem dois ensaios curtos dentre três que foram propostos. Os ensaios continham partes descritivas e conceituais. Eles foram feitos para servir como ferramentas de ensino. 62% de 106 ensaios de 55 alunos ganhou graus A, B ou C. 21% dos 47 entrevistados que responderam ao levantamento posterior sentiu que os ensaios aumentaram seu interesse na astronomia. 49% dos inquiridos consideraram que os ensaios não eram benéficos para a educação e que não devem ser propostos novamente. As respostas escritas mais comuns da nossa pesquisa indicaram que os alunos precisam de mais orientação e melhor preparação para escrever ensaios bem sucedidos. Como os alunos consideraram difíceis os aspectos conceituais dos ensaios, no futuro iremos fornecer atividades relevantes antes dos ensaios para ajudar os alunos a escrevê-los com sucesso.

ISO-LWS Spectroscopy of Centaurus A: Extended Star Formation

DTIC Science & Technology

2000-01-01

Astron. Astrophys. 355, 885–890 (2000) ASTRONOMY AND ASTROPHYSICS ISO-LWS spectroscopy of Centaurus A: extended star formation S.J. Unger1, P.E...University of Maryland, College Park, MD, USA Received 31 August 1999 / Accepted 18 January 2000 Abstract. We present the first full FIR spectrum of Centaurus ...individual: Centaurus A = NGC 5128 – infrared: galaxies – galaxies: ISM – galaxies: starburst – galax- ies: active 1. Introduction Centaurus A (NGC 5128

Optical classification of 8 INTEGRAL sources

NASA Astrophysics Data System (ADS)

Masetti, N.; Morelli, L.; Palazzi, E.; Stephen, J.; Bazzano, A.; Dean, A. J.; Walter, R.; Minniti, D.

2006-03-01

On 20-22 March 2006 we used the R-C spectrograph of the CTIO 1.5m telescope in Cerro Tololo (Chile) to get optical spectra of the putative counterparts of 8 X-ray sources discovered by INTEGRAL (see Bird et al. 2006, ApJ, 636, 765; Halpern 2005, ATel #572; Kuiper et al. 2006, ATel #684; Sazonov et al. 2005, A&A, 444, L37; Revnivtsev et al. 2006, Astron. Lett., 32, 145).

Course Lectures Abstracts of Participants Fellows Project Reports

DTIC Science & Technology

1990-10-01

Whitehead and Karl R. Helfrich 188 A Long Laboratory Salt Finger George Veronis 189 Applications of Compactly Supported Wavelets to the Numerical Solution...when it is negative, we have instability. This criterion for the onset of convection is called the Schwarzschild criterion, after one of the many who...and Astrophys. 85, 263-264 (1980) [14] Schwarzschild M., Harm R., Ap.J. 184, 5-8 (1973) [15) Shibahashi H., Osaki Y., Unno W., Publ. Astron. Soc

Astronomía y Física: un matrimonio Sartriano

NASA Astrophysics Data System (ADS)

Vucetich, H.

Desde el siglo XVII, Física y Astronomía han formado un matrimonio similar al de Sartre y Beauvoir: lleno de amores contingentes, pero firme y duradero. En la charla examino tres de los frutos más recientes de este matrimonio: - La confirmación de la Relatividad General con datos astronómicos. - Astrofísica y Física de neutrinos. - Teorías de supercuerdas y astronomía.

Ways of Changing the Number and Size Distribution of Ecliptic Comets

NASA Astrophysics Data System (ADS)

Dones, Henry C. Luke; Womack, Maria; Alvarellos, Jose; Bierhaus, Edward B.; Bottke, William; Hamill, Patrick; Nesvorny, David; Robbins, Stuart J.; Zahnle, Kevin

2017-06-01

The existence of the Kuiper Belt was proposed because of the need for a low-inclination source for the Jupiter-family comets (JFCs). Indeed, the Kuiper Belt is thought to be the main reservoir of ecliptic comets (ECs), which include the JFCs and Centaurs. Ironically, we still do not know whether the belt, specifically its Scattered Disk, provides an adequate source for the ECs (Volk and Malhotra 2008). ECs are also thought to be the main source of Sun-orbiting impactors on the regular moons of the giant planets (Zahnle et al. 2003 [Z03]). Some models of the cometary orbital distribution used by Z03 and others to estimate impact rates assume comets are indestructible; in fact, many cometssplit, sometimes far from the Sun (Fernández 2009). Assuming shatterproof comets may lead to incorrect results for cometary orbital distributions. Other models impose a physical lifetime for bodies that approach within ~3 AU of the Sun, where sublimation of water ice begins, after which a comet is assumed to be dormant or disrupted (Nesvorný et al. 2017). In reality, some comets (e.g., 29P, Hale-Bopp) are active due to volatiles such as CO and CO2 beyond the orbit of Jupiter (Womack et al. 2017). 174P/Echeclus underwent a 7-magnitude outburst 13 AU from the Sun (Rousselot et al. 2016), and CO emission was recently detected from Echeclus at 6 AU (Wierzchos et al. 2017). We will estimate the effects of several mechanisms on the number and size distribution of comet nuclei as a function of distance from the Sun, including cometary activity and spontaneous disruption; tidal disruption by a giant planet, as happened for Shoemaker-Levy 9; and tidal disruption of binaries, which are numerous among "cold classical" Kuiper Belt Objects (Fraser et al. 2017). We thank the Cassini Data Analysis Program for support.Fernández Y (2009). Planet. Space. Sci. 57, 1218.Fraser WC, et al. (2017). Nat. Astron. 1, 0088.Nesvorný D, et al. (2017). In preparation.Rousselot P, et al. (2016). MNRAS 462, S432.Volk K, Malhotra R (2008). Astrophys. J. 687, 714.Wierzchos K, Womack M, Sarid G. (2017). Astron. J., in press.Womack M, Sarid G, Wierzchos, K (2017). Publ. Astron. Soc. Pac. 129, 031001.Zahnle K, et al. (2003). Icarus 163, 263.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kalemci, Emrah

This work summarizes the efforts in Turkey to build a laboratory capable of building and testing high energy astrophysics detectors that work in space. The EC FP6 ASTRONS project contributed strongly to these efforts, and as a result a fully operational laboratory at Sabanci University have been developed. In this laboratory we test and develop Si and CdZnTe based room temperature semiconductor strip detectors and develop detector and electronics system to be used as a payload on potential small Turkish satellites.

The effect of accelerated ageing on colour stability of visible light-cured (VLC) chairside denture liners.

PubMed

Kostoulas, Ioannis; Polyzois, Gregory; Mitsoudis, Anastasios; Kavoura, Victoria; Frangou, Maria

2012-06-01

The purpose of this study was to assess the colour stability of seven visible light-cured (VLC) hard and soft denture liners by an in vitro accelerated ageing test and compare them with two autopolymerised hard and soft liners. Ten specimens of each material were fabricated. The initial colour was measured with a tri-stimulus colorimeter. One set of five specimens was placed in distilled water at 37°C in the dark for 15 days, while the remaining were subjected to UV/visible light-accelerated ageing initially for 24 h and then for 144 h. Colour change (ΔΕ) was calculated. Data were statistically analysed by anova, Tukey and t-tests at α = 0.05. All the liners showed clinically acceptable colour change (ΔΕ ≤ 6.8) in distilled water. The colour changes after ageing for Triad DuaLine, Lightdon U, Ufi Gel H and Light Liner Hard were clinically unacceptable (ΔΕ ≥ 6.8), whereas LightLiner Soft, Astron LC Soft, Triad Resiline and Flexacryl Soft presented slighter and clinically acceptable colour change (ΔΕ ≤ 6.8). Accelerated ageing affected significantly the colour stability of all denture liners tested except Astron LC Soft. Soft VLC denture liners were more colour-stable than hard VLC liners. © 2011 The Gerodontology Society and John Wiley & Sons A/S.

Improved electron collisional line broadening for low-temperature ions and neutrals in plasma modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johns, H. M.; Kilcrease, D. P.; Colgan, J.

In this study, electron collisional broadening of observed spectral lines depends on plasma electron temperature and density. Including this effect in models of measured spectra is necessary to determine plasma conditions; however, computational limits make accurate line broadening treatments difficult to implement in large-scale plasma modeling efforts. In this paper, we report on improvements to the treatment of electron collisional line broadening and illustrate this with calculations using the Los Alamos ATOMIC code. We implement the Dimitrijevic and Konjevic modified semi-empirical model Dimitrijevic and Konjevic (1986 Astron. and Astrophy. 163 297 and 1987 Astron. Astrophys. 172 345), which we amendmore » by employing oscillator strengths from Hartree–Fock calculations. This line broadening model applies to near-neutral plasmas with electron temperatures of Te ~ 1 eV and electron densities of N e ~10 17 cm -3. We evaluate the D.K.-inspired model against the previous hydrogenic approach in ATOMIC through comparison to NIST-rated measurements for selected neutral and singly-ionized Ca, O, Fe, and Sn lines using both fine-structure and configuration-averaged oscillator strengths. The new D.K.-inspired model is significantly more accurate than the previous hydrogenic model and we find the use of configuration-averaged oscillator strengths a good approximation for applications such as LIBS (laser induced breakdown spectroscopy), for which we demonstrate the use of the D.K.-inspired model.« less

Improved electron collisional line broadening for low-temperature ions and neutrals in plasma modeling

DOE PAGES

Johns, H. M.; Kilcrease, D. P.; Colgan, J.; ...

2015-09-29

In this study, electron collisional broadening of observed spectral lines depends on plasma electron temperature and density. Including this effect in models of measured spectra is necessary to determine plasma conditions; however, computational limits make accurate line broadening treatments difficult to implement in large-scale plasma modeling efforts. In this paper, we report on improvements to the treatment of electron collisional line broadening and illustrate this with calculations using the Los Alamos ATOMIC code. We implement the Dimitrijevic and Konjevic modified semi-empirical model Dimitrijevic and Konjevic (1986 Astron. and Astrophy. 163 297 and 1987 Astron. Astrophys. 172 345), which we amendmore » by employing oscillator strengths from Hartree–Fock calculations. This line broadening model applies to near-neutral plasmas with electron temperatures of Te ~ 1 eV and electron densities of N e ~10 17 cm -3. We evaluate the D.K.-inspired model against the previous hydrogenic approach in ATOMIC through comparison to NIST-rated measurements for selected neutral and singly-ionized Ca, O, Fe, and Sn lines using both fine-structure and configuration-averaged oscillator strengths. The new D.K.-inspired model is significantly more accurate than the previous hydrogenic model and we find the use of configuration-averaged oscillator strengths a good approximation for applications such as LIBS (laser induced breakdown spectroscopy), for which we demonstrate the use of the D.K.-inspired model.« less

Energy Levels, wavelengths and hyperfine structure measurements of Sc II

NASA Astrophysics Data System (ADS)

Hala, Fnu; Nave, Gillian

2018-01-01

Lines of singly ionized Scandium (Sc II) along with other Iron group elements have been observed [1] in the region surrounding the massive star Eta Carinae [2,3] called the strontium filament (SrF). The last extensive analysis of Sc II was the four-decade old work of Johansson & Litzen [4], using low-resolution grating spectroscopy. To update and extend the Sc II spectra, we have made observation of Sc/Ar, Sc/Ne and Sc/Ge/Ar hollow cathode emission spectrum on the NIST high resolution FT700 UV/Vis and 2 m UV/Vis/IR Fourier transform spectrometers (FTS). More than 850 Sc II lines have been measured in the wavelength range of 187 nm to 3.2 μm. connecting a total of 152 energy levels. The present work also focuses to resolve hyperfine structure (HFS) in Sc II lines. We aim to obtain accurate transition wavelengths, improved energy levels and HFS constants of Sc II. The latest results from work in progress will be presented.Reference[1] Hartman H, Gull T, Johansson S and Smith N 2004 Astron. Astrophys. 419 215[2] Smith N, Morse J A and Gull T R 2004 Astrophys. J. 605 405[3] Davidson K and Humphreys R M 1997 Annu. Rev. Astron. Astrophys. 35[4] Johansson S and Litzén U 1980 Phys. Scr. 22 49

Observatorio Astronómico De Cantabria

NASA Astrophysics Data System (ADS)

Domínguez, R. M.; Carrera, F. J.

The Astronomical Observatory of Cantabria is a center of the Consejería de Medio Ambiente del Gobierno de Cantabria managed by the Centro de Investigación del Medio Ambiente (CIMA), an autonomous organism which depends on such Consejería. The development of different activities of the Observatory is a joint collaboration between the University of Cantabria and the Agrupación Astronómica Cántabra (AstroCantabria). As part of the University of Cantabria, the Instituto de Física de Cantabria (IFCA, CSIC-UC) is in charge of the direction, management and coordination of scientific, observational, educational and outreach activities of the Observatory. AstroCantabria takes care of the outreach activities for the general public as well as the astronomical observations. In addition, it is responsible for the calibration and maintenance of the astronomical instrumentation of the Observatory. The Astronomical Observatory of Cantabria is located on the Southern edge of the Comunidad Autónoma de Cantabria, on the high plateau of La Lora (Valderredible county), at an altitude of 1,080m, with longitude 3∘ 56 ' 36' W and latitude 42∘ 46 ' 18' N. Rocamundo is the closest town. The Observatory aims to become a center of reference for scientific, observational, educational and public outreach activities in Cantabria. In the near future, an observational proposal system for outside users will be set in place.

Application of Three-Dimensional Models for the Teaching of Time Zones. (Breton Title: Aplicação de Modelos Tridimensionais Para o Ensino de Fusos Horários.) Aplicación de Modelos Tridimensionales Para la Enseñanza de Husos Horarios

NASA Astrophysics Data System (ADS)

Azevedo Sobreira, Paulo Henrique

2012-07-01

There are several interesting astronomical topics that must be addressed in the High School and Elementary/Middle School in the disciplines of Geography and of Sciences. Among them, the topic of time zones which is one of the most important to understand the correlation of the Earth's rotation and its implications on daily activities of citizens in local scale, regional and global scales which involve problems of time differences. For the teaching of time zones in the lessons of Geography, for example, there are bi-dimensional representations of thematic maps of world time zones, textbooks and atlas. It happens that teachers face some difficulties to permit its students to view three-dimensionally this astronomical phenomenon from the textbooks available in schools. The aim of this paper is to present two proposals with low-cost materials, which allow the preparation of three-dimensional models for the teaching of time zones. Há vários temas astronômicos interessantes que devem ser trabalhados nos Ensinos Médio e Fundamental, nas disciplinas de Geografia e de Ciências. Entre eles, o tema dos fusos horários que é um dos mais importantes para se correlacionar a rotação da Terra e suas implicações nas atividades cotidianas dos cidadãos em escala local, regional e global, que envolvem problemas de diferenças horárias. Para o ensino dos fusos horários nas aulas de Geografia, por exemplo, há representações bidimensionais de mapas temáticos de fusos horários mundiais, nos livros didáticos e nos atlas. Ocorre que os professores enfrentam algumas dificuldades para possibilitar aos seus alunos a visão tridimensional deste fenômeno astronômico, a partir dos materiais didáticos disponíveis nas escolas. O objetivo deste trabalho é apresentar duas propostas para a confecção de materiais de baixo custo, que possibilitem a elaboração de modelos tridimensionais para o ensino dos fusos horários. Hay algunos temas astronómicos interesantes que se deben trabajar en la enseñanza media y básica, en las asignaturas de Geografía y de Ciencias. Entre ellos, el de los husos horarios que es uno de los más importantes para correlacionar la rotación de la Tierra y sus implicaciones en las actividades diarias de los ciudadanos en escala local, regional y global, y en general, cuestiones que implican problemas de las diferencias horarias. Para la enseñanza de los husos horarios en las clases de Geografía, por ejemplo, hay representaciones bidimensionales de los mapas temáticos de husos horarios mundiales, en libros y atlas didácticos. Sin embargo, los profesores se enfrentan con algunas dificultades para hacer posible que sus alumnos tengan una visión tridimensional de este fenómeno astronómico, usando los materiales didácticos disponibles en las escuelas. El objetivo de este trabajo es presentar la construcción de dos propuestas de materiales de bajo costo, que hacen posible la elaboración de modelos tridimensionales para la enseñanza de los husos horarios.

Learning Astronomy by Playing in a Park. (Spanish Title: Aprender AstronoMía Jugando en Una Plaza.) Aprender Astronomia Brincando em Uma Praça

NASA Astrophysics Data System (ADS)

Camino, Néstor

2012-12-01

Some public-square games are presented in this paper, considered as didactic modules to help children imagine astronomical processes, based on the concept that learning in Astronomy should be developed to strengthen the relationship of our body with three-dimensional space and time, much in the same way we experience when observing the actual sky, holding a permanent "dialogue" between the actual world and what is to be learned. The games presented (merry-go-rounds and slides) were designed to work on the astronomical concepts related to the translation of the Earth around the Sun, the phases of the Moon and gravity, and on what is perceived by an observer about those phenomena. The description of each game, their physical and astronomical foundations, and a critical comment about their didactical importance are the key parts of the paper. Finally, a recommendation is given about the role teachers should play to be essential partners in the process of learning Astronomy by means of the interaction with these games. Se presentan en este trabajo algunos juegos de plaza, considerados como módulos didácticos para imaginar procesos astronómicos, a partir de la concepción de que el aprendizaje en Astronomía debe desarrollarse fortaleciendo la relación del propio cuerpo con el espacio tridimensional y con el tiempo, tal como se vive al observar el cielo, construyendo un "diálogo" entre el mundo real y los aprendizajes a construir. Los juegos presentados (calesitas y toboganes) fueron diseñados para trabajar sobre la traslación de la Tierra en torno al Sol, las fases de la Luna y la gravedad, y sobre lo que un observador percibe de los mismos. Se da la descripción de cada juego, se discuten sus fundamentos físicos y astronómicos, y se desarrolla una crítica didáctica de los mismos. Finalmente, se comenta el rol que deberían tener los docentes en el acompañamiento a los aprendices en el proceso de interacción con los juegos presentados. Apresentam-se neste trabalho alguns jogos de praça, considerados como módulos didáticos para imaginar processos astronômicos, a partir da concepção de que a aprendizagem em Astronomia deve-se desenvolver fortalecendo a relação do próprio corpo com o espaço tridimensional e com o tempo, tal como se vive ao observar o céu, construindo um "diálogo" entre o mundo real e as aprendizagens a construir. Os jogos apresentados (carrosséis e tobogãs) foram desenhados para trabalhar sobre a translação da Terra em torno do Sol, as fases da Lua e a gravidade, e sobre o que um observador percebe dos mesmos. Dá-se a descrição de cada jogo, discutem-se seus fundamentos físicos e astronômicos, e desenvolve-se uma crítica didática dos mesmos. Finalmente, comenta-se o papel que deveriam ter os docentes no apoio aos aprendizes no processo de interação com os jogos apresentados.

Satellite and lunar laser ranging in infrared

NASA Astrophysics Data System (ADS)

Courde, Clement; Torre, Jean-Marie; Samain, Etienne; Martinot-Lagarde, Gregoire; Aimar, Mourad; Albanese, Dominique; Maurice, Nicolas; Mariey, Hervé; Viot, Hervé; Exertier, Pierre; Fienga, Agnes; Viswanathan, Vishnu

2017-05-01

We report on the implementation of a new infrared detection at the Grasse lunar laser ranging station and describe how infrared telemetry improves the situation. We present our first results on the lunar reflectors and show that infrared detection permits us to densify the observations and allows measurements during the new and the full moon periods. We also present the benefit obtained on the ranging of Global Navigation Satellite System (GNSS) satellites and on RadioAstron which have a very elliptic orbit.

Developing an Optical Lunar Occultation Measurement Reduction System for Observations at Kaau Observatory

NASA Astrophysics Data System (ADS)

Malawi, Abdulrahman A.

2013-06-01

We present here a detailed explanation of the reduction method that we use to determine the angular diameters of the stars occulted by the dark limb of the moon. This is a main part of the lunar occultation observation program running at King Abdul Aziz University observatory since late 1993. The process is based on the least square model fitting method of analyzing occultation data, first introduced by Nather et al. (Astron. J. 75:963, 1970).

Towards well posed and robust image reconstruction in optical interferometry: redundant spacing calibration with generalized closure phases

DTIC Science & Technology

2016-05-18

Astrophysical Journal, 809, 61 Arnot N., Atherton P., Greenaway A., Noordam J., 1985, Traite- ment du Signal, 2, 129 Babai L., 1986, Combinatorica, 6, 1 Becker...Buscher, D. F. 2012, Astronomy and Astrophysics , 541, A46 Gorham P., Ghez A., Kulkarni S., Nakajima T., Neugebauer G., Oke J., Prince T., 1989...Series. Series C: Mathematical and Physical Sciences, Vol. 423, Adaptive Optics for Astron- omy. Kluwer Academic Publishers, Boston, USA Greenbaum A

VizieR Online Data Catalog: Baade's variables in Sagitta and Cygnus (Skiff, 1997)

NASA Astrophysics Data System (ADS)

Skiff, B. A.

2002-10-01

The tables below show identifications and precise positions for a group of variables found by Walter Baade (1928AN....232...65B) during his Bergedorfer days. The stars reported in this survey are of some historical interest because it was as a result of this work that Baade conceived ideas that led to his later recognition of the two stellar populations among Galactic stars (cf. Osterbrock, 1995, Journ. Hist. Astron., 26, 1). (3 data files).

Earth Rotation Monitoring, UT1 Determinaiton and Prediction

DTIC Science & Technology

2011-07-20

Reference Frame Astron. Astrophys. 355 398–405 [8] Coulot D, Berio P, Biancale R, Loyer S, Soudarin L and Gontier A-M 2007 Toward a direct combination of...Stamatakos N, Brockett G, Carter M S, Stetzler B and Wooden W 2009 Rapid Service/Prediction Centre contribution to 2007 IERS Annual Report pp 68–77 [25...45 57–73 [37] Thaller D, Krügel M, Rothacher M, Tesmer V, Schmid R and Angermann D 2007 Combined Earth orientation parameters based on homogeneous

Structure of the Extended Emission in the Infrared Celestial Background,

DTIC Science & Technology

1986-09-30

the energy cascade to smaller sizes due to turbulence. Such a steep function would predict little energy in microfilaments at the resolution of a meter...Neugebauer, H.H. Aumann, N. Boggess, J.P. Emerson, J.R. Fuck , B.T. Soifer and R.G. Walker, "IRAS Observations of the Diffuse Infrared Background", Astrophys. J...Astrcphys., Vol. 100, 116, 1981. " 80. Little , S.J. and S.D. Price, "Infrared Mapping of the Galactic Plane. IV. The Galactic Center", Astron. J., Vol

The Theory of Canonical Perturbations Applied to Attitude Dynamics and to the Earth Rotation. Osculating and Nonosculating Andoyer Variables

DTIC Science & Technology

2007-06-21

Hiroshi Kinoshita for his extremely valuable consultations on some subtleties of his theory. ME is also grateful to Pini Gurfil , George Kaplan, Jean...that the Andoyer elements are introduced 20 It can be shown ( Gurfil et al. 2007) that the body-frame-related components gi of the angular momentum are...oblate precessing planet. Astron. J. 70, 5–9 (1965) Goldstein, H.: Classical Mechanics. 2nd ed. Addison-Wesley, Reading MA (1981) Gurfil , P., Elipe

Eventos Planetarios Periodicos

NASA Astrophysics Data System (ADS)

Flores Gutierrez, J. D.

1987-05-01

El análisis de las coordenadas ecuatoriales para los planetas Mercurio, Venus, Marte, Júpiter, Saturno, en los instantes en que ocurren algunos eventos astronómicos, como conjunciones, oposiciones,etc., muestra un comportamiento periódico, característico a cada planeta. El caso de Venus es el mejor estudiado. El cálculo de las efemérides a lo largo de 1000 años , indica un período característico de aproximadamente 260 años. Resultados preliminares con otros planetas muestran períodos distintos.

Double C-NOT attack and counterattack on `Three-step semi-quantum secure direct communication protocol'

NASA Astrophysics Data System (ADS)

Gu, Jun; Lin, Po-hua; Hwang, Tzonelih

2018-07-01

Recently, Zou and Qiu (Sci China Phys Mech Astron 57:1696-1702, 2014) proposed a three-step semi-quantum secure direct communication protocol allowing a classical participant who does not have a quantum register to securely send his/her secret message to a quantum participant. However, this study points out that an eavesdropper can use the double C-NOT attack to obtain the secret message. To solve this problem, a modification is proposed.

PSR B0329+54: Statistics of Substructure Discovered within the Scattering Disk on RadioAstron Baselines of up to 235,000 km

NASA Astrophysics Data System (ADS)

Gwinn, C. R.; Popov, M. V.; Bartel, N.; Andrianov, A. S.; Johnson, M. D.; Joshi, B. C.; Kardashev, N. S.; Karuppusamy, R.; Kovalev, Y. Y.; Kramer, M.; Rudnitskii, A. G.; Safutdinov, E. R.; Shishov, V. I.; Smirnova, T. V.; Soglasnov, V. A.; Steinmassl, S. F.; Zensus, J. A.; Zhuravlev, V. I.

2016-05-01

We discovered fine-scale structure within the scattering disk of PSR B0329+54 in observations with the RadioAstron ground-space radio interferometer. Here we describe this phenomenon, characterize it with averages and correlation functions, and interpret it as the result of decorrelation of the impulse-response function of interstellar scattering between the widely separated antennas. This instrument included the 10 m Space Radio Telescope, the 110 m Green Bank Telescope, the 14 × 25 m Westerbork Synthesis Radio Telescope, and the 64 m Kalyazin Radio Telescope. The observations were performed at 324 MHz on baselines of up to 235,000 km in 2012 November and 2014 January. In the delay domain, on long baselines the interferometric visibility consists of many discrete spikes within a limited range of delays. On short baselines it consists of a sharp spike surrounded by lower spikes. The average envelope of correlations of the visibility function shows two exponential scales, with characteristic delays of {τ }1=4.1+/- 0.3 μ {{s}} and {τ }2=23+/- 3 μ {{s}}, indicating the presence of two scales of scattering in the interstellar medium. These two scales are present in the pulse-broadening function. The longer scale contains 0.38 times the scattered power of the shorter one. We suggest that the longer tail arises from highly scattered paths, possibly from anisotropic scattering or from substructure at large angles.

Deployable Camera (DCAM3) System for Observation of Hayabusa2 Impact Experiment

NASA Astrophysics Data System (ADS)

Sawada, Hirotaka; Ogawa, Kazunori; Shirai, Kei; Kimura, Shinichi; Hiromori, Yuichi; Mimasu, Yuya

2017-07-01

An asteroid exploration probe "Hayabusa2", that was developed by Japan Aerospace Exploration Agency (JAXA), was launched on December 3rd, 2014 to challenge complicated and accurate operations during the mission phase around the C-type asteroid 162137 Ryugu (1999 JU3) (Tsuda et al. in Acta Astron. 91:356-362, 2013). An impact experiment on a surface of the asteroid will be conducted using the Small Carry-on Impactor (SCI) system, which will be the world's first artificial crater creation experiment on asteroids (Saiki et al. in Proc. International Astronautical Congress, IAC-12.A3.4.8, 2012, Acta Astron. 84:227-236, 2013a; Proc. International Symposium on Space Technology and Science, 2013b). We developed a new micro Deployable CAMera (DCAM3) system for remote observations of the impact phenomenon applying our conventional DCAM technology that is one of the smallest probes in space missions and gained a great success in past Japanese mission IKAROS (Interplanetary Kite-craft Accelerated by Radiation Of the Sun). DCAM3 is a miniaturized separable unit that contains two cameras and radio communication devices for transmission image data to the mothership "Hayabusa2", and it observes the impact experiment at an unsafe region in where the "Hayabusa2" is difficult to stay because of a risk of exploding and impacting debris hitting. In this paper, we report details of the DCAM3 system and development results as well as our mission plan for the DCAM3 observation during the SCI experiment.

Shrinking of Binaries in a WIMPY Background at the Galactic Center

NASA Astrophysics Data System (ADS)

Hills, J. G.

2001-12-01

The nature of the dark matter in the Galactic Halo is still not clear. Constraints can be placed on it; e.g., it cannot be in baryons less massive than about 1022 grams (Hills, 1986, Astron. J. 92, 595). It may be in elementary weakly interacting massive particles, WIMPS. Apart from providing most of the mass of the Galaxy, the only known significant dynamical effect of WIMPS is to cause a gradual shrinking of tightly bound binaries (Hills 1983, Astron. J. 88, 1269) as they interact with the background soup of WIMPS. This effect may be observable in binaries close to the Galactic Center if a significant fraction of the mass density near the central black hole is from WIMPS. The requisite binaries would have to have orbital velocities greater than the local velocity dispersion of the WIMPS relative to the binary. The velocity dispersion increases near the black hole. The binary cannot be too close to the black hole or its tidal field will breakup the binary. If the local WIMP density is 107 g/cm3, the fractional rate of reduction in the binary orbital period is about 5 x 10-10/yr for a binary having a semimajor axis equal to 3 solar radii in a soup of WIMPS having a velocity dispersion of 200 km/s relative to the binary. This gradual erosion of the binary period may be detectable, particularly, if one of the binary components is a pulsar.

Conformally non-flat spacetime representing dense compact objects

NASA Astrophysics Data System (ADS)

Singh, Ksh. Newton; Bhar, Piyali; Rahaman, Farook; Pant, Neeraj; Rahaman, Mansur

2017-06-01

A new conformally non-flat interior spacetime embedded in five-dimensional (5D) pseudo Euclidean space is explored in this paper. We proceed our calculation with the assumption of spherically symmetric anisotropic matter distribution and Karmarkar condition (necessary condition for class one). This solution is free from geometrical singularity and well-behaved in all respects. We ansatz a new type of metric potential g11 and solve for the metric potential g00 via Karmarkar condition. Further, all the physical parameters are determined from Einstein’s field equations using the two metric potentials. All the constants of integration are determined using boundary conditions. Due to its conformally non-flat character, it can represent bounded configurations. Therefore, we have used it to model two compact stars Vela X-1 and Cyg X-2. Indeed, the obtained masses and radii of these two objects from our solution are well matched with those observed values given in [T. Gangopadhyay et al., Mon. Not. R. Astron. Soc. 431, 3216 (2013)] and [J. Casares et al., Mon. Not. R. Astron. Soc. 401, 2517 (2010)]. The equilibrium of the models is investigated from generalized TOV-equation. We have adopted [L. Herrera’s, Phys. Lett. A 165, 206 (1992)] method and static stability criterion of Harisson-Zeldovich-Novikov [B. K. Harrison et al., Gravitational Theory and Gravitational Collapse (University of Chicago Press, 1965); Ya. B. Zeldovich and I. D. Novikov, Relativistic Astrophysics, Vol. 1, Stars and Relativity (University of Chicago Press, 1971)] to analyze the stability of the models.

Calidad de Imagen del Telescopio UNAM212

NASA Astrophysics Data System (ADS)

Cobos, F. J.; Teiada de Vargas, C.

1987-05-01

El telescopio UNAM2l2, del Observatorio Astronómico Nacional, situado en la Sierra de San Pedro Mártir (Baja California, México), cumplira en un futuro muy cercano siete años de uso para fines de investigación astronómica. Aunque en este tiempo no se ha efectuado un estudio sistemático acerca de su comportamiento óptico y de los factores que influyen en la calidad de las imágenes, se han realizado pruebas diversas, estudios parciales y reuniones especificas, cuyos resultados no siempre se han difundido ampliamente y generalmente no se han presentado por escrito. Es por ello que hemos creido necesario intentar una recopilación de la información existente para poder con ella establecer un diagnóstjco que, aunque no sea definitivo, sirva de base para futuros trabajos tendientes a optimizar el comportamiento óptico del telescopio. Es evidente que un buen número de las conclusiones que se presentan son resultado del trabajo de muchas personas ó de esfuerzos colectivos. Asimismo, hemos tratado de localizar información bibliográfica que pueda ser de utilidad. Nuestro objetivo primordial ha consistido en centrarnos en la óptica del telescopio y su calidad, pero también se han considerado otros aspectos que puedan afectar las imágenes obtenidas tales como: celda del primario, `seeing' local y externo, flexiones posibles en la estructura mecánica del telescopio, etc.

PSR B0329+54: substructure in the scatter-broadened image discovered with RadioAstron on baselines up to 330 000 km

NASA Astrophysics Data System (ADS)

Popov, Mikhail V.; Bartel, Norbert; Gwinn, Carl R.; Johnson, Michael D.; Andrianov, Andrey; Fadeev, Evgeny; Joshi, Bhal Chandra; Kardashev, Nikolay; Karuppusamy, Ramesh; Kovalev, Yuri Y.; Kramer, Michael; Rudnitskiy, Alexey; Shishov, Vladimir; Smirnova, Tatiana; Soglasnov, Vladimir A.; Zensus, J. Anton

2017-02-01

We have resolved the scatter-broadened image of PSR B0329+54 and detected a substructure within it. These results are not influenced by any extended structure of a source but instead are directly attributed to the interstellar medium. We obtained these results at 324 MHz with the ground-space interferometer RadioAstron, which included the Space Radio Telescope, ground-based Westerbork Synthesis Radio Telescope and 64-m Kalyazin Radio Telescope on baseline projections up to 330 000 km in 2013 November 22 and 2014 January 1 to 2. At short 15 000 to 35 000 km ground-space baseline projections, the visibility amplitude decreases with baseline length, providing a direct measurement of the size of the scattering disc of 4.8 ± 0.8 mas. At longer baselines, no visibility detections from the scattering disc would be expected. However, significant detections were obtained with visibility amplitudes of 3 to 5 per cent of the maximum scattered around a mean and approximately constant up to 330 000 km. These visibilities reflect a substructure from scattering in the interstellar medium and offer a new probe of ionized interstellar material. The size of the diffraction spot near Earth is 17 000 ± 3 000 km. With the assumption of turbulent irregularities in the plasma of the interstellar medium, we estimate that the effective scattering screen is located 0.6 ± 0.1 of the distance from the Earth towards the pulsar.

Qual o Papel da Escola e da Mídia na Obtenção dos Conhecimentos Astronômicos?

NASA Astrophysics Data System (ADS)

da Cunha, W. S.; Voelzke, M. R.; Amaral, L. H.

2007-08-01

É amplamente reconhecido que as pessoas em geral têm grande fascínio e interesse pela Astronomia. Por outro lado, o conteúdo dessa área incluído no ensino formal está longe de ser abrangente e suficiente para suprir a demanda. Esse interesse permite aperfeiçoar a divulgação e o ensino não formal de Astronomia através da mídia aliando a adequação do conteúdo à expectativa das pessoas. A reforma do Currículo Básico da Escola Pública da maioria dos Estados brasileiros tem introduzido Astronomia desde a pré-escola até o Ensino Médio. Num estudo realizado com 1180 alunos do Ensino Médio de seis escolas estaduais, revelou-se através da aplicação de um formulário contendo questões que abordavam conhecimentos básicos em Astronomia, como foram adquiridos tais conhecimentos e à infra-estrutura da escola. Para 66,1% dos entrevistados o professor já fez alguma apresentação a respeito de Astronomia. O presente estudo revelou também que 54,4% dos alunos entrevistados adquiriram seus conhecimentos astronômicos na escola, 18,4% através da televisão e 27,1% afirmaram que seus conhecimentos foram obtidos através de outros tipos de mídia (internet, livros didáticos, filmes e revistas). Embora o estudo revele claramente que há certo equilíbrio no meio em que os alunos obtiveram seus conhecimentos astronômicos, a mídia busca não somente sua difusão, mas a disponibilização desse conhecimento de maneira correta, que às vezes, não é atingido, apresentando conceitos sem fundamentação e incorretos. Por outro lado, no dia-a-dia escolar, é comum encontrar professores que vêm para as aulas com concepções prévias, que podem diferir substancialmente das idéias a serem ensinadas, dificultando o aprendizado de futuros conceitos científicos. Uma avaliação criteriosa, avaliando as dificuldades dos professores em determinar o sentido correto dos conceitos e observando a metodologia que utilizam no ensino, poderá proporcionar uma melhor compreensão sobre as concepções alternativas, presentes no ensino de Astronomia.

Three years of RadioAstron in flight and future prospects

NASA Astrophysics Data System (ADS)

Kardashev, Nikolay

The Russian Academy of Sciences and Federal Space Agency, together with many international organizations, prepared the launch of the RadioAstron orbiting space observatory. The spacecraft was launched by the Ukranian Zenit-3F rocket with onboard 10-m reflector radio telescope (spectral bands 1.2-1.6, 6.2, 18 and 92 cm and both circular polarizations) from the Baikonur cosmodrome on July 18, 2011. The orbital period in 2012-2015 will vary from 8.3 to 9.0 days, the perigee - from 7,065 km to 81,500 km, the apogee - from 280,000 to 353,000 km. Together with ground-based radio telescopes and a set of stations for tracking, collecting, and reducing the data obtained, this space radio telescope forms a multi-antenna ground-space radio interferometer with extremely long baselines, making it possible for the first time to study various objects in the Universe with angular resolutions a million times better than it is possible with the human eye. The project is targeted at systematic studies of compact radio-emitting sources and their dynamics. Objects to be studied include supermassive black holes and relativistic jets in active galactic nuclei, stellar-mass black holes, neutron stars and hypothetical quark stars, regions of formation of stars and planetary systems in our and other galaxies, interplanetary and interstellar plasma, and the gravitational field of the Earth. The fringes with the ground-space interferometer were founded at the baseline projections up to 25 diameters of the Earth, and corresponding models of the sources will be reported. Millimetron is the next space mission with a 10-m cooled space telescope optimized for observations in the millimeter and far infrared wavelengths. This mission will be able to contribute to the solution of several key problems in astrophysics, such as study of formation and evolution of stars and planets, galaxies, quasars and many others. The mission will have a cryogenic instruments and antenna, which will be cooled passively with radiation shields and actively with mechanical coolers. With this cooling combination the 10-m space telescope may reach a temperature of about 4.5 K. The telescope will have an unprecedented sensitivity in the single-dish observation mode in the band 0.02-1.4 mm and an extremely high spatial resolution by ground-space interferometer in the band 0.3-16 mm with maximum baseline 5 times larger than RadioAstron.

On the dark matter as a geometric effect in f (R) gravity

NASA Astrophysics Data System (ADS)

Usman, Muhammad

2016-11-01

A mysterious type of matter is supposed to exist because the observed rotational velocity curves of particles moving around the galactic center and the expected rotational velocity curves do not match. This type of matter is called dark matter. There are also a number of proposals in the modified gravity which are alternatives to the dark matter. In this contrast, in 2008, Christian G. Böhmer, Tiberiu Harko and Francisco S.N. Lobo presented an interesting idea in Böhmer et al. (Astropart Phys 29(6):386-392, 2008) where they showed that a f (R) gravity model could actually explain dark matter to be a geometric effect only. They solved the gravitational field equations in vacuum using generic f (R) gravity model for constant velocity regions (i.e. dark matter regions around the galaxy). They found that the resulting modifications in the Einstein Hilbert Lagrangian is of the form R^{1+m}, where m=V_{tg}^2/c^2; V_{tg} being the tangential velocity of the test particle moving around the galaxy in the dark matter regions and c being the speed of light. From observations it is known that m≈ O(10^{-6}) (Böhmer et al. 2008; Salucci et al. in Mon Not R Astron Soc 378(1):41-47, 2007; Persic et al. in Mon Not R Astron Soc 281:27-47, 1996; Borriello and Salucci in Mon Not R Astron Soc 323(2):285-292, 2001). In this article, we perform two things (1) We show that the form of f (R) they claimed is not correct. In doing the calculations, we found that when the radial component of the metric for constant velocity regions is a constant then the exact solutions for f (R) obtained is of the form of R^{1-α } which corresponds to a negative correction rather than positive claimed by the authors of Böhmer et al. (2008), where α is the function of m. (2) We also show that we can not have an analytic solution of f(R) for all values of tangential velocity including the observed value of tangential velocity 200-300 km/s (Salucci et al. 2007; Persic et al. 1996; Borriello and Salucci 2001) if the radial coefficient of the metric which describes the dark matter regions is not a constant. Thus, we have to rely on the numerical solutions to get an approximate model for dark matter in f (R) gravity.

US Space VLBI Proposed Outreach Web Site

NASA Technical Reports Server (NTRS)

2000-01-01

The study of how VLBI might be pursued in space began in the late 1970's, when it was realized that the size of the earth was a serious limitation to the study of compact radio sources. By going to space, achieving angular resolution at radio wavelengths that could not be obtained with VLBI systems that were limited by the size of the earth, important tests could not be made of quasar models. The technology appeared to be within reach, and an early space VLBI concept, QUASAT, emerged as a joint project, involving both US and European scientists. In 1984, a workshop was held in Gross Enzerdorf, Austria, under joint sponsorship of NASA and the European Space Agency (ESA). The principal conclusion of the workshop was that a VLBI station in space, telemetering its data to ground data stations, working in connection with ground-based radio telescopes, would give the opportunity to achieve angular resolution of a few tens of micro-arc-seconds, and could develop high-quality radio maps of many classes of radio sources. The ground telemetry stations would also function as the source of a stable local oscillator for the spacecraft, which needs a highly stable frequency reference. The Deep Space Network of NASA could play a vital role in both the frequency-locking system and data acquisition. One outcome of the Gross Enzerdorf workshop was the convening, by COSPAR, of an ad hoc Committee on Space VLBI, to review and recommend procedures by which international collaboration on VLBI in space might be coordinated and promoted. In October 1985, the committee met in Budapest and recommended that the Inter-Agency Consultative Group (IACG) would be an appropriate body to coordinate VLBI activities in space. At the same time ESA convened a committee to explore the technical aspects of coordinating ground and space VLBI activities. At this stage both NASA and ESA were supporting preliminary studies of the QUASAT mission, with effective coordination between the two groups. The Soviet Union had also begun planning a mission with the clear intent to fly it as soon as the could; the mission was designated RadioAstron. In December 1985, the Soviets formed an international study team for the RadioAstron mission, holding the first meeting in Moscow. Subsequent meetings of this international committee were held in Budapest in May 1986 and in Moscow in December 1986. Thus, in 1986 there were three VLBI mission concepts under study: the NASA QUASAT mission, an ESA counterpart, and the Soviet RadioAstron mission.

Can Ecliptic Comets Be Created En Route from the Kuiper Belt?

NASA Astrophysics Data System (ADS)

Dones, Henry C. Luke; Womack, Maria; Nesvorny, David; Bierhaus, Edward B.; Zahnle, Kevin; Robbins, Stuart J.; Bottke, William; Alvarellos, Jose; Hamill, Patrick

2017-10-01

The Kuiper Belt is thought to be the reservoir of ecliptic comets (ECs), which include the Jupiter-family comets (JFCs) and Centaurs. ECs are also the main source of Sun-orbiting impactors on the regular moons of the giant planets (Zahnle et al. 2003). Ironically, we still do not know whether the belt, specifically its Scattered Disk, provides enough ECs (Volk and Malhotra 2008). We are investigating whether cometary breakup in the planetary region (Fernández 2009) can substantially increase the number of ECs. In support of this idea, the Kreutz sungrazers may derive from a hierarchical series of fragmentation events of a progenitor long-period comet (e.g., Sekanina and Chodas 2007), and the JFCs 42P and 53P appear to be fragments of a comet that split in 1845 (Kresák et al. 1984). On the other hand, although 16P was tidally disrupted by Jupiter in 1886, only one fragment survives.Models of the cometary orbital distribution ignore activity or apply a physical lifetime based on the number of passages within 2 or 3 AU of the Sun, where sublimation of water ice occurs (Nesvorný et al. 2017). In reality, some comets (e.g., 29P, Hale-Bopp) are active beyond Jupiter due to volatiles such as CO and CO2 (Womack et al. 2017). 174P/Echeclus underwent a 7-magnitude outburst at 13 AU (Rousselot et al. 2016), and CO emission was detected from Echeclus at 6 AU (Wierzchos et al. 2017). We will estimate how the number and size distribution of comet nuclei change with distance from the Sun due to cometary activity and spontaneous disruption, tidal disruption by a giant planet, and tidal disruption of binaries (Fraser et al. 2017).We thank the Cassini Data Analysis Program for support.Fernández Y (2009). Planet. Space. Sci. 57, 1218.Fraser WC, et al. (2017). Nat. Astron. 1, 0088.Kresák L, et al. (1984). IAU Circular 3940.Nesvorný D, et al. (2017). arXiv:1706.07447.Rousselot P, et al. (2016). MNRAS 462, S432.Sekanina, Z, Chodas, PW (2007). Astrophys. J. 663, 657.Volk K, Malhotra R (2008). Astrophys. J. 687, 714.Wierzchos K, Womack M, Sarid G. (2017). Astron. J. 153, id 230.Womack M, Sarid G, Wierzchos, K (2017). Publ. Astron. Soc. Pac. 129,031001.Zahnle K, et al. (2003). Icarus 163, 263.

Studying AGN Jets At Extreme Angular Resolution

NASA Astrophysics Data System (ADS)

Bruni, Gabriele

2016-10-01

RadioAstron is a 10m antenna orbiting on the Russian Speckt-R spacecraft, launched in 2011. Performing radio interferometry with a global array of ground telescopes, it is providing record angular resolution. The Key Science Project on AGN polarization is exploiting it to study in great detail the configuration of magnetic fields in AGN jets, and understand their formation and collimation. To date, the project has already achieved the highest angular resolution image ever obtained in Astronomy, and detected brightness temperatures exceeding the ones predicted by theory of AGN.

Application of a new non-linear least squares velocity curve analysis technique for spectroscopic binary stars

NASA Astrophysics Data System (ADS)

Karami, K.; Mohebi, R.; Soltanzadeh, M. M.

2008-11-01

Using measured radial velocity data of nine double lined spectroscopic binary systems NSV 223, AB And, V2082 Cyg, HS Her, V918 Her, BV Dra, BW Dra, V2357 Oph, and YZ Cas, we find corresponding orbital and spectroscopic elements via the method introduced by Karami and Mohebi (Chin. J. Astron. Astrophys. 7:558, 2007a) and Karami and Teimoorinia (Astrophys. Space Sci. 311:435, 2007). Our numerical results are in good agreement with those obtained by others using more traditional methods.

Quantitative Measurements of Daytime Near Infrared Sky Brightness at the AEOS 3.6 m Telescope

DTIC Science & Technology

2014-09-01

photometric filters. In the case of the 1250 nm filter, the quoted results reflect the brightness that would be seen through a standard 2MASS J filter [9...brightness per unit wavelength through the broader 2MASS filter with 162 nm bandpass. Given the known colors of the star, we estimate this error to be...Megeath, S. T. “Spectral irradiance calibration in the infrared. XIV. The absolute calibration of 2MASS ,” Astron. J., 126, 1090–1096 (2003) [10] Jim

Influencias socioculturales en conceptos astronómicos: el caso del horizonte en la reforma copernicana

NASA Astrophysics Data System (ADS)

Szapiro, A.

2017-10-01

I analyze the meaning given by Ptolemy to the concept of horizon; especially how it allowed him to prove, through astronomical observations, the central position of the Earth in the Universe. I review the ways in which Copernicus and Galileo gave heliocentric answers to the Ptolemaic proof. I show that Galilean solution entailed a radical conceptual change, which brought with it a new sense to the concept of horizon. I state that this change was the product of sociocultural influences of the period.

The Mira Variable S Orionis: Relationships Between the Photosphere, Molecular Layer, Dust Shell, and SiO Maser Shell at 4 Epochs

DTIC Science & Technology

2007-01-01

C ., Gray, M. D., Humphreys, E. M. L ., Braithwaite, M. F ., & Field, D. 1995, A & A , 302, 797 Feast, M. W., Glass, I. S., Whitelock, P. A ., & Catchpole... C ., Bester, M., Degiacomi, C . G., Greenhill, L . J., & Townes, C . H. 1994, AJ, 107, 1469 Desmurs, J. F ., Bujarrabal, V., Colomer, F ., & Alcolea, J...2003, Proc. SPIE, 4838, 89 Gray, M. D., & Humphreys, E. M. L . 2000, New Astron., 5, 155 Haniff, C . A ., Scholz, M., & Tuthill,

Pulsar B0329+54: scattering disk resolved by RadioAstron interferometer at 324 MHz

NASA Astrophysics Data System (ADS)

Popov, M.

Propagation of pulsar radio emission through the interstellar plasma is accompanied with scattering by inhomogeneities of the plasma. The scattering produces a range of effects: angular broadening, pulse broadening, intensity modulation (scintillations), and distortion of radio spectra (diffraction pattern). In this presentation, we will primarily deal with scattering effects affecting interferometric measurements. Pulsars are point like radio sources at angular resolution provided by space VLBI even at largest baseline projections. Therefore, any structure, observed by the space-ground interferometer, is due to scattering effects. The objective of our study was to measure parameters of a scattering disk for the PSR B0329+54 at a frequency of 324 MHz with the space-ground interferometer RadioAstron. Observations were conducted on November 26-29 2012 in four sessions, one hour duration each, with progressively increasing baseline projections of 70, 90,175, and 235 thousand kilometers correspondingly. Only one ground radio telescope observed the pulsar together with the space radio telescope (SRT); it was 100-m telescope in Green Bank (GBT). Notable visibility amplitudes were detected at all baseline projections at a maximum level of 0.05 with the SNR of about 20. It was found that visibility function in delay consists of many isolated unresolved spikes. The overall spread of such spikes in delay corresponds to the scattering disk of about 4 mas at a half wide. Fine structure of the visibility amplitude in delay domain corresponds to a model of amplitude modulated noise (AMN). Fringe rate behavior with time indicates on dominant influence of refraction on traveling ionospheric disturbances (TID).

RadioAstron Studies of the Nearby, Turbulent Interstellar Plasma with the Longest Space-Ground Interferometer Baseline

NASA Astrophysics Data System (ADS)

Smirnova, T. V.; Shishov, V. I.; Popov, M. V.; Gwinn, C. R.; Anderson, J. M.; Andrianov, A. S.; Bartel, N.; Deller, A.; Johnson, M. D.; Joshi, B. C.; Kardashev, N. S.; Karuppusamy, R.; Kovalev, Y. Y.; Kramer, M.; Soglasnov, V. A.; Zensus, J. A.; Zhuravlev, V. I.

2014-05-01

RadioAstron space-ground very long baseline interferometry observations of the pulsar B0950+08, conducted with the 10 m Space Radio Telescope in conjunction with the Arecibo 300 m telescope and the Westerbork Synthesis Radio Telescope at a frequency of 324 MHz were analyzed in order to investigate plasma inhomogeneities in the direction of this nearby pulsar. The observations were conducted at a spacecraft distance of 330,000 km, resulting in a projected baseline of 220,000 km, providing the greatest angular resolution ever achieved at meter wavelengths. Our analysis is based on fundamental behavior of structure and coherence functions. We find that the pulsar shows scintillation on two frequency scales, both much less than the observing frequency, but modulation is less than 100%. We infer that the scattering is weak, but a refracting wedge disperses the scintillation pattern. The refraction angle of this "cosmic prism" is measured as θ0 = 1.1-4.4 mas, with the refraction direction being approximately perpendicular to the observer velocity. We show that the observed parameters of scintillation effects indicate that two plasma layers lie along the line of sight to the pulsar, at distances of 4.4-16.4 pc and 26-170 pc, and traveling in different directions relative to the line of sight. Spectra of turbulence for the two layers are found to follow a power law with the indices γ1 = γ2 = 3.00 ± 0.08, significantly different from the index expected for a Kolmogorov spectrum of turbulence, γ = 11/3.

Projeto observatórios virtuais: educação através de telescópios robóticos

NASA Astrophysics Data System (ADS)

Santana, P. H. S.; Shida, R. Y.

2003-08-01

O principal objetivo do projeto Observatórios Virtuais é o ensino na área de ciências através de atividades práticas desenvolvidas em colaboração entre instituições de pesquisa em astronomia e escolas de ensino médio e fundamental. Este ano deverá ser concluída a implantação do programa piloto de estudos, pesquisas e observação astronômica direta, com utilização em tempo real de telescópios robóticos, que assim funcionarão como "observatórios virtuais". O objetivo pedagógico das atividades práticas baseadas nas imagens atronômicas é desenvolver as habilidades e competências dos alunos no uso do método científico. Para isso, serão realizados projetos interdisciplinares, a partir de observações astronômicas, já que a astronomia é uma área interdisciplinar por excelência. Essas atividades terão níveis diferenciados de complexidade, que podem ser adequados aos vários graus do ensino e realidades regionais. Será dada ênfase ao desenvolvimento e aplicação em São Paulo, onde atua a equipe do IAG/USP. Como resultados apresentados no presente trabalho, temos a criação de um software em português para o processamento de imagens obtidas através de CCDs e a elaboração de material para as atividades educacionais relacionadas.

Coupling the nongravitational forces and modified Newton dynamics for cometary orbits

NASA Astrophysics Data System (ADS)

Maquet, Lucie; Pierret, Frédéric

2015-04-01

In recent work [L. Blanchet and J. Novak, Mon. Not. R. Astron. Soc. 412, 2530 (2011); L. Blanchet and J. Novak, Testing MOND in the Solar System (2011); and M. Milgrom, Mon. Not. R. Astron. Soc. 399, 474 (2009)], the authors showed that modified Newton dynamics (MOND) has a non-negligible secular perturbation effect on planets with large semimajor axes (gaseous planets) in the Solar System. Some comets also have a very eccentric orbit with a large semimajor axis (Halley family comets) going far away from the Sun (more than 15 AU) in a low acceleration regime where they would be subject to MOND perturbation. They also approach the Sun very closely (less than 3 AU) and are affected by the sublimation of ices from their nucleus, triggering so-called nongravitational forces. The main goal of this paper is to investigate the effect of MOND perturbation on three comets with various orbital elements (2 P /Encke , 1 P /Halley and 153 P /Ikeya-Zhang ) and then compare it to the nongravitational perturbations. It is motivated by the fact that when fitting an outgassing model for a comet, we have to take into account all of the small perturbing effects to avoid absorbing these effects into the nongravitational parameters. Otherwise, we could derive a completely wrong estimation of the outgassing. For this work, we use six different forms of MOND functions and compute the secular variations of the orbital elements due to MOND and nongravitational perturbations. We show that, for comets with large semimajor axis, the MONDian effects are not negligible compared to the nongravitational perturbations.

Frequency Determination for the Slowly Pulsating B Star, HD21071, From Combined Geneva and Stromgren Photometry

NASA Astrophysics Data System (ADS)

Sims, Melissa; Dukes, R. J., Jr.

2006-12-01

This project is comparison of several studies done on the variable star HD21071, which was previously determined to be Slowly Pulsating B star by Waelkens, et. al. (Astron. Astrophys. 330, 215-221, 1998) with a suggested period of .841 day (1.19 c d-1). Several later studies including Mills, L. R., et. al. (BAAS 31, 1482, 1999) and Andrews, J. E, et. al. (AAS Meeting 203, #83.14, 2003) confirmed the .841 period and tentatively suggested other possible periods based on new data, including 0.704 day (1.42 c d-1), 0.775 day (1.29 c d-1), and 1.14 day (0.878 c d-1) periods. This project merges Geneva V data and data from the y filter from the FCAPT data in the Stromgren uvby system by using a bilinear transformation from Harmanec et. al. (Astron. Astrophys. 369, 1140, 2001). Frequencies were determined using the Period04 program, which utilizes a least square fitting technique, to determine frequencies in the two data sets separately. We then analyzed the merged data set resulting in confirmation of the periods found in the individual data sets. The reality of the these frequencies was tested using multiple methods including least squares analysis and a check of the signal to noise ratio. We would like to thank Connie Aerts and Peter De Cat for providing the Geneva data as well as a copy of their preliminary analysis of this data. This work has been supported by NSF Grant AST-0071260 & AST-050755

Hair Cell Heterogeneity in the Goldfish Saccule

NASA Technical Reports Server (NTRS)

Saidel, William M.; Lanford, Pamela J.; Yan, Hong Y.; Popper, Arthur N.

1995-01-01

A set of cytological studies performed in the utricle and saccule of Astronotus ocellatus (Teleostei, Percomorphi, Cichlidae) identified two basic types of hair cells and others with some intermediate characteristics. This paper reports on applying the same techniques to the saccule of Carassius auratus (Teleostei, Otophysi, Cyprinidae) and demonstrates similar types of hair cells to those found in Astronotus. Since Carassius and Astronous are species of extreme taxonomic distance within the Euteteostei, two classes of mechanoreceptive hair cells are likely to represent the primitive condition for sensory receptors in the euteleost inner ear and perhaps in all bony fish ears.

Raízes pós-mitológicas da Astronomia Clássica

NASA Astrophysics Data System (ADS)

di Bartolo, L.; Villas da Rocha, J. F.

2004-02-01

Apresentamos como a invenção de um modelo astronômico e cosmológico fundado em causas naturais foi um processo gestado num ambiente cultural específico, o do advento do pensamento pós-mitológico, que tem como sua raiz mais funda a trajetória particular da Grécia Antiga, com ênfase na resolução de uma grave crise social e a evolução do mundo clássico para o contexto espiritual de um império universal.

VizieR Online Data Catalog: 100-Mpc-scale structures of radio galaxies (Brand+, 2003)

NASA Astrophysics Data System (ADS)

Brand, K.; Rawlings, S.; Hill, G. J.; Lacy, M.; Mitchell, E.; Tufts, J.

2003-09-01

The TONS08 survey is in one of the areas covered by the 7CRS (Willott et al., 2002MNRAS.335.1120W) and the TexOx-1000 (TOOT) survey (Hill & Rawlings, 2002, ASP Conf. Proc., Leiden. Astron. Soc. Pac., San Francisco). It covers the region 08h 10m 20s <= RA <= 08h 29m 20s and 24{deg} 10' 00" <= DE<= 29{deg} 30' 00" (J2000). Unlike the low-frequency-selected 7CRS and TOOT, the TONS08 survey is selected at 1.4GHz from the NVSS. (1 data file).

Educación no formal

NASA Astrophysics Data System (ADS)

Tignanelli, H.

Se comentan en esta comunicación, las principales contribuciones realizadas en el campo de la educación en astronomía en los niveles primario, secundario y terciario, como punto de partida para la discusión de la actual inserción de los contenidos astronómicos en los nuevos contenidos curriculares de la EGB - Educación General Básica- y Polimodal, de la Reforma Educativa. En particular, se discuten los alcances de la educación formal y no formal, su importancia para la capacitación de profesores y maestros, y perspectivas a futuro.

Disk Chemistry and Cometary Composition

NASA Astrophysics Data System (ADS)

Markwick, A. J.; Charnley, S. B.

2003-05-01

We will describe current chemical modelling of disks similar to the protosolar nebula. Calculations are being undertaken to determine the spatial and temporal chemistry of the gas and dust within the 5-40AU comet-forming region of the nebula. These theoretical studies aim to determine the contribution of pristine and partially-processed interstellar material from the cool outer nebula, as compared to that obtained from outward radial mixing of matter from the hot inner nebula. Reference Molecular distributions in the inner regions of protostellar disks, Markwick, A. J., Ilgner, M., Millar, T. J., Henning, Th. (2002), Astron. Astrophys., 385, 632.

Disk Chemistry and Cometary Composition

NASA Astrophysics Data System (ADS)

Markwick, A. J.; Charnley, S. B.

2005-01-01

We will describe current chemical modelling of disks similar to the protosolar nebula. Calculations are being undertaken to determine the spatial and temporal chemistry of the gas and dust within the 5-40AU comet-forming region of the nebula. These theoretical studies aim to determine the contribution of pristine and partially-processed interstellar material from the cool outer nebula as compared to that obtained from outward radial mixing of matter from the hot inner nebula. Reference Molecular distributions in the inner regions of protostellar disks Markwick A. J. Ilgner M. Millar T. J. Henning Th. (2002) Astron. Astrophys. 385 632

Modelling of charged satellite motion in Earth's gravitational and magnetic fields

NASA Astrophysics Data System (ADS)

Abd El-Bar, S. E.; Abd El-Salam, F. A.

2018-05-01

In this work Lagrange's planetary equations for a charged satellite subjected to the Earth's gravitational and magnetic force fields are solved. The Earth's gravity, and magnetic and electric force components are obtained and expressed in terms of orbital elements. The variational equations of orbit with the considered model in Keplerian elements are derived. The solution of the problem in a fully analytical way is obtained. The temporal rate of changes of the orbital elements of the spacecraft are integrated via Lagrange's planetary equations and integrals of the normalized Keplerian motion obtained by Ahmed (Astron. J. 107(5):1900, 1994).

Foreground contribution to the inferred cosmological parameters from Planck

NASA Astrophysics Data System (ADS)

Vincent, Aaron C.; Wibig, Tadeusz; Wolfendale, Arnold W.

Previous analyses of cosmic microwave background (CMB) measurements [T. Wibig and A. W. Wolfendale, Mon. Not. R. Astron. Soc. 360 (2005) 236, arXiv:astro-ph/0409397; Mon. Not. R. Astron. Soc. 448 (2015) 1030, arXiv:1507.0677.] have revealed contamination by areas of high cosmic ray activity in the Milky Way. Here, we update studies, looking at the most recent Planck release of residual maps. We search for possible effects of foreground contamination in the reconstruction of the ΛCDM cosmological parameters. We focus on the Hubble parameter H0 and the optical depth to reionization τ, both of which exhibit discrepancies between CMB-inferred values and low-redshift measurements (“the delta H0 problem”). Using the publicly available “component separated” Planck temperature maps, we single out three distinct regions: the “loops”, “chimneys” and “low CR” regions, which disproportionately contributed to CR contamination of WMAP data. We find that two of the four maps are strongly affected by removal of anomalously high or low CR activity regions. However, the Commander method, used to produce the angular power spectrum at low ( < 30) multipoles in cosmological analyses, appears robust under these changes. Finally, we use the inferred Hubble parameter H0 as a proxy to look for general directional dependence of the CMB power spectrum, finding a small but robust dependence on the Galactic longitude. Although there is some evidence for a continuing CR contamination, it is insufficient to provide an answer to the delta H0 problem, or to the optical depth problem, though dependence of the derived H0 on direction seems significant. The geometrical pattern — striations along constant longitudes — suggests CR contamination as distinct from a truly cosmological effect.

Polarimetric survey of main-belt asteroids. IV. New results from the first epoch of the CASLEO survey

NASA Astrophysics Data System (ADS)

Gil-Hutton, R.; Cellino, A.; Bendjoya, Ph.

2014-09-01

Aims: We present results of a polarimetric survey of main-belt asteroids at Complejo Astronómico El Leoncito (CASLEO), San Juan, Argentina. The aims of this survey are to increase the database of asteroid polarimetry, to estimate diversity in polarimetric properties of asteroids that belong to different taxonomic classes, and to search for objects that exhibit anomalous polarimetric properties. Methods: The data were obtained using the Torino and CASPROF polarimeters at the 2.15m telescope. The Torino polarimeter is an instrument that allows simultaneous measurement of polarization in five different bands, and the CASPROF polarimeter is a two-hole aperture polarimeter with rapid modulation. Results: The survey began in 1995, and until 2012 data on a large sample of asteroids were obtained. We here present and analyze the unpublished results for 129 asteroids of different taxonomic types, 56 which were polarimetrically observed for the first time. We find that the asteroids (402) Chloe and (729) Watsonia are Barbarians, and asteroid (269) Justitia shows a phase - polarization curve that seems to have a small inversion angle. Data obtained in UBVRI colors allow us to sketch an analysis of the wavelength dependence of the degree of linear polarization for 31 asteroids, in spite of some large error bars in some cases. Based on observations carried out at the Complejo Astronómico El Leoncito, operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba, and San Juan.Table 1 is only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/569/A122

La Enseñanza/Aprendizaje del Modelo Sol-Tierra Análisis de la Situación Actual y Propuesta de Mejora Para la Formación de los Futuros Profesores de Primaria

NASA Astrophysics Data System (ADS)

Martínez Sebastià, Bernat

2004-12-01

This work is an extened summary of the autor's PhD thesis. It deals with the teaching of astronomy (day/night, seasons) in primary school. At first, students teachers' undestanding of astronomical concepts related to Sun-Earth system have been analysed. Taking into account the results of the previous analysis and using a socio-constructivist approach a teaching sequence has been designed. This sequence has been tested with different groups of students teachers showing an improvement in their undestanding of elementary astronomical concepts. El trabajo que presentamos es un resumen extenso de la tesis doctoral del autor. El enfoque utilizado ha sido tratar de ligar la investigación sobre las ideas, razonamientos y obstáculos de los profesores de primaria con la planificación de la enseñanza del modelo Sol-Tierra que permite explicar el ciclo día/noche y las estaciones. En primer lugar, se ha procedido a realizar un análisis crítico de los resultados que se obtienen en el aprendizaje de los contenidos astronómicos en la enseñanza habitual. En segundo lugar se ha diseñado un curriculum potencialmente superador de esta situación desde una orientación que concibe la enseñanza y el aprendizaje como un proceso de construcción de conocimientos en una estructura problematizada. Finalmente, esta secuencia didáctica ha sido experimentada con diferentes grupos de estudiantes de magisterio, mostrando una mejora relevante en la comprensión de los conceptos astronómicos fundamentales.

Determination of the Charon/Pluto Mass Ratio from Center-of-Light Astrometry

NASA Technical Reports Server (NTRS)

Foust, Jeffrey A.; Elliot, J. L.; Olkin, Catherine B.; McDonald, Stephen W.; Dunham, Edward W.; Stone, Remington P. S.; McDonald, John S.; Stone, Ronald C.

1997-01-01

The Charon/Pluto mass ratio is a fundamental but poorly known parameter of the two-body system. Previous values for the mass ratio have ranged from 0.0837 plus or minus 0.0147 (Null et al., 1993, Astron. J. 105, 2319-2335) to 0.1566 plus or minus 0.0035 (Young et al., 1994, Icarus 108,186-199). We report here a new determination of the Charon/Pluto mass ratio, using five sets of groundbased images taken at four sites in support of Pluto occultation predictions. Unlike the Null et al. and Young et A determinations, where the centers of light for Pluto and Charon could be determined separately, this technique examines the motion of the center of light of the blended Pluto-Charon image. We compute the offsets of the observed center-of-light position of Pluto-Charon from the ephemeris position of the system and fit these offsets to a model of the Pluto-Charon system. The least-squares fits to the five data sets agree within their errors, and the weighted mean mass ratio is 0.117 plus or minus 0.006. The effects of errors in the Charon light fraction, semimajor axis, and ephemeris have been examined and are equal to only a small fraction of the formal error from the fit. This result is intermediate between those of Null et al., and Young et al. and matches a new value of 0.124 plus or minus 0.008 by Null and Owen (1996, Astron. J. 111, 1368-1381). The mass ratio and resulting individual masses and densities of Pluto and Charon are consistent with a collisional origin for the Pluto-Charon system.

Inauguração do Telescópio SOAR

NASA Astrophysics Data System (ADS)

Steiner, João

2004-04-01

A comunidade astronômica brasileira de há muito almeja ter a sua disposição um instrumento científico com o qual possa fazer pesquisa de vanguarda e manter a competitividade científica a nível internacional. Hoje este sonho se torna uma realidade. O Brasil tem tido uma política de pesquisa e de pós-graduação bem sucedida. Estamos formando 7000 doutores por ano e produzimos 1,5% da ciência mundial. Nosso desafio, hoje, é associar a esta capacidade de gerar conhecimento também a capacidade de usar o conhecimento em beneficio da sociedade. A Astronomia não é exceção. Temos 7 programas de pós-graduação em nível de doutorado e 11 em nível de mestrado. O telescópio SOAR será o principal instrumento que sustentará estes programas nas próximas décadas. A inauguração do telescópio SOAR simboliza de forma concreta e decidida o apoio do MCT, do CNPq e da FAPESP para o financiamento à pesquisa básica em nosso país. O Laboratório Nacional de Astrofísica, criado a cerca de 20 anos pelo CNPq, a par do Laboratório Nacional de Luz Sincrotron, são até hoje, os únicos laboratórios nacionais do Brasil e ambos voltados basicamente ao avanço do conhecimento. Os vinte anos de existência do LNA foram decisivos para a estruturação da comunidade astronômica no Brasil e para a construção das parcerias como o SOAR.

Mediciones de irradiancia solar y capa de ozono durante el eclipse de Sol de 1994 en el Observatorio Astronómico de Rosario, Argentina

NASA Astrophysics Data System (ADS)

Piacentini, R. D.; Micheletti, M. I.

We show results of measurements made during the Sun's eclipse of November 3, 1994, in Observatorio Astronómico de Rosario (32o 57' S, 60o 37' W, 25 m a.s.l.). The eclipse begin at 8:41 local hour, reached its maximum with 77% of the surface covered at 9:51 and finished at 11:04. The direct solar irradiance of 300 nm and 313 nm were able to be measured, due to the fact that during the whole period the sky remained completed uncovered (zero percent cloudiness). The measurements were made with the portable ozonometer developed by Tocho and co-workers. They show the characterictic decrease due to the occultation of the source, which is approximately proportional to the surface's diminution. When crossing the earth's atmosphere to arrive to the observation point, these irradiances are affected mainly by the ozone layer, specially the irradiance at lower wavelength, what let it to determine by comparison the thickness of this layer. The total ozone thickness distributed between the troposphere and the stratosphere shows an oscillation, whose amplitude, since the occurence of the maximum of occulation, has a mean value of 4%, and whose period is of approximately 2100 seconds, being both numbers considerably larger than the ones registred by Mims III y Mims (Geophysical Research Letters, 20, 367, 1993) during the eclipse of July 11, 1991 and by Tocho, Da Silva y Rivas (XVIII Quadriennial Ozone Symposiom, Italy, September, 1996) during the same eclipse analyzed in the present work, but observed in Salta. As complementary results, we measured the global irradiance and the ambient temperature during this astronomical event.

The extreme blazar AO 0235+164 as seen by extensive ground and space radio observations

NASA Astrophysics Data System (ADS)

Kutkin, A. M.; Pashchenko, I. N.; Lisakov, M. M.; Voytsik, P. A.; Sokolovsky, K. V.; Kovalev, Y. Y.; Lobanov, A. P.; Ipatov, A. V.; Aller, M. F.; Aller, H. D.; Lahteenmaki, A.; Tornikoski, M.; Gurvits, L. I.

2018-04-01

Clues to the physical conditions in radio cores of blazars come from measurements of brightness temperatures as well as effects produced by intrinsic opacity. We study the properties of the ultra-compact blazar AO 0235+164 with RadioAstron ground-space radio interferometer, multifrequency VLBA, EVN, and single-dish radio observations. We employ visibility modelling and image stacking for deriving structure and kinematics of the source, and use Gaussian process regression to find the relative multiband time delays of the flares. The multifrequency core size and time lags support prevailing synchrotron self-absorption. The intrinsic brightness temperature of the core derived from ground-based very long baseline interferometry (VLBI) is close to the equipartition regime value. In the same time, there is evidence for ultra-compact features of the size of less than 10 μas in the source, which might be responsible for the extreme apparent brightness temperatures of up to 1014 K as measured by RadioAstron. In 2007-2016 the VLBI components in the source at 43 GHz are found predominantly in two directions, suggesting a bend of the outflow from southern to northern direction. The apparent opening angle of the jet seen in the stacked image at 43 GHz is two times wider than that at 15 GHz, indicating a collimation of the flow within the central 1.5 mas. We estimate the Lorentz factor Γ = 14, the Doppler factor δ = 21, and the viewing angle θ = 1.7° of the apparent jet base, derive the gradients of magnetic field strength and electron density in the outflow, and the distance between jet apex and the core at each frequency.

Asteroid (90) Antiope: Another icy member of the Themis family?

NASA Astrophysics Data System (ADS)

Hargrove, Kelsey D.; Emery, Joshua P.; Campins, Humberto; Kelley, Michael S. P.

2015-07-01

Many members of the Themis family show evidence of hydration in the form of oxidized iron in phyllosilicates (Florczak, M. et al. [1999]. Astron. Astrophys. Suppl. Ser. 134, 463-471), and OH-bearing minerals (Takir, D., Emery, J.P. [2012]. Icarus 219, 641-654). The largest member, (24) Themis, has H2O ice covering its surface (Campins, H. et al. [2010]. Nature 464, 1320-1321; Rivkin, A.S., Emery, J.P. [2010]. Nature 464, 1322-1323). We have investigated the second largest Themis-family asteroid, (90) Antiope, which Castillo-Rogez and Schmidt (Castillo-Rogez, J.C., Schmidt, B.E. [2010]. Geophys. Res. Lett. 37, L10202) predict to have a composition that includes water ice and organics. We obtained 2-4-μm spectroscopy of (90) Antiope in 2006 and 2008, and we find an absorption in the 3-μm region clearly present in our 2008 spectrum and likely in our 2006 spectrum. Both spectra have rounded, bowl-shaped absorptions consistent with those ascribed to water ice as in the spectrum of Asteroid (24) Themis. We also present and compare Spitzer 8-12-μm mid-infrared spectra of (24) Themis and (90) Antiope. We find that (90) Antiope is lacking a "fairy castle" dusty surface, which is in contrast to (24) Themis, other Themis family members (Licandro, J. et al. [2012]. Astron. Astrophys. 537, A73), and Jupiter Trojans (e.g. Emery, J.P., Cruikshank, D.P., Van Cleve, J. [2006]. Icarus 182, 496-512). We conclude that the surface structure of (90) Antiope is most similar to Cybele Asteroid (121) Hermione (Hargrove, K.D. et al. [2012]. Icarus 221, 453-455).

Inclusion of Astronomy Themes in an Inovative Approach of Informal Physics Teaching for High School Students. (Spanish Title: Inclusión de Temas Astronómicos en Uma Abordaje Innovadora de la Enseñanza Informal de Física Para Estudiantes de Secumdaria.) Inclusão de Temas Astronômicos Numa Abordagem Inovadora do Ensino Informal de Física Para Estudantes do Ensino Médio

NASA Astrophysics Data System (ADS)

Tiara Mota, Aline; de Morais Bonomini, Iracema Ariel; Meloni Martins Rosado, Ricardo

2009-12-01

The current work reports on an experience on Astronomy education at the Federal University of Itajubá through an extra-curricular course offered for High School students. This initiative was motivated by the low attention paid to the Astronomy subjects at this stage of the Brazilian Formal Education, in spite that the National Curricular Parameters (PCN and PCN+, in Brazil) point out the importance of their inclusion Este artículo relata una experiencia en la enseñanza de la astronomía efectuada en la Universidad Federal de Itajubá en la forma de un curso de extensión orientado para los estudiantes del colegio secundario. Esta iniciativa surgió de constatar la poca atención dada a la Astronomía en esta etapa de la Educación formal brasileña, a pesar que los Parámetros Curriculares Nacionales (PCN y PCN+, en Brasil) destacan la importancia de su inclusión. Este artigo relata uma experiência em ensino de Astronomia realizada na Universidade Federal de Itajubá na forma de um curso de extensão voltado para alunos do Ensino Médio. Esta iniciativa surgiu da pouca atenção que se dá à Astronomia nesta etapa da Educação embora os Parâmetros Curriculares Nacionais (PCN e PCN+) apontem a importância de sua inclusão.

Dynamical evolution of comet pairs

NASA Astrophysics Data System (ADS)

Sosa, Andrea; Fernández, Julio A.

2016-10-01

Some Jupiter family comets in near-Earth orbits (thereafter NEJFCs) show a remarkable similarity in their present orbits, like for instance 169P/NEAT and P/2003 T12 (SOHO), or 252P/LINEAR and P/2016 BA14 (PANSTARRS). By means of numerical integrations we studied the dynamical evolution of these objects. In particular, for each pair of presumably related objects, we are interested in assessing the stability of the orbital parameters for several thousand years, and to find a minimum of their relative spatial distance, coincident with a low value of their relative velocity. For those cases for which we find a well defined minimum of their relative orbital separation, we are trying to reproduce the actual orbit of the hypothetical fragment by modeling a fragmentation of the parent body. Some model parameters are the relative ejection velocity (a few m/s), the orbital point at which the fragmentation could have happened (e.g. perihelion), and the elapsed time since fragmentation. In addition, some possible fragmentation mechanisms, like thermal stress, rotational instability, or collisions, could be explored. According to Fernández J.A and Sosa A. 2015 (Planetary and Space Science 118,pp.14-24), some NEJFCs might come from the outer asteroid belt, and then they would have a more consolidated structure and a higher mineral content than that of comets coming from the trans-Neptunian belt or the Oort cloud. Therefore, such objects would have a much longer physical lifetime in the near-Earth region, and could become potential candidates to produce visible meteor showers (as for example 169P/NEAT which has been identified as the parent body of the alpha-Capricornid meteoroid stream, according to Jenniskens, P., Vaubaillon, J., 2010 (Astron. J. 139), and Kasuga, T., Balam, D.D., Wiegert, P.A., 2010 (Astron. J. 139).

Alternative approaches to plasma confinement

NASA Technical Reports Server (NTRS)

Roth, J. R.

1978-01-01

The paper discusses 20 plasma confinement schemes each representing an alternative to the tokamak fusion reactor. Attention is given to: (1) tokamak-like devices (TORMAC, Topolotron, and the Extrap concept), (2) stellarator-like devices (Torsatron and twisted-coil stellarators), (3) mirror machines (Astron and reversed-field devices, the 2XII B experiment, laser-heated solenoids, the LITE experiment, the Kaktus-Surmac concept), (4) bumpy tori (hot electron bumpy torus, toroidal minimum-B configurations), (5) electrostatically assisted confinement (electrostatically stuffed cusps and mirrors, electrostatically assisted toroidal confinement), (6) the Migma concept, and (7) wall-confined plasmas. The plasma parameters of the devices are presented and the advantages and disadvantages of each are listed.

Onsala Space Observatory: IVS Network Station

NASA Technical Reports Server (NTRS)

Haas, Ruediger; Elgered, Gunnar; Loefgren, Johan; Ning, Tong; Scherneck, Hans-Georg

2013-01-01

During 2012 we participated in 40 IVS sessions. As in the previous four years, we used the majority of the sessions that involved both Onsala and Tsukuba to do ultra-rapid dUT1 observations together with our colleagues in Tsukuba. We observed one four-station ultra-rapid EOP session together with Tsukuba, Hobart, and HartRAO. We also observed the RadioAstron satellite and several GLONASS satellites using the Onsala 25-m telescope. The highlight in 2012 was that our proposal to the Knut and Alice Wallenberg Foundation to establish a twin-telescope system at Onsala in accordance with the VLBI2010 recommendations was accepted.

Deciphering the embedded wave in Saturn's Maxwell ringlet

NASA Astrophysics Data System (ADS)

French, Richard G.; Nicholson, Philip D.; Hedman, Mathew M.; Hahn, Joseph M.; McGhee-French, Colleen A.; Colwell, Joshua E.; Marouf, Essam A.; Rappaport, Nicole J.

2016-11-01

The eccentric Maxwell ringlet in Saturn's C ring is home to a prominent wavelike structure that varies strongly and systematically with true anomaly, as revealed by nearly a decade of high-SNR Cassini occultation observations. Using a simple linear "accordion" model to compensate for the compression and expansion of the ringlet and the wave, we derive a mean optical depth profile for the ringlet and a set of rescaled, background-subtracted radial wave profiles. We use wavelet analysis to identify the wave as a 2-armed trailing spiral, consistent with a density wave driven by an m = 2 outer Lindblad resonance (OLR), with a pattern speed Ωp = 1769.17° d-1 and a corresponding resonance radius ares = 87530.0 km. Estimates of the surface mass density of the Maxwell ringlet range from a mean value of 11g cm-2 derived from the self-gravity model to 5 - 12gcm-2 , as inferred from the wave's phase profile and a theoretical dispersion relation. The corresponding opacity is about 0.12 cm2 g-1, comparable to several plateaus in the outer C ring (Hedman, M.N., Nicholson, P.D. [2014]. Mont. Not. Roy. Astron. Soc. 444, 1369-1388). A linear density wave model using the derived wave phase profile nicely matches the wave's amplitude, wavelength, and phase in most of our observations, confirming the accuracy of the pattern speed and demonstrating the wave's coherence over a period of 8 years. However, the linear model fails to reproduce the narrow, spike-like structures that are prominent in the observed optical depth profiles. Using a symplectic N-body streamline-based dynamical code (Hahn, J.M., Spitale, J.N. [2013]. Astrophys. J. 772, 122), we simulate analogs of the Maxwell ringlet, modeled as an eccentric ringlet with an embedded wave driven by a fictitious satellite with an OLR located within the ring. The simulations reproduce many of the features of the actual observations, including strongly asymmetric peaks and troughs in the inward-propagating density wave. We argue that the Maxwell ringlet wave is generated by a sectoral normal-mode oscillation inside Saturn with ℓ = m = 2 , similar to other planetary internal modes that have been inferred from density waves observed in Saturn's C ring (Hedman, M.N., Nicholson, P.D. [2013]. Astron. J. 146, 12; Hedman, M.N., Nicholson, P.D. [2014]. Mont. Not. Roy. Astron. Soc. 444, 1369-1388). Our identification of a third m = 2 mode associated with saturnian internal oscillations supports the suggestions of mode splitting by Fuller et al. (Fuller, J., Lai, D., Storch, N.I. [2014]. Icarus 231, 34-50) and Fuller (Fuller, J. [2014]. Icarus 242, 283-296). The fitted amplitude of the wave, if it is interpreted as driven by the ℓ = m = 2 f-mode, implies a radial amplitude at the 1 bar level of ∼ 50 cm, according to the models of Marley and Porco (Marley, M.S., Porco, C.C. [1993]. Icarus 106, 508).

The Science Teachers and Their way of Thinking about Astronomy. (Spanish Title: Los Profesores de Ciencias y Sus Formas de Pensar la Astronomía.) Os Professores de Ciências e Suas Formas de Pensar a Astronomia

NASA Astrophysics Data System (ADS)

Leite, Cristina; Hosoume, Yassuko

2007-12-01

The research presented in this article is about the way science teachers from Elementary School think about astronomical elements. Its methodology is based on semi-structured interviews, which were video recorded. The research is centered in a three-dimensional perspective of astronomical Earth, the Sun, the Moon, the planets and the stars, and also the conceptions about sky and Universe. The esults indicate a Universe that contains: Sun, stars, planets and Moon; where the Solar System is a little part of the whole. Sometimes they think that the Solar System is the Universe. The objects are in the sky or in the Universe, which, for many of them, is only the space above the Earth. The flat shape of astronomical objects and the spatial structure of the Universe are striking features. Many of them think that Sun and stars are different: the Sun is a hot object and the stars are cold ones. These results worry us and they certainly indicate how urgent it is to plan Professional Development in Astronomy for teachers, after all the PCN's emphasize that this subject is important to be taught. El objeto de investigación de este artículo es la manera de pensar sobre los elementos de la Astronomía de los profesores de Ciencias en la enseñanza fundamental. La metodología consiste en entrevistas semi-estructuradas, filmadas en video y centradas en la tridimensionalidad de los elementos astronómicos, para posibilitar un mapeamiento de las concepciones sobre las formas y dimensiones de la Tierra, del Sol, de la Luna, de los planetas y de las estrellas, como también de la concepción de cielo y de Universo en su totalidad. Los resultados indican un Universo conteniendo: Sol, estrellas, planetas y Luna, donde el Sistema Solar se ubica como parte. Algunas veces, el Universo es concebido como el propio Sistema Solar. Los objetos están en el cielo o en el Universo, que, para muchos, se restringe al espacio que está arriba de la Tierra. La forma plana de los objetos astronómicos y la estructura espacial del montaje del Universo son características fundamentales. Muchos indican Sol y estrellas como cosas distintas: el Sol es un objeto caliente y las estrellas son frías. Esos resultados nos preocupan y ciertamente señalan una urgencia de programas de formación continuada para profesores en el contenido de astronomía, pues los PCN's (Parámetros Curriculares Nacionales) recomiendan con énfasis la enseñanza de este contenido. O modo de pensar dos professores de Ciências do ensino fundamental sobre os elementos da Astronomia é o objeto de pesquisa presente neste artigo, cuja metodologia consiste em entrevistas semiestruturadas, filmadas em vídeo e centradas numa perspectiva tridimensional dos elementos astronômicos, possibilitando um mapeamento das concepções das formas e das dimensões da Terra, do Sol, da Lua, dos planetas e das estrelas, bem como da concepção de céu e de Universo como um todo. Os resultados indicam um Universo contendo: Sol, estrelas, planetas e Lua, onde o Sistema Solar é parte do todo. Algumas vezes o Universo é concebido como o próprio Sistema Solar. Os objetos estão no céu ou no Universo o qual, para muitos, se restringe ao espaço que está acima da Terra. A forma plana dos objetos astronômicos e a estrutura espacial da montagem do Universo são características marcantes. Muitos indicam Sol e estrelas como coisas diferentes: Sol é um objeto quente e as estrelas são frias. Esses resultados nos preocupam e certamente sinalizam uma urgência de programas de formação continuada para professores no conteúdo de astronomia, uma vez que os PCN's indicam fortemente o ensino desse conteúdo.

Time Resolved Precision Differential Photometry with OAFA's Double Astrograph

NASA Astrophysics Data System (ADS)

González, E. P. A.; Podestá, F.; Podestá, R.; Pacheco, A. M.

2018-01-01

For the last 50 years, the Double Astrograph located at the Carlos U. Cesco station of the Observatorio Astronómico Félix Aguilar (OAFA), San Juan province, Argentina, was used for astrometric observations and research. The main programs involved the study of asteroid positions and proper motions of stars in the Southern hemisphere, being the latter a long time project that is near completion from which the SPM4 catalog is the most recent version (Girard et al. 2011). In this paper, new scientific applications in the field of photometry that can be accomplished with this telescope are presented. These first attempts show the potential of the instrument for such tasks.

`Site Testing' en la Puna de Atacama

NASA Astrophysics Data System (ADS)

Recabarren, P.; Mosconi, M.

We present a report of the activities developed by the IATE group from the Observatorio Astronómico de Córdoba and astronomers from the Pontificia Universidad Católica de Chile, from 14 till 22. of April of 2000. We have made seeing and meteorological measurements and a topographical prospecting in order to characterize the environmental conditions in Cerro Toco (5574m), in the region of the Puna de Atacama. The seeing measurements were made with a DIMM (Differential Image Motin Monitor) camera. The seeing measurements during 20. and 21. of April gave an average value of 0.85 arc seconds. We think that more places in the region should be studied.

NASA and Russian Space Agency sign agreement for additional Space Shuttle/Mir missions

PubMed

Huff, W

1994-01-01

On December 16, 1993 NASA Administrator Daniel S. Goldin [correction of Golden] and the Russian Space Agency (RSA) director Yuri Koptev signed a protocol agreeing to up to 10 Shuttle flights to Mir with a total of 24 months time aboard Mir for U.S. astronants, a program of scientific and technological research, and the upgrade and extension of the Mir lifetime during the period 1995-1997. This is the first of a three-phase program in human spaceflight cooperation which may culminate in the construction of an international Space Station. This agreement starts joint development of spacecraft environmental control and life support systems and potential common space suit.

Cámara CCD Directa con el Telescopio de 2.15 m del CASLEO: algunos diagnósticos

NASA Astrophysics Data System (ADS)

Cellone, S. A.

Se efectuaron algunas pruebas con la cámara CCD (+ Reductor Focal) instalada en el foco Cassegrain del Telescopio de 2.15 m del Complejo Astronómico El Leoncito (CASLEO). Las conclusiones más significativas son: Los tiempos de exposición efectivos difieren de los nominales en una fracción apreciable de segundo. En exposiciones de menos de 3 segundos, la iluminación no es pareja en todo el detector. En consecuencia, se recomiendan los pasos a seguir por los astrónomos tanto durante la observación como en la reducción de sus datos.

Perspectivas Futuras para o Observatório do Pico dos Dias

NASA Astrophysics Data System (ADS)

Bruch, Albert

2004-02-01

Com o Observatório Gemini plenamente operacional e o telescópio SOAR iniciando suas operações em breve, a astronomia observacional brasileira encontra-se no auge de uma transformação profunda que terá um impacto grave no Observatório do Pico dos Dias - OPD. Refletimos aqui sobre a natureza desse impacto e estratégias para manter a competitividade do OPD. Não queremos apresentar receitas prontas, mas idéias que poderão servir como base de discussão sobre o uso inteligente dos telescópios do OPD como parte do conjunto de instrumentos disponíveis à comunidade astronômica brasileira.

High-pressure chemistry of hydrocarbons relevant to planetary interiors and inertial confinement fusion

NASA Astrophysics Data System (ADS)

Kraus, D.; Hartley, N. J.; Frydrych, S.; Schuster, A. K.; Rohatsch, K.; Rödel, M.; Cowan, T. E.; Brown, S.; Cunningham, E.; van Driel, T.; Fletcher, L. B.; Galtier, E.; Gamboa, E. J.; Laso Garcia, A.; Gericke, D. O.; Granados, E.; Heimann, P. A.; Lee, H. J.; MacDonald, M. J.; MacKinnon, A. J.; McBride, E. E.; Nam, I.; Neumayer, P.; Pak, A.; Pelka, A.; Prencipe, I.; Ravasio, A.; Redmer, R.; Saunders, A. M.; Schölmerich, M.; Schörner, M.; Sun, P.; Turner, S. J.; Zettl, A.; Falcone, R. W.; Glenzer, S. H.; Döppner, T.; Vorberger, J.

2018-05-01

Diamond formation in polystyrene (C8H8)n, which is laser-compressed and heated to conditions around 150 GPa and 5000 K, has recently been demonstrated in the laboratory [Kraus et al., Nat. Astron. 1, 606-611 (2017)]. Here, we show an extended analysis and comparison to first-principles simulations of the acquired data and their implications for planetary physics and inertial confinement fusion. Moreover, we discuss the advanced diagnostic capabilities of adding high-quality small angle X-ray scattering and spectrally resolved X-ray scattering to the platform, which shows great prospects of precisely studying the kinetics of chemical reactions in dense plasma environments at pressures exceeding 100 GPa.

The Gran Telescopio Canarias and Calar Alto Virtual Observatory Compliant Archives

NASA Astrophysics Data System (ADS)

Alacid, J. M.; Solano, E.; Jiménez-Esteban, F. M.; Velasco, A.

2014-05-01

The Gran Telescopio Canarias and Calar Alto archives are the result of the collaboration agreements between the Centro de Astrobiología and two entities: GRANTECAN S.A. and the Centro Astronómico Hispano Alemán (CAHA). The archives have been developed in the framework of the Spanish Virtual Observatory and are maintained by the Data Archive Unit at Centro de Astrobiología. The archives contain both raw and science ready data and have been designed in compliance with the standards defined by the International Virtual Observatory Alliance, which guarantees a high level of data accessibility and handling. In this paper we describe the main characteristics and functionalities of both archives.

The Gran Telescopio Canarias and Calar Alto Virtual Observatory compliant archives

NASA Astrophysics Data System (ADS)

Solano, Enrique; Gutiérrez, Raúl; Alacid, José Manuel; Jiménez-Esteban, Francisco; Velasco Trasmonte, Almudena

2012-09-01

The Gran Telescopio Canarias (GTC) and Calar Alto archives are the result of the collaboration agreements between the Centro de Astrobiología (CAB, INTA-CSIC)) and two entities: GRANTECAN S.A. and the Centro Astronómico Hispano Alemán (CAHA). The archives have been developed in the framework of the Spanish Virtual Observatory and are maintained by the Data Archive Unit at CAB. The archives contain both raw and science ready data and have been designed in compliance with the standards defined by the International Virtual Observatory Alliance (IVOA) which guarantees a high level of data accessibility and handling. In this paper we describe the main characteristics and functionalities of both archives.

Comportamiento de la cromósfera solar en la línea H-alfa durante el período enero/05-agosto/06

NASA Astrophysics Data System (ADS)

Missio, H.; Davoli, D.; Aquilano, R.

Using the instrument at Observatorio Astronómico Municipal de Rosario (OAMR), we analyze the solar chromospheric activity during the period January/05-August/06. The instrument is a Carl Zeiss refractor telescope of 150 mm aperture and 2250 mm of focal distance with a monochromatic filter in the H-alpha line. We take as proxy for the solar activity the area covered by chromospheric ``plages''. The measurements are done using photographic registers. We describe our technique and the results obtained. We observe a decrease of solar activity that corresponds to the end of cycle 23. FULL TEXT IN SPANISH

Polarimetric survey of main-belt asteroids. V. The unusual polarimetric behavior of V-type asteroids

NASA Astrophysics Data System (ADS)

Gil-Hutton, R.; López-Sisterna, C.; Calandra, M. F.

2017-03-01

Aims: We present the results of a polarimetric survey of main-belt asteroids at Complejo Astronómico El Leoncito (CASLEO), San Juan, Argentina. The aims of this survey are to increase the database of asteroid polarimetry, to estimate diversity in polarimetric properties of asteroids that belong to different taxonomic classes, and to search for objects that exhibit anomalous polarimetric properties. Methods: The data were obtained using the CASPROF and CASPOL polarimeters at the 2.15 m telescope. The CASPROF polarimeter is a two-hole aperture polarimeter with rapid modulation and CASPOL is a polarimeter based on a CCD detector, which allows us to observe fainter objects with better signal-to-noise ratio. Results: The survey began in 1995 and data on a large sample of asteroids were obtained until 2012. A second period began in 2013 using a polarimeter with a more sensitive detector in order to study small asteroids, families, and special taxonomic groups. We obtained 55 polarimetric measurements for 28 V-type main belt asteroids, all of them polarimetrically observed for the first time. The data obtained in this survey let us find polarimetric parameters for (1459) Magnya and for a group of 11 small V-type objects with similar polarimetric behavior. These polarization curves are unusual since they show a shallow minimum and a small inversion angle in comparison with (4) Vesta, although they have a steeper slope at α0. This polarimetric behavior could be explained by differences in the regoliths of these asteroids. The observations of (2579) Spartacus, and perhaps also (3944) Halliday, indicate a inversion angle larger than 24-25°. Based on observations carried out at the Complejo Astronómico El Leoncito, operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba, and San Juan.

The Universe Observing Center a modern center to teach and communicate astronomy

NASA Astrophysics Data System (ADS)

Ribas, Salvador J.

2011-06-01

The Universe Observing Center is one of the parts of the Parc Astronòmic Montsec (PAM). PAM is an initiative of the Catalan government, through the Consorci del Montsec (Montsec Consortium), to take advantage of the capabilities and potential of the Montsec region to develop scientific research, training and outreach activities, particularly in the field of Astronomy. The choice of the Montsec mountains to install the PAM was motivated by the magnificent conditions for observing the sky at night; the sky above Montsec is the best (natural sky free of light pollution) in Catalonia for astronomical observations. The PAM has two main parts: the Observatori Astronòmic del Montsec (OAdM) and the Universe Observing Center (COU). The OAdM is a professional observatory with an 80-cm catadioptric telescope (Joan Oró Telescope). This telescope is a robotic telescope that can be controlled from anywhere in the world via the Internet. The COU is a large multipurpose center which is intended to become an educational benchmark for teaching and communicate astronomy and other sciences in Catalonia. The management of the COU has three main goals: 1) Teach primary and secondary school students in our Educational Training Camp. 2) Teach university students housing the practical astronomy lectures of the universities. 3) Communicate astronomy to the general public. The COU comprises special areas for these purposes: the Telescopes Park with more than 20 telescopes, a coelostat for solar observations and two dome containing full-automated telescopes. The most special equipment is ``The Eye of Montsec'', with its 12m dome containing a multimedia digital planetarium and a platform for direct observation of the sky and the environment. During 2009 we expect around 10000 visitors in Montsec area to enjoy science with Montsec dark skies and an special natural environment.

Millimeter and Submillimeter Observations of Comet 67P's Nucleus, Gas, and Dust with the Rosetta/MIRO Instrument

NASA Astrophysics Data System (ADS)

Hofstadter, Mark

2016-04-01

The Microwave Instrument for the Rosetta Orbiter (MIRO) has been making measurements of comet 67P/C-G since June 2014, when the comet was 3.92 AU from the Sun and Rosetta was approximately 400,000 km from the nucleus. Those first observations were spatially unresolved measurements of the 556 GHz water line, used to infer the abundance and velocity of water vapor in the coma (Gulkis et al. 2015, Science 347). In the almost two years since that time, as the spacecraft has moved closer to the nucleus and the comet has become more active (perihelion at 1.2 AU from the Sun occurred in August 2015), MIRO's submillimeter spectrometer (working at frequencies near 550 GHz, or wavelengths near 0.5 mm) has been used to determine the velocity, abundance, and spatial distribution of H216O, H217O, H218O, CH3OH, NH3, and CO in the coma as a function of time (e.g. water is discussed by Biver et al. 2015 and Lee et al. 2015, Astron. and Astrophys. 583). In addition to its submillimeter spectrometer, MIRO has two broad band continuum channels operating at wavelengths near 0.5 and 1.6 millimeter. These channels are designed to probe the nucleus ˜1 millimeter to 10 cm below the surface. Data have been used to infer properties such as thermal inertia, porosity, and ice content as functions of location, depth, and time (e.g. Schloerb et al. 2015 and Choukroun et al. 2015, Astron. and Astrophys. 583). These channels have also been used to map the distribution of relatively large dust grains (radius > ˜1 mm) in the inner coma of the comet, with the potential to constrain models of dust acceleration, cooling, and fragmentation. This talk will review the latest results from MIRO's measurements of the nucleus, coma, and dust, and discuss some of the processes that couple these components of the comet.

Polarimetry of an intermediate-age open cluster: NGC 5617

NASA Astrophysics Data System (ADS)

Orsatti, A. M.; Feinstein, C.; Vergne, M. M.; Martínez, R. E.; Vega, E. I.

2010-04-01

Aims: We present polarimetric observations in the UBVRI bands of 72 stars located in the direction of the medium age open cluster NGC 5617. Our intention is to use polarimetry as a tool in membership identification, by building on previous investigations intended mainly to determine the cluster's general characteristics rather than provide membership suitable for studies such as stellar content and metallicity, as well as study the characteristics of the dust lying between the Sun and the cluster. Methods: The obsevations were carried out using the five-channel photopolarimeter of the Torino Astronomical Observatory attached to the 2.15 m telescope at the Complejo Astronómico El Leoncito (CASLEO; Argentina). Results: We are able to add 32 stars to the list of members of NGC 5617, and review the situation for others listed in the literature. In particular, we find that five blue straggler stars in the region of the cluster are located behind the same dust as the member stars are and we confirm the membership of two red giants. The proposed polarimetric memberships are compared with those derived by photometric and kinematical methods, with excellent results. Among the observed stars, we identify 10 with intrinsic polarization in their light. NGC 5617 can be polarimetrically characterized with Pmax = 4.40 % and θv = 73.1 deg. The spread in polarization values for the stars observed in the direction of the cluster seems to be caused by the uneven distribution of dust in front of the cluster's face. Finally, we find that in the direction of the cluster, the interstellar medium is apparently free of dust, from the Sun's position up to the Carina-Sagittarius arm, where NGC 5617 seems to be located at its farthest border. Based on observations obtained at Complejo Astronómico El Leoncito, operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the Universities of La Plata, Córdoba, and San Juan.

The Laboratory Rotational Spectrum of Iso-Propyl Cyanide and AN Astronomical Search in Sagittarius B2(N)

NASA Astrophysics Data System (ADS)

Müller, Holger S. P.; Coutens, A.; Walters, A.; Grabow, J.-U.; Belloche, A.; Menten, K. M.; Schlemmer, S.

2009-06-01

We have carried out a molecular line survey of Sagittarius B2(N) in the 3 mm region with selected recordings at 2 and 1.3 mm to probe the chemical complexity in massive star-forming regions. Noteworthy results include the detection of aminoacetonitrile, a possible precursor of the aminoacid glycine, the detection of ^{13}C isotopologs of vinyl cyanide, and the detection of ethyl formate as well as normal-propyl cyanide. The heavy atoms in the latter molecule form a chain. An isomer with a branched structure, iso-propyl cyanide, also exists, but its rotational spectrum has only been recorded in few transitions up to 40 GHz. Therefore, laboratory measurements were extended. The molecule is rather asymmetric (κ = -0.5766) with a strong a-dipole moment component of 4.05 (2) D and a still sizable c-component of 1.4 (2) D.^e Measurements in Köln were carried out in selected regions between 40 and 600 GHz. Since the c-type transitions appeared to be weaker than predicted additional Stark (and also zero-field) measurements have been carried out in Hannover between 6 and 20 GHz. We will present results of these laboratory spectroscopic investigations as well as the outcome of a search for the molecule in our Sgr B2(N) line survey. A. Belloche, K. M. Menten, C. Comito, H. S. P. Müller, P. Schilke, J. Ott, S. Thorwirth, C. Hieret, Astron. Astrophys. 482 (2008) 179; Erratum 492 (2008) 796. H. S. P. Müller, A. Belloche, K. M. Menten, C. Comito, P. Schilke, J. Mol. Spectrosc. 251 (2008) 319. A. Belloche, R. T. Garrod, H. S. P. Müller, K. M. Menten, C. Comito, P. Schilke, Astron. Astrophys. (2009), accepted. G. E. Herberich, Z. Naturforsch. 22a (1967) 543. J. R. Durig, Y. S. Li, J. Mol. Struct. 21 (1974) 289.

The 2003 November 14 occultation by Titan of TYC 1343-1865-1. II. Analysis of light curves

NASA Astrophysics Data System (ADS)

Zalucha, A.; Fitzsimmons, A.; Elliot, J. L.; Thomas-Osip, J.; Hammel, H. B.; Dhillon, V. S.; Marsh, T. R.; Taylor, F. W.; Irwin, P. G. J.

2007-12-01

We observed a stellar occultation by Titan on 2003 November 14 from La Palma Observatory using ULTRACAM with three Sloan filters: u, g, and i (358, 487, and 758 nm, respectively). The occultation probed latitudes 2° S and 1° N during immersion and emersion, respectively. A prominent central flash was present in only the i filter, indicating wavelength-dependent atmospheric extinction. We inverted the light curves to obtain six lower-limit temperature profiles between 335 and 485 km (0.04 and 0.003 mb) altitude. The i profiles agreed with the temperature measured by the Huygens Atmospheric Structure Instrument [Fulchignoni, M., and 43 colleagues, 2005. Nature 438, 785-791] above 415 km (0.01 mb). The profiles obtained from different wavelength filters systematically diverge as altitude decreases, which implies significant extinction in the light curves. Applying an extinction model [Elliot, J.L., Young, L.A., 1992. Astron. J. 103, 991-1015] gave the altitudes of line of sight optical depth equal to unity: 396±7 and 401±20 km ( u immersion and emersion); 354±7 and 387±7 km ( g immersion and emersion); and 336±5 and 318±4 km ( i immersion and emersion). Further analysis showed that the optical depth follows a power law in wavelength with index 1.3±0.2. We present a new method for determining temperature from scintillation spikes in the occulting body's atmosphere. Temperatures derived with this method are equal to or warmer than those measured by the Huygens Atmospheric Structure Instrument. Using the highly structured, three-peaked central flash, we confirmed the shape of Titan's middle atmosphere using a model originally derived for a previous Titan occultation [Hubbard, W.B., and 45 colleagues, 1993. Astron. Astrophys. 269, 541-563].

"Prospecting Asteroids: Indirect technique to estimate overall density and inner composition"

NASA Astrophysics Data System (ADS)

Such, Pamela

2016-07-01

Spectroscopic studies of asteroids make possible to obtain some information on their composition from the surface but say little about the innermost material, porosity and density of the object. In addition, spectroscopic observations are affected by the effects of "space weathering" produced by the bombardment of charged particles for certain materials that change their chemical structure, albedo and other physical properties, partly altering their chances of identification. Data such as the mass, size and density of the asteroids are essential at the time to propose space missions in order to determine the best candidates for space exploration and is of great importance to determine a priori any of them remotely from Earth. From many years ago its determined masses of largest asteroids studying the gravitational effects they have on smaller asteroids when they approach them (see Davis and Bender, 1977; Schubart and Matson, 1979; School et al 1987; Hoffman, 1989b, among others), but estimates of the masses of the smallest objects is limited to the effects that occur in extreme close encounters to other asteroids of similar size. This paper presents the results of a search for approaches of pair of asteroids that approximate distances less than 0.0004 UA (50,000 km) of each other in order to study their masses through the astrometric method and to estimate in a future their densities and internal composition. References Davis, D. R., and D. F. Bender. 1977. Asteroid mass determinations: search for futher encounter opportunities. Bull. Am. Astron. Soc. 9, 502-503. Hoffman, M. 1989b. Asteroid mass determination: Present situation and perspectives. In asteroids II (R. P. Binzel, T. Gehreis, and M. S. Matthews, Eds.), pp 228-239. Univ. Arizona Press, Tucson. School, H. L. D. Schmadel and S. Roser 1987. The mass of the asteroid (10) Hygiea derived from observations of (829) Academia. Astron. Astrophys. 179, 311-316. Schubart, J. And D. L. Matson 1979. Masses and densities of asteroids. In Asteroids (T. Gehrels, Ed.), pp.

Testing cosmology from fundamental considerations: Is the Friedmann universe intrinsically flat

NASA Astrophysics Data System (ADS)

Mitra, Abhas

2014-02-01

Recently Melia and Shevchuk (Mon Not R Astron Soc 419:2579,2012) (MS) have proposed the so-called cosmology where the "Gravitational Horizon" of the universe is equal to the distance travelled by light since "Big Bang". Here we would like to see whether the basic claim is correct or not because MS have not given any cogent derivation for the same. Essentially we will compare the twin expressions for the Einstein energy momentum complex (EMC) of the Friedmann universe obtained by using an appropriate superpotential and also by a direct method. To enable a meaningful comparison of the twin expressions, both are computed by using the same quasi-Cartesian coordinates. We however do not claim that Einstein EMC is superior to many other routes of defining EM of a self-gravitating system. In fact, for static isolated spherical syatems, the idea of a coordinate independent field energy of Lynden-Bell and Katz (Mon Not R Astron Soc 213:21, 1985) might be quite physically significant. Yet, here, we use Einstein EMC because (i) our system is non-static and not isolated one (ii) our primary aim is not find any absolute value of EM, and, finally, (iii) only Einstein pseudo-tensor offers equivalent twin expressions for EM which one can be equated irrespective of any physical significance. Following such comparison of equivalent twin expressions of Einstein energy, we find an exact proof as to why Friedmann universe must be spatially flat even though, mathematically one can conceive of curved spaces in any dimension. Additionally, it follows that, apparently, the scale factor as insisted by proposition. Nonetheless, because of close similarity of this form, , with the (vacuum) Milne metric, and also because of implied unphysical equation of state, cosmology is unlikely to represent the physical universe.

Space Observatories RadioAstron and Millimetron: Results and Prospects

NASA Astrophysics Data System (ADS)

Kardashev, Nikolay

The Russian Academy of Sciences and Federal Space Agency, together with many international organizations, prepared the launch of the RadioAstron orbiting space observatory from the Baikonur cosmodrome on July 18, 2011. The spacecraft was launched by the Ukrainian Zenit-3F rocket with onboard 10-m reflector radio telescope, four feed and low noise receivers for operating at 1.2-1.6, 6.2, 18 and 92 cm wavelengths and both circular polarizations, a data formatter, a data transmission module and a hydrogen maser frequency standard. The orbital period in 2012-2015 will vary from 8.3 to 9.0 days, the perigee - from 7,065 km to 81,500 km, the apogee - from 280,000 to 353,000 km. Together with ground-based radio telescopes and a set of stations for tracking, collecting, and reducing the data obtained, this space radio telescope forms a multi-antenna ground-space radio interferometer with extremely long baselines, making it possible for the first time to study various objects in the Universe with angular resolutions a million times better than it is possible with the human eye. The project is targeted at systematic studies of compact radio-emitting sources and their dynamics. Objects to be studied include quasars (super massive black holes and relativistic jets in active galactic nuclei, pulsars (neutron stars and hypothetical quark stars), cosmic masers (regions of stars and planetary systems formation in our and other galaxies), interplanetary and interstellar plasma, and the gravitational field of the Earth. The fringes with the ground-space interferometer were founded at the baseline projections up to 25 diameters of the Earth, and corresponding models of the sources will be reported. Millimetron is the next space mission with a 10-m cooled space telescope optimized for observations in the millimeter and far infrared wavelengths. This mission will be able to contribute to the explorations of several key problems in astrophysics, such as study of formation and evolution of stars and planets, galaxies, quasars and many others. The mission will have a cryogenic instruments and antenna, which will be cooled passively by radiation shields and actively by mechanical coolers. With this cooling combination the 10-m space telescope may reach a temperature of about 4.5 K. The telescope will have an unprecedented sensitivity in the single-dish observation mode in the band 0.02-1.4 mm and an extremely high spatial resolution by ground-space interferometer in the band 0.3-16 mm with maximum baseline 5 times larger than RadioAstron (a halo orbit around L2 Lagrange point of the Earth-Sun system, 1,500, 000 km from the Earth). The critical experiments of Millimetron mission are 1. near horizon black holes physics, cosmic rays accelerators, 2. super massive black holes evolution, cosmological parameters, hidden matter and dark energy, 3. the most powerful in the Universe explosions and its beaming, 4. coldest objects on the border of Solar system, in our and other galaxies, SETI, 5. very early objects in the Universe, first stars and galaxies, primordial black holes, wormholes and Multiverse.

The internal structure of Jupiter family cometary nuclei from Deep Impact observations: The “talps” or “layered pile” model

NASA Astrophysics Data System (ADS)

Belton, Michael J. S.; Thomas, Peter; Veverka, J.; Schultz, Peter; A'Hearn, Michael F.; Feaga, Lori; Farnham, Tony; Groussin, Olivier; Li, Jian-Yang; Lisse, Casey; McFadden, Lucy; Sunshine, Jessica; Meech, Karen J.; Delamere, W. Alan; Kissel, Jochen

2007-03-01

We consider the hypothesis that the layering observed on the surface of Comet 9P/Tempel 1 from the Deep Impact spacecraft and identified on other comet nuclei imaged by spacecraft (i.e., 19P/Borrelly and 81P/Wild 2) is ubiquitous on Jupiter family cometary nuclei and is an essential element of their internal structure. The observational characteristics of the layers on 9P/Tempel 1 are detailed and considered in the context of current theories of the accumulation and dynamical evolution of cometary nuclei. The works of Donn [Donn, B.D., 1990. Astron. Astrophys. 235, 441-446], Sirono and Greenberg [Sirono, S.-I., Greenberg, J.M., 2000. Icarus 145, 230-238] and the experiments of Wurm et al. [Wurm, G., Paraskov, G., Krauss, O., 2005. Icarus 178, 253-263] on the collision physics of porous aggregate bodies are used as basis for a conceptual model of the formation of layers. Our hypothesis is found to have implications for the place of origin of the JFCs and their subsequent dynamical history. Models of fragmentation and rubble pile building in the Kuiper belt in a period of collisional activity (e.g., [Kenyon, S.J., Luu, J.X., 1998. Astron. J. 115, 2136-2160; 1999a. Astron. J. 118, 1101-1119; 1999b. Astrophys. J. 526, 465-470; Farinella, P., Davis, D.R., Stern, S.A., 2000. In: Mannings, V., Boss, A.P., Russell, S.S. (Eds.), Protostars and Planets IV. Univ. of Arizona Press, Tucson, pp. 1255-1282; Durda, D.D., Stern, S.J., 2000. Icarus 145, 220-229]) following the formation of Neptune appear to be in conflict with the observed properties of the layers and irreconcilable with the hypothesis. Long-term residence in the scattered disk [Duncan, M.J., Levison, H.F., 1997. Science 276, 1670-1672; Duncan, M., Levison, H., Dones, L., 2004. In: Festou, M., Keller, H.U., Weaver, H.A. (Eds.), Comets II. Univ. of Arizona Press, Tucson, pp. 193-204] and/or a change in fragmentation outcome modeling may explain the long-term persistence of primordial layers. In any event, the existence of layers places constraints on the environment seen by the population of objects from which the Jupiter family comets originated. If correct, our hypothesis implies that the nuclei of Jupiter family comets are primordial remnants of the early agglomeration phase and that the physical structure of their interiors, except for the possible effects of compositional phase changes, is largely as it was when they were formed. We propose a new model for the interiors of Jupiter family cometary nuclei, called the talps or "layered pile" model, in which the interior consists of a core overlain by a pile of randomly stacked layers. We discuss how several cometary characteristics—layers, surface texture, indications of flow, compositional inhomogeneity, low bulk density low strength, propensity to split, etc., might be explained in terms of this model. Finally, we make some observational predictions and suggest goals for future space observations of these objects.

The internal structure of Jupiter family cometary nuclei from Deep Impact observations: The “talps” or “layered pile” model

NASA Astrophysics Data System (ADS)

Belton, Michael J. S.; Thomas, Peter; Veverka, J.; Schultz, Peter; A'Hearn, Michael F.; Feaga, Lori; Farnham, Tony; Groussin, Olivier; Li, Jian-Yang; Lisse, Casey; McFadden, Lucy; Sunshine, Jessica; Meech, Karen J.; Delamere, W. Alan; Kissel, Jochen

We consider the hypothesis that the layering observed on the surface of Comet 9P/Tempel 1 from the Deep Impact spacecraft and identified on other comet nuclei imaged by spacecraft (i.e., 19P/Borrelly and 81P/Wild 2) is ubiquitous on Jupiter family cometary nuclei and is an essential element of their internal structure. The observational characteristics of the layers on 9P/Tempel 1 are detailed and considered in the context of current theories of the accumulation and dynamical evolution of cometary nuclei. The works of Donn [Donn, B.D., 1990. Astron. Astrophys. 235, 441 446], Sirono and Greenberg [Sirono, S.-I., Greenberg, J.M., 2000. Icarus 145, 230 238] and the experiments of Wurm et al. [Wurm, G., Paraskov, G., Krauss, O., 2005. Icarus 178, 253 263] on the collision physics of porous aggregate bodies are used as basis for a conceptual model of the formation of layers. Our hypothesis is found to have implications for the place of origin of the JFCs and their subsequent dynamical history. Models of fragmentation and rubble pile building in the Kuiper belt in a period of collisional activity (e.g., [Kenyon, S.J., Luu, J.X., 1998. Astron. J. 115, 2136 2160; 1999a. Astron. J. 118, 1101 1119; 1999b. Astrophys. J. 526, 465 470; Farinella, P., Davis, D.R., Stern, S.A., 2000. In: Mannings, V., Boss, A.P., Russell, S.S. (Eds.), Protostars and Planets IV. Univ. of Arizona Press, Tucson, pp. 1255 1282; Durda, D.D., Stern, S.J., 2000. Icarus 145, 220 229]) following the formation of Neptune appear to be in conflict with the observed properties of the layers and irreconcilable with the hypothesis. Long-term residence in the scattered disk [Duncan, M.J., Levison, H.F., 1997. Science 276, 1670 1672; Duncan, M., Levison, H., Dones, L., 2004. In: Festou, M., Keller, H.U., Weaver, H.A. (Eds.), Comets II. Univ. of Arizona Press, Tucson, pp. 193 204] and/or a change in fragmentation outcome modeling may explain the long-term persistence of primordial layers. In any event, the existence of layers places constraints on the environment seen by the population of objects from which the Jupiter family comets originated. If correct, our hypothesis implies that the nuclei of Jupiter family comets are primordial remnants of the early agglomeration phase and that the physical structure of their interiors, except for the possible effects of compositional phase changes, is largely as it was when they were formed. We propose a new model for the interiors of Jupiter family cometary nuclei, called the talps or “layered pile” model, in which the interior consists of a core overlain by a pile of randomly stacked layers. We discuss how several cometary characteristics—layers, surface texture, indications of flow, compositional inhomogeneity, low bulk density low strength, propensity to split, etc., might be explained in terms of this model. Finally, we make some observational predictions and suggest goals for future space observations of these objects.

Tratamiento formal de imágenes astronómicas con PSF espacialmente variable

NASA Astrophysics Data System (ADS)

Sánchez, B. O.; Domínguez, M. J.; Lares, M.

2017-10-01

We present a python implementation of a method for PSF determination in the context of optimal subtraction of astronomical images. We introduce an expansion of the spatially variant point spread function (PSF) in terms of the Karhunen Loève basis. The advantage of this approach is that the basis is able to naturally adapt to the data, instead of imposing a fixed ad-hoc analytic form. Simulated image reconstruction was analyzed, by using the measured PSF, with good agreement in terms of sky background level between the reconstructed and original images. The technique is simple enough to be implemented on more sophisticated image subtraction methods, since it improves its results without extra computational cost in a spatially variant PSF environment.

Bright end of the color-magnitude relation for cD, E and S0 galaxies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lugger, P.M.

1979-11-01

Schild and Davis's (Astron. J. 84, 311 (1979)) galaxy photometry for cD's in poor clusters is compared with Sandage's (Astrophys. J. 176, 21(1979)) color-magnitude relation defined by elliptical and S0 galaxies in the Virgo and Coma clusters. The cD galaxies are found to be somewhat bluer on average than galaxies of similar magnitude in the Virgo and Coma sample, consistent with the predictions of the galactic cannibalism model proposed by Hausman and Ostriker (Astrophys. J. 224, 320 (1978)). However, a more uniform selection of galaxy photometry is required before any definitive conclusions regarding the bright end of the color-magnitude relationmore » can be made.« less

Accreting Black Holes an All Out Effort

NASA Technical Reports Server (NTRS)

2003-01-01

This final report lists many publications resulting from this grant. The following is a representative listing of several dozen title: (1) '1100 Days of BATSE observations of Cyg X-1', D Crary, C. Kouveliotou, J. van Paradijs, F. v.d. Hooft, B. Rubin, S. Zhang, W. Paciesas, M. Fini:er, B. Harmon, M. v.d. Klis, W.H.G. Lewin, and J. Norris, Astron. Astrophys. Suppl., 120, 153-156, (1997) (2) 'Spectral and Temporal Variability in the X-ray Flux'. of GSll24-683, Nova Muscae 1991", M. Takizawa, T. Dotani, K. Mitsuda, E. Matsuba, M. O;;awa, T. Aoki, K. Asai, K. Ebisawa, K. Makishima, S. Miyamoto, S . Iga, B. Vaughan, R. Rc.tledge, & W. Lewin, Astrophys, J., 489, 272, (1997).

Flamsteed's Supernova of 1680

NASA Astrophysics Data System (ADS)

Fesen, R. A.

2001-12-01

A recent proper motion study of 40 knots in the Cas A supernova remnant indicated a knot convergent date of A.D. 1671.3 +/-0.9 assuming no deceleration (Thorstensen, Fesen, & van den Bergh 2001, AJ, 122, 297). However, because these optical knots are made visible by their shock passage through the local ISM/CSM, some deceleration is expected. A deceleration of just ~ 1.6 km s-1 yr-1 over a 300 yr time span would yield an explosion date around A.D. 1680, consistent with a suspected sighting of the Cas A supernova by J. Flamsteed in August 1680 (Ashworth, 1980, J. Hist. Astron., 11, 1). We discuss Flamsteed's likely observations of SN 1680 in terms of their constrains on the light curve and peak brightness and possible implications regarding the Cas A SN subtype.

Antenna Efficiency and the Genius of the IEEE Standard for Antenna Terms [Education Column

NASA Astrophysics Data System (ADS)

Warnick, Karl F.

2012-08-01

At a 2007 Square Kilometre Array Design Studies (SKADS) workshop in Dwingeloo, Wim van Cappellen of the Nether lands Institute for Radio Astronomy (ASTRON) gave a presentation on figures of merit, in which he memorably compared antenna terms to apples. What seems like a simple, homogeneous fruit comes in all colors and varieties. Similarly, a survey of antenna literature and textbooks shows that authors use a wide variety of antenna figures of merit, often not in compliance with the relevant IEEE Standard Definitions of Terms for Antennas [1]. Since this standard is now in the process of revision by the Antennas and Propagation Society Antenna Standards Committee, it seems worth while to consider the standard, and clarify some common misunderstandings and inconsistent usages.

Link between interplanetary & cometary dust: Polarimetric observations and space studies with Rosetta & Eye-Sat

NASA Astrophysics Data System (ADS)

Levasseur-Regourd, Anny-Chantal; Gaboriaud, Alain; Buil, Christian; Ressouche, Antoine; Lasue, J.; Palun, Adrien; Apper, Fabien; Elmaleh, Marc

Intensity and linear polarization observations of the solar light scattered by interplanetary dust, the so-called zodiacal light, provide information on properties of the dust particles, such as their spatial density, local changes, morphology and albedo. Earth-based polarimetric observations, with a resolution of 5° or more, have been used to derive the polarization phase curve of interplanetary dust particles and to establish that the polarization at 90° phase angle increases with increasing solar distance, at least up to 1.5 au in the ecliptic, while the albedo decreases [1, 2]. Analysis of such studies will be revisited. Numerical simulations of the polarimetric behavior of interplanetary dust particles strongly suggest that, in the inner solar system, interplanetary dust particles consist of absorbing (e.g., organic compounds) and less absorbing (e.g., silicates) materials, that radial changes originate in a decrease of organics with decreasing solar distance (probably due to alteration processes), and that a significant fraction of the interplanetary dust is of cometary origin, in agreement with dynamical studies [3, 4]. The polarimetric behaviors of interplanetary dust and cometary dust particles seem to present striking similarities. The properties of cometary dust particles, as derived from remote polarimetric observations of comets including 67P/Churyumov-Gerasimenko, the target of the Rosetta rendezvous mission, at various wavelengths, will be summarized [5, 6]. The ground truth expected from Rosetta dust experiments, i.e., MIDAS, COSIMA, GIADA, about dust particles’ morphology, composition, and evolution (with distance to the nucleus before Philae release and with distance to the Sun before and after perihelion passage) over the year and a half of nominal mission, will be discussed. Finally, the Eye-Sat nanosatellite will be presented. This triple cubesat, developed by students from engineering schools working as interns at CNES, is to be launched in 2016 [7]. Its main purpose is to study the zodiacal light intensity and polarization from a Sun-synchronous orbit, for the first time at the high spatial resolution of 1° over a wide portion of the sky and at four different wavelengths (in the visible and near-IR domains). The instrumental choices and new on-board technologies will be summarized, together with the results that may be expected on local properties of the interplanetary dust particles and thus on their similarities and differences with cometary dust particles. Support from CNES is warmly acknowledged. [1] Leinert, C., Bowyer, S., Haikala, L.K., et al. The 1997 reference of diffuse night sky brightness, Astron. Astrophys. Supp., 127, 1-99, 1998. [2] Levasseur-Regourd, A.C., Mann, I., Dumont, R., et al. Optical and thermal properties of interplanetary dust. In Interplanetary dust (Grün, E. et al. Eds), 57-94, Springer-Verlag, Berlin, 2001. [3] Lasue, J., Levasseur-Regourd, A.C., Fray, N., et al. Inferring the interplanetary dust properties from remote observations and simulations, Astron. Astrophys., 473, 641-649, 2007. [4] Nesvorny, D., Jenniskens, P., Levison, H.F., et al. Cometary origin of the zodiacal cloud and carbonaceous micrometeorites: implications for hot debris disks. Astrophys. J. 713, 816-836, 2010. [5] Levasseur-Regourd, A.C., Mukai, T., Lasue, J., et al. Physical properties of cometary and interplanetary dust, Planet. Space Sci., 55, 1010-1020, 2007. [6] Hadamcik, E., Sen, A.K., Levasseur-Regourd, A.C., et al., Astron. Astrophys., 517, A86, 2010. [7] CNES internal report. Eye-Sat end of phase A internal review, EYESAT-PR-0-022-CNES, 2013.

Planetesimal-driven planet migration in the presence of a gas disk

NASA Astrophysics Data System (ADS)

Capobianco, Christopher C.; Duncan, Martin; Levison, Harold F.

2011-01-01

We report here on an extension of a previous study by Kirsh et al. (Kirsh, D.R., Duncan, M., Brasser, R., Levison, H.F. [2009]. Icarus 199, 197-209) of planetesimal-driven migration using our N-body code SyMBA (Duncan, M.J., Levison, H.F., Lee, M.H. [1998]. Astron. J. 116, 2067-2077). The previous work focused on the case of a single planet of mass Mem, immersed in a planetesimal disk with a power-law surface density distribution and Rayleigh distributed eccentricities and inclinations. Typically 10 4-10 5 equal-mass planetesimals were used, where the gravitational force (and the back-reaction) on each planetesimal by the Sun and planet were included, while planetesimal-planetesimal interactions were neglected. The runs reported on here incorporate the dynamical effects of a gas disk, where the Adachi et al. (Adachi, I., Hayashi, C., Nakazawa, K. [1976]. Prog. Theor. Phys. 56, 1756-1771) prescription of aerodynamic gas drag is implemented for all bodies. In some cases the Papaloizou and Larwood (Papaloizou, J.C.B., Larwood, J.D. [2000]. Mon. Not. R. Astron. Soc. 315, 823-833) prescription of Type-I migration for the planet are implemented, as well as a mass distribution. In the gas-free cases, rapid planet migration was observed - at a rate independent of the planet's mass - provided the planet's mass was not large compared to the mass in planetesimals capable of entering its Hill sphere. In such cases, both inward and outward migrations can be self-sustaining, but there is a strong propensity for inward migration. When a gas disk is present, aerodynamic drag can substantially modify the dynamics of scattered planetesimals. For sufficiently large or small mono-dispersed planetesimals, the planet typically migrates inward. However, for a range of plausible planetesimal sizes (i.e. 0.5-5.0 km at 5.0 AU in a minimum mass Hayashi disk) outward migration is usually triggered, often accompanied by substantial planetary mass accretion. The origins of this behaviour are explained in terms of a toy model. The effects of including a size distribution and torques associated with Type-I migration are also discussed.

Distribution of inhomogeneities in the interstellar plasma in the directions of three distant pulsars from observations with the RadioAstron ground-space interferometer

NASA Astrophysics Data System (ADS)

Popov, M. V.; Andrianov, A. S.; Bartel, N.; Gwinn, C.; Joshi, B. C.; Jauncey, D.; Kardashev, N. S.; Rudnitskii, A. G.; Smirnova, T. V.; Soglasnov, V. A.; Fadeev, E. N.; Shishov, V. I.

2016-09-01

The RadioAstron ground-space interferometer has been used to measure the angular sizes of the scattering disks of the three distant pulsars B1641-45, B1749-28, and B1933+16. The observations were carried out with the participation of the Westerbork Synthesis Radio Telescope; two 32-m telescopes at Torun, Poland and Svetloe, Russia (the latter being one antenna of the KVAZAR network); the Saint Croix VLBA antenna; the Arecibo radio telescope; the Parkes, Narrabri (ATCA), Mopra, Hobart, and Ceduna Australian radio telescopes; and the Hartebeesthoek radio telescope in South Africa. The full widths at half maximum of the scattering disks were 27 mas at 1668 MHz for B1641-45, 0.5 mas at 1668 MHz for B1749-28, and 12.3 at 316 MHz and 0.84 mas at 1668 MHz for B1933+16. The characteristic time scales for scatter-broadening of the pulses on inhomogeneities in the interstellar plasma τsc were also measured for these pulsars using various methods. Joint knowledge of the size of the scattering disk and the scatter-broadening time scale enables estimation of the distance to the effective scattering screen d. For B1641-45, d = 3.0 kpc for a distance to the pulsar D = 4.9 kpc, and for B1749-28, d = 0.95 kpc for D = 1.3 kpc. Observations of B1933+16 were carried out simultaneously at 316 and 1668 MHz. The positions of the screen derived using the measurements at the two frequencies agree: d 1 = 2.6 and d 2 = 2.7 kpc, for a distance to the pulsar of 3.7 kpc. Two screens were detected for this pulsar from an analysis of parabolic arcs in the secondary dynamic spectrum at 1668 MHz, at 1.3 and 3.1 kpc. The scattering screens for two of the pulsars are identified with real physical objects located along the lines of sight toward the pulsars: G339.1-04 (B1641-45) and G0.55-0.85 (B1749-28).

Detecting signatures of cosmological recombination and reionization in the cosmic radio background

NASA Astrophysics Data System (ADS)

Subrahmanyan, Ravi; Shankar Narayana Rao, Udaya; Sathyanarayana Rao, Mayuri; Singh, Saurabh

2015-08-01

Evolution of the baryons during the Epochs of cosmological Recombination and Reionization has left traces in the cosmic radio background in the form of spectral distortions (Sunyaev & Chluba 2008 Astron. Nachrichten, 330, 657; Pritchard & Loeb 2012 Rep Prog Phys 75(8):086901). The spectral signature depends on the evolution in the ionization state in hydrogen and helium and on the spin temperature of hydrogen. These probe the physics of energy release beyond the last scattering surface at redshifts exceeding 1090 and the nature of the first sources and gas evolution down to redshift about 6. The spectral distortions are sensitive to the nature of the first stars, ultra-dwarf galaxies, accreting compact objects, and the evolving ambient radiation field: X-rays and UV from the first sources. Detection of the all-sky or global spectral distortions in the radio background is hence a probe of cosmological recombination and reionization.We present new spectral radiometers that we have purpose designed for precision measurements of spectral distortions at radio wavelengths. New antenna elements include frequency independent and electrically small fat-dipole (Raghunathan et al. 2013 IEEE TAP, 61, 3411) and monopole designs. Receiver configurations have been devised that are self-calibratable (Patra et al. 2013 Expt Astron, 36, 319) so that switching of signal paths and of calibration noise sources provide real time calibration for systematics and receiver noise. Observing strategies (Patra et al. arXiv:1412.7762) and analysis methods (Satyanarayana Rao et al. arXiv:1501.07191) have been evolved that are capable of discriminating between the cosmological signals and the substantially brighter foregrounds. We have also demonstrated the value of system designs that exploit advantages of interferometer detection (Mahesh et al. arXiv:1406.2585) of global spectral distortions.Finally we discuss how the Square Kilometer Array stations may be outfitted with precision spectral radiometer outriggers (Subrahmanyan et al. arXiv:1501.04340) to provide the zero-spacing measurement sets, complement the interferometer visibilities and give the SKA a capability for measurements of cosmic radio background spectral distortions.

Low Optical Depth Features in Saturn's Rings: The Occultation of GSC5249-01240 by Saturn and Its Rings

NASA Astrophysics Data System (ADS)

Bosh, A. S.; Olkin, C. B.

1996-06-01

On 21 November 1995, Saturn and its rings occulted the star GSC5249-01240 (Bosh & McDonald 1992, Astron. J. 103, 983). Although the star is relatively faint (V = 11.9), other circumstances conspired to make this an excellent event: (i) the normally-bright rings were dark because the sun was crossing through the ring plane, reducing the amount of ring contribution to the background noise and therefore increasing the observed S/N, (ii) the ring opening angle was small (B ~ 3deg ), enhancing detection of low-optical-depth material, and (iii) the low sky-plane velocity allowed longer integration times without loss of spatial resolution. Thus this occultation was particularly well-suited to produce high S/N detections of low-tau ring material. We observed this atmosphere and ring occultation with the Faint Object Spectrograph (FOS) on the Hubble Space Telescope. Using the FOS in its high-speed mode, we sampled the starlight with the G650L grating, recording the stellar signal as a function of both wavelength and time. For the initial analysis of these data, the spectral information was sacrificed by binning all wavelengths together; this in turn increased the detected S/N. We performed a geometric solution for the event, using the known locations of circular ring features as fiducials (Elliot et al., Astron. J. 106, 2544). The scattered light from Saturn and the rings was modelled and subtracted from the light curves to obtain line-of-sight optical depth as a function of ring-plane radius. With these processed data we have made the first occultation detection of Saturn's innermost and very tenuous D ring. We find a line-of-sight optical depth for the thickest part of this ring of tau_ {obs} ~ 0.02. The location and morphology of this feature will be discussed. Comparison of the observed structure will be made with the previous Voyager imaging detection of this ring (Smith et al. 1981, Science 212, 163; Marley & Porco 1993, Icarus 106, 508).

Retrograde resonance in the planar three-body problem

NASA Astrophysics Data System (ADS)

Morais, M. H. M.; Namouni, F.

2013-12-01

We continue the investigation of the dynamics of retrograde resonances initiated in Morais and Giuppone (Mon Notices R Astron Soc 424:52-64, doi:10.1111/j.1365-2966.2012.21151.x, 2012). After deriving a procedure to deduce the retrograde resonance terms from the standard expansion of the three-dimensional disturbing function, we concentrate on the planar problem and construct surfaces of section that explore phase-space in the vicinity of the main retrograde resonances (2/1, 1/1 and 1/2). In the case of the 1/1 resonance for which the standard expansion is not adequate to describe the dynamics, we develop a semi-analytic model based on numerical averaging of the unexpanded disturbing function, and show that the predicted libration modes are in agreement with the behavior seen in the surfaces of section.

New International Agreements About Space Techniques Among Argentina, China and France

NASA Astrophysics Data System (ADS)

Pacheco, A. M.; Podestá, R.; Actis, E.; Adarvez, S.; Quinteros, J.; Li, J.; Saunier, J.; Podestá, F.; Ramos, F.; Aguilera, J.; Sosa, G.; Hauser, D.

2018-01-01

The International Earth Rotation and Reference Systems (IERS) is in charge of defining and materializing celestial reference systems (ICRS - ICRF) and terrestrial reference systems (ITRS - ITRF). In order to perform this task it uses data from the following techniques: Very Long Baseline Interferometry (VLBI), Satellite Laser Ranging (SLR), Global Navigation Satellite System (GNSS) and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS). Nowadays, the Observatorio Astronómico Félix Aguilar (OAFA) has two instruments with these advanced techniques: SLR and a permanent GNSS station. In the nearby future a 40 m diameter radio telescope will be available that will be operated in VLBI mode along with a DORIS buoy which will be co-localized with a SLR telescope and GNSS antennas. In this way OAFA will become a zero station, first class, of the ITRF 2014 frame.

Cen A Radio Optical Gamma Composite

NASA Image and Video Library

2017-12-08

NASA release April 1, 2010 It takes the addition of radio data (orange) to fully appreciate the scale of Cen A's giant radio-emitting lobes, which stretch more than 1.4 million light-years. Gamma-rays from Fermi's Large Area Telescope (purple) and an image of the galaxy in visible light are also included in this composite. Credit: NASA/DOE/Fermi LAT Collaboration, Capella Observatory, and Ilana Feain, Tim Cornwell, and Ron Ekers (CSIRO/ATNF), R. Morganti (ASTRON), and N. Junkes (MPIfR) To learn more about these images go to: www.nasa.gov/mission_pages/GLAST/news/smokestack-plumes.html NASA Goddard Space Flight Center is home to the nation's largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

SUPERFAST THERMALIZATION OF PLASMA

DOEpatents

Chang, C.C.

1962-06-12

A method is given for the superfast thermalization of plasma by shock conversion of the kinetic energy stored in rotating plasma rings or plasmoids colliding at near supersonic speeds in a containment field to heat energy in the resultant confined plasma mass. The method includes means for generating rotating plasmoids at the opposite ends of a Pyrotron or Astron containment field. The plasmoids are magnetically accelerated towards each other into the opposite ends of time containment field. During acceleration of the plasmoids toward the center of the containment field, the intensity of the field is sequentially increased to adiabatically compress the plasmoids and increase the plasma energy. The plasmoids hence collide with a violent shock at the eenter of the containment field, causing the substantial kinetic energy stored in the plasmoids to be converted to heat in the resultant plasma mass. (AEC)

Precipitable water vapor and 212 GHz atmospheric optical depth correlation at El Leoncito site

NASA Astrophysics Data System (ADS)

Cassiano, Marta M.; Cornejo Espinoza, Deysi; Raulin, Jean-Pierre; Giménez de Castro, Carlos G.

2018-03-01

Time series of precipitable water vapor (PWV) and 212 GHz atmospheric optical depth were obtained in CASLEO (Complejo Astronómico El Leoncito), at El Leoncito site, Argentinean Andes, for the period of 2011-2013. The 212 GHz atmospheric optical depth data were derived from measurements by the Solar Submillimeter Telescope (SST) and the PWV data were obtained by the AERONET CASLEO station. The correlation between PWV and 212 GHz optical depth was analyzed for the whole period, when both parameters were simultaneously available. A very significant correlation was observed. Similar correlation was found when data were analyzed year by year. The results indicate that the correlation of PWV versus 212 GHz optical depth could be used as an indirect estimation method for PWV, when direct measurements are not available.

Proyecto para la medición sistemática de seeing en CASLEO

NASA Astrophysics Data System (ADS)

Fernández Lajus, E.; Forte, J. C.

La calidad del seeing astronómico es ciertamente uno de los parámetros mas importantes que caracterizan el sitio de un observatorio. Por tanto se desea determinar si el alto valor de seeing observado con el telescopio de 2.15 m se debe a efectos internos y/o del entorno a la cupula o si se debe simplemente al seeing propio del lugar. El actual mecanismo de refrigeración del espejo primario del 2.15, parece haber mejorado notablemente la calidad del seeing. Sin embargo se hace necesario saber hasta que punto el valor del seeing puede ser mejorado. La primera etapa del proyecto consistió en la puesta a punto del telescopio emplazado para este propósito y la adquisición de las primeras medidas tentativas de seeing.

Introduction to the Special Issue on Digital Signal Processing in Radio Astronomy

NASA Astrophysics Data System (ADS)

Price, D. C.; Kocz, J.; Bailes, M.; Greenhill, L. J.

2016-03-01

Advances in astronomy are intimately linked to advances in digital signal processing (DSP). This special issue is focused upon advances in DSP within radio astronomy. The trend within that community is to use off-the-shelf digital hardware where possible and leverage advances in high performance computing. In particular, graphics processing units (GPUs) and field programmable gate arrays (FPGAs) are being used in place of application-specific circuits (ASICs); high-speed Ethernet and Infiniband are being used for interconnect in place of custom backplanes. Further, to lower hurdles in digital engineering, communities have designed and released general-purpose FPGA-based DSP systems, such as the CASPER ROACH board, ASTRON Uniboard, and CSIRO Redback board. In this introductory paper, we give a brief historical overview, a summary of recent trends, and provide an outlook on future directions.

Comportamiento de la cromósfera solar en la línea H-alpha durante el ciclo 23

NASA Astrophysics Data System (ADS)

Davoli, D.; Aquilano, R.; Missio, H.

Using the instrumental of the Observatorio Astronómico Municipal de Rosario (OAMR), we analyze the solar chromospheric activity during an approximate period of 11 years. The instrument is a Carl Zeiss refractor telescope of 150 mm aperture and 2250 mm of focal distance with monochromatic filter in the H-alpha line. We take as proxy for the solar activity the area covered by chromospheric plages. Simultaneously, we determine the relative wolf number from observations of the solar photosphere. We describe our technique and the results obtained. We observe 2 maxima of solar activity in the years 2000 and 2001 respectively, and a later decrease of this activity with low average values starting around 2006 that corresponds to the end of cycle 23. FULL TEXT IN SPANISH

Segunda discontinuidad de Balmer y procesos físicos en envolturas extendidas de estrellas Be

NASA Astrophysics Data System (ADS)

Bibbo, I.; Cruzado, A.; Ringuelet, A.

We study a group of Be stars in which the second Balmer jump is observed. Our aim is to correlate the second Balmer jump with other spectral features. Spectroscopic observations were performed with the 2.15 m telescope at Complejo Astronómico el Leoncito, CASLEO (San Juan, Argentina). In December 2001 and August 2002 high resolution echelle spectra were obtained with a REOSC echelle spectrograph. We find that, when a second Balmer jump in emission is observed, an emission in λ = 4233,17 Å of FeII multiplet 27 is also, generally seen. Besides, the electron temperature of the region of the envelope where the second jump is formed is estimated assuming that radiative recombinations cause the flux emission in the Balmer continuum. The temperature values obtained in this way are found correlated with the measure of the second Balmer jump.

Giant pulses of the Crab Nebula pulsar as an indicator of a strong electromagnetic wave

NASA Astrophysics Data System (ADS)

Popov, M. V.; Rudnitskii, A. G.; Soglasnov, V. A.

2017-03-01

The spectra and visibility functions of giant pulses of the Crab Nebula pulsar derived from VLBI observations carried out through the "RadioAstron" project in 2015 are analyzed. Parameters of the scattering of the pulses in the interstellar medium are measured, namely, the scattering time and decorrelation bandwidth. A comparative analysis of the shapes of the spectra and visibility functions of giant pulses obtained in real observations and via modeling of their scattering is carried out. The results suggest the presence of short bursts ( dt < 30 ns) in the structure of the giant pulses at 1668 MHz, whose brightness temperatures exceed 1038 K. These pulses propagate in the pulsar magnetosphere in a strong electromagneticwave regime, leading to the generation of additional radiation perpendicular to the direction of propagation of the giant pulses. This radiation may be associated with anomalous components of the mean pulse profile observed at frequencies above 4 GHz.

Very high energy observations of the BL Lac objects 3C 66A and OJ 287

NASA Astrophysics Data System (ADS)

Lindner, T.; Hanna, D. S.; Kildea, J.; Ball, J.; Bramel, D. A.; Carson, J.; Covault, C. E.; Driscoll, D.; Fortin, P.; Gingrich, D. M.; Jarvis, A.; Mueller, C.; Mukherjee, R.; Ong, R. A.; Ragan, K.; Scalzo, R. A.; Williams, D. A.; Zweerink, J.

2007-11-01

Using the Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE), we have observed the BL Lac objects 3C 66A and OJ 287. These are members of the class of low-frequency-peaked BL Lac objects (LBLs) and are two of the three LBLs predicted by Costamante and Ghisellini [L. Costamante, G. Ghisellini, Astron. Astrophys. 384 (2002) 56] to be potential sources of very high energy (>100 GeV) gamma-ray emission. The third candidate, BL Lacertae, has recently been detected by the MAGIC collaboration [J. Albert et al., arXiv:astro-ph/0703084v1 (2007)]. Our observations have not produced detections; we calculate a 99% CL upper limit of flux from 3C 66A of 0.15 Crab flux units and from OJ 287 our limit is 0.52 Crab. These limits assume a Crab-like energy spectrum with an effective energy threshold of 185 GeV.

Peculiar Supernovae

NASA Astrophysics Data System (ADS)

Milisavljevic, Dan; Margutti, Raffaella

2018-06-01

What makes a supernova truly "peculiar?" In this review we attempt to address this question by tracing the history of the use of "peculiar" as a descriptor of non-standard supernovae back to the original binary spectroscopic classification of Type I vs. Type II proposed by Minkowski (Publ. Astron. Soc. Pac., 53:224, 1941). A handful of noteworthy examples are highlighted to illustrate a general theme: classes of supernovae that were once thought to be peculiar are later seen as logical branches of standard events. This is not always the case, however, and we discuss ASASSN-15lh as an example of a transient with an origin that remains contentious. We remark on how late-time observations at all wavelengths (radio-through-X-ray) that probe 1) the kinematic and chemical properties of the supernova ejecta and 2) the progenitor star system's mass loss in the terminal phases preceding the explosion, have often been critical in understanding the nature of seemingly unusual events.

Origin of the fundamental plane of elliptical galaxies in the Coma cluster without fine-tuning

NASA Astrophysics Data System (ADS)

Chiu, Mu-Chen; Ko, Chung-Ming; Shu, Chenggang

2017-03-01

Thirty years after the discovery of the fundamental plane, explanations of the tilt of the fundamental plane with respect to the virial plane are still in need of fine-tuning. In this paper, we try to explore the origin of this tilt from the perspective of modified Newtonian dynamics (MOND) by applying the 16 Coma galaxies available in J. Thomas et al. [Mon. Not. R. Astron. Soc. 415, 545 (2011), 10.1111/j.1365-2966.2011.18725.x]. Based on the mass models that can reproduce de Vaucouleurs' law closely, we find that the tilt of the traditional fundamental plane is naturally explained by the simple form of the MONDian interpolating function, if we assume a well motivated choice of anisotropic velocity distribution, and adopt the Kroupa or Salpeter stellar mass-to-light ratio. Our analysis does not necessarily rule out a varying stellar mass-to-light ratio.

Astronomía gamma con telescopios Cherenkov: hacia un observatorio astronómico abierto a la comunidad

NASA Astrophysics Data System (ADS)

Rovero, A. C.

Gamma-ray astronomy is opening the way to a universe far more energetic than anyone could have imagined half a century ago. The understanding of the processes of nature which carry a large portion of the energy in the universe, has astrophysical and cosmological implications. The next gen- eration of Cherenkov telescopes, an order of magnitude more sensitive and with higher resolution than the current systems, will mean a significant step forward for ground-based gamma-ray astronomy. This paper presents the current status of this field as well as the next generation of telescopes in this energy range, which are being designed for the first international observa- tory open to the astronomical community. The Cherenkov Telescope Array project and the Argentine sites proposed for the southern observatory are described in this paper. FULL TEXT IN SPANISH

Angular Momentum Transport in Turbulent Flow between Independently Rotating Cylinders

DOE Office of Scientific and Technical Information (OSTI.GOV)

Paoletti, M. S.; Lathrop, D. P.; Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742

2011-01-14

We present measurements of the angular momentum flux (torque) in Taylor-Couette flow of water between independently rotating cylinders for all regions of the ({Omega}{sub 1}, {Omega}{sub 2}) parameter space at high Reynolds numbers, where {Omega}{sub 1} ({Omega}{sub 2}) is the inner (outer) cylinder angular velocity. We find that the Rossby number Ro=({Omega}{sub 1}-{Omega}{sub 2})/{Omega}{sub 2} fully determines the state and torque G as compared to G(Ro={infinity}){identical_to}G{sub {infinity}.} The ratio G/G{sub {infinity}} is a linear function of Ro{sup -1} in four sections of the parameter space. For flows with radially increasing angular momentum, our measured torques greatly exceed those of previousmore » experiments [Ji et al., Nature (London), 444, 343 (2006)], but agree with the analysis of Richard and Zahn [Astron. Astrophys. 347, 734 (1999)].« less

Best-Ever Snapshot of a Black Hole's Jets

NASA Image and Video Library

2017-12-08

NASA image release May 20, 2011 To see a really cool video related to this image go here: www.flickr.com/photos/gsfc/5740451675/in/photostream The giant elliptical galaxy NGC 5128 is the radio source known as Centaurus A. Vast radio-emitting lobes (shown as orange in this optical/radio composite) extend nearly a million light-years from the galaxy. Credit: Capella Observatory (optical), with radio data from Ilana Feain, Tim Cornwell, and Ron Ekers (CSIRO/ATNF), R. Morganti (ASTRON), and N. Junkes (MPIfR). To read more go to: www.nasa.gov/topics/universe/features/radio-particle-jets... NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Join us on Facebook

A photometric survey of Near-Earth Objects in support of the NEOShield-2 project

NASA Astrophysics Data System (ADS)

Ieva, S.; Dotto, E.; Mazzotta Epifani, E.; Perna, D.; Barucci, M. A.; Di Paola, A.; Micheli, M.; Perozzi, E.; Speziali, R.; Lazzarin, M.; Bertini, I.; Giunta, A.; Lazzaro, D.; Arcoverde, P.

2017-09-01

More than 85% of the 16,000 NEOs discovered up to now lack a physical characterization. The study of their physical properties is essential to define a proper mitigation scenario. One of the main aims of the NEOShield-2 project (2015-2017), financed by the European Community in the framework of the Horizon 2020 program, is therefore to retrieve physical properties of a wide number of NEOs, in order to design impact mitigation missions and assess the consequences of an impact on Earth. We present the results obtained during a 2-year Long-Term Program at the Telescopio Nazionale Galileo (TNG, La Palma, Spain), where we carried out BVRI photometry of about 150 NEOs, and the analysis of the phase curves obtained at the Campo Imperatore telescope (L'Aquila, Italy) and the Observatório Astronômico do Sertão de Itaparica (Nova Itacuruba, Brazil).

Linear polarization of a group of symbiotic systems

NASA Astrophysics Data System (ADS)

Brandi, E.; García, L. G.; Piirola, V.; Scaltriti, F.; Quiroga, C.

2000-08-01

We report linear polarization measurements of a set of symbiotic stars, made at several epochs during the period 1994-1998. Evidence of intrinsic polarization is looked for from the wavelength dependence of the polarization degree and position angle in UBVRI bands. The results have also been analysed to search for temporal variability of polarization. Several objects have shown a polarization spectrum different from that produced by interstellar dust grains and/or polarimetric variations on time scales as short as several days or months, indicating the presence of polarization component of circumstellar origin. Based on observations taken at Complejo Astronómico El Leoncito (CASLEO), operated under an agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina, the Secretaría de Ciencia y Tecnología de la Nación and the National Universities of La Plata, Córdoba and San Juan.

The Faint Young Sun Paradox in the Context of Modern Cosmology

NASA Astrophysics Data System (ADS)

Dumin, Yu. V.

2015-09-01

The Faint Young Sun Paradox comes from the fact that solar luminosity (2-4)x10^9 years ago was insufficient to support the Earth's temperature necessary for the efficient development of geological and biological evolution (particularly, for the existence of considerable volumes of liquid water). It remains unclear by now if the so-called greenhouse effect on the Earth can resolve this problem. An interesting alternative explanation was put forward recently by M.Krizek (New Astron. 2012, 17, 1), who suggested that planetary orbits expand with time due to the local Hubble effect, caused by the uniformly-distributed Dark Energy. Then, under a reasonable value of the local Hubble constant, it is easy to explain why the Earth was receiving an approximately constant amount of solar irradiation for a long period in the past and will continue to do so for a quite long time in future.

Monitoring non-periodic comet C/2011 L4 PANSTARRS using Joan Oró 0.8 m robotic telescope at OAdM

NASA Astrophysics Data System (ADS)

Trigo-Rodríguez, J. M.; Rodríguez, D.; Lacruz, J.; Sánchez, A.

2013-09-01

Comet C/2011 L4 PANSTARRS was discovered in June 2011 by R. Wainscoat and D. Tholen using the Pan-STARRS telescope located near the summit of Haleakala, on the island of Maui in Hawaii (USA) [1]. Once its orbit was computed it was noticed its non-periodic nature and the favorable geometry during its approach to perihelion in March 2013. It first became visible to the naked eye from the Southern hemisphere, and later on it started to be seen during mid-March from the Northern one. Due to the limited observational period in right conditions we introduce here some observations obtained taken from robotic 0.8 m Telescope Joan Oró (JO) from the Observatori Astronòmic del Montsec (OAdM: www.oadm.cat) and other Spanish observatories.

Visits to La Plata Observatory

NASA Astrophysics Data System (ADS)

Feinstein, A.

1985-03-01

La Plata Observatory will welcome visitors to ESO-La Silla that are willing to make a stop at Buenos Aires on their trip to Chile or on their way back. There is a nice guesthouse at the Observatory that can be used, for a couple of days or so, by astronomers interested in visiting the Observatory and delivering talks on their research work to the Argentine colleagues. No payments can, however, be made at present. La Plata is at 60 km from Buenos Aires. In the same area lie the Instituto de Astronomia y Fisica dei Espacio (IAFE), in Buenos Aires proper, and the Instituto Argentino de Radioastronomia (IAR). about 40 km from Buenos Aires on the way to La Plata. Those interested should contacl: Sr Decano Prof. Cesar A. Mondinalli, or Dr Alejandro Feinstein, Observatorio Astron6mico, Paseo dei Bosque, 1900 La Plata, Argentina. Telex: 31216 CESLA AR.

Period change in GP And

NASA Astrophysics Data System (ADS)

Rodriguez, E.; Rolland, A.; Lopez de Coca, P.

1993-05-01

GP And is a high amplitude d Scuti type star with V~10.m75, DV~0.m55, P=0.d0787 and spectral type A3 (Lopez de Coca et al. 1990, A & A 83, 51). To study the stability of its fundamental pulsation we have carried out simultaneous uvby photometry of this star in the years 1987 and 1992 at Sierra Nevada and Caltar Alto observatories, both in Spain. Ten new times of light maxima were obtained. In total, forty-one time s of light maxima (from 1973 to 1992, collected from Splittgerber 1976, Mitt. Veraend. Sterne 7, 137; Eggen 1978, IBVS 1517; Gieseking et al. 1979, A & AS 36, 457; Burchi et al. 1992, Mem. Soc. Astron. Ital. 63, 87 and us) were used to determinate the ephemeris of the light curve of GP And by means of the classical O-C method.

International data transfer for space very long baseline interferometry

NASA Technical Reports Server (NTRS)

Wiercigroch, Alexandria B.

1994-01-01

Space very long baseline interferometry (SVLBI) experiments using a TDRSS satellite have successfully demonstrated the capability of using spacecraft to extend the effective baseline length of VLBI observations beyond the diameter of the Earth, thereby improving the resolution for imaging of active galactic nuclei at centimeter wavelengths. As a result, two spacecraft dedicated to SVLBI, VSOP (Japan) and RadioAstron (Russia), are scheduled to be launched into high Earth orbit in 1996 and 1997. The success of these missions depends on the cooperation of the international community in providing support from ground tracking stations, ground radio telescopes, and correlation facilities. The timely exchange and monitoring of data among the participants requires a well-designed and automated international data transfer system. In this paper, we will discuss the design requirements, data types and flows, and the operational responsibilities associated with the SVLBI data transfer system.

Lab Astro and the Origins of the Chemical Elements

NASA Astrophysics Data System (ADS)

Lawler, James E.

2010-03-01

Interpretation of the spectra of metal-poor Galactic halo stars is dependent on AMO laboratory data [1,2]. Metal-poor Galactic halo stars were born when the Milky Way was young and they provide a record of the chemical evolution of the Galaxy. Elements heavier than iron are produced via r(apid)-process and s(low)-process n(eutron)-capture mechanisms. The s-process mechanism, which occurs in certain AGB stars, is relatively well understood. The explosive r-process is not well understood. The r-process n-capture mechanism was dominant early in the Galaxy's history [3]. New large aperture telescopes make it possible to record high-resolution spectra with high signal-to-noise ratios on a growing number of metal-poor stars. In addition to mapping the chemical evolution of the Galaxy, these studies are yielding an increasingly well-defined r-process elemental abundance pattern which constrains models of r-process nucleosynthesis [1]. The next phase of this ongoing research will address challenges in modeling stellar photospheres. Peculiar trends in abundances of specific Fe-group elements as a function of stellar age or metallicity may be due to limitations in traditional one dimensional (1d) local thermodynamic equilibrium (LTE) models of stellar photospheres or may be due to poorly understood nucleosynthesis [4]. Efforts are now underway to test the Saha or ionization equilibrium in a variety of stellar atmospheres for several Fe-group elements using the best available spectroscopic data for selected transitions. More comprehensive spectroscopic data of improved accuracy and accurate collisional data, especially for inelastic collisions of H atoms with metal atoms and ions, will be needed to fully develop 3d/non-LTE models of photospheres [e.g. 5]. [4pt] [1] C. Sneden, J. E. Lawler, J. J. Cowan, I. I. Ivans, and E. A. Den Hartog, Astrophys. J. Suppl. Ser. 182, 80-96 (2009). [0pt] [2] J. E. Lawler, C. Sneden, J. J. Cowan, I. I. Ivans, and E. A. Den Hartog, Astrophys. J. Suppl. Ser. 182, 51-79 (2009). [0pt] [3] J. Simmerer, C. Sneden, J. J. Cowan, J. Collier, V. M. Woolf, and J. E. Lawler, Astrophys. J. 617, 1091-1114 (2004). [0pt] [4] A. McWilliam, Ann. Rev. Astron. & Astrophys. 35, 503 (1997). [0pt] [5] M. Asplund, Ann. Rev. Astron. & Astrophys. 43, 481 (2005).

Tidal-Induced Internal Ocean Waves as an Explanation for Enceladus' Tiger Stripe Pattern and Hotspot Activity

NASA Astrophysics Data System (ADS)

Vermeersen, B. L. A.; Maas, L. R.; van Oers, S.; Rabitti, A.; Jara-Orue, H.

2014-12-01

One of the most peculiar features on Saturn moon Enceladus is its so-called tiger stripe pattern at the geologically active South Polar Terrain (SPT), as first observed in detail by the Cassini spacecraft early 2005. It is generally assumed that the four almost parallel surface lines that constitute this pattern are faults in the icy surface overlying a confined salty water reservoir. Indeed, later Cassini observations have shown that salty water jets originate from the tiger stripes [e.g., Hansen et al., Science, 311, 1422-1425, 2006; Postberg et al., Nature, 474, 620-622, 2011]. More recently, Porco et al. [Astron. J., 148:45, Sep. 2014] and Nimmo et al. [Astron. J., 148:46, Sep. 2014] have reported strong evidence that the geysers are not caused by frictional heating at the surface, but that geysers must originate deeper in Enceladus' interior. Tidal flexing models, like those of Hurford et al., Nature, 447, 292-294, 2007, give a good match for the brightness variations Cassini observes, but they seem to fail to reproduce the exact timing of plume brightening. Although jet activity is thus strongly connected to tidal forcing, another mechanism must be involved as well. Last year, we formulated the original idea [Vermeersen et al., AGU Fall Meeting 2013, abstract #P53B-1848] that the tiger stripe pattern is formed and maintained by induced, tidally and rotationally driven, wave-attractor motions in the ocean underneath the icy surface of the tiger-stripe region. Such wave-attractor motions are observed in water tank experiments in laboratories on Earth and in numerical experiments [Maas et al., Nature, 338, 557-561, 1997; Drijfhout and Maas, J. Phys. Oceanogr., 37, 2740-2763, 2007; Hazewinkel et al., Phys. Fluids, 22, 107102, 2010]. The latest observations by Porco et al. and Nimmo et al. seem to be in agreement with this tidal-induced wave attractor phenomenon, both with respect to tiger stripe pattern and with respect to timing of hotspot activity. However, in contrast to the thin ocean/thick ice sheet model as anticipated in Fig. 12 of Porco et al. (2014), our lab experiments suggest that attractors are generated most efficiently at aspect ratio O(1), implying that distance between stripes might actually approximately directly represent local ocean depth in a thin ice sheet/thick ocean setting.

Polarimetric survey of main-belt asteroids. VI. New results from the second epoch of the CASLEO survey

NASA Astrophysics Data System (ADS)

Gil-Hutton, R.; García-Migani, E.

2017-11-01

Aims: We present the results of a polarimetric survey of main-belt asteroids at Complejo Astronómico El Leoncito (CASLEO), San Juan, Argentina. The aims of this survey are to increase the database of asteroid polarimetry and to estimate the diversity in the polarimetric properties of asteroids that belong to different taxonomic classes. Methods: The data were obtained using the CASPOL polarimeter at the 2.15 m telescope. CASPOL is a polarimeter based on a CCD detector and a Savart plate. The survey began in 1995 and data on a large sample of asteroids were obtained until 2012. A second period began in 2013 using a polarimeter with a more sensitive detector in order to study small asteroids, families, and special taxonomic groups. Results: We present and analyze the unpublished results for 128 asteroids of different taxonomic types, 55 of them observed for the first time. The observational data allowed us to find probable new cases of Barbarian objects but also two D-type objects, (565) Marbachia and (1481) Tubingia, that seem to have phase-polarization curves with a large inversion angle. The data obtained combined with data from the literature enabled us to find phase-polarization curves for 121 objects of different taxonomic types and to study the relations between several polarimetric and physical parameters. Using an approximation for the phase-polarization curve we found the index of refraction of the surface material and the scatter separation distance for all the objects with known polarimetric parameters. We also found that the inversion angle is a function of the index of refraction of the surface, while the phase angle where the minimum of polarization is produced provides information about the distance between scatter particles or, to some extent, the porosity of the surface. Based on observations carried out at the Complejo Astronómico El Leoncito, operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba, and San Juan.Tables 1 and 2 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/607/A103

Ensino de astronomia e óptica: é possível fazê-lo de forma contextualizada no nível médio?

NASA Astrophysics Data System (ADS)

Sobrinho, A. A.; Jafelice, L. C.

2003-08-01

Discutimos nossa participação em um curso de treinamento para professores de diversas disciplinas do ensino médio. Nossa preocupação básica foi desenvolver instrumentos educacionais adequados para levar à sala de aula, nesse nível de ensino, de forma contextualizada, questionamentos freqüentes dos alunos sobre astronomia e sua relação com tecnologia e sociedade. Encaminhamos questões como: a evolução da astronomia, suas relações com outros ramos do conhecimento humano e conseqüentes aplicações; avanços na tecnologia dos instrumentos ópticos versus a importância da observação do céu a olho nu; a relação entre olho humano, luneta e telescópio; e desenvolvimento da tecnologia espacial e sua influência em nosso cotidiano. Objetivamos com isto fazer um resgate histórico e pedagógico das aplicações e observações do céu no cenário escolar, destacando a relação entre eventos astronômicos, olho humano, instrumentos mediadores e suas contextualizações históricas e sociais. Produtos desta abordagem foram o desenvolvimento e a adaptação de práticas e materiais instrucionais diversos (e.g., "espelhos" de isopor e "raios luminosos" de bolinhas de gude; montagens envolvendo velas, lasers, lentes e espelhos; desmonte e análise de peças de um telescópio; etc.). Além disto, como outro resultado deste trabalho, elaboramos textos sobre história da astronomia e da óptica para atividades em classe. Com estas ações visamos facilitar a concretização de conceitos físicos envolvidos, exemplificar um ensino contextualizado e interdisciplinar motivado por temas astronômicos e favorecer que práticas e discussões feitas com os treinandos possam ser transpostas para a sala de aula. A reação dos professores às práticas propostas foi bastante positiva. Todos esses aspectos são discutidos em detalhe neste trabalho. (PPGECNM/UFRN; PRONEX/FINEP; NUPA/USP; Temáticos/FAPESP)

Análise dos Conceitos Astronômicos Apresentados por Professores de Algumas Escolas Estaduais Brasileiras

NASA Astrophysics Data System (ADS)

Voelzke, Marcos Rincon; Gonzaga, Edson Pereira

2011-12-01

A razão para o desenvolvimento deste trabalho baseia-se no fato de que muitos professores da Educação Básica (EB) não lidam com conceitos relacionados à astronomia, e quando o fazem eles simplesmente seguem livros didáticos que podem conter erros conceituais. Como é de conhecimento geral a astronomia é um dos conteúdos a serem ensinados na EB fazendo parte dos Parâmetros Curriculares Nacionais e das Propostas Curriculares do Estado de São Paulo, mas é um fato, que vários pesquisadores apontam, a existência de muitos problemas no ensino da astronomia. Com o propósito de minimizar algumas dessas deficiências foi realizado um trabalho de pesquisa com a utilização de questionários pré e pós pesquisa, para tanto foi desenvolvido um Curso de Extensão Universitária para professores da Diretoria de Ensino Regional (DE) que abrange Mauá, Ribeirão Pires e Rio Grande da Serra (no Estado de São Paulo) com os seguintes objetivos: levantar concepções alternativas; subsidiar os professores por meio de palestras, debates e workshops, e verificar o sucesso da aprendizagem após o curso, adotando-se como referência, para a análise dos resultados, os dicionários de Língua Portuguesa (FERREIRA, 2004) e Enciclopédico de Astronomia e Astronáutica (MOURĀO, 1995). Portanto, dezesseis questões foram aplicadas antes e após o curso, assim pode-se verificar após a pesquisa que 100,0% dos professores sabiam os nomes das fases da Lua, 97,0% entenderam que o Sistema Solar é composto por oito planetas, 78,1% foram capazes de explicar como ocorre um eclipse lunar, um eclipse solar e um solstício, 72,7% sabiam como explicar a ocorrência das estações do ano; 64,5% explicaram corretamente a ocorrência do equinócio, 89,7% foram capazes de definir adequadamente o termo cometa; 63,6% definiram asteróide, 54,5% meteoro, 58,1% galáxia, e 42,4% planeta. Os resultados obtidos indicam uma aprendizagem significativa por parte dos participantes.

Physical properties of (2) Pallas

NASA Astrophysics Data System (ADS)

Carry, Benoît; Dumas, Christophe; Kaasalainen, Mikko; Berthier, Jérôme; Merline, William J.; Erard, Stéphane; Conrad, Al; Drummond, Jack D.; Hestroffer, Daniel; Fulchignoni, Marcello; Fusco, Thierry

2010-02-01

Ground-based high angular-resolution images of asteroid (2) Pallas at near-infrared wavelengths have been used to determine its physical properties (shape, dimensions, spatial orientation and albedo distribution). We acquired and analyzed adaptive optics (AO) J/H/K-band observations from Keck II and the Very Large Telescope taken during four Pallas oppositions between 2003 and 2007, with spatial resolution spanning 32-88 km (image scales 13-20 km/pixel). We improve our determination of the size, shape, and pole by a novel method that combines our AO data with 51 visual light-curves spanning 34 years of observations as well as archived occultation data. The shape model of Pallas derived here reproduces well both the projected shape of Pallas on the sky (average deviation of edge profile of 0.4 pixel) and light-curve behavior (average deviation of 0.019 mag) at all the epochs considered. We resolved the pole ambiguity and found the spin-vector coordinates to be within 5° of [longitude, latitude] = [30°, -16°] in the Ecliptic J2000.0 reference frame, indicating a high obliquity of about 84°, leading to high seasonal contrast. The best triaxial-ellipsoid fit returns ellipsoidal radii of a=275km,b=258km, and c=238km. From the mass of Pallas determined by gravitational perturbation on other minor bodies (1.2±0.3)×10-10M⊙, [Michalak, G., 2000. Astron. Astrophys. 360, 363-374], we derive a density of 3.4±0.9gcm significantly different from the density of C-type (1) Ceres of 2.2±0.1gcm [Carry, B., Dumas, C., Fulchignoni, M., Merline, W.J., Berthier, J., Hestroffer, D., Fusco, T., Tamblyn, P., 2008. Astron. Astrophys. 478 (4), 235-244]. Considering the spectral similarities of Pallas and Ceres at visible and near-infrared wavelengths, this may point to fundamental differences in the interior composition or structure of these two bodies. We define a planetocentric longitude system for Pallas, following IAU guidelines. We also present the first albedo maps of Pallas covering ˜80% of the surface in K-band. These maps reveal features with diameters in the 70-180 km range and an albedo contrast of about 6% with respect to the mean surface albedo.

The Teaching of Astronomy in Uruguay. (Spanish Title: La Enseñanza de la Astronomía en Uruguay.) O Ensino da Astronomia no Uruguai

NASA Astrophysics Data System (ADS)

Pintos Ganón, Reina; Fernández, Julio Angel

2008-07-01

We present in this work the development of astronomy in Uruguay since the colony times up to the present, stressing in particular those aspects related to the formal as well as informal teaching of astronomy. The first antecedents of astronomical studies in our country go back to the beginnings of the XVIIIth century related to the scientific expeditions from Europe coming to our shores. The teaching of astronomy was generalized at the high school level as soon as the end of the XIXth century, while itsintroduction at the university level happened much later, around the middle of the last century. We analyze the current situation of this subject, its problems, and some measures to strengthen its development. Se presenta en este trabajo el desarrollo de la astronomía en el Uruguay desde la época colonial hasta el presente, destacando en particular los aspectos vinculados a su enseñanza tanto formal como informal. Los primeros antecedentes de estudios astronómicos datan de la época colonial relacionados con las expediciones científicas del Viejo Mundo que llegaban a nuestras costas. La enseñanza de la Astronomía se generalizó en el ámbito de los estudios secundarios ya a fines del siglo XIX, mientras que en la Universidad su arribo fue mucho más tardío, a mediados del siglo pasado. Se analiza la situación actual de esta disciplina, sus problemas, y algunas medidas para fortalecer su desarrollo. Apresentamos, neste trabalho, o desenvolvimento da Astronomia no Uruguai desde a época colonial até o presente, destacando em particular os aspectos vinculados ao seu ensino tanto formal quanto informal. Os primeiros antecedentes de estudos astronômicos em nosso país datam da época colonial relacionados com as expedições científicas do Velho Mundo que chegavam às nossas costas. O ensino da Astronomia se generalizou no âmbito dos estudos secundários já no final do século XIX, enquanto que sua introdução na universidade foi muito mais tardia, em meados do século passado. Se analisa a situação atual dessa disciplina, seus problemas, e algumas medidas para fortalecer seu desenvolvimento.

From 9 to 12 and Finally 8: how Many Planets are around the Sun? (Spanish Title: De 9 a 12 y Finalmente 8: ¿Cuántos Planetas Hay Alrededor del Sol?) De 9 a 12 e Finalmente 8: Quantos Planetas Existem AO Redor do Sol?

NASA Astrophysics Data System (ADS)

Tancredi, Gonzalo

2007-12-01

The International Astronomical Union, the organization that groups together the professional astronomers over the world, has recently adopted a historical definition: What is a planet in the Solar System? Changing 76 years of tradition, our Solar System has now 8 planets and an increasing number of a new category of bodies named "dwarf planets", among them is the former planet Pluto. In this article we present the reasons that support the resolution and we describe the participation of the Latin-American astronomers in the process to adopt it. La Unión Astronómica Internacional, la organización que agrupa a los astrónomos profesionales del planeta, acaba de adoptar una definición histórica: ¿Qué es un planeta en nuestro Sistema Solar? Cambiando 76 años de tradición, según esta definición, nuestro Sistema Solar cuenta con 8 planetas y una creciente cantidad de "planetas enanos", entre los que quedó incluido el hasta hace poco planeta Plutón. En el presente artículo se presentarán los argumentos que fundamentan esta resolución y la participación que han tenido los astrónomos latinoamericanos en la adopción de la misma. A União Astronômica Internacional, a organização que agrupa os astrônomos profissionais do planeta, acaba de adotar uma definição histórica: O que é um planeta em nosso Sistema Solar? Mudando 76 anos de tradição, segundo esta definição, nosso Sistema Solar conta com 8 planetas e uma crescente quantidade de "planetas anões", entre os quais foi incluido o até há pouco planeta Plutão. No presente artigo serão apresentados os argumentos que fundamentam esta resolução e a participação que tiveram os astrônomos latino-americanos na adoção da mesma.

Impact and cratering rates onto Pluto

NASA Astrophysics Data System (ADS)

Greenstreet, Sarah; Gladman, Brett; McKinnon, William B.

2015-09-01

The New Horizons spacecraft fly-through of the Pluto system in July 2015 will provide humanity's first data for the crater populations on Pluto and its binary companion, Charon. In principle, these surfaces could be dated in an absolute sense, using the observed surface crater density (# craters/km2 larger than some threshold crater diameter D). Success, however, requires an understanding of both the cratering physics and absolute impactor flux. The Canada-France Ecliptic Plane Survey (CFEPS) L7 synthetic model of classical and resonant Kuiper belt populations (Petit, J.M. et al. [2011]. Astron. J. 142, 131-155; Gladman, B. et al. [2012]. Astron. J. 144, 23-47) and the scattering object model of Kaib et al. (Kaib, N., Roškar, R., Quinn, T. [2011]. Icarus 215, 491-507) calibrated by Shankman et al. (Shankman, C. et al. [2013]. Astrophys. J. 764, L2-L5) provide such impact fluxes and thus current primary cratering rates for each dynamical sub-population. We find that four sub-populations (the q < 42AU hot and stirred main classicals, the classical outers, and the plutinos) dominate Pluto's impact flux, each providing ≈ 15- 25 % of the total rate. Due to the uncertainty in how the well-characterized size distribution for Kuiper belt objects (with impactor diameter d > 100km) connects to smaller projectiles, we compute cratering rates using five model impactor size distributions: a single power-law, a power-law with a knee, a power-law with a divot, as well as the "wavy" size distributions described in Minton et al. (Minton, D.A. et al. [2012]. Asteroids Comets Meteors Conf. 1667, 6348) and Schlichting et al. (Schlichting, H.E., Fuentes, C.I., Trilling, D.E. [2013]. Astron. J. 146, 36-42). We find that there is only a small chance that Pluto has been hit in the past 4 Gyr by even one impactor with a diameter larger than the known break in the projectile size distribution (d ≈ 100km) which would create a basin on Pluto (D ⩾ 400km in diameter). We show that due to present uncertainties in the impactor size distribution between d = 1- 100km , computing absolute ages for the surface of Pluto is entirely dependent on the extrapolation to small sizes and thus fraught with uncertainty. We show, however, what the ages would be for several cases and illustrate the relative importance of each Kuiper belt sub-population to the cratering rate, both now and integrated into the past. In addition, we compute the largest "fresh" crater expected to have formed in 1 Gyr on the surface of Pluto and in 3 Gyr on Charon (to 95% confidence) and use the "wavy" size distribution models to predict whether these largest "fresh" craters will provide surfaces for which portions of the crater production function can be measured should most of the target's surface appear saturated. The fly-through results coupled with telescopic surveys that bridge current uncertainties in the d = 10- 100km regime should eventually result in the population estimate uncertainties for the Kuiper belt sub-populations, and thus the impact fluxes onto Pluto and Charon, dipping to < 30 % . We also compute "disruption timescales" (to a factor of three accuracy) for Pluto's smaller satellites: Styx, Nix, Kerberos, and Hydra. We find that none of the four satellites have likely undergone a catastrophic disruption and reassembly event in the past ≈ 4Gyr . In addition, we find that for a knee size distribution with αfaint ⩽ 0.4 (down to sub-km diameters), satellites of all sizes are able to survive catastrophic disruption over the past 4 Gyr.

N-body simulations of viscous instability of planetary rings

NASA Astrophysics Data System (ADS)

Salo, Heikki; Schmidt, Jürgen

2010-04-01

We study viscous instability of planetary rings in terms of N-body simulations. We show that for rings composed of fairly elastic particles (e.g. as in Hatzes et al. [Hatzes, A., Bridges, F.G., Lin, D.N.C., 1988. Collisional properties of ice spheres at low impact velocities. Mon. Not. R. Astron. Soc. 231, 1091-1115]) the instability may lead to the spontaneous formation of dense ringlets in a background of lower density. In most parts of Saturn's rings the particle collisions are probably much more dissipative, as suggested by the presence of self-gravity wakes, and classic viscous instability should be suppressed. However, our results demonstrate that the mechanism of viscous instability itself is valid. The dynamical effects of size-dependent elasticity in a system with a size distribution have never been studied before. We show that this may in principle lead to a size-selective viscous instability, small particles concentrating on ringlets against the more uniform background of large particles.

Central stars of planetary nebulae. II. New OB-type and emission-line stars

NASA Astrophysics Data System (ADS)

Weidmann, W. A.; Gamen, R.

2011-07-01

Context. There are more than 3000 confirmed and probably known Galactic planetary nebulae (PNe), but central star spectroscopic information is available for only 13% of them. Aims: We have undertaken a spectroscopic survey of the central stars in PNe to identify their spectral types. Methods: We performed spectroscopic observations at low resolution with the 2-m telescope at CASLEO, Argentina. Results: We present the spectra of 46 central stars of PNe, most of them are OB-type and emission-line stars. Based on data collected at the Complejo Astronómico El Leoncito (CASLEO), which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina y Universidades Nacionales de La Plata, Córdoba y San Juan, Argentina.The reduced spectra (FITS files) are available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/531/A172

Successful model for cooperative student learning centers in physics and astronomy

NASA Astrophysics Data System (ADS)

Bieniek, Ronald J.; Johnson, John A.

2003-04-01

We have established successful problem-based learning centers for introductory courses in physics [1] and astronomy [2] that fully implement the Seven Principles of Good Practice in Undergraduate Education [3] without increased demand on faculty time. Large percentages of students at our two institutions voluntarily utilize these learning venues. Course instructors guide self-forming groups of students to mastery of technical concepts and skills, building greater student self-confidence through direct interaction and feedback. The approach's immediacy helps students recognize ambiguities in their understanding, thereby increasing impact at teachable moments. Underperforming students are assisted along side students who wish to hone their skills. The format also facilitates racial and gender mixing within learning center camaraderie. Specific pedagogical and operational techniques for running learning centers will be presented. [1] http://www.umr.edu/ physics/plc [2] http://astron.berkeley.edu/talc.html [3] A.W. Chickering & Z.F. Gamson, Am. Assoc. Higher Ed. Bulletin, 1987, 39(7) 3-7.

El círculo meridiano automático de San Fernando - San Juan. Sus primeros pasos en el hemisferio sur

NASA Astrophysics Data System (ADS)

Mallamaci, C. C.; Muiños, J. L.; Gallego, M.; Pérez, J. A.; Marmolejo, L.; Navarro, J. L.; Sedeño, J.; Vallejos, M.; Belizón, F.

Se informa sobre el estado actual del Círculo Meridiano Automático de San Fernando-San Juan. El instrumento (Grubb-Parson, de 178mm de abertura y 2665 mm de distancia focal) es gemelo del que se encuentra en las Islas Canarias, y fue instalado durante los meses de julio y agosto de 1996 en la estación astronómica ``Dr. C.U.Cesco" (El Leoncito, Barreal), a unos 200 km de distancia de la ciudad de San Juan, merced a un Convenio de Cooperación Científica, firmado en 1994 entre el ROA (España) y el OAFA (Argentina). En la actualidad se está llevando a cabo un programa de prueba cuyos resultados preliminares muestran que el telescopio está en buenas condiciones para observar estrellas de hasta magnitud aproximada 14.5, con buenos errores de observación (<0.12" en ascensión recta y declinación).

Model shape and spin direction of the asteroid 2011 UW158

NASA Astrophysics Data System (ADS)

Silva, José; Monteiro, Filipe; Tamayo, Francisco

2017-10-01

We determinate the spin direction and convex model shape of the Near Earth Asteroid 2011 UW158 using the lightcurves from the Minor Planet Center database and obtained from the San Pedro Mártir observatory (Ensenada, Baja California, Mexico) and the Observatório Astronômico do Sertão de Itaparica (Itacuruba, Pernambuco, Brazil) by mean of the light-curve inversion technique.The shape model was compared with the radar images obtained from the 230-foot-wide Deep Space Network antenna at Goldstone, California, in concert with the National Radio Astronomy Observatory's 330-foot Green Bank Telescope in July 2015 and with the spin direction published for Carbognani et. al (2016).We found that the spin direction given for Carbognani et al. does not correspond with the visual geometry observed from the radar images. Also, we try to minimize the number of lightcurves that reproduce the shape in a robust way, with the objective of to plan future observations of asteroids better and prioritize time.

CCC Observations of Pluto, Neptune and Triton with the San Fernando automatic meridian circle.

NASA Astrophysics Data System (ADS)

Muiños, J. L.; Belizón, F.; Vallejo, M.; Mallamaci, C. C.; Pérez, J. A.; Marmolejo, L. F.; Navarro, J. L.; Sedeño, J. A.

2003-11-01

The San Fernando automatic meridian circle (CMASF) is a meridian telescope built by Grubb-Parsons in 1948 fully automated between 1987 and 1995. In 1996 was moved from the Real Instituto y Observatorio de la Armada (ROA) in San Fernando to the Carlos U. Cesco (CUC) mountain observatory in San Juan (Argentine). The CUC is owned by the Observatorio Astronómico Félix Aguilar (OAFA) of National University of San Juan. In 1999 the telescope was provided with a CCD camera borrowed by the Copenhagen University Observatory (CUO). Between March and October of 2001 a campaign of observations of Pluto, Neptune and its satellite Triton was carried out with the CMASF. They were observed every five days while their transits through the CUC meridian happened during the night. In total 12 transits of Pluto, 15 of Neptune and 16 of Triton were got during that period. In this paper we present the results of the campaign.

Distribución espacial de órbitas con diferentes grados de caoticidad en modelos autoconsistentes de satélites galácticos

NASA Astrophysics Data System (ADS)

Muzzio, J. C.; Mosquera, M.

En trabajos anteriores (Carpintero et al., Cel. Mech. Dynam. Astron. 85, 247, 2003), mostramos que las órbitas caóticas son muy importantes en los satélites galácticos. Sin embargo, los únicos modelos autoconsistentes de los que se disponía para ellos eran los de Heggie-Ramamani, cuya función de distribución depende sólo de la energía por lo que no mostraban diferencias entre las distribuciones de sus órbitas regulares y caóticas. Ahora, mediante una aproximación cuadrupolar, hemos logrado construir modelos autoconsistentes de satélites galácticos con distribuciones de velocidades anisotrópicas (lo que indica que sus funciones de distribución no dependen sólo de la energía) y hemos logrado revelar las diferencias entre las estructuras espaciales de las órbitas de distinta caoticidad.

MONET/North: a very fast 1.2m robotic telescope

NASA Astrophysics Data System (ADS)

Bischoff, Karsten; Tuparev, Georg; Hessman, Frederic V.; Nikolova, Irina

2006-06-01

The first of two 1.2m MONET robotic telescopes became operational at McDonald Observatory in Texas in spring 2006, the second one will be erected at the South African Astronomical Observatory's Sutherland Station. About 60% of the observing time is dedicated to scientific use by the consortium (Univ. Göttingen, McDonald Obs. and the South African Astron. Obs.) and 40% is for public and school outreach. The alt-az-mounted f/7 RC imaging telescopes are optimized for fast operations, with slewing speeds up to 10°/sec in all axes, making them some of the fastest of their class in the world. The unusual clam-shell enclosures provide the telescopes with nearly unobstructed views of the sky. The new observatory control system fully utilizes the hardware capabilities and permits local, remote, and robotic operations and scheduling, including the monitoring of the weather, electric power, the building, current seeing, all software processes, and the archiving of new data.

Relativistic g-modes in rapidly rotating neutron stars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gaertig, Erich; Kokkotas, Kostas D.; Department of Physics, Aristotle University of Thessaloniki, Thessaloniki 54124

2009-09-15

We study the g-modes of fast rotating stratified neutron stars in the general relativistic Cowling approximation, where we neglect metric perturbations and where the background models take into account the buoyant force due to composition gradients. This is the first paper studying this problem in a general relativistic framework. In a recent paper [A. Passamonti, B. Haskell, N. Andersson, D. I. Jones, and I. Hawke, Mon. Not. R. Astron. Soc. 394, 730 (2009)], a similar study was performed within the Newtonian framework, where the authors presented results about the onset of CFS-unstable g-modes and the close connection between inertial andmore » gravity modes for sufficiently high rotation rates and small composition gradients. This correlation arises from the interplay between the buoyant force which is the restoring force for g-modes and the Coriolis force which is responsible for the existence of inertial modes. In our relativistic treatment of the problem, we find an excellent qualitative agreement with respect to the Newtonian results.« less

STS-61 crew utilizing Virtual Reality in training for HST repair mission

NASA Technical Reports Server (NTRS)

1993-01-01

Astronaut Jeffrey A. Hoffman, one of four crewmembers for STS-61 that will conduct scheduled spacewalks during the flight, wears a special helmet and gloves designed to assist in proper positioning near the telescope while on the end of the robot arm. Crewmembers are utilizing a new virtual reality training aid which assists in refining positioning patterns for Space Shuttle Endeavour's Remote Manipulator System (RMS) (36890); Astronaut Claude Nicollier looks at a computer display of the Shuttle's robot arm movements as Thomas D. Akers and Kathryn C. Thornton, mission specialists look on. Nicollier will be responsible for maneuvering the astronauts while they stand in a foot restraint on the end of the RMS arm (36891,36894); Hoffman wears a special helmet and gloves designed to assist in proper positioning near the telescope while on the end of the robot arm (35892); Nicollier looks at a computer display of the Shuttle's robot arm movements as Akers looks on (36893); While (l-r) Astron

Optical Design of COATLI: A Diffraction-Limited Visible Imager with Fast Guiding and Active Optics Correction

NASA Astrophysics Data System (ADS)

Fuentes-Fernández, J.; Cuevas, S.; Watson, A. M.

2018-04-01

We present the optical design of COATLI, a two channel visible imager for a comercial 50 cm robotic telescope. COATLI will deliver diffraction-limited images (approximately 0.3 arcsec FWHM) in the riz bands, inside a 4.2 arcmin field, and seeing limited images (approximately 0.6 arcsec FWHM) in the B and g bands, inside a 5 arcmin field, by means of a tip-tilt mirror for fast guiding, and a deformable mirror for active optics, both located on two optically transferred pupil planes. The optical design is based on two collimator-camera systems plus a pupil transfer relay, using achromatic doublets of CaF2 and S-FTM16 and one triplet of N-BK7 and CaF2. We discuss the effciency, tolerancing, thermal behavior and ghosts. COATLI will be installed at the Observatorio Astronómico Nacional in Sierra San Pedro Mártir, Baja California, Mexico, in 2018.

Fast numerics for the spin orbit equation with realistic tidal dissipation and constant eccentricity

NASA Astrophysics Data System (ADS)

Bartuccelli, Michele; Deane, Jonathan; Gentile, Guido

2017-08-01

We present an algorithm for the rapid numerical integration of a time-periodic ODE with a small dissipation term that is C^1 in the velocity. Such an ODE arises as a model of spin-orbit coupling in a star/planet system, and the motivation for devising a fast algorithm for its solution comes from the desire to estimate probability of capture in various solutions, via Monte Carlo simulation: the integration times are very long, since we are interested in phenomena occurring on timescales of the order of 10^6-10^7 years. The proposed algorithm is based on the high-order Euler method which was described in Bartuccelli et al. (Celest Mech Dyn Astron 121(3):233-260, 2015), and it requires computer algebra to set up the code for its implementation. The payoff is an overall increase in speed by a factor of about 7.5 compared to standard numerical methods. Means for accelerating the purely numerical computation are also discussed.

Status of the Transneptunian Automated Occultation Survey (TAOS II)

NASA Astrophysics Data System (ADS)

Lehner, Matthew; Wang, Shiang-Yu; Reyes-Ruiz, Mauricio; Alcock, Charles; Castro Chacón, Joel; Chen, Wen-Ping; Chu, You-Hua; Cook, Kem H.; Figueroa, Liliana; Geary, John C.; Hernandez, Benjamin; Huang, Chung-Kai; Norton, Timothy; Szentgyorgyi, Andrew; Yen, Wei-Ling; Zhang, Zhi-Wei

2017-10-01

The Transneptunian Automated Occultation Survey (TAOS II) will aim to detect occultations of stars by small (~1 km diameter) objects in the Kuiper Belt and beyond. Such events are very rare (<0.001 events per star per year) and short in duration (~200 ms), so many stars must be monitored at a high readout cadence. TAOS II will operate three 1.3 meter telescopes at the Observatorio Astronómico Nacional at San Pedro Mártir in Baja California, México. With a 2.3 square degree field of view and a high speed camera comprising CMOS imagers, the survey will monitor 10,000 stars simultaneously with all three telescopes at a readout cadence of 20 Hz. Construction of the site began in the fall of 2013 and was completed this summer. Telescope installation began in August 2017. This poster will provide an update on the status of the survey development and the schedule leading to the beginning of survey operations.

A Close Association of Three Carbon Stars in the Direction of M92

NASA Astrophysics Data System (ADS)

Kurtanidze, O. M.; Nikolashvili, M. G.

The discovery of the first faint (V>15.0) high-latitude carbon star (FHLCS) was announced by Sanduleak (1980, PASP, 92, 246).It is located in the direction of the Magellanic Stream.On low-dispersion spectral plates (1250 AA μm at Hγ, 0IIIa--J,F) taken with the 70-cm meniscus telescope for identification of blue horizontal-branch stars in the globular cluster M92, two FHLCS were accidentally discovered (Kurtanidze 1980, Astron.Tsirk., 1109, 3) near the known bright carbon star HD156074 = Ste3795. The surface density of C stars in this region is equal to 30 per sq.deg. although their mean surface density is only about 0.03 C star per sq.deg. at b>30deg. None of these objects shows detectable proper motion except of Ste3795 (MacConnell 1996, private communication). The astrometric and photometric data were obtained from plates taken with 2-m Tautenburg Schmidt (1961-1990) and the 0.7-m Abastumani meniscus telescope (1978-1989).

Polarization and photometric observations of the gamma-ray blazar PG 1553+113

NASA Astrophysics Data System (ADS)

Andruchow, I.; Combi, J. A.; Muñoz-Arjonilla, A. J.; Romero, G. E.; Cellone, S. A.; Martí, J.

2011-07-01

We present the results of an observational photo-polarimetry campaign of the blazar PG 1553+113 at optical wavelengths. The blazar was recently detected at very high energies (>100 GeV) by the HESS and MAGIC γ-ray Cherenkov telescopes. Our high-temporal resolution data show significant variations in the linear polarization percentage and position angle at inter-night time-scales, while at shorter (intra-night) time-scales both parameters varied less significantly, if at all. Changes in the polarization angle seem to be common in γ-ray emitting blazars. Simultaneous differential photometry (through the B and R bands) shows no significant variability in the total optical flux. We provide B and R magnitudes, along with a finding chart, for a set of field stars suitable for differential photometry. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).

Stellar Archaeology and Galaxy Genesis: The Need for Large Area Multi-Object Spectrograph on 8 m-Class Telescopes

NASA Astrophysics Data System (ADS)

Irwin, Mike J.; Lewis, Geraint F.

The origin and evolution of galaxies like the Milky Way and M31 remain among the key questions in astrophysics. The galaxies we see today in and around the Local Group are representatives of the general field population of the Universe and have been evolving for the majority of cosmic time. As our nearest neighbour systems they can be studied in far more detail than their distant counterparts and hence provide our best hope for understanding star formation and prototypical galaxy evolution over the lifetime of the Universe [K. Freeman, J. Bland-Hawthorn in Annu. Rev. Astron. Astrophys. 40, 487 (2002)]. Significant observational progress has been made, but we are still a long way from understanding galaxy genesis. To unravel this formative epoch, detailed large area multi-object spectroscopy of spatial, kinematic and chemical structures on 8 m-class telescopes are required, to provide the link between local near-field cosmology and predictions from the high-redshift Universe.

On the Origin of Pulsations of Sub-THz Emission from Solar Flares

NASA Astrophysics Data System (ADS)

Zaitsev, V. V.; Stepanov, A. V.; Kaufmann, P.

2014-08-01

We propose a model to explain fast pulsations in sub-THz emission from solar flares. The model is based on the approach of a flaring loop as an equivalent electric circuit and explains the pulse-repetition rate, the high-quality factor, Q≥103, low modulation depth, pulse synchronism at different frequencies, and the dependence of the pulse-repetition rate on the emission flux, observed by Kaufmann et al. ( Astrophys. J. 697, 420, 2009). We solved the nonlinear equation for electric current oscillations using a Van der Pol method and found the steady-state value for the amplitude of the current oscillations. Using the pulse rate variation during the flare on 4 November 2003, we found a decrease of the electric current from 1.7×1012 A in the flare maximum to 4×1010 A just after the burst. Our model is consistent with the plasma mechanism of sub-THz emission suggested recently by Zaitsev, Stepanov, and Melnikov ( Astron. Lett. 39, 650, 2013).

Proving the Orbits of the Galilean Moons Through Astrophotography. (Spanish Title: Comprobando Las Órbitas de Las Lunas Galileanas a Través de la Astrofotografía.) Evidenciando as Órbitas das Luas Galileanas Atravéd da Astrofotografia

NASA Astrophysics Data System (ADS)

Iachel, Gustavo

2009-12-01

An activity related to the observation of the Galilean moons and to amateur astrophotography is presented in this work. Through the reading of excerpts of the book Sidereus Nuncius (Sidereal Messenger), by Galileo, it is possible to trace a methodology to observe the planet and its natural satellites and, with the aid of the astrophotography, to analyze the field recordings. Moreover, it is possible to compare the images obtained after plotting the relative positions of these moons to prove their orbits. This activity can be conducted by teachers, students and amateur astronomers, in order to develop their capabilities of observation of astronomical phenomena. Se presenta en este trabajo una actividad relacionada a la observación de las lunas Galileanas y a la astrofotografía amateur. A través de la lectura de tramos de la obra Sidereus Nuncius (El Mensajero Sideral) de Galileo, es posible trazar una metodología para la observación del planeta y de sus satélites naturales y, con el auxilio de la astrofotografía, analizar las anotaciones de campo. Además, es posible comparar las imágenes obtenidas con el gráfico de las posiciones relativas de estas lunas para comprobar sus órbitas. Esa actividad puede ser realizada por maestros, estudiantes y astrónomos amateurs, de forma a desarrollar sus capacidades de observación de los fenómenos astronómicos. Uma atividade relacionada à observação das luas Galileanas e à astrofotografia amadora é apresentada neste trabalho. Através da leitura de trechos da obra Sidereus Nuncius (Mensageiro Sideral), de Galileu, é possível traçar uma metodologia para a observação do planeta e de seus satélites naturais e, com o auxílio da astrofotografia, analisar as anotações de campo. Além disso, é possível comparar as imagens obtidas com o gráfico das posições relativas destas luas para evidenciar suas órbitas. Essa atividade pode ser realizada por professores, estudantes e astrônomos amadores, de forma a desenvolverem suas capacidades de observar fenômenos astronômicos.

Valine radiolysis by MeV ions

NASA Astrophysics Data System (ADS)

Da Silveira, Enio

2016-07-01

Valine, (CH3)2 CHCH (NH2) COOH, is a protein amino acid that has been identified in extraterrestrial environments and in the Murchison meteorite [1]. The knowledge of half-lives of small organic molecules under ionizing radiation is important for the setup of models describing the spread out of prebiotics across the Solar System or the Galaxy. We have investigated typical effects of MeV cosmic ray ions on prebiotic molecules in laboratory by impinging ions produced by the PUC-Rio Van de Graaff accelerator. Pure valine films, deposited by evaporation on KBr substrates, were irradiated by H ^{+}, He ^{+} and N ^{+} ion beams, from 0.5 to 1.5 MeV and up to a fluence of 10 ^{15} projectiles/cm ^{2}. The sample temperature was varied from 10 K to 300 K. The irradiation was interrupted several times for Mid-FTIR analysis of the sample. The main findings are: 1- The column density of the valine decreases exponentially with fluence. 2- In some cases, a second exponential appears in the beginning of irradiation; this feature has been attributed to sample compaction by the ion beam [2]. 3- Destruction cross sections of valine are in the 10 ^{-15} cm ^{2} range, while compaction cross sections are in the 10 ^{-14} cm ^{2} range. 4- Destruction cross section increases with the stopping power of the beam and also with the sample temperature. 5- Surprisingly, during the radiolysis of valine, just CO _{2} is seen by as a daughter molecule formed in the bulk. 6- After long beam fluence, also a CO peak appears in the infrared spectrum; this species is however interpreted as a fragment of the formed CO2 molecules. 7- Considering the flux ratio between laboratory experiments and actual galactic cosmic rays, half-life of valine is predicted for ISM conditions [3]. This work on pure valine is the first measurement of a series. New experiments are planned for determining cross sections of valine dissolved in H _{2}O or CO _{2}, inspired by the study performed for glycine [4]. [1] P. Ehrenfreund and S. B. Charnley, Annu. Rev. Astron. Astrophys. 2000. 38:427. [2] C. Mejía et al., Icarus 250 (2015) 222. [3] D. P. P. Andrade et al., Mon. Not. R. Astron. Soc. 430 (2013) 787. [4] P. A. Gerakines and R. L. Hudson, Icarus 252 (2015) 466. Acknowledgments. The agencies CNPq (INEspaço) and FAPERJ are acknowledged for partial support to this work.

Astronomy Teaching and Teachers Continuing Education: the Interdisciplinarity during a Total Lunar Eclipse. (Spanish Title: Enseñanza de la Astronomía y la Formación Continua de Profesores: la Interdisciplinariedad Durante un Eclipse Total de Luna.) Educação EM Astronomia E Formação Continuada de Professores: a Interdisciplinaridade Durante um Eclipse Lunar TOTAL

NASA Astrophysics Data System (ADS)

Langhi, Rodolfo

2009-07-01

This paper describes how 67 teachers from 23 cities, could awaken, in students, the scientific interest, using a natural astronomical phenomenon: a total lunar eclipse. Before and after of eclipse, meetings for continuing education were characterized by interdisciplinarity of astronomy and the importance of these observations. Working groups were formed by teachers and students, who organized the survey data, mobilizing the people in their cities. The results point ways about how to provide the scientific culture and the motivation to learn science in students, using approaches between the following communities: scientific, amateur and school. En este artículo se describe cómo 67 profesores de 23 ciudades, despertó el interés científico en los estudiantes mediante un fenómeno astronómico: un eclipse total de Luna. Antes y después del eclipse, reuniones para la formación continua se centraron en la interdisciplinariedad de la astronomía, y la importancia de las observaciones de este tipo de fenómeno. Profesores y estudiantes formaron grupos de trabajo para investigar datos durante el eclipse, con el participación de la comunidad en sus ciudades. Los resultados apuntan a las opciones que conducen a la cultura científica y la motivación para aprender la ciencia, utilizando las relaciones de los siguientes grupos: científicos, aficionados y la escuela. Este texto relata como 67 professores, provenientes de 23 cidades, puderam despertar, nos alunos, o interesse científico utilizando um fenômeno natural astronômico: um eclipse lunar total. O evento foi precedido e procedido por encontros de formação continuada, onde se caracterizou a interdisciplinaridade da astronomia e a importância das observações de fenômenos como estes. Grupos de trabalho foram formados por professores e alunos, que se organizaram para o levantamento conjunto de dados durante o fenômeno, além do envolvimento da comunidade em suas respectivas cidades. Os resultados apontam para caminhos que podem proporcionar a motivação e a cultura científica, através de aproximações entre as comunidades científica, amadora e escolar.

Measurement of Reactions on 30P for Nova Nucleosynthesis

NASA Astrophysics Data System (ADS)

Ma, Z.; Guidry, M. W.; Hix, W. R.; Smith, M. S.

2003-05-01

Replace these paragraphs with your abstract. We encourage you to include a sentence acknowledging your funding agency. In a recent study the 30P(p,gamma)31S rate played a crucial role in the synthesis of heavier nuclear species, from Si to Ca, in nova outbursts on ONe White Dwarfs [1]. The adopted rate of this reaction, based on a Hauser-Feshbach calculation [2], has a large uncertainty and could be as much as a factor of 100 too high or too low [3]. In their study, Jose et al.[1] varied the 30P(p,gamma)31S reaction rate within this uncertainty and found that, when rate is reduced by a factor of 100, the synthesis of elements above Si is lowered by a factor 10 with respect to the values found with the nominal rate. This has important consequences for nova nucleosynthesis, as overproduction of isotopes in the Si to Ca mass region has been observed in the ejecta from some nova explosions (e.g.,[4,5]). While generally valid at higher temperatures, Hauser-Feshbach calculations of the rates at nova temperatures can have large uncertainties. At these temperatures, the rate is more likely dominated by a few individual nuclear resonances. At present there are about 10 31S resonances known above the 30P + p threshold that may contribute to the 30P(p,gamma)31S reaction rate at nova temperatures. The excitation energies of these levels are known but spins and parities (for all but two) are not. We plan to measure the 30P(p,p)30P and 30P(p,gamma)31S reactions at HRIBF to better determine this reaction rate. A detailed description of the experiments will be given. We are also conducting a new nova nucleosynthesis simulation over multiple spatial zones of the exploding envelope to investigate the influence of the 30P(p,gamma)31S reaction rate on nova nucleosynthesis. The results of these calculations will be discussed. 1. Jose , J., Coc, A., Hernanz, M., Astrophys. J., 560, 897(2001). 2. Thielemann, F.-K et al., 1987, Advances in Nuclear Astrophysics, ed. E. Vangioni-Flam ( Gif-sur-Yvette: Editions Frontiere), 525(SMOKER). 3. Iliadis, C. et al., Astrophys. J. Suppl., 134,151(2001). 4. Snijders et al., 1987 Snijders, M. A. J., et al., Mon. Not. Roy. Astron. Soc., 228, 329(1987). 5. Andrea, J., Drechsel, H., Starrfield, S., Astron. Astrophys., 291,869(1994) *Managed by UT-Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725.

Polar wander caused by the Quaternary glacial cycles and fluid Love number

NASA Astrophysics Data System (ADS)

Nakada, Masao

2002-06-01

Perturbations of the Earth's rotation caused by the Quaternary glacial cycles provide an important constraint on the viscosity of the deep mantle because they represent a long-wavelength response of the Earth to surface load redistribution. The predicted present-day polar wander speed (PWS) is, however, sensitive to both the lower mantle viscosity ( ηlm), the density jump at 670 km depth, and the lithospheric thickness and viscosity (e.g., Sabadini and Peltier, Geophys. J. R. Astron. Soc. 66 (1981) 553-578; Yuen et al., J. Geophys. Res. 87 (1982) 10745-10762; Peltier and Wu, Geophys. Res. Lett. 10 (1983) 181-184; Wu and Peltier, Geophys, J. R. Astron. Soc. 76 (1984) 753-791; Peltier, J. Geophys. Res. 89 (1984) 11303-11316; Vermeersen et al., J. Geophys. Res. 102 (1997) 27689-27702; Mitrovica and Milne, J. Geophys. Res. 103 (1998) 985-1005; Johnston and Lambeck, Geophys. J. Int. 136 (1999) 537-558; Nakada, Geophys. J. Int. 143 (2000) 230-238). For earth models with ηlm<5×10 21 Pa s and an elastic lithosphere, the present-day PWS is very sensitive to the M1 mode (buoyancy mode) related to the density jump at 670 km depth [Mitrovica and Milne, J. Geophys. Res. 103 (1998) 985-1005]. The contribution of the M1 mode, however, is less significant for earth models with a viscoelastic lithosphere [Nakada, Geophys. J. Int. 143 (2000) 230-238]. This is due to the fact that this contribution depends on the relative strength of the M1 mode, Δ k2T(M1)/ kfT, where Δ k2T(M1) is the magnitude of tidal Love number ( k2T) of the M1 mode and kfT is the value of k2T in the fluid limit (fluid Love number). The magnitude of kfT for earth models with a viscoelastic lithosphere is larger than that for an elastic lithosphere, and it is smaller for a thicker elastic lithosphere than for a thinner one. Thus, for earth models with a viscoelastic lithosphere, the PWS is mainly sensitive to the lower mantle viscosity regardless of the behavior of the 670 km density discontinuity. This relation also explains why the predicted PWS increases with increasing thickness of an elastic lithosphere. That is, since the value of Δ k2T(M1)/ kfT with a thicker elastic lithosphere is larger than that with a thinner elastic lithosphere, the M1 mode will have a higher contribution in the case of a thicker elastic lithosphere.

Analysis of Hubble Space Telescope Observations of an Outburst of Comet 29P/Schwassmann-Wachmann 1

NASA Astrophysics Data System (ADS)

Schambeau, Charles Alfred; Fernandez, Yanga R.; Samarasinha, Nalin H.; Kundu, Arunav

2016-10-01

We present results of a continuing analysis on the spin state of the enigmatic Comet 29P/Schwassmann-Wachmann 1 (SW1). Previous works have reported possible constraints on the spin state including a non-principal axis state [1] or a rotation period of tens of days [2]. This diversity of published answers highlights the complexity of determining the spin state of an active comet nucleus. Previous work by our group using 3D Monte Carlo coma modeling of ground-based outburst observations from 2008 [3] has placed constraints on the spin period for a set of assumed spin-pole orientations. Due to the nature of the 2008 outburst morphology no constraints on the spin-pole orientation could be found.We present here an analysis of Hubble Space Telescope WFPC2 observations of SW1 shortly after a 1996 outburst [4] with which we have further constrained the spin state. The 0.046-arcsec/pixel scale (176 km/pixel at SW1) of the PC detector gives an order-of-magnitude improvement in spatial resolution over our ground-based observations. Two sets of observations from UT 1996 Mar. 11.3 and 12.1 show the ejected dust forming an asymmetric outflow contained on the sunward side of the coma. A projected outflow velocity of 0.15 ± 0.02 km/s was measured, similar to our measured value from the 2008 observations. Enhancements of the images were performed [5] to bring out subtle variations in coma brightness (i.e., jets) and to allow us to search for signatures of the nucleus' rotation during the outburst. Three curved features are seen in both sets of observations and were modeled using the 3D Monte Carlo coma model [6]. We find a spin period on the order of several days, in agreement with our earlier 2008 analysis.[1] Meech, K. J., et al.: 1993, Astron. J., 106, 1222. [2] Miles, R., et al.: 2016, Icarus, 272, 327. [3] Schambeau, C. A., et al.: 2016, Icarus, submitted. [4] Feldman, P. D., et al.: 1996, AAS/DPS Meeting Abstracts, 28, 1084. [5] Samarasinha, N. and Larson, S.: 2014, Icarus, 239, 168. [6] Samarasinha, N. H., 2000, Astron. J. Letters, 529, L107-L110. We thank the Space Telescope Science Institute (AR14294), and the Center for Lunar and Asteroid Surface Science (CLASS, NNA14AB05A) for support of this work.

The many facets of extragalactic radio surveys: towards new scientific challenges

NASA Astrophysics Data System (ADS)

2015-10-01

Radio continuum surveys are a powerful tool to detect large number of objects over a wide range of redshifts and obtain information on the intensity, polarization and distribution properties of radio sources across the sky. They are essential to answer to fundamental questions of modern astrophysics. Radio astronomy is in the midst of a transformation. Developments in high-speed digital signal processing and broad-band optical fibre links between antennas have enabled significant upgrades of the existing radio facilities (e-MERLIN, JVLA, ATCA-CABB, eEVN, APERTIF), and are leading to next-generation radio telescopes (LOFAR, MWA, ASKAP, MeerKAT). All these efforts will ultimately lead to the realization of the Square Kilometre Array (SKA), which, owing to advances in sensitivity, field-of-view, frequency range and spectral resolution, will yield transformational science in many astrophysical research fields. The purpose of this meeting is to explore new scientific perspectives offered by modern radio surveys, focusing on synergies allowed by multi-frequency, multi-resolution observations. We will bring together researchers working on wide aspects of the physics and evolution of extra-galactic radio sources, from star-forming galaxies to AGNs and clusters of galaxies, including their role as cosmological probes. The organization of this conference has been inspired by the recent celebration of the 50th anniversary of the Northern Cross Radio Telescope in Medicina (BO), whose pioneering B2 and B3 surveys provided a significant contribution to radio astronomical studies for many decades afterwards. The conference was organized by the Istituto di Radioastronomia (INAF), and was held at the CNR Research Area in Bologna, on 20-23 October 2015. This Conference has received support from the following bodies and funding agencies: National Institute for Astrophysics (INAF), ASTRON, RadioNet3 (through the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 283393) and the Ministry of Foreign Affairs and International Cooperation, Directorate General for the Country Promotion (under the Bilateral Grant Agreement ZA14GR02 - Mapping the Universe on the Pathway to SKA). Scientific Organizing Committee: I. Prandoni (INAF-IRA) co-chair R. Morganti (ASTRON) co-chair P. Best (ROE) A. Bonafede (Hamburg Univ.) R. Braun (SKA Org) L. Feretti (INAF-IRA) M. Jarvis (Western Cape/Oxford Univ.) E. Murphy (Caltech) R. Norris (CSIRO) M. Perez-Torres (IAA) L. Saripalli (Raman) T. Venturi (INAF-IRA) Local Organizing Committee: R. Cassano (co-chair) I. Prandoni (co-chair) A. Casoni D. Guidetti R. Lico R. Ricci M. Stagni

Astronomy Teaching in Argentina in the 19th Century. (Spanish Title: La Enseñanza de la Astronomía en la Argentina del Siglo XIX.) O Ensino de Astronomia na Argentina no Século XIX

NASA Astrophysics Data System (ADS)

Norberto Cornejo, Jorge; Santilli, Haydée

2010-12-01

Sarmiento believed that Copernican astronomy was one of the critical scientific disciplines to the formation of a "modern" citizen. In this work, we shall study astronomical science from two points of view: from the scientific knowledge and the educational presentation of such knowledge. Our study will address in Argentina in 19th century, starting from the initiative of Bernardino Rivadavia in 1821, who founded an astronomic observatory at Buenos Aires, until the first activities of the observatories at Córdoba and La Plata. On both lines, scientific and educative, we shall analyze the influence of positivist ideas. We shall highlight epistemological differences between both observatories, Córdoba's based on French positivism and La Plata's based on German positivism. We shall also show the different attitude of both observatories towards education. We shall see the way in which positivist ideas had great relevance in the training of elementary school teachers. We shall also establish the relevant influence of the socio-historical context over the astronomical development, and show that astronomy was a fundamental social factor at Argentina history. Domingo F. Sarmiento consideraba que la astronomía copernicana era una de las disciplinas científicas fundamentales para la conformación de un ciudadano "moderno". En este trabajo estudiaremos la ciencia astronómica desde dos vertientes: la referida específicamente al conocimiento científico y aquella vinculada con la presentación educativa de dicho conocimiento. Nuestro estudio se desarrollará en Argentina durante el siglo XIX, desde la iniciativa de Bernardino Rivadavia en 1821, de establecer en Buenos Aires un observatorio astronómico, hasta las primeras actividades de los observatorios de Córdoba y de La Plata. En ambas vertientes, científica y educativa, analizaremos la influencia de las ideas positivistas. Resaltaremos las diferencias epistemológicas entre los dos observatorios, orientado el primero según el positivismo francés, y el segundo de acuerdo al positivismo alemán. También señalaremos la distinta actitud de ambos observatorios frente a la educación. En esta última dimensión veremos cómo las ideas positivistas tuvieron gran importancia en la formación de maestros impartida en las Escuelas Normales. Estableceremos también la relevante influencia del contexto socio-histórico en el desarrollo de la astronomía, y, a su vez, apreciaremos que esta última fue un actor social fundamental en la Historia Argentina. Domingo F. Sarmiento acreditava que a astronomia de Copérnico fosse uma das disciplinas científicas fundamentais para a formação de um cidadão "moderno". Neste trabalho estudaremos astronomia a partir de duas perspectivas: a científica e a educacional Nosso estudo será desenvolvido para a Argentina no século XIX, a partir da iniciativa de Bernardino Rivadavia, em 1821, que estabeleceu um observatório astronômico em Buenos Aires, até as primeiras atividades dos observatórios de Córdoba e La Plata. Em ambas as perspectivas, científica e educativa, vamos analisar a influência das ideias positivistas. Discutiremos como existiram diferenças epistemológicas entre eles, o Observatório de Córdoba orientado de acordo com o positivismo francês, e La Plata, de acordo com o positivismo alemão. Ambos os observatórios tinha uma atitude diferente em relação à educação. As ideias positivistas foram muito importantes para treinar professores do ensino primário na Argentina. Nós iremos enfatizar a importante influência do contexto sócio-histórico na astronomia, já que esta ciência foi um importante ator social na história da Argentina.

Conversations with Marcgrave: the Origin of Modern Astronomy in the Southern Hemisphere (Spanish Title: Conversando con Marcgrave: El Origen de la Astronomía Moderna en el Hemisferio Sur) Conversando Com Marcgrave: a Origem da Moderna Astronomia no Hemisfério Sul

NASA Astrophysics Data System (ADS)

Medeiros, Alexandre; Araújo, Fábio

2005-12-01

The year 2004 signals the 400th anniversary of the birth of count Mauricio of Nassau, an important character in the history of Brazil. The present text is related to the period of Dutch domination in Pernambuco. The article attempts to rescue the beginnings of Astronomy study in the South hemisphere. Therefore, we idealized a dramatization of a fictitious interview with German astronomer Georg Marcgrave, who was the constructor of the first astronomical observatory in this hemisphere and the author of the first systematic astronomical observations using telescopes in this side of the world. Our "conversation" with Marcgrave is idealized in the old Recife scenario, a place where he lived in Mauricio of Nassau's period and gathers some fellow teachers who love the teaching of Astronomy. The story, this way, is reported in a possibly light and funny atmosphere. Nevertheless, the conceptual and historical framework presented is based on reliable bibliographical sources pointed out at the end of the text. The sources range from the original book of that scientist, in which a solar eclipse is reported, passing through some other classical texts, such as that of Professor Juliano Moreira, up to more recent sources such as the very influential work of professor John North. Other influential texts about the Dutch period in Brazil, such as the classical works of Charles Boxer, Bouman and Boogaart, among others, are also used in the construction of this pedagogical dramatization, which involves an interesting chapter of the history of Astronomy. El año 2004 marca los 400 años del nacimineto del conde Mauricio de Nassau, un importante personaje de la historia del Brasil. El presente texto está relacionado con el período del dominio holandés en Pernambuco. El artículo intenta rescatar los comienzos del estudio de la Astronomía en el hemisferio Sur. Para esto, ideamos una dramatización de una entrevista ficticia con el astrónomo alemán Georg Marcgrave, constructor del primer observatorio astronómico del hemisferio y autor de las primeras observaciones astronómicas sistemáticas utilizando telescopios de este lado del mundo. Nuestra "conversación" con Marcgrave es imaginada en el marco del Recife antiguo, lugar donde él vivió durante el período de Mauricio de Nassau, y reune algunos colegas profesores apasionados por la enseñanza de la Astronomía. La historia es contada, de esta forma, dentro de un clima ameno y hasta un poco divertido, si bien las informaciones históricas y conceptuales contenidas en ella están basadas en fuentes bibliográficas confiables, debidamente referenciadas al final del texto. Estas fuentes van desde la obra original de este científico, en la cual aparece su relato sobre la observación de un eclipse solar en Recife, pasando por obras clásicas respecto de él mismo, como la del profesor Juliano Moreira, hasta fuentes mucho más recientes como el influyente trabajo del profesor John North. Otros textos importantes referidos al período de la colonización holandesa en el Brasil, tales como las obras clásicas de Charles Boxer, Bouman y Boogaart entre otros, son también utilizados en la construcción de esta dramatización pedagógica que se refiere a un interesante capítulo de la Historia de la Astronomía. O ano de 2004 assinala os 400 anos do nascimento do conde Maurício de Nassau, um importante personagem da história do Brasil. O presente texto está relacionado com o período do domínio holandês em Pernambuco. O artigo tenta resgatar o começo do estudo da Astronomia no hemisfério Sul. Para tal, idealizamos uma dramatização de uma entrevista fictícia com o astrônomo alemão Georg Marcgrave, construtor do primeiro observatório astronômico deste hemisfério e autor das primeiras observações astronômicas sistemáticas com o uso de telescópios neste lado do mundo. Nossa "conversa" com Marcgrave é idealizada no cenário do Recife antigo, local em que ele viveu no período de Maurício de Nassau e reúne alguns colegas professores apaixonados pelo ensino da Astronomia. A história é contada, deste modo, em um clima ameno e pretensamente divertido, mas as informações históricas e conceituais nele contidas estão apoiadas em fontes bibliográficas confiáveis devidamente apontadas ao final do texto. Elas vão desde a obra original desse cientista, na qual aparece o seu relato sobre a observação de um eclipse solar no Recife, passando por obras clássicas a seu respeito, como a do professor Juliano Moreira, até fontes bem mais recentes, como o trabalho muito influente do Professor John North. Outros textos de porte sobre o período da colonização holandesa no Brasil, como as obras já clássicas de Charles Boxer, Bouman e Boogaart, dentre outras, são também utilizados na construção desta dramatização pedagógica envolvendo um interessante capítulo da História da Astronomia.

Central stars of planetary nebulae: New spectral classifications and catalogue

NASA Astrophysics Data System (ADS)

Weidmann, W. A.; Gamen, R.

2011-02-01

Context. There are more than 3000 confirmed and probable known Galactic planetary nebulae (PNe), but central star spectroscopic information is available for only 13% of them. Aims: We undertook a spectroscopic survey of central stars of PNe at low resolution and compiled a large list of central stars for which information was dispersed in the literature. Methods: We observed 45 PNs using the 2.15 m telescope at Casleo, Argentina. Results: We present a catalogue of 492 confirmed and probable CSPN and provide a preliminary spectral classification for 45 central star of PNe. This revises previous values of the proportion of CSPN with atmospheres poor in hydrogen in at least 30% of cases and provide statistical information that allows us to infer the origin of H-poor stars. Based on data collected at the Complejo Astronómico El Leoncito (CASLEO), which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina y Universidades Nacionales de La Plata, Córdoba y San Juan, Argentina.

An analytic approach for the study of pulsar spindown

NASA Astrophysics Data System (ADS)

Chishtie, F. A.; Zhang, Xiyang; Valluri, S. R.

2018-07-01

In this work we develop an analytic approach to study pulsar spindown. We use the monopolar spindown model by Alvarez and Carramiñana (2004 Astron. Astrophys. 414 651–8), which assumes an inverse linear law of magnetic field decay of the pulsar, to extract an all-order formula for the spindown parameters using the Taylor series representation of Jaranowski et al (1998 Phys. Rev. D 58 6300). We further extend the analytic model to incorporate the quadrupole term that accounts for the emission of gravitational radiation, and obtain expressions for the period P and frequency f in terms of transcendental equations. We derive the analytic solution for pulsar frequency spindown in the absence of glitches. We examine the different cases that arise in the analysis of the roots in the solution of the non-linear differential equation for pulsar period evolution. We provide expressions for the spin-down parameters and find that the spindown values are in reasonable agreement with observations. A detection of gravitational waves from pulsars will be the next landmark in the field of multi-messenger gravitational wave astronomy.

The Owl and other strigiform nebulae: multipolar cavities within a filled shell

NASA Astrophysics Data System (ADS)

García-Díaz, Ma T.; Steffen, W.; Henney, W. J.; López, J. A.; García-López, F.; González-Buitrago, D.; Áviles, A.

2018-06-01

We present the results of long-slit echelle spectroscopy and deep narrow-band imaging of the Owl Nebula (NGC 3587), obtained at the Observatorio Astronómico Nacional, San Pedro Mártir. These data allow us to construct an iso-velocity data cube and develop a 3-D morpho-kinematic model. We find that, instead of the previously assumed bipolar dumbbell shape, the inner cavity consists of multi-polar fingers within an overall tripolar structure. We identify three additional planetary nebulae that show very similar morphologies and kinematics to the Owl, and propose that these constitute a new class of strigiform (owl-like) nebulae. Common characteristics of the strigiform nebulae include a double-shell (thin outside thick) structure, low-luminosity and high-gravity central stars, the absence of a present-day stellar wind, and asymmetric inner cavities, visible in both optical and mid-infrared emission lines, that show no evidence for surrounding bright rims. The origin of the cavities is unclear, but they may constitute relics of an earlier stage of evolution when the stellar wind was active.

Distribution of interstellar plasma in the direction of PSR B0525+21 from data obtained on a ground-space interferometer

NASA Astrophysics Data System (ADS)

Andrianov, A. S.; Smirnova, T. V.; Shishov, V. I.; Gwinn, C.; Popov, M. V.

2017-06-01

Observations on the RadioAstron ground-space interferometer with the participation of the Green Bank and Arecibo ground telescopes at 1668 MHz have enabled studies of the characteristics of the interstellar plasma in the direction of the pulsar PSR B0525+21. The maximum projected baseline for the ground-space interferometer was 233 600 km. The scintillations in these observations were strong, and the spectrum of inhomogeneties in the interstellar plasma was a power law with index n = 3.74, corresponding to a Kolmogorov spectrum. A new method for estimating the size of the scattering disk was applied to estimate the scattering angle (scattering disk radius) in the direction toward PSR B0525+21, θ scat = 0.028 ± 0.002 milliarcsecond. The scattering in this direction occurs in a plasma layer located at a distance of 0.1 Z from the pulsar, where Z is the distance from the pulsar to the observer. For the adopted distance Z = 1.6 kpc, the screen is located at a distance of 1.44 kpc from the observer.

Desarrollo de una Interfaz de Control para un Observatorio Astronómico Robotizado con fines educativos en la Facultad de Ciencias Exactas; Físicas y Naturales de la UNSJ

NASA Astrophysics Data System (ADS)

Pogrebinsky, L.; Francile, C.

We report the development and the construction of an Interface to Control a robotized Astronomical Observatory (ICOA), which allows to control the operation of an observatory based on a Meade LX200 telescope. The interface operates together with a computer to control and supervise all the local variables of the observatory, and can take the control of it in risky situations. It serves as a link among the control computer and all the necessary devices for the astronomical observation such as the telescope, the dome, the weather station, the CCD camera, the calibration devices and the security devices. The computer receives orders from an operator who can be or not at the site of observation. The goal of this robotized observatory is the operation in a secure, autonomous and unattended way, with the purpose of to be used remotely by the students of the "Facultad de Ciencias Exactas, Físicas y Naturales" of the UNSJ. FULL TEXT IN SPANISH

The "Cool Algol" BD+05 706 : Photometric observations of a new eclipsing double-lined spectroscopic binary

NASA Astrophysics Data System (ADS)

Marschall, L. A.; Torres, G.; Neuhauser, R.

1998-05-01

BVRI Observations of the star BD+05 706, carried out between January, 1997, and April 1998 using the 0.4m reflector and Photometrics CCD camera at the Gettysburg College Observatory, show that the star is an eclipsing binary system with a light curve characteristic of a class of semi-detached binaries known as the "cool Algols". These results are in good agreement with the previous report of BD+05 706 as a cool Algol by Torres, Neuhauser, and Wichmann,(Astron. J., 115, May 1998) who based their classification on the strong X-ray emission detected by Rosat and on a series of spectroscopic observations of the radial velocities of both components of the system obtained at the Oak Ridge Observatory, the Fred L. Whipple Observatory, and the Multiple Mirror Telescope. Only 10 other examples of cool Algols are known, and the current photometric light curve, together with the radial velocity curves obtained previously, allows us to derive a complete solution for the physical parameters of each component, providing important constraints on models for these interesting systems.

Fokker Planck Rosenbluth-type equations for self-gravitating systems in the 1PN approximation

NASA Astrophysics Data System (ADS)

Ramos-Caro, Javier; González, Guillermo A.

2008-02-01

We present two formulations of Fokker Planck Rosenbluth-type (FPR) equations for many-particle self-gravitating systems, with first-order relativistic corrections in the post-Newtonian approach (1PN). The first starts from a covariant Fokker Planck equation for a simple gas, introduced recently by Chacón-Acosta and Kremer (2007 Phys. Rev. E 76 021201). The second derivation is based on the establishment of an 1PN-BBGKY hierarchy, developed systematically from the 1PN microscopic law of force and using the Klimontovich Dupree (KD) method. We close the hierarchy by the introduction of a two-point correlation function that describes adequately the relaxation process. This picture reveals an aspect that is not considered in the first formulation: the contribution of ternary correlation patterns to the diffusion coefficients, as a consequence of the nature of 1PN interaction. Both formulations can be considered as a generalization of the equation derived by Rezania and Sobouti (2000 Astron. Astrophys. 354 1110), to stellar systems where the relativistic effects of gravitation play a significant role.

Algorithms for Stellar Perturbation Computations on Oort Cloud Comets

NASA Astrophysics Data System (ADS)

Rickman, Hans; Fouchard, Marc; Valsecchi, Giovanni B.; Froeschlé, Christiane

2005-12-01

We investigate different approximate methods of computing the perturbations on the orbits of Oort cloud comets caused by passing stars, by checking them against an accurate numerical integration using Everhart’s RA15 code. The scenario under study is the one relevant for long-term simulations of the cloud’s response to a predefined set of stellar passages. Our sample of stellar encounters simulates those experienced by the Solar System currently, but extrapolated over a time of 1010 years. We measure the errors of perihelion distance perturbations for high-eccentricity orbits introduced by several estimators including the classical impulse approximation and Dybczyński’s (1994, Celest. Mech. Dynam. Astron. 58, 1330 1338) method and we study how they depend on the encounter parameters (approach distance and relative velocity). We introduce a sequential variant of Dybczyński’s approach, cutting the encounter into several steps whereby the heliocentric motion of the comet is taken into account. For the scenario at hand this is found to offer an efficient means to obtain accurate results for practically any domain of the parameter space.

Fractal Dimensions of Umbral and Penumbral Regions of Sunspots

NASA Astrophysics Data System (ADS)

Rajkumar, B.; Haque, S.; Hrudey, W.

2017-11-01

The images of sunspots in 16 active regions taken at the University College of the Cayman Islands (UCCI) Observatory on Grand Cayman during June-November 2015 were used to determine their fractal dimensions using the perimeter-area method for the umbral and the penumbral region. Scale-free fractal dimensions of 2.09 ±0.42 and 1.72 ±0.4 were found, respectively. This value was higher than the value determined by Chumak and Chumak ( Astron. Astrophys. Trans. 10, 329, 1996), who used a similar method, but only for the penumbral region of their sample set. The umbral and penumbral fractal dimensions for the specific sunspots are positively correlated with r = 0.58. Furthermore, a similar time-series analysis was performed on eight images of AR 12403, from 21 August 2015 to 28 August 2015 taken from the Debrecen Photoheliographic Data (DPD). The correlation is r = 0.623 between the umbral and penumbral fractal dimensions in the time series, indicating that the complexity in morphology indicated by the fractal dimension between the umbra and penumbra followed each other in time as well.

Gas-drag-assisted capture of Himalia's family

NASA Astrophysics Data System (ADS)

Ćuk, Matija; Burns, Joseph A.

2004-02-01

To elucidate the capture of Jupiter's outer moons, we reverse-evolve satellites from their present orbits to their original heliocentric paths in the presence of Jupiter's primordial circumplanetary disk (Lubow et al., 1999, Astrophys. J. 526, 1001-1012; Canup and Ward, 2003, Astron. J. 124, 3404-3423). Our orbital histories use a symplectic integrator that allows dissipation. We assume that the present satellites Himalia, Elara, Lysithea, Leda, and S/2000 J11 are collisional fragments of a single parent. Our simulations show that this "prograde-cluster progenitor" (PCP) could be derived from objects with heliocentric orbits like those of the Hilda asteroid group. We show analytically that this capture is energetically possible. We also compare the spectroscopic characteristics of the prograde cluster members (Grav et al., 2003, Icarus, submitted for publication) with those of the Hildas, and conclude that the surface color of the prograde-cluster progenitor is consistent with an origin within the Hilda group. Accordingly, gas drag in the primordial jovian nebula is found to offer a plausible explanation for the origin of the prograde cluster. A similar capture mechanism is proposed for Saturn's Phoebe.

Transformation of Galilean satellite parameters to J2000

NASA Astrophysics Data System (ADS)

Lieske, J. H.

1998-09-01

The so-called galsat software has the capability of computing Earth-equatorial coordinates of Jupiter's Galilean satellies in an arbitrary reference frame, not just that of B1950. The 50 parameters which define the theory of motion of the Galilean satellites (Lieske 1977, Astron. Astrophys. 56, 333--352) could also be transformed in a manner such that the same galsat computer program can be employed to compute rectangular coordinates with their values being in the J2000 system. One of the input parameters (varepsilon_ {27}) is related to the obliquity of the ecliptic and its value is normally zero in the B1950 frame. If that parameter is changed from 0 to -0.0002771, and if other input parameters are changed in a prescribed manner, then the same galsat software can be employed to produce ephemerides on the J2000 system for any of the ephemerides which employ the galsat parameters, such as those of Arlot (1982), Vasundhara (1994) and Lieske. In this paper we present the parameters whose values must be altered in order for the software to produce coordinates directly in the J2000 system.

Spectroscopic determination of fundamental parameters of small angular diameter galactic open clusters

NASA Astrophysics Data System (ADS)

Ahumada, A. V.; Claria, J. J.; Bica, E.; Parisi, M. C.; Torres, M. C.; Pavani, D. B.

We present integrated spectra obtained at CASLEO (Argentina) for 9 galactic open clusters of small angular diameter. Two of them (BH 55 and Rup 159) have not been the target of previous research. The flux-calibrated spectra cover the spectral range approx. 3600-6900 A. Using the equivalent widths (EWs) of the Balmer lines and comparing the cluster spectra with template spectra, we determined E(B-V) colour excesses and ages for the present cluster sample. The parameters obtained for 6 of the clusters show good agreement with previous determinations based mainly on photometric methods. This is not the case, however, for BH 90, a scarcely reddened cluster, for which Moffat and Vogt (1975, Astron. and Astroph. SS, 20, 125) derived E(B-V) = 0.51. We explain and justify the strong discrepancy found for this object. According to the present analysis, 3 clusters are very young (Bo 14, Tr 15 and Tr 27), 2 are moderately young (NGC 6268 and BH 205), 3 are Hyades-like clusters (Rup 164, BH 90 and BH 55) and only one is an intermediate-age cluster (Rup 159).

A New Scaling Relation for H II Regions in Spiral Galaxies: Unveiling the True Nature of the Mass-Metallicity Relation

NASA Astrophysics Data System (ADS)

Rosales-Ortega, F. F.; Sánchez, S. F.; Iglesias-Páramo, J.; Díaz, A. I.; Vílchez, J. M.; Bland-Hawthorn, J.; Husemann, B.; Mast, D.

2012-09-01

We demonstrate the existence of a local mass, metallicity, star formation relation using spatially resolved optical spectroscopy of H II regions in the local universe. One of the projections of this distribution—the local mass-metallicity relation—extends over a wide range in this parameter space: three orders of magnitude in mass and a factor of eight in metallicity. We explain the new relation as the combined effect of the differential distributions of mass and metallicity in the disks of galaxies, and a selective star formation efficiency. We use this local relation to reproduce—with a noticeable agreement—the mass-metallicity relation seen in galaxies, and conclude that the latter is a scale-up integrated effect of a local relation, supporting the inside-out growth and downsizing scenarios of galaxy evolution. Based on observations collected at the Centro Astronómico Hispano-Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).

H2 16O line list for the study of atmospheres of Venus and Mars

NASA Astrophysics Data System (ADS)

Lavrentieva, N. N.; Voronin, B. A.; Fedorova, A. A.

2015-01-01

IR spectroscopy is an important method of remote measurement of H2 16O content in planetary atmospheres with initial spectroscopic information from the HITRAN, GEISA, etc., databases adapted for studies in the Earth's atmosphere. Unlike the Earth, the atmospheres of Mars and Venus mainly consist of carbon dioxide with a CO2 content of about 95%. In this paper, the line list of H2 16O is obtained on the basis of the BT2 line list (R.J. Barber, J. Tennyson, G.J. Harris, et al., Mon. Not. R. Astron. Soc. 368, 1087 (2006)). The BT2 line list containing information on the centers, intensities, and quantum identification of lines is supplemented with the line contour parameters: the self-broadening and carbon dioxide broadening coefficients and the temperature dependence coefficient at 296 K in the range of 0.001-30000 cm-1. Transitions with intensity values 10-30, 10-32, and 10-35 cm/molecule, the total number of which is 323310, 753529, and 2011072, respectively, were chosen from the BT2 line list.

Numerical Treatment of Thin Accretion Disk Dynamics around Rotating Black Holes

NASA Astrophysics Data System (ADS)

Yildiran, Deniz; Donmez, Orhan

In the present study, we perform the numerical simulation of a relativistic thin accretion disk around the nonrotating and rapidly rotating black holes using the general relativistic hydrodynamic code with Kerr in Kerr-Schild coordinate that describes the central rotating black hole. Since the high energy X-rays are produced close to the event horizon resulting the black hole-disk interaction, this interaction should be modeled in the relativistic region. We have set up two different initial conditions depending on the values of thermodynamical variables around the black hole. In the first setup, the computational domain is filled with constant parameters without injecting gas from the outer boundary. In the second, the computational domain is filled with the matter which is then injected from the outer boundary. The matter is assumed to be at rest far from the black hole. Both cases are modeled over a wide range of initial parameters such as the black hole angular momentum, adiabatic index, Mach number and asymptotic velocity of the fluid. It has been found that initial values and setups play an important role in determining the types of the shock cone and in designating the events on the accretion disk. The continuing injection from the outer boundary presents a tail shock to the steady state accretion disk. The opening angle of shock cone grows as long as the rotation parameter becomes larger. A more compressible fluid (bigger adiabatic index) also presents a bigger opening angle, a spherical shock around the rotating black hole, and less accumulated gas in the computational domain. While results from [J. A. Font, J. M. A. Ibanez and P. Papadopoulos, Mon. Not. R. Astron. Soc. 305 (1999) 920] indicate that the tail shock is warped around for the rotating hole, our study shows that it is the case not only for the warped tail shock but also for the spherical and elliptical shocks around the rotating black hole. The warping around the rotating black hole in our case is much smaller than the one by [J. A. Font, J. M. A. Ibanez and P. Papadopoulos, Mon. Not. R. Astron. Soc. 305 (1999) 920], due to the representation of results at the different coordinates. Contrary to the nonrotating black hole, the tail shock is slightly warped around the rotating black hole. The filled computational domain without any injection leads to an unstable accretion disk. However much of it reaches a steady state for a short period of time and presents quasi-periodic oscillation (QPO). Furthermore, the disk tends to loose mass during the whole dynamical evolution. The time-variability of these types of accretion flowing close to the black hole may clarify the light curves in Sgr A*.

Long-Term Stability of Planets in the Alpha Centauri System

NASA Technical Reports Server (NTRS)

Lissauer, Jack; Quarles, Billy

2015-01-01

The alpha Centauri system is billions of years old, so planets are only expected to be found in regions where their orbits are long-lived. We evaluate the extent of the regions within the alpha Centauri AB star system where small planets are able to orbit for billion-year timescales, and we map the positions in the sky plane where planets on stable orbits about either stellar component may appear. We confirm the qualitative results of Wiegert & Holman (Astron. J. 113, 1445, 1997) regarding the approximate size of the regions of stable orbits of a single planet, which are larger for retrograde orbits relative to the binary than for pro-grade orbits. Additionally, we find that mean motion resonances with the binary orbit leave an imprint on the limits of orbital stability, and the effects of the Lidov-Kozai mechanism are also readily apparent. Overall, orbits of a single planet in the habitable zones near the plane of the binary are stable, whereas high-inclination orbits are short-lived. However, even well within regions where single planets are stable, multiple planet systems must be significantly more widely-spaced than they need to be around an isolated star in order to be long-lived.

PIRATE: A Remotely Operable Telescope Facility for Research and Education

NASA Astrophysics Data System (ADS)

Holmes, S.; Kolb, U.; Haswell, C. A.; Burwitz, V.; Lucas, R. J.; Rodriguez, J.; Rolfe, S. M.; Rostron, J.; Barker, J.

2011-10-01

We introduce PIRATE, a new remotely operable telescope facility for use in research and education, constructed from off-the-shelf hardware, operated by The Open University. We focus on the PIRATE Mark 1 operational phase, in which PIRATE was equipped with a widely used 0.35 m Schmidt-Cassegrain system (now replaced with a 0.425 m corrected Dall-Kirkham astrograph). Situated at the Observatori Astronòmic de Mallorca, PIRATE is currently used to follow up potential transiting extrasolar planet candidates produced by the SuperWASP North experiment, as well as to hunt for novae in M31 and other nearby galaxies. It is operated by a mixture of commercially available software and proprietary software developed at the Open University. We discuss problems associated with performing precision time-series photometry when using a German Equatorial Mount, investigating the overall performance of such off-the-shelf solutions in both research and teaching applications. We conclude that PIRATE is a cost-effective research facility, and it also provides exciting prospects for undergraduate astronomy. PIRATE has broken new ground in offering practical astronomy education to distance-learning students in their own homes.

A model for rotation and shape of Asteroid 9969 Braille from ground-based observations and images obtained during the deep space 1 (DS1) flyby

USGS Publications Warehouse

Oberst, J.; Mottola, S.; Di, Martino M.; Hicks, M.; Buratti, B.; Soderblom, L.; Thomas, N.

2001-01-01

Image data from the DS1 encounter with Asteroid 9969 Braille and data from a coordinated ground-based photometric observing campaign are combined to study the physical properties of this small Mars crosser. From telescope data the object's brightness was found to vary by up to 0.5 mag from night to night, with the most probable synodic rotational period being 226.4 ?? 1.3 h (9.4 days) and a mean lightcurve magnitude R(1, ?? = 24??) = 17.04 ?? 0.10. During the flyby of the spacecraft, two frame images from a range of approximately 13,500 km and phase angle 82.4??, which impose strong constraints on size, shape, and albedo of the object, were obtained. Using telescope and flyby data in combination, the asteroid is estimated to have a size of 2.1 ?? 1 ?? 1 km3 and shown to have photometric properties similar to the asteroid 4 Vesta, notably a comparably high albedo. The high albedo supports the notion (L. Soderblom et al. 1999, Bull. Am. Astron. Soc. 31,) that Braille is of the V or Q taxonomic type. ?? 2001 Academic Press.

Comment on ‘Gravitational lensing of massive particles in Schwarzschild gravity’ (2016 Class. Quantum Grav. 33 175014)

NASA Astrophysics Data System (ADS)

Zakharov, Alexander F.

2018-01-01

Recently, Liu et al published a paper (2016 Class. Quantum Grav. 33 175014). In the abstract, the authors claimed as a key result of the paper that a particle sphere is found for the Schwarzschild black hole (BH), with its radius as a simple function of the particle velocity and proportional to the BH mass. Usually, if there are no references for the result it is assumed that the result was obtained originally in the paper; but this is not the case for the quoted paper. The concept of a particle sphere was introduced by Mielnik and Plebański (1962 Acta Phys. Pol. 21 239) and a simple derivation of the critical impact parameter was given in Zakharov A F (1988 Sov. Astron. 32 456 and Zakharov A F 1994 Class. Quantum Grav. 11 1027). We show that in slightly different notations, equation (17) for the critical impact parameter in Liu X et al (2016 Class. Quantum Grav. 33 175014) coincides with equation (12) in Zakharov (1994 Class. Quantum Grav. 11 1027) and with the corresponding equation (10.10) in Mielnik and Plebański (1962 Acta Phys. Pol. 21 239).

Three-Dimensional Properties of Coronal Mass Ejections from STEREO/SECCHI Observations

NASA Astrophysics Data System (ADS)

Bosman, E.; Bothmer, V.; Nisticò, G.; Vourlidas, A.; Howard, R. A.; Davies, J. A.

2012-11-01

We identify 565 coronal mass ejections (CMEs) between January 2007 and December 2010 in observations from the twin STEREO/SECCHI/COR2 coronagraphs aboard the STEREO mission. Our list is in full agreement with the corresponding SOHO/LASCO CME Catalog (http://cdaw.gsfc.nasa.gov/CME_list/) for events with angular widths of 45∘ and up. The monthly event rates behave similarly to sunspot rates showing a three- to fourfold rise between September 2009 and March 2010. We select 51 events with well-defined white-light structure and model them as three-dimensional (3D) flux ropes using a forward-modeling technique developed by Thernisien, Howard and Vourlidas (Astrophys. J. 652, 763 - 773, 2006). We derive their 3D properties and identify their source regions. We find that the majority of the CME flux ropes (82 %) lie within 30∘ of the solar equator. Also, 82 % of the events are displaced from their source region, to a lower latitude, by 25∘ or less. These findings provide strong support for the deflection of CMEs towards the solar equator reported in earlier observations, e.g. by Cremades and Bothmer ( Astron. Astrophys. 422, 307 - 322, 2004).

XMM-Newton, powerful AGN winds and galaxy feedback

NASA Astrophysics Data System (ADS)

Pounds, K.; King, A.

2016-06-01

The discovery that ultra-fast ionized winds - sufficiently powerful to disrupt growth of the host galaxy - are a common feature of luminous AGN is major scientific breakthrough led by XMM-Newton. An extended observation in 2014 of the prototype UFO, PG1211+143, has revealed an unusually complex outflow, with distinct and persisting velocities detected in both hard and soft X-ray spectra. While the general properties of UFOs are consistent with being launched - at the local escape velocity - from the inner disc where the accretion rate is modestly super-Eddington (King and Pounds, Ann Rev Astron Astro- phys 2015), these more complex flows have raised questions about the outflow geometry and the importance of shocks and enhanced cooling. XMM-Newton seems likely to remain the best Observatory to study UFOs prior to Athena, and further extended observations, of PG1211+143 and other bright AGN, have the exciting potential to establish the typical wind dynamics, while providing new insights on the accretion geometry and continuum source structure. An emphasis on such large, coordinated observing programmes with XMM-Newton over the next decade will continue the successful philosophy pioneered by EXOSAT, while helping to inform the optimum planning for Athena

Autonomous landing guidance program

NASA Astrophysics Data System (ADS)

Brown, John A.

1996-05-01

The Autonomous Landing Guidance program is partly funded by the US Government under the Technology Reinvestment Project. The program consortium consists of avionics and other equipment vendors, airlines and the USAF. A Sextant Avionique HUD is used to present flight symbology in cursive form as well as millimeter wave radar imagery from Lear Astronics equipment and FLIR Systems dual-channel, forward-looking, infrared imagery. All sensor imagery is presented in raster form. A future aim is to fuse all imagery data into a single presentation. Sensor testing has been accomplished in a Cessna 402 operated by the Maryland Advanced Development Laboratory. Development testing is under way in a Northwest Airlines simulator equipped with HUD and image simulation. Testing is also being carried out using United Airlines Boeing 727 and USAF C-135C (Boeing 707) test aircraft. The paper addresses the technology utilized in sensory and display systems as well as modifications made to accommodate the elements in the aircraft. Additions to the system test aircraft include global positioning systems, inertial navigation systems and extensive data collection equipment. Operational philosophy and benefits for both civil and military users are apparent. Approach procedures have been developed allowing use of Category 1 ground installations in Category 3 conditions.

The Meteorological Stations of the 1.5 and 0.84 m Telescopes of the OAN: Description and Results

NASA Astrophysics Data System (ADS)

Michel, R.; Bohigas, J.; Arroyo, E.; Zazueta, S.

2001-10-01

Meteorological stations for the 1.5 and 0.84 m telescopes at the Observatorio Astronómico Nacional at San Pedro Mártir (OAN) are described. The stations include devices for measuring temperature, atmospheric pressure, relative humidity and wind conditions. All the meteorological variables are monitored continuously and mean values are determined every 5 minutes and written on the hard disk of the control computer. This information is continuously refreshed in an HTML page that can be accessed from the OAN home page. In this paper we present the results of measurements taken over 2 years. We find that both primary mirrors are substantially warmer than the surrounding air during the night (up to ~ 5oC). This thermal gradient degrades image quality. For the primary mirror of the 1.5 m telescope this effect can be corrected with a temperature control system. For the 0.84 m telescope, where the primary mirror is located in a closed structure, ventilators moving air from the dome into the closed tube may suffice. During the night the air is colder within both domes than outside, and we conclude that no dome ventilation is necessary in these telescopes.

Maximum gravitational-wave energy emissible in magnetar flares

NASA Astrophysics Data System (ADS)

Corsi, Alessandra; Owen, Benjamin J.

2011-05-01

Recent searches of gravitational-wave data raise the question of what maximum gravitational-wave energies could be emitted during gamma-ray flares of highly magnetized neutron stars (magnetars). The highest energies (˜1049erg) predicted so far come from a model [K. Ioka, Mon. Not. R. Astron. Soc.MNRAA40035-8711 327, 639 (2001), http://adsabs.harvard.edu/abs/2001MNRAS.327..639I] in which the internal magnetic field of a magnetar experiences a global reconfiguration, changing the hydromagnetic equilibrium structure of the star and tapping the gravitational potential energy without changing the magnetic potential energy. The largest energies in this model assume very special conditions, including a large change in moment of inertia (which was observed in at most one flare), a very high internal magnetic field, and a very soft equation of state. Here we show that energies of 1048-1049erg are possible under more generic conditions by tapping the magnetic energy, and we note that similar energies may also be available through cracking of exotic solid cores. Current observational limits on gravitational waves from magnetar fundamental modes are just reaching these energies and will beat them in the era of advanced interferometers.

Stability of Multi-Planet Systems in the Alpha Centauri System

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.

2017-01-01

We evaluate the extent of the regions within the alpha Centauri AB star system where small planets are able to orbit for billion-year timescales (Quarles & Lissauer 2016, Astron. J. 151, 111), as well as how closely-spaced planetary orbits can be within those regions in which individual planets can survive. Although individual planets on low inclination, low eccentricity, orbits can survive throughout the habitable zones of both stars, perturbations from the companion star imply that the spacing of planets in multi-planet systems within the habitable zones of each star must be significantly larger than the spacing of similar multi-planet systems orbiting single stars in order to be long-lived. Because the binary companion induces a forced eccentricity upon the orbits of planets in orbit around either star, appropriately-aligned circumstellar orbits with small initial eccentricities are stable to slightly larger initial semimajor axes than are initially circular orbits. Initial eccentricities close to forced eccentricities can have a much larger affect on how closely planetary orbits can be spaced, and therefore on how many planets may remain in the habitable zones, although the required spacing remains significantly higher than for planets orbiting single stars.

Dating star clusters in the Small Magellanic Cloud by means of integrated spectra

NASA Astrophysics Data System (ADS)

Ahumada, A. V.; Clariá, J. J.; Bica, E.; Dutra, C. M.

2002-10-01

In this study flux-calibrated integrated spectra in the range (3600-6800) Å are presented for 16 concentrated star clusters in the Small Magellanic Cloud (SMC), approximately half of which constitute unstudied objects. We have estimated ages and foreground interstellar reddening values from the comparison of the line strengths and continuum distribution of the cluster spectra with those of template cluster spectra with known parameters. Most of the sample clusters are young blue clusters (6-50 Myr), while L 28, NGC 643 and L 114 are found to be intermediate-age clusters (1-6 Gyr). One well known SMC cluster (NGC 416) was observed for comparison purposes. The sample includes clusters in the surroundings and main body of the SMC, and the derived foreground reddening values are in the range 0.00 <= E(B-V) <= 0.15. The present data also make up a cluster spectral library at SMC metallicity. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina.

Foco Nasmyth para el telescopio 2,15mts. de CASLEO

NASA Astrophysics Data System (ADS)

Casagrande, A. R.

En principio, este proyecto intenta lograr el mayor aprovechamiento posible del instrumental que se dispone, buscando la manera de optimizar y hacer más eficiente el servicio que brinda el CASLEO a la comunidad astronómica. El mismo consiste en utilizar dispositivos ya existentes en el telescopio, y darle una utilidad. Tal es el caso del camino óptico destinado al foco Coude. Si tenemos en cuenta que disponemos de un tercer espejo Coude, con todos sus mecanismos automatizados, (actualmente sin uso), una distancia apropiada del plano focal, el espacio y el lugar físico necesario para instalar un periférico, es posible la habilitación de un foco Nasmyth en el telescopio 2,15mts. El hecho de contar con este nuevo foco, redundará en importantes beneficios. En primer lugar, posibilitará la observación, casi simultánea, con dos instrumentos. Otro aspecto a tener en cuenta, es que disminuirá el frecuente cambio del instrumental periférico, motivo este que degrada su ideal puesta a punto. Por último, también de interés, es de destacar su escaso costo de ejecución.

ΛCDM Cosmology Through the Lens of Einstein's Static Universe, the Mother of Λ

NASA Astrophysics Data System (ADS)

Mitra, Abhas; Bhattacharyya, S.; Bhatt, Nilay

2013-03-01

We show here that, in the context of Einstein's static universe (ESU), the static cosmological constant Λs = 0. We do so by extending (and not contradicting) the ESU relationship from Λs = 4πρ to Λs = 4πρ = 0, where ρ is the ESU matter density (G = c = 1). This extension follows from the fact that the elements of the spacetime geometry depend on pressure and energy density (ρ). Note in the ΛCDM model, Λ is associated with "Dark Energy (DE)." And, if Λ would be considered as a fundamental constant, it should be zero even for a dynamic universe. In such a case, the observed accelerated expansion could be an artifact of inhomogeneity [D. L. Wiltshire, Phys. Rev. D80 (2009) 123512; E. W. Kolb, Class. Quantum. Grav.28 (2011) 164009] or large peculiar acceleration of the Milky way [C. Tasgas, Phys. Rev. D84 (2011) 063503] or extinction of light of distant supernovae [R. E. Schild and M. Dekker, Astron. Nachr.327 (2006) 729, arXiv:astro-ph/0512236]. The same conclusion has also been obtained in an independent manner [A. Mitra, JCAP03 (2013) 007, doi: 10.1088/1475-7516/2013/03/007].

Sitnikov problem in the square configuration: elliptic case

NASA Astrophysics Data System (ADS)

Shahbaz Ullah, M.

2016-05-01

This paper is extension to the classical Sitnikov problem, when the four primaries of equal masses lie at the vertices of a square for all time and moving in elliptic orbits around their center of mass of the system, the distances between the primaries vary with time but always in such a way that their mutual distances remain in the same ratio. First we have established averaged equation of motion of the Sitnikov five-body problem in the light of Jalali and Pourtakdoust (Celest. Mech. Dyn. Astron. 68:151-162, 1997), by applying the Van der Pol transformation and averaging technique of Guckenheimer and Holmes (Nonlinear oscillations, dynamical system bifurcations of vector fields, Springer, Berlin, 1983). Next the Hamiltonian equation of motion has been solved with the help of action angle variables I and φ. Finally the periodicity and stability of the Sitnikov five-body problem have been examined with the help of Poincare surfaces of section (PSS). It is shown that chaotic region emerging from the destroyed islands, can easily be seen by increasing the eccentricity of the primaries to e = 0.21. It is valid for bounded small amplitude solutions z_{max} ( z_{max} = 0.65 ) and 0 ≤ e < 0.3.

Dynamical and collisional evolution of Halley-type comets

NASA Astrophysics Data System (ADS)

van der Helm, E.; Jeffers, S. V.

2012-03-01

The number of observed Halley-type comets is hundreds of times less than predicted by models (Levison, H.F., Dones, L., Duncan, M.J. [2001]. Astron. J. 121, 2253-2267). In this paper we investigate the impact of collisions with planetesimals on the evolution of Halley-type comets. First we compute the dynamical evolution of a sub-set of 21 comets using the MERCURY integrator package over 100 Myr. The dynamical lifetime is determined to be of the order of 105-106 years in agreement with previous work. The collisional probability of Halley-type comets colliding with known asteroids, a simulated population of Kuiper-belt objects, and planets, is calculated using a modified, Öpik-based collision code. Our results show that the catastrophic disruption of the cometary nucleus has a very low probability of occurring, and disruption through cumulative minor impacts is concluded to be negligible. The dust mantle formed from ejected material falling back to the comet’s surface is calculated to be less than a few centimeters thick, which is insignificant compared to the mantle formed by volatile depletion, while planetary encounters were found to be a negligible disruption mechanism.

A new look at photometry of the Moon

USGS Publications Warehouse

Goguen, J.D.; Stone, T.C.; Kieffer, H.H.; Buratti, B.J.

2010-01-01

We use ROLO photometry (Kieffer, H.H., Stone, T.C. [2005]. Astron. J. 129, 2887-2901) to characterize the before and after full Moon radiance variation for a typical highlands site and a typical mare site. Focusing on the phase angle range 45??. ) to calculate the scattering matrix and solve the radiative transfer equation for I/. F. The mean single scattering albedo is ??=0.808, the asymmetry parameter is ???cos. ?????=0.77 and the phase function is very strongly peaked in both the forward and backward scattering directions. The fit to the observations for the highland site is excellent and multiply scattered photons contribute 80% of I/. F. We conclude that either model, roughness or multiple scattering, can match the observations, but that the strongly anisotropic phase functions of realistic particles require rigorous calculation of many orders of scattering or spurious photometric roughness estimates are guaranteed. Our multiple scattering calculation is the first to combine: (1) a regolith model matched to the measured particle size distribution and index of refraction of the lunar soil, (2) a rigorous calculation of the particle phase function and solution of the radiative transfer equation, and (3) application to lunar photometry with absolute radiance calibration. ?? 2010 Elsevier Inc.

Cosmological implications of a large complete quasar sample.

PubMed

Segal, I E; Nicoll, J F

1998-04-28

Objective and reproducible determinations of the probabilistic significance levels of the deviations between theoretical cosmological prediction and direct model-independent observation are made for the Large Bright Quasar Sample [Foltz, C., Chaffee, F. H., Hewett, P. C., MacAlpine, G. M., Turnshek, D. A., et al. (1987) Astron. J. 94, 1423-1460]. The Expanding Universe model as represented by the Friedman-Lemaitre cosmology with parameters qo = 0, Lambda = 0 denoted as C1 and chronometric cosmology (no relevant adjustable parameters) denoted as C2 are the cosmologies considered. The mean and the dispersion of the apparent magnitudes and the slope of the apparent magnitude-redshift relation are the directly observed statistics predicted. The C1 predictions of these cosmology-independent quantities are deviant by as much as 11sigma from direct observation; none of the C2 predictions deviate by >2sigma. The C1 deviations may be reconciled with theory by the hypothesis of quasar "evolution," which, however, appears incapable of being substantiated through direct observation. The excellent quantitative agreement of the C1 deviations with those predicted by C2 without adjustable parameters for the results of analysis predicated on C1 indicates that the evolution hypothesis may well be a theoretical artifact.

The Spin-Orbit Resonant Rotation of Mercury: A Two Degree of Freedom Hamiltonian Model

NASA Astrophysics Data System (ADS)

D'Hoedt, Sandrine; Lemaitre, Anne

2004-04-01

The paper develops a hamiltonian formulation describing the coupled orbital and spin motions of a rigid Mercury rotation about its axis of maximum moment of inertia in the frame of a 3:2 spin orbit resonance; the (ecliptic) obliquity is not constant, the gravitational potential of mercury is developed up to the second degree terms (the only ones for which an approximate numerical value can be given) and is reduced to a two degree of freedom model in the absence of planetary perturbations. Four equilibria can be calculated, corresponding to four different values of the (ecliptic) obliquity. The present situation of Mercury corresponds to one of them, which is proved to be stable. We introduce action-angle variables in the neighborhood of this stable equilibrium, by several successive canonical transformations, so to get two constant frequencies, the first one for the free spin-orbit libration, the other one for the 1:1 resonant precession of both nodes (orbital and rotational) on the ecliptic plane. The numerical values obtained by this simplified model are in perfect agreement with those obtained by Rambaux and Bois [Astron. Astrophys. 413, 381 393].

On the shear instability in relativistic neutron stars

NASA Astrophysics Data System (ADS)

Corvino, Giovanni; Rezzolla, Luciano; Bernuzzi, Sebastiano; De Pietri, Roberto; Giacomazzo, Bruno

2010-06-01

We present new results on instabilities in rapidly and differentially rotating neutron stars. We model the stars in full general relativity and describe the stellar matter adopting a cold realistic equation of state based on the unified SLy prescription (Douchin and Haensel 2001 Astron. Astrophys. 380 151-67). We provide evidence that rapidly and differentially rotating stars that are below the expected threshold for the dynamical bar-mode instability, βc ≡ T/|W| ~= 0.25, do nevertheless develop a shear instability on a dynamical timescale and for a wide range of values of β. This class of instability, which has so far been found only for small values of β and with very small growth rates, is therefore more generic than previously found and potentially more effective in producing strong sources of gravitational waves. Overall, our findings support the phenomenological predictions made by Watts et al (2005 Astrophys. J. 618 L37) on the nature of the low-T/|W| instability as the manifestation of a shear instability in a region where the latter is possible only for small values of β. Furthermore, our results provide additional insight on shear instabilities and on the necessary conditions for their development.

Development of a Lunar Scintillometer as part of the national large optical telescope site survey

NASA Astrophysics Data System (ADS)

Surendran, Avinash; Parihar, Padmakar S.; Banyal, Ravinder K.; Kalyaan, Anusha

2018-03-01

Ground layer turbulence is a very important site characterization parameter used to assess the quality of an astronomical site. The Lunar Scintillometer is a simple and effective site-testing device for measuring the ground layer turbulence. It consists of a linear array of photodiodes which are sensitive to the slight variations in the moon's brightness due to scintillation by the lower layers of the Earth's atmosphere. The covariance of intensity values between the non-redundant photodiode baselines can be used to measure the turbulence profile from the ground up to a height determined by the furthest pair of detectors. The six channel lunar scintillometer that has been developed at the Indian Institute of Astrophysics is based closely on an instrument built by the team led by Andrei Tokovinin of Cerro Tololo Inter-American Observatory (CTIO), Chile (Tokovinin et al., Mon. Not. R. Astron. Soc. 404(3), 1186-1196 2010). We have fabricated the instrument based on the existing electronic design, and have worked on the noise analysis, an EMI (Electromagnetic Induction) resistant PCB design and the software pipeline for analyzing the data from the same. The results from the instrument's multi-year campaign at Mount Saraswati, Hanle is also presented.

Constraints on a Second Planet in the WASP-3 System

NASA Astrophysics Data System (ADS)

Maciejewski, G.; Niedzielski, A.; Wolszczan, A.; Nowak, G.; Neuhäuser, R.; Winn, J. N.; Deka, B.; Adamów, M.; Górecka, M.; Fernández, M.; Aceituno, F. J.; Ohlert, J.; Errmann, R.; Seeliger, M.; Dimitrov, D.; Latham, D. W.; Esquerdo, G. A.; McKnight, L.; Holman, M. J.; Jensen, E. L. N.; Kramm, U.; Pribulla, T.; Raetz, St.; Schmidt, T. O. B.; Ginski, Ch.; Mottola, S.; Hellmich, S.; Adam, Ch.; Gilbert, H.; Mugrauer, M.; Saral, G.; Popov, V.; Raetz, M.

2013-12-01

There have been previous hints that the transiting planet WASP-3b is accompanied by a second planet in a nearby orbit, based on small deviations from strict periodicity of the observed transits. Here we present 17 precise radial velocity (RV) measurements and 32 transit light curves that were acquired between 2009 and 2011. These data were used to refine the parameters of the host star and transiting planet. This has resulted in reduced uncertainties for the radii and masses of the star and planet. The RV data and the transit times show no evidence for an additional planet in the system. Therefore, we have determined the upper limit on the mass of any hypothetical second planet, as a function of its orbital period. Partly based on (1) observations made at the Centro Astronómico Hispano Alemán (CAHA), operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC), (2) data collected with telescopes at the Rozhen National Astronomical Observatory, and (3) observations obtained with telescopes of the University Observatory Jena, which is operated by the Astrophysical Institute of the Friedrich-Schiller-University.

A unifying fractional wave equation for compressional and shear waves.

PubMed

Holm, Sverre; Sinkus, Ralph

2010-01-01

This study has been motivated by the observed difference in the range of the power-law attenuation exponent for compressional and shear waves. Usually compressional attenuation increases with frequency to a power between 1 and 2, while shear wave attenuation often is described with powers less than 1. Another motivation is the apparent lack of partial differential equations with desirable properties such as causality that describe such wave propagation. Starting with a constitutive equation which is a generalized Hooke's law with a loss term containing a fractional derivative, one can derive a causal fractional wave equation previously given by Caputo [Geophys J. R. Astron. Soc. 13, 529-539 (1967)] and Wismer [J. Acoust. Soc. Am. 120, 3493-3502 (2006)]. In the low omegatau (low-frequency) case, this equation has an attenuation with a power-law in the range from 1 to 2. This is consistent with, e.g., attenuation in tissue. In the often neglected high omegatau (high-frequency) case, it describes attenuation with a power-law between 0 and 1, consistent with what is observed in, e.g., dynamic elastography. Thus a unifying wave equation derived properly from constitutive equations can describe both cases.

Vertical Profiles of Phosphine and Ammonia on Saturn Derived from the First Cassini RSS Occultation Observation Using Forward Modeling

NASA Astrophysics Data System (ADS)

Mohammed, P. N.; Steffes, P. G.; Kliore, A. J.; Anabtawi, A.; Asmar, S. W.; Barbinis, E.; Goltz, G.; Johnston, D.; Marouf, E. A.

2005-08-01

The results from the first Cassini Radio Science Subsystem(RSS) occultation, which occurred at the Rev 7 periapse, are being used to derive profiles of the atmospheric constituents encountered by the three frequency (S-, X-, and Ka-band) radio link. A computer model has been developed to simulate ray paths and the ray path parameters in the atmosphere of Saturn encountered during occultation (see Mohammed and Steffes, Bull. Amer. Astron. Soc., 36, no. 4, 1107, 2004). This forward model, which can be used on any oblate planet, will be used to determine the refractive defocusing and derive the profiles of phosphine and ammonia using data observed at Ka-band (32 GHz or 9.3 mm), X-band (8.4 GHz or 3.6 cm) and S-band (2.3 GHz or 13 cm). The results of laboratory measurements of the 9 mm opacity of phosphine and ammonia (Mohammed and Steffes, ICARUS 166, 425-435, 2003) and the centimeter wavelength opacity of these constituents measured under simulated conditions for Saturn (see, e.g., Hoffman et. al. ICARUS 152, 172-184, 2001) were incorporated into the forward radio occultation model used in these derivations.

Examining Rotational Variability in the Upper Tropospheres and Lower Stratospheres of Uranus and Neptune from Herschel PACS OT1 Observations: Implications for the Stability of Temperature and Compositional Structure

NASA Astrophysics Data System (ADS)

Orton, G.; Feuchtgruber, H.; Fletcher, L.; Lellouch, E.; Moreno, R.; Billebaud, F.; Cavalie, T.; Decin, L.; Dobreijecvic, M.; Encrenaz, T.; Hartogh, P.; Jarchow, C.; Lara, L. M.; Liu, J.

2012-04-01

The power of high-resolution submillimeter spectroscopy of Uranus and Neptune was put to use to survey the rotational variability of stratospheric and tropospheric constituents of their atmospheres. These observations were motivated by the surprising discovery of as much as 12% rotational variability of emission from stratospheric constituents in the atmosphere of Uranus by the Spitzer Infrared Spectrometer and the detection of spatial variability in thermal images of Neptune's stratospheric emission (Orton et al. 2007, Astron. & Astrophys 473, L3). Our observing program consisted of three separate sequences of observations to look at the strongest lines of H2O in the high-resolution PACS spectra of both planets, whose upwelling radiance emerges from the same vertical region as the Spitzer IRS observations of Uranus and ground-based images of Neptune, and the strongest line of CH4 in the PACS spectrum of Neptune. We omitted measurements of CH4 lines in Uranus, which are almost non-detectable. We added the strongest HD line in Uranus to measure variability of tropospheric temperatures that could modulate stratospheric CH4 abundances through local cold-trapping and the strongest two HD lines in Neptune (Lellouch et al. 2010, Astron. & Astrophys. 518, L152) that determine both the tropopause temperature to limit local cold-trapping efficacy and the lower stratospheric temperature, to help differentiate between longitudinal variability of stratospheric H2O and CH4 abundances vs. temperatures. These were repeated over the 17-hour interval that is common to the equatorial rotation periods of both Uranus and Neptune. Although these lines had already been observed in Uranus and Neptune by PACS, no repeat measurements had ever been made to determine longitudinal variability. The observations were consistent with previous measurements, but no significant rotational variability was detected. It is possible that the absence of rotational variability in the HD and CH4 lines is because variability is confined to very low pressures, e.g. much lower than a microbar. However, the absence of variable emission from high-altitude exogenic H2O vapor is harder to explain, unless the variability seen in Uranus by Spitzer and in Neptune from the VLT, is not the result of variations in temperature by in the hydrocarbon abundances. Alternatively, the stratospheres of both planets are variable in time. The cause of such variability is unknown, but spatially confined outbursts have been detected in the visible and near infrared, and they may have as much influence on the stratosphere of Uranus as the great springtime storm in Saturn's northern hemisphere, creating a strong, localized "beacon" of thermal radiation (cf. Fletcher et al. 2011, Science, 332,1413) that could dominate the emission observed over the hemisphere.

Near Earth asteroids associated with the Sigma-Capricornids meteoroid stream

NASA Astrophysics Data System (ADS)

Gulchekhra, Kokhirova; Pulat, Babadzhanov; Umed, Khamroev

The Near Earth Asteroids (NEAs) 2008BO16, 2011EC41, and 2013CT36 (http://newton.dm.\\unipi.it/neodys, 2013) have very similar orbits according to the D_{SH} criterion of Southworth, Hawkins (1963). Additionally, their orbits are classed as comet-like by the Tisserand invariant values (Kresak 1982; Kosai 1992). The orbital evolution investigation shows, that during one cycle of variations of the argument of perihelion omega, the asteroids cross the Earth’s orbit four times. Consequently, a developed meteoroid stream, possible associated with them, might produce four meteor showers (Babadzhanov, Obrubov 1992). Theoretical parameters of the predicted showers were calculated and identified with the observable nighttime sigma-Capricornids (Sekanina 1973; Jenniskens 2006) and chi-Sagittarids (Sekanina 1976), and daytime chi-Capricornids (Sekanina 1976) and Capricornids-Sagittarids (Sekanina 1973) meteor showers. The similar and comet-like orbits and association with the meteoroid stream producing four active showers are strong indications that these asteroids have a common cometary origin. Earlier the NEAs (2101) Adonis and 1995CS, which additionally is potentially hazardous asteroid (PHA), were recognized as dormant comets because of their link with the same meteoroid stream (Babadzhanov 2003). So, a conclusion was made, that either the considered NEAs are large sized splinters of the Adonis, or all five objects are fragments of a larger comet that was the parent body of the sigma-Capricornids meteoroid stream, and whose break-up occurred several tens of thousands years ago. During 2010-2011 years three fireballs were photographed by the Tajikistan fireball network (Babadzhanov, Kokhirova 2009), belonging to the sigma-Capricornids meteor shower. Taking into account the observations else six fireballs of this shower in the Canada and USA (Halliday et al. 1996; McCrosky et al. 1978), the mean radiant coordinates, the period of activity, as well as the mean daily radiant drift of the sigma-Capricornids were determined. Further to the PE criterion (Ceplecha, McCrosky 1976), the values of bulk density of the nine fireball producing meteoroids are in the range 0.2-3.5 g cm(-3) that suggests a non-homogeneous compound of the comet-progenitor of the sigma-Capricornids fireball shower. size{ References Babadzhanov, P.B., 2003, A&A,397, 319 Babadzhanov, P.B., Kokhirova, G.I., 2009, Izv. Ak. Nauk Resp. Taj.,2(135),46 Babadzhanov, P.B., Obrubov, Yu.V., 1992, Cel. Mech.& Dyn. Astron., v.54, p.111 Ceplecha, Z., McCrosky, R.E.J., 1976, J. Geophys. Res., 81, 6257 Halliday, I., Griffin, A.A., Blackwell, A.T., 1996, Met.& Planet. Sci., 31, 185 Jenniskens, P., 2006, Meteor showers and their parent comets, New- York: Cambridge Univ. Press, p. 790 Kosai, H., 1992, Cel. Mech. & Dyn. Astron., 54, 237 Kresak, L., 1982, BAC, 33, 104 McCrosky, R.E., Shao, C.Y., Posen, A., 1978, Meteoritika, 37, 44 Sekanina Z., 1973, Icarus, 18, 253 Sekanina Z., 1976, Icarus, 27, 265 Southworth, R.B., Hawkins, G.S., 1963, Smith. Cont. Aph. 7, 261}

Bodily tides near the 1:1 spin-orbit resonance: correction to Goldreich's dynamical model

NASA Astrophysics Data System (ADS)

Williams, James G.; Efroimsky, Michael

2012-12-01

Spin-orbit coupling is often described in an approach known as " the MacDonald torque", which has long become the textbook standard due to its apparent simplicity. Within this method, a concise expression for the additional tidal potential, derived by MacDonald (Rev Geophys 2:467-541, 1994), is combined with a convenient assumption that the quality factor Q is frequency-independent (or, equivalently, that the geometric lag angle is constant in time). This makes the treatment unphysical because MacDonald's derivation of the said formula was, very implicitly, based on keeping the time lag frequency-independent, which is equivalent to setting Q scale as the inverse tidal frequency. This contradiction requires the entire MacDonald treatment of both non-resonant and resonant rotation to be rewritten. The non-resonant case was reconsidered by Efroimsky and Williams (Cel Mech Dyn Astron 104:257-289, 2009), in application to spin modes distant from the major commensurabilities. In the current paper, we continue this work by introducing the necessary alterations into the MacDonald-torque-based model of falling into a 1-to-1 resonance. (The original version of this model was offered by Goldreich (Astron J 71:1-7, 1996). Although the MacDonald torque, both in its original formulation and in its corrected version, is incompatible with realistic rheologies of minerals and mantles, it remains a useful toy model, which enables one to obtain, in some situations, qualitatively meaningful results without resorting to the more rigorous (and complicated) theory of Darwin and Kaula. We first address this simplified model in application to an oblate primary body, with tides raised on it by an orbiting zero-inclination secondary. (Here the role of the tidally-perturbed primary can be played by a satellite, the perturbing secondary being its host planet. A planet may as well be the perturbed primary, its host star acting as the tide-raising secondary). We then extend the model to a triaxial primary body experiencing both a tidal and a permanent-figure torque exerted by an orbiting secondary. We consider the effect of the triaxiality on both circulating and librating rotation near the synchronous state. Circulating rotation may evolve toward the libration region or toward a spin faster than synchronous (the so-called pseudosynchronous spin). Which behaviour depends on the orbit eccentricity, the triaxial figure of the primary, and the mass ratio of the secondary and primary bodies. The spin evolution will always stall for the oblate case. For libration with a small amplitude, expressions are derived for the libration frequency, damping rate, and average orientation. Importantly, the stability of pseudosynchronous spin hinges upon the dissipation model. Makarove and Efroimsky (Astrophys J, 2012) have found that a more realistic tidal dissipation model than the corrected MacDonald torque makes pseudosynchronous spin unstable. Besides, for a sufficiently large triaxiality, pseudosynchronism is impossible, no matter what dissipation model is used.

Percepção astronómica de um grupo de alunos do ensino médio de uma escola da rede estadual de São Paulo

NASA Astrophysics Data System (ADS)

de Oliveria, E. F.; Voelzke, M. R.

2009-03-01

Sendo a Astronomia uma das cièncias mais antigas da humanidade, e considerando sua importáncia histórica e cultural, é de extrema releváncia que tópicos relacionados a ela sejam tratados nas escolas. Embora os Parámetros Curriculares Nacionais do Ensino Médio (PCN-EM) e as Orientaçiacute;es Complementares aos Parámetros (PCN+) apontem a importáncia de uma abordagem significativa de conceitos relacionados à Astronomia nas aulas de Física, muitos estudantes terminam o Ensino Médio (EM) sem compreender a razão de certos acontecimentos de origem celeste, ainda que estes façam parte de seu cotidiano e sejam alvos da curiosidade natural dos jovens. Da observação dessa curiosidade em alunos de uma escola pública paulista, na cidade de Suzano, surgiu o interesse em investigar os conhecimentos básicos em Astronomia dos alunos do Ensino Médio desta escola, constituindo-se este como principal objetivo desta pesquisa. Para tanto foi elaborado um questionário de múltipla escolha aplicado inicialmente a 34 alunos do primeiro ano e, posteriormente, a mais 310, distribuídos entre as très séries do Ensino Médio dos períodos matutino e noturno. Dessa forma, observou-se que 73,9% dos estudantes identificaram o Sol como sendo uma estrela, 67,1% mostraram compreender a sucessão entre dia e noite e 52,3% relacionaram o Big Bang à origem do Universo. Em contrapartida, apenas 34,5% relacionaram as estaçíes do ano à inclinação do eixo de rotação da Terra, 21,3% indicaram a influència gravitacional simultánea da Lua e do Sol como responsável pelo fenòmeno das marés, 24,5% indicaram corretamente quais são os objetos celestes mais próximos da Terra, 36,1% identificaram ano-luz como uma medida de distáncia e 34,2% reconheceram as estrelas cadentes como meteoros, evidenciando-se assim o pequeno discernimento dos estudantes quanto aos fenòmenos e termos astronòmicos do cotidiano. Além disso, foram comparadas as respostas de alun! os de diferentes séries e períodos, observando-se, dentre ou tras coi sas, que os estudantes do terceiro ano apresentam um percentual de acertos semelhante ao dos alunos do primeiro, caracterizando que a abordagem de tópicos relacionados à astronomia no Ensino Médio não tem contribuído de forma significativa para uma maior compreensão dos fenòmenos e conceitos.

Mutual Events in the Uranian satellite system in 2007

NASA Astrophysics Data System (ADS)

Arlot, J. E.

2008-09-01

The equinox time on the giant planets When the Sun crosses the equatorial plane of a giant planet, it is the equinox time occurring every half orbit of the planet, i.e. every 6 years for Jupiter, 14 years for Saturn, 42 years for Uranus and 82 years for Neptune. Except Neptune, each planet have several major satellites orbiting in the equatorial plane, then, during the equinox time, the satellites will eclipse each other mutually. Since the Earth follows the Sun, during the equinox time, a terrestrial observer will see each satellite occulting each other during the same period. These events may be observed with photometric receivers since the light from the satellites will decrease during the events. The light curve will provide information on the geometric configuration of the the satellites at the time of the event with an accuracy of a few kilometers, not depending on the distance of the satellite system. Then, we are able to get an astrometric observation with an accuracy several times better than using direct imaging for positions. Equinox on Uranus in 2007 In 2007, it was equinox time on Uranus. The Sun crossed the equatorial plane of Uranus on December 6, 2007. Since the opposition Uranus-Sun was at the end of August 2007, observations were performed from May to December 2007. Since the declination of Uranus was between -5 and -6 degrees, observations were better to make in the southern hemisphere. However, some difficulties had to be solved: the faintness of the satellites (magnitude between 14 and 16), the brightness of the planet (magnitude 5) making difficult the photometric observation of the satellites. The used of K' filter associated to a large telescope allows to increase the number of observable events. Dynamics of the Uranian satellites One of the goals of the observations was to evaluate the accuracy of the current dynamical models of the motion of the satellites. This knowledge is important for several reasons: most of time the Uranian system is observed "pole-on" and the relative inclinations of the orbits of the satellites are very difficult to know. More, this knowledge should allow us to determine the precession of Uranus which is not yet known. Another reason to improve the dynamics of the Uranian satellites is to quantify the dissipation of energy inside the satellites because of the tides: only very accurate astrometric observations may allow to reach such a result. We used two models for our purpose: the one from Laskar and Jacobson (GUST86) based upon observations made using observations made from 1911 to 1986 [1] and the one from Arlot, Lainey and Thuillot (LA06) [2] based upon a different sets of observations made from 1950 to 2006. Astrometric observations Since the mutual events are observable only every 42 years (in fact, 2007 was the first time where mutual events were observed on the Uranian system), many other astrometric observations were performed, mainly with photographic plates, CCD targets or using a meridian transit circle. These observations and their accuracy will be compared with mutual events. Note that these observations introduce some biases in the data (date of the opposition, absolute position of the planet), different than those of mutual events (equinox time). Observations of mutual events in 2007 Due to the difficulty of the observations, very few observations were made: about 15 events were observed using telescopes with apertures from 40 cm to 8 meters... The observing sites which reported observations were Marseille and Pic du Midi (France), Canarian Islands (Spain), La Silla and Paranal (Chile), Itajuba (Brazil), Tubitak (Turkey), Hanle (India) and Siding Spring (Australia). A preliminary analysis Some light curves were reduced and a comparison has been made with the theoretical calculations of the events. A preliminary analysis shows that LA06 has smaller residuals in the longitudes of the satellites than GUST86 but the residuals are equivalent in latitude. This confirms the problem due to the "pole-on" observation of this system and shows the necessity to improve the knowledge of the inclinations of the orbits of the satellites since the positions in longitudes are better determined using recent astrometric observations. Other observations performed during the equinox At the same time of the observation of mutual events, direct imaging was made allowing astrometric measurements of the positions of most of the Uranian satellites including the small inner ones. As a result, it appears that the model published by Showalter and Lissauer [3] provides very small residuals showing a high quality. Making observations after the equinox on Uranus During the next five years, when the Uranian system will be seen from its equatorial plane, astrometric EPSC Abstracts, Vol. 3, EPSC2008-A-xxxx (Abstract number will be completed later on), 2008 European Planetary Science Congress, Author(s) 2008 EPSC Abstracts, Vol. 3, EPSC2008-A-00523, 2008 European Planetary Science Congress, Author(s) 2008 observations are urged to be made being the lonely period where observations provide information on the inclinations of the orbits of the satellites. The equinox on Jupiter and Saturn in 2009 The equinox on Jupiter will occur on June 22, 2009 allowing events as for the Uranian system. Since the opposition of Jupiter occurs on August 14, 2009, observations should be numerous. The negative declination of Jupiter will encourage the observers to use southern sites. The predictions of the mutual events has been made [4] and are also available at the web address: http://www.imcce.fr/phemu09. The equinox on Saturn will occur on August 12, 2009 allowing events as for the Uranian and Jovian systems. Since the opposition occurs on March 9, 2009, observations should be difficult to make and a special effort has to be made by the observers. The declination of Saturn is favourable for both hemispheres. Such event occurs every 14 years and the satellites are fainter than the Jovian ones. The predictions of the mutual events has been made [5] and are also available at the web address: http://www.imcce.fr/phemu09. References [1] Laskar J., Jacobson R.A.. (1987) Astron. Astrophys, 188, 212-224. [2] Arlot J.E. et al. (2006) Astron. Astrophys., 456, 1173-1179. [3] Showalter M., Lissauer J. (2006) Science, 311, 973- 977. [4] Arlot J.E. (2008) Astron. Astrophys., 478, 285-298. [5] Arlot J.E. et al. (2008) Astron. Astrophys., 485, 293- 298.

Equinoxes on Jupiter and Saturn in 2009: call for observations

NASA Astrophysics Data System (ADS)

Arlot, J. E.

2008-09-01

The equinox time on the giant planets The equinox occurs on the giant planets as on Earth, when the Sun crosses the equatorial plane i.e. every 6 years for Jupiter, 14 years for Saturn, 42 years for Uranus and 82 years for Neptune. The main large satellites of these planets have their orbits in the equatorial plane and, except Neptune, each planet have several major satellites. Note that at the time of the equinox, the Earth will also cross the equatorial plane of the planet since, as seen from the giant planets, the Earth is very close to the Sun. Then, the satellites will eclipse and occult each other mutually for a groundbased observer during a one-year period around the equinox. These events are observed with photometric receivers since the light from the satellites will decrease during the events. The light curve will provide information on the geometric configuration of the satellites at the time of the event with an accuracy of a few kilometers, not depending on the distance to Earth of the satellite system. Then, we are able to get an astrometric observation with an accuracy several times better than using direct imaging for astrometric positions. The equinox on Jupiter in 2009 The equinox on Jupiter will occur on June 22, 2009 allowing mutual events during about one year around the equinox time (mutual events will occur from January 2009 to April 2010 not regularly due to the small inclinations of the orbits of the satellites on the Jovian equator) as shown on figure n°1. observable events should be numerous. The negative declination of Jupiter will make the observations easier from southern sites but they are not sufficient as seen on figure n°5 and a special effort should be made in the northern hemisphere to make observations even when Jupiter is low above the horizon. The Galilean satellites of Jupiter are very bright (magnitude 5) and their observation is possible even with a very small telescope. Amateur astronomers are able to make such observations of a high astrometric accuracy (similar to space observations): for that purpose they need to follow very precise recommendations. The photometric accuracy should be good enough for further analysis. Such a photometric accuracy may be reached even with cheap camera and we encourage the potential observers to read the Technical notes dedicated to the observation of the mutual events and the recommendations to be followed by the observers on the web site http://www.imcce.fr/phemu09. Note that all the light curves must be dated in Universal Time with an accuracy of 0.1 second of time to be useful for scientific purpose. GPS may be used for that purpose. Such events occur every 6 years and we have experience of these observations. In the past, many campaigns of observations were made [1] providing a large amount of accurate data allowing to improve the dynamics of the system and we know how useful are the observations made by amateur astronomers. The predictions of the mutual events have been made [2] and are also available at the web address given above. We provide below examples of light curves to be obtained on figures n°2 and 3. On figure n°2, the light curve is quite symmetrical (the surface of Europa is quite uniform) but on figure n°3, the light curve is not symmetrical (the surface of Callisto is less uniform) providing information of the surfaces of the satellite and on the laws of reflexion of light. This information allows to improve the astrometric accuracy of the observations by helping to find the center of mass or center of figure of the satellite from the observation of its center of light or photocenter. The equinox on Saturn in 2009 The equinox on Saturn will occur on August 12, 2009 allowing events as for the Jovian system as shown on figure n°4. The mutual events will occur from September 2008 to June 2010. observable events will be less numerous and a special effort has to be made by the observers. The declination of Saturn is favourable for both hemispheres. Such event occurs every 14 years and the satellites are fainter than the Jovian ones. We have experience of these observations. In the past, two campaigns of observations were made [3] providing accurate data allowing to improve the dynamics of the system. The predictions of the mutual events have been made [4] and are also available at the web address: http://www.imcce.fr/phemu09. Call for observations These observations have shown their high interest allowing quantifying the dissipation of energy due to the tidal effects inside the satellites. A constraint on the internal structure of the satellites may be deduced from the analysis of these observations thanks to the theoretical models developed either at JPL or at IMCCE. As we did in the past, we need the participation of as many observers as possible since the events occur at any time and that the satellites must be above the horizon to be observed. Observing sites at all possible longitudes are required. For the last campaigns, we had about 40 sites of observations as shown on figure n°5. More observing sites are required in the southern hemisphere for the Jovian events. The Saturnian events are more difficult to catch (fainter satellites closer to the bright planet) but are observable easily with a CCD camera and a telescope with a not too short focal length. All explanations are provided on Technical notes available on the web site of IMCCE at: http://www.imcce.fr/phemu09. 2009 will be the International Year of Astronomy supported by IAU. We proposed that the opportunity of the equinoxes on Jupiter and Saturn were used to ask professional and amateur astronomers to make together observations of the mutual events presented in this communication. It will be a commemoration of the observations by Galileo four centuries ago. He extensively observed the Jovian system discovering the eclipses by Jupiter. Such an international campaign of observation will gather professional and amateurs for a common scientific work as we did in the past as shown by common publications (see [1] and [3] ). Do not hesitate to join the network of observers to participate to observations! Contact: arlot@imcce.fr Web site: http://www.imcce.fr/phemu09 References [1] Arlot J.E. et al. (2006) Astron. Astrophys., 451, 733-737. [2] Arlot J.E. (2008) Astron. Astrophys., 478, 285-298. [3] Thuillot W.. et al. (2001) Astron. Astrophys., 371, 343-349. [4] Arlot J.E. et al. (2008) Astron. Astrophys., 485, 293- 298.

Morfología de la Coma del Cometa Hale - Bopp

NASA Astrophysics Data System (ADS)

Gil-Hutton, R.; Caballero, M.; Coldwell, G.; Cañada, M.; Godoy, G.; Trozzo, C.; Gómez, G.

Para lograr comprender plenamente los procesos físicos que se desarrollan en los núcleos cometarios y obtener un modelo que explique, no sólo su actividad, sino también sus efectos sobre la coma, es necesario obtener información detallada para el mayor número de cometas posible, siendo las características más interesantes para estudiar la ubicación de las regiones activas, la presencia de jets, las tasas de producción de gas y polvo y la interacción de la coma con el viento solar. En la actualidad, con técnicas de procesamiento de imágenes y tecnología CCD se pueden obtener este tipo de datos para cometas que ingresan al sistema solar interior y estudiar, de esta manera, la morfología de sus comas, tratando de correlacionar la actividad detectada con algún modelo teórico. En este trabajo se presenta un estudio parcial de la actividad desarrollada por el cometa Hale-Bopp, y sus efectos sobre la morfología de su coma, desde agosto de 1995 hasta la fecha en base a imágenes adquiridas con el telescopio de 0.76 m. de la Estación Astronómica Dr. Carlos Ulrrico Cesco.

Mapping the Region in the Nearest Star System to Search for Habitable Planets

NASA Technical Reports Server (NTRS)

Lissauer, Jack J.; Quarles, B.

2015-01-01

Circumstellar planets within the alpha Centauri AB star system have been suggested through formation models and recent observations, and ACESat (Belikov et al. AAS Meeting #225, #311.01, 2015) is a proposed space mission designed to directly image Earth-sized planets in the habitable zones of both of these stars. The alpha Centauri system is billions of years old, so planets are only expected to be found in regions where their orbits are long-lived. We evaluate the extent of the regions within the alpha Centauri AB star system where small planets are able to orbit for billion-year timescales and we map the positions in the sky plane where planets on stable orbits about either stellar component may appear. We confirm the qualitative results of Wiegert & Holman (Astron. J. 113, 1445, 1997) regarding the approximate size of the regions of stable orbits, which are larger for retrograde orbits relative to the binary than for prograde orbits. Additionally, we find that mean motion resonances with the binary orbit leave an imprint on the limits of orbital stability, and the effects of the Lidov-Kozai mechanism are also readily apparent. Overall, orbits in the habitable zones near the plane of the binary are stable, whereas high-inclination orbits are short-lived.

Novel matched amplifiers with low noise positive feedback. Part II: Resistive-capacitive feedback

NASA Astrophysics Data System (ADS)

Bruck, Y.; Zakharenko, V.

2010-02-01

This article is a continuation of consideration for an amplifier with resistive positive feedback (RPF) (Bruck (2008), 'Novel Matched LNA with Low Noise Positive Feedback. Part 1: General Features and Resistive Feedback', International Journal of Electronics, 95, 441-456). We propose here new configuration schematics of a transformer-less selective LNA with resistive-capacitive positive feedback (RCPF). A circuit of an amplifier with a transistor connected into a circuit with a common base (CB) configuration is analysed in detail. RCPF and RPF circuits are compared. It is shown that the LNA RCPF provides any pass-band, a good level of input and output matching, a minimum noise temperature which is significantly lower than that of the LNA RPF, a rather high linearity, and stability of amplification. The simulation results and some experimental data for the amplifiers intended for use in the LOFAR radiotelescope (Konovalenko et al. (2003), 'Thirty Element Array Antenna as a Prototype of a Huge Low-Frequency Radio Telescope,' Experimental Astronomy, 16, 149-164; Konovalenko (2007), 'Ukrainian Contribution to LOFAR', A scientific workshop, organised by LOFAR/ASTRON' Emmen, Netherlands, 23-27. http://www.lofar.org/workshop) are given. It is assumed that such devices are of a special interest for high-frequency integral circuits (IC).

Telescope Fabra ROA Montsec: A New Robotic Wide Field Baker-Nunn Facility

NASA Astrophysics Data System (ADS)

Fors, Octavi; Núñez, Jorge; Muiños, José Luis; Montojo, Francisco Javier; Baena-Gallé, Roberto; Boloix, Jaime; Morcillo, Ricardo; Merino, María Teresa; Downey, Elwood C.; Mazur, Michael J.

2013-05-01

A Baker-Nunn Camera (BNC), originally installed at the Real Instituto y Observatorio de la Armada (ROA) in 1958, was refurbished and robotized. The new facility, called Telescope Fabra ROA Montsec (TFRM), was installed at the Observatori Astronòmic del Montsec (OAdM). The process of refurbishment is described in detail. Most of the steps of the refurbishment project were accomplished by purchasing commercial components, which involve little posterior engineering assembling work. The TFRM is a 0.5 m aperture f/0.96 optically modified BNC, which offers a unique combination of instrumental specifications: fully robotic and remote operation, wide field of view (4°.4 × 4°.4), moderate limiting magnitude (V ˜ 19.5 mag), ability of tracking at arbitrary right ascension (α) and declination (δ) rates, as well as opening and closing CCD shutter at will during an exposure. Nearly all kinds of image survey programs can benefit from those specifications. Apart from other less time-consuming programs, since the beginning of science TFRM operations we have been conducting two specific and distinct surveys: super-Earths transiting around M-type dwarfs stars, and geostationary debris in the context of Space Situational Awareness/Space Surveillance and Tracking (SSA/SST) programs. Preliminary results for both cases will be shown.

Night Sky Brightness at San Pedro Martir Observatory

NASA Astrophysics Data System (ADS)

Plauchu-Frayn, I.; Richer, M. G.; Colorado, E.; Herrera, J.; Córdova, A.; Ceseña, U.; Ávila, F.

2017-03-01

We present optical UBVRI zenith night sky brightness measurements collected on 18 nights during 2013 to 2016 and SQM measurements obtained daily over 20 months during 2014 to 2016 at the Observatorio Astronómico Nacional on the Sierra San Pedro Mártir (OAN-SPM) in México. The UBVRI data is based upon CCD images obtained with the 0.84 m and 2.12 m telescopes, while the SQM data is obtained with a high-sensitivity, low-cost photometer. The typical moonless night sky brightness at zenith averaged over the whole period is U = 22.68, B = 23.10, V = 21.84, R = 21.04, I = 19.36, and SQM = 21.88 {mag} {{arcsec}}-2, once corrected for zodiacal light. We find no seasonal variation of the night sky brightness measured with the SQM. The typical night sky brightness values found at OAN-SPM are similar to those reported for other astronomical dark sites at a similar phase of the solar cycle. We find a trend of decreasing night sky brightness with decreasing solar activity during period of the observations. This trend implies that the sky has become darker by Δ U = 0.7, Δ B = 0.5, Δ V = 0.3, Δ R=0.5 mag arcsec-2 since early 2014 due to the present solar cycle.

New UV-source catalogs, UV spectral database, UV variables and science tools from the GALEX surveys

NASA Astrophysics Data System (ADS)

Bianchi, Luciana; de la Vega, Alexander; Shiao, Bernard; Bohlin, Ralph

2018-03-01

We present a new, expanded and improved catalog of Ultraviolet (UV) sources from the GALEX All-Sky Imaging survey: GUVcat_AIS (Bianchi et al. in Astrophys. J. Suppl. Ser. 230:24, 2017). The catalog includes 83 million unique sources (duplicate measurements and rim artifacts are removed) measured in far-UV and near-UV. With respect to previous versions (Bianchi et al. in Mon. Not. R. Astron. Soc. 411:2770 2011a, Adv. Space Res. 53:900-991, 2014), GUVcat_AIS covers a slightly larger area, 24,790 square degrees, and includes critical corrections and improvements, as well as new tags, in particular to identify sources in the footprint of extended objects, where pipeline source detection may fail and custom-photometry may be necessary. The UV unique-source catalog facilitates studies of density of sources, and matching of the UV samples with databases at other wavelengths. We also present first results from two ongoing projects, addressing respectively UV variability searches on time scales from seconds to years by mining the GALEX photon archive, and the construction of a database of ˜120,000 GALEX UV spectra (range ˜1300-3000 Å), including quality and calibration assessment and classification of the grism, hence serendipitous, spectral sources.

Radio observations of atmospheric gravity waves with Callisto

NASA Astrophysics Data System (ADS)

Monstein, C.

2013-12-01

On December 12th 2013 NOAA reported between 08:04 and 12:08 only radio noise at 245 MHz observed in San Vito. But some European observatories of the e-Callisto network (Germany, UK and Ireland) observed very strange reverse drifting and v-type bursts which was never recognized by the author before. Private communication with P. Zucca from TCD showed that these strange structures are due to focusing effects in the ionosphere. Interestingly it is possible to observe complex ionospheric behavior with cheap and simple radio-telescopes like Callisto. People who are interested in such kind of observations to study ionospheric gravity waves should generate observing programs for frequencies below 100 MHz, ideally with an additional up-converter for frequencies from 15 MHz - 100 MHz. Callisto again proved to be a powerful tool for solar science and radio-monitoring. Below are shown recent observations from Bir castle in Ireland, Essen in Germany and Glasgow in Scotland. For comparison I added an observation from a LOFAR node from Chibolton in UK which was provided by Richard Fallows from Astron NL. And finally a plot from Nançay radio heliograph, provided by Karl-Heinz Gansel, Dingden Amateur Radio- Astronomy Observatory DARO, Germany. Although Callisto instruments are almost identical, the spectra look completely different, depending on their geographical longitude and latitude.

A versatile entropic measure of grey level inhomogeneity

NASA Astrophysics Data System (ADS)

Piasecki, Ryszard

2009-06-01

An entropic measure for the analysis of grey level inhomogeneity (GLI) is proposed as a function of length scale. It allows us to quantify the statistical dissimilarity of the actual macrostate and the maximizing entropy of the reference one. The maximums (minimums) of the measure indicate those scales at which higher (lower) average grey level inhomogeneity appears compared to neighbour scales. Even a deeply hidden statistical grey level periodicity can be detected by the equally distant minimums of the measure. The striking effect of multiple intersecting curves (MICs) of the measure has been revealed for pairs of simulated patterns, which differ in shades of grey or symmetry properties only. In turn, for evolving photosphere granulation patterns, the stability in time of the first peak position has been found. Interestingly, the third peak is dominant at initial steps of the evolution. This indicates a temporary grouping of granules at a length scale that may belong to the mesogranulation phenomenon. This behaviour has similarities with that reported by Consolini, Berrilli et al. [G. Consolini, F. Berrilli, A. Florio, E. Pietropaolo, L.A. Smaldone, Astron. Astrophys. 402 (2003) 1115; F. Berrilli, D. Del Moro, S. Russo, G. Consolini, Th. Straus, Astrophys. J. 632 (2005) 677] for binarized granulation images of a different data set.

Ten years of SLR production in Argentina

NASA Astrophysics Data System (ADS)

Pacheco, A.; Podestá, R.; Yin, Z.; Liu, W.; Actis, E.; Adarvez, S.; Quinteros, J.; Podestá, F.

2017-07-01

SLR technique is a proved astro-geodetic art with a significant power to contribute to Earth and Space Sciences. Therefore, scientific applications of SLR System are able to perform multiple tasks in the fields of Astrometry, Geodesy and Geophysics. The results we show here were obtained from satellite observations made at SLR 7406 Station of Observatorio Astronómico Félix Aguilar (OAFA) in San Juan, Argentina. The telescope was installed early on 2006, in concordance with an International Cooperation Agreement between Universidad Nacional de San Juan, Argentina and Chinese Academy of Sciences. In this abstract we show the current research being done with ILRS 7406 station: Length of day (LOD) and Angular velocity of Earth Rotation, calculated weekly; Pole Motion. ILRS7406 is daily surveying Pole coordinates x and y; Tracking SLR to GNSS constellations. SLR System contributes to the adjustment and validation of satellite GALILEO, GPS, GLONASS, and BEIDOU orbits. Our station is nowadays member of the new ITRF 2014 frame, and these past years has been one of the 3 highest producing SLR Stations on the ILRS net, composed of about 40 stations distributed all around the world. The obtained results during this first 10 years of experience are useful to enhance the traditional collaboration between OAFA and international services such as ILRS, IERS and NASA.

The High Resolution Vibration-Rotation Spectrum of SiH^+

NASA Astrophysics Data System (ADS)

Domenech, Jose Luis

2017-06-01

Silicon bearing molecules account for ˜ 10% of the identified molecules in space. Among those containg hydrogen, SiH and SiH_4 have been identified in the solar spectrum, in some cold stars, and SiH_4 in IRC+1026. However the simple SiH^+ cation (silylidinium) has only been observed in the solar photosphere and it remains undetected in interstellar space. Most of the spectroscopic information on SiH^+ comes from the analisis of its vis-UV spectrum, and from a diode laser spectrum combined with velocity modulation of the v=1-0 band. The latter contained just eight lines measured with an estimated accuracy of 0.001 \\wn. We present the results obtained with a difference frequency laser spectrometer coupled to a hollow cathode discharge, with an increased number of lines and improved accuracy (1× 10^{-4} \\wn), allowing for an accurate prediction of the pure rotational transitions. These will be searched for in the Cologne Center for Terahertz Spectroscopy (CCTS). These data will be of use in future searches for this molecule in different astronomical environments. A. E. Douglas & B. Lutz, Can. J. Phys. 48 (1970) 247 T. Carlson et al. Astron. & Astrophys. 83 (1980) 238 P. B. Davies, P. M. Martineau, J. Chem. Phys. 88 (1985) 485

DOE Office of Scientific and Technical Information (OSTI.GOV)

Richer, Michael G.; Suárez, Genaro; López, José Alberto

We present spectroscopic observations of the C ii λ 6578 permitted line for 83 lines of sight in 76 planetary nebulae at high spectral resolution, most of them obtained with the Manchester Echelle Spectrograph on the 2.1 m telescope at the Observatorio Astronómico Nacional on the Sierra San Pedro Mártir. We study the kinematics of the C ii λ 6578 permitted line with respect to other permitted and collisionally excited lines. Statistically, we find that the kinematics of the C ii λ 6578 line are not those expected if this line arises from the recombination of C{sup 2+} ions ormore » the fluorescence of C{sup +} ions in ionization equilibrium in a chemically homogeneous nebular plasma, but instead its kinematics are those appropriate for a volume more internal than expected. The planetary nebulae in this sample have well-defined morphology and are restricted to a limited range in H α line widths (no large values) compared to their counterparts in the Milky Way bulge; both these features could be interpreted as the result of young nebular shells, an inference that is also supported by nebular modeling. Concerning the long-standing discrepancy between chemical abundances inferred from permitted and collisionally excited emission lines in photoionized nebulae, our results imply that multiple plasma components occur commonly in planetary nebulae.« less

Velocidades radiales en Collinder 121

NASA Astrophysics Data System (ADS)

Arnal, M.; Morrell, N.

Se han llevado a cabo observaciones espectroscópicas de unas treinta estrellas que son posibles miembros del cúmulo abierto Collinder 121. Las mismas fueron realizadas con el telescopio de 2.15m del Complejo Astronómico El Leoncito (CASLEO). El análisis de las velocidades radiales derivadas del material obtenido, confirma la realidad de Collinder 121, al menos desde el punto de vista cinemático. La velocidad radial baricentral (LSR) del cúmulo es de +17 ± 3 km.s-1. Esta velocidad coincide, dentro de los errores, con la velocidad radial (LSR) de la nebulosa anillo S308, la cual es de ~20 ± 10 km.s-1. Como S308 se encuentra físicamente asociada a la estrella Wolf-Rayet HD~50896, es muy probable que esta última sea un miembro de Collinder 121. Desde un punto de vista cinemático, la supergigante roja HD~50877 (K3Iab) también pertenecería a Collinder 121. Basándonos en la pertenencia de HD~50896 a Collinder 121, y en la interacción encontrada entre el viento de esta estrella y el medio interestelar circundante a la misma, se estima para este cúmulo una distancia del orden de 1 kpc.

Ruprecht 3: An old star cluster remnant?

NASA Astrophysics Data System (ADS)

Pavani, D. B.; Bica, E.; Ahumada, A. V.; Clariá, J. J.

2003-02-01

2MASS J and H photometry and integrated spectroscopy are employed to study the nature of the poorly populated compact concentration of stars Ruprecht 3, which was previously catalogued as an open cluster. The integrated spectrum remarkably resembles that of a moderately metal-rich globular cluster. The distribution of the object stars in the colour-magnitude diagram is compatible with that of a 1.5 +/- 0.5 Gyr open cluster or older, depending on whether the bluer stars are interpreted as turnoff stars or blue stragglers, respectively. We derive for the object a distance from the Sun dsun = 0.72 +0.04-0.03 kpc and a colour excess E(B-V) = 0.04. Although a globular cluster remnant cannot be ruled out, the integrated spectrum resemblance to that of a globular cluster probably reflects a stochastic effect owing to the few brighter stars. The structural and photometric properties of Ruprecht 3 are compatible with what would be expected for an intermediate-age open cluster remnant. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina.

Fundamental parameters of the highly reddened young open clusters Westerlund 1 and 2

NASA Astrophysics Data System (ADS)

Piatti, A. E.; Bica, E.; Claria, J. J.

1998-02-01

We study the compact open clusters Westerlund1 (BH197) and Westerlund2. We present CCD integrated spectroscopy for both clusters, and CCD imaging in the V and I bands for the former one. So far, Westerlund1 is possibly the most reddened open cluster studied in detail (Av ~ 13.0). It has an age of 8 +/- 3 Myr and a distance from the Sun of d_sun ~ 1.0 +/- 0.4 kpc. For Westerlund2 we derive a visual absorption AV~ 5.0 mag, an age of 2-3 Myr, and d_sun=5.7+/- 0.3 kpc. From luminosity and structural arguments we conclude that Westerlund1, although young and compact, it is a massive cluster, in contrast to Westerlund2. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Cientificas y Tecnicas de la Republica Argentina and the Universities of La Plata, Cordoba and San Juan, Argentina, and at the University of Toronto (David Dunlap Observatory) 24-inch telescope, Las Campanas, Chile. The photometric observations are available at CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html

Progress in SLR-GPS co-location at San Juan (Argentina) station

NASA Astrophysics Data System (ADS)

Luis, Hernan; Rojas, Alvis; Adarvez, Sonia; Quinteros, Johana; Cobos, Pablo; Aracena, Andrés; Pacheco, Ana M.; Podestá, Ricardo; Actis, Eloy V.; Li, Jinzeng; Yin, Zhiqiang; Wang, Rui; Huang, Dongping; Márquez, Raúl

2012-08-01

From February, 2006, performing a Cooperation Agreement with National Astronomical Observatories of China (NAOC) of the Chinese Academy of Sciences (CAS), Observatorio Astronómico Félix Aguilar (OAFA) of Universidad Nacional de San Juan (UNSJ) is operating a SLR System (ILRS 7406 Station). From the beginning of 2012 a GPS Aztech - Micro Z CGRS is operative at the same place, which made the SLR - GPS co - location possible. The prior objective is to reach co - location between both techniques, so the Station became of 1st order in ITRF net. For that we study and adopt an appropriate strategy to select and place Survey Control Points that ensures higher precision in determination of 3D vectors between the selected reference point s. Afterwards we perform translocation tasks of receptor and antenna checking that the GPS verifies builder standards. Then we design and compensate survey control network, by means of software of our own draught. We expect to obtain definitive local ties with precision better than 3 mm, as suggested by IERS for co - located stations. There are very few stations with co - located spatial techniques in the Southern Hemisphere, so it is of great importance to have one in Argentina for improve our participation in IERS on the new realizations of ITRF from now on.

Cosmological implications of a large complete quasar sample

PubMed Central

Segal, I. E.; Nicoll, J. F.

1998-01-01

Objective and reproducible determinations of the probabilistic significance levels of the deviations between theoretical cosmological prediction and direct model-independent observation are made for the Large Bright Quasar Sample [Foltz, C., Chaffee, F. H., Hewett, P. C., MacAlpine, G. M., Turnshek, D. A., et al. (1987) Astron. J. 94, 1423–1460]. The Expanding Universe model as represented by the Friedman–Lemaitre cosmology with parameters qo = 0, Λ = 0 denoted as C1 and chronometric cosmology (no relevant adjustable parameters) denoted as C2 are the cosmologies considered. The mean and the dispersion of the apparent magnitudes and the slope of the apparent magnitude–redshift relation are the directly observed statistics predicted. The C1 predictions of these cosmology-independent quantities are deviant by as much as 11σ from direct observation; none of the C2 predictions deviate by >2σ. The C1 deviations may be reconciled with theory by the hypothesis of quasar “evolution,” which, however, appears incapable of being substantiated through direct observation. The excellent quantitative agreement of the C1 deviations with those predicted by C2 without adjustable parameters for the results of analysis predicated on C1 indicates that the evolution hypothesis may well be a theoretical artifact. PMID:9560182

Divulgación del Programa Consolider-GTC

NASA Astrophysics Data System (ADS)

Ruiz Zelmanovitch, N.; Mass Hesse, M.; Alfaro, E.

2013-05-01

The Gran Telescopio Canarias (GTC) is the biggest telescope of its class in the world. The CONSOLIDER INGENIO 2010-GTC project, First Science with the GTC: Spanish Astron- omy on the Forefront of the European Astronomy, funded by the Spanish Ministry of Science and Innovation, MICINN (now the Ministry of Economy and competitiveness, MINECO) has used the GTC to: (i) obtain leading science with its data, (ii) increase the involvement of the Spanish astronomical community in developing astronomical instrumentation, (iii) get an important Spanish participation in the new extremely large telescopes generation (ELTs), and (iv) make outreach and communicating to the society the main results. The project CONSOLIDER INGENIO 2010-GTC is structured and defined by objectives: 1) GTC: To optimize the GTC and its instruments; 2) SCIENCE: To develop leading science with the GTC; 3) E-ELT: To take advantage of the technological experience obtained with the GTC for the new generation of giant telescopes; 4) INSTRUMENTATION: To promote the Spanish participation in the new instrument developments for the GTC, VLT and the future ELTs; 5) EDUCATION: International School for Advanced Instrumentation (IScAI); and 6) OUTREACH: Outreach and communication of the project scientific results. This poster resumes five years of science communication around the Consolider-GTC project.

Indicators for the evaluation of the quality of education and career development in the hard science: a case report

NASA Astrophysics Data System (ADS)

Arany-Prado, L. I.

2003-08-01

We report the results of the self-evaluation of the Astronomy Bachelor Course of the Observatório do Valongo (OV), Universidade Federal do Rio de Janeiro (UFRJ). We have created, heuristically, data indicators capable of quantifying the impact of curriculum and institutional improvements on the student's background and career development in the last 30 years. It is remarkable that the institution in study: i) has undergone appreciable recent development; ii) has its graduation course as a long term investment and an essentially complete database on past professors and students; iii) is inserted in a young scientific Society (Sociedade Astronômica Brasileira - SAB), which has shown marked recent maturation and a large rate of growth. This enabled us to diagnose the evolution of the institution and its suitability to the different requirements of the astronomical career. We show that, in the hard science field, the increase of the number of graduated students and the decrease of the time spent as an undergraduate student are not sufficient, or even adequate, to evaluate the efficiency of education in science (Arany-Prado, L., 2003, Revista Brasileira de Ensino de Física, vol. 25, no. 1, 105-115; http://sbf.if.usp.br/rbef/Vol25/Num1).

Spiral-like star-forming patterns in CALIFA early-type galaxies

NASA Astrophysics Data System (ADS)

Gomes, J. M.; Papaderos, P.; Vílchez, J. M.; Kehrig, C.; Iglesias-Páramo, J.; Breda, I.; Lehnert, M. D.; Sánchez, S. F.; Ziegler, B.; Dos Reis, S. N.; Bland-Hawthorn, J.; Galbany, L.; Bomans, D. J.; Rosales-Ortega, F. F.; Walcher, C. J.; García-Benito, R.; Márquez, I.; Del Olmo, A.; Mollá, M.; Marino, R. A.; Catalán-Torrecilla, C.; González Delgado, R. M.; López-Sánchez, Á. R.; Califa Collaboration

2016-01-01

Based on a combined analysis of SDSS imaging and CALIFA integral field spectroscopy data, we report on the detection of faint (24 <μr mag/□″< 26) star-forming spiral-arm-like features in the periphery of three nearby early-type galaxies (ETGs). These features are of considerable interest because they document the still ongoing inside-out growth of some local ETGs and may add valuable observational insight into the origin and evolution of spiral structure in triaxial stellar systems. A characteristic property of the nebular component in the studied ETGs, classified I+, is a two-radial-zone structure, with the inner zone that displays faint (EW(Hα) ≃ 1 Å) low-ionization nuclear emission-line region (LINER) properties, and the outer one (3 Å

Parallax measurements of six brown dwarfs.

NASA Astrophysics Data System (ADS)

Manjavacas, E.; Goldman, B.; Reffert, S.; Henning, T.

Accurate parallax measurements allow us to determine physical properties of brown dwarfs, and help us to constrain evolutionary and atmospheric models and reveal unresolved binaries. We measured absolute trigonometric parallaxes and proper motions of six cool brown dwarfs using background galaxies to establish an absolute reference frame. The brown dwarfs in our sample have spectral types between T2.5 and T7.5. The observations were taken in the J-band with the Omega2000 camera at the 3.5 m telescope at CAHA during a time period of 27 months. We obtained absolute parallaxes for our 6 brown dwarfs with a precision between 3 and 6 mas. We compared our results with the study by \\cite{Dupuy} and with the evolutionary models of \\cite{Allard}. For four of the six targets we found a good agreement in luminosity among objects of similar spectral types. The object 2MASS J11061197+2754225 is more than 1 mag overluminous in all bands pointing to binarity or higher order multiplicity. Based on observations taken with Omega-2000 at the 3.5 m telescope at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated by the Max Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).

Telescopio Solar en Hα (HASTA)

NASA Astrophysics Data System (ADS)

Fernández Borda, R.; Francile, C.; Bagala, G.; Bauer, O.; Haerendel, G.; Rieger, E.; Rovira, M.

El Telescopio Solar en Hα (Hα Solar Telescope for Argentina (-HASTA-) fue recientemente instalado en la Estación Astronómica de Altura Carlos Ulrrico Cesco (OAFA) en El Leoncito. Este instrumento estudiará la evolución de las fulguraciones solares desde tierra con alta resolución temporal y espacial. HASTA es un telescopio refractor de 110 mm con una distancia focal de 165 cm, un filtro Lyot sintonizable (±1Å) con un ancho de banda de 0.3 Å y una cámara CCD de alta resolución (1280×1024 pixels). Todo el conjunto es controlado en forma remota por una PC, la cual además adquiere datos del Sistema de Posicionamiento Global (GPS) y de la estación meteorológica. Diseñado para detectar fulguraciones, el instrumento trabaja en dos modos (patrullaje y fulguración) con una resolución espacial de 1.5 arcseg por pixel y una resolución temporal de 2 seg. HASTA comenzó a operar en Mayo de 1998 y, junto con otros tres instrumentos solares, que se están instalando o se instalaron, harán de El Leoncito un polo de observación solar importante en el Hemisferio Sur.

Richardson-Lucy/maximum likelihood image restoration algorithm for fluorescence microscopy: further testing.

PubMed

Holmes, T J; Liu, Y H

1989-11-15

A maximum likelihood based iterative algorithm adapted from nuclear medicine imaging for noncoherent optical imaging was presented in a previous publication with some initial computer-simulation testing. This algorithm is identical in form to that previously derived in a different way by W. H. Richardson "Bayesian-Based Iterative Method of Image Restoration," J. Opt. Soc. Am. 62, 55-59 (1972) and L. B. Lucy "An Iterative Technique for the Rectification of Observed Distributions," Astron. J. 79, 745-765 (1974). Foreseen applications include superresolution and 3-D fluorescence microscopy. This paper presents further simulation testing of this algorithm and a preliminary experiment with a defocused camera. The simulations show quantified resolution improvement as a function of iteration number, and they show qualitatively the trend in limitations on restored resolution when noise is present in the data. Also shown are results of a simulation in restoring missing-cone information for 3-D imaging. Conclusions are in support of the feasibility of using these methods with real systems, while computational cost and timing estimates indicate that it should be realistic to implement these methods. Itis suggested in the Appendix that future extensions to the maximum likelihood based derivation of this algorithm will address some of the limitations that are experienced with the nonextended form of the algorithm presented here.

Interstellar scintillations of PSR B1919+21: space-ground interferometry

NASA Astrophysics Data System (ADS)

Shishov, V. I.; Smirnova, T. V.; Gwinn, C. R.; Andrianov, A. S.; Popov, M. V.; Rudnitskiy, A. G.; Soglasnov, V. A.

2017-07-01

We carried out observations of pulsar PSR B1919+21 at 324 MHz to study the distribution of interstellar plasma in the direction of this pulsar. We used the RadioAstron (RA) space radio telescope, together with two ground telescopes: Westerbork (WB) and Green Bank (GB). The maximum baseline projection for the space-ground interferometer was about 60 000 km. We show that interstellar scintillation of this pulsar consists of two components: diffractive scintillations from inhomogeneities in a layer of turbulent plasma at a distance z1 = 440 pc from the observer or homogeneously distributed scattering material to the pulsar; and weak scintillations from a screen located near the observer at z2 = 0.14 ± 0.05 pc. Furthermore, in the direction to the pulsar we detected a prism that deflects radiation, leading to a shift in observed source position. We show that the influence of the ionosphere can be ignored for the space-ground baseline. Analysis of the spatial coherence function for the space-ground baseline (RA-GB) yielded a scattering angle in the observer plane of θscat = 0.7 mas. An analysis of the time-frequency correlation function for weak scintillations yielded an angle of refraction in the direction to the pulsar θref, 0 = 110 ms and a distance to the prism zprism ≤ 2 pc.

Comparación del funcionamiento entre PMT y SiPM para la detección de Cherenkov atmosférico en el Complejo Astronómico El Leoncito

NASA Astrophysics Data System (ADS)

Yelós, L. D.; Suarez, F.; García, B.

2017-10-01

Most recent discoveries in gamma ray astronomy with energies around 50 GeV to 30 TeV, were achieved with ground Cherenkov Telescopes, traditionally composed of a parabolic mirror and a single or an array of photo multiplier tubes (PMTs) in their focus. The same detectors (or similar) are used in most astrophysics experiments. Recently, a new detector, the silicon photo-multiplier (SiPM), is progressively replacing the PMTs due to their technical advantages. However some limitations in their functioning make them more complex to use than PMTs and forces their characterization for each project. This work describes the characterization of SiPM from SensL (model MicroFC-SMA-30035) and a PMT from Hamamatsu (model R1463), both detectors are possible options to be used in an array of three Cherenkov telescopes at CASLEO. Additionally, we include the results of the operation of both detectors under controlled laboratory conditions that simulate expected conditions at field. Laboratory test were run in a darkbox with a data acquisition system, a personalized data analyze system with ROOT libraries, temperature control and monitoring, polarization control, a controlled light source, and humidity monitoring.

Dynamical passage to approximate equilibrium shapes for spinning, gravitating rubble asteroids

NASA Astrophysics Data System (ADS)

Sharma, Ishan; Jenkins, James T.; Burns, Joseph A.

2009-03-01

Many asteroids are thought to be particle aggregates held together principally by self-gravity. Here we study — for static and dynamical situations — the equilibrium shapes of spinning asteroids that are permitted for rubble piles. As in the case of spinning fluid masses, not all shapes are compatible with a granular rheology. We take the asteroid to always be an ellipsoid with an interior modeled as a rigid-plastic, cohesion-less material with a Drucker-Prager yield criterion. Using an approximate volume-averaged procedure, based on the classical method of moments, we investigate the dynamical process by which such objects may achieve equilibrium. We first collapse our dynamical approach to its statical limit to derive regions in spin-shape parameter space that allow equilibrium solutions to exist. At present, only a graphical illustration of these solutions for a prolate ellipsoid following the Drucker-Prager failure law is available [Sharma, I., Jenkins, J.T., Burns, J.A., 2005a. Bull. Am. Astron. Soc. 37, 643; Sharma, I., Jenkins, J.T., Burns, J.A., 2005b. Equilibrium shapes of ellipsoidal soil asteroids. In: García-Rojo, R., Hermann, H.J., McNamara, S. (Eds.), Proceedings of the 5th International Conference on Micromechanics of Granular Media, vol. 1. A.A. Balkema, UK; Holsapple, K.A., 2007. Icarus 187, 500-509]. Here, we obtain the equilibrium landscapes for general triaxial ellipsoids, as well as provide the requisite governing formulae. In addition, we demonstrate that it may be possible to better interpret the results of Richardson et al. [Richardson, D.C., Elankumaran, P., Sanderson, R.E., 2005. Icarus 173, 349-361] within the context of a Drucker-Prager material. The graphical result for prolate ellipsoids in the static limit is the same as those of Holsapple [Holsapple, K.A., 2007. Icarus 187, 500-509] because, when worked out, his final equations will match ours. This is because, though the formalisms to reach these expressions differ, in statics, at the lowest level of approximation, volume-averaging and the approach of Holsapple [Holsapple, K.A., 2007. Icarus 187, 500-509] coincide. We note that the approach applied here was obtained independently [Sharma, I., Jenkins, J.T., Burns, J.A., 2003. Bull. Am. Astron. Soc. 35, 1034; Sharma, I., 2004. Rotational Dynamics of Deformable Ellipsoids with Applications to Asteroids. Ph.D. thesis, Cornell University] and it provides a general, though approximate, framework that is amenable to systematic improvements and is flexible enough to incorporate the dynamical effects of a changing shape, different rheologies and complex rotational histories. To demonstrate our technique, we investigate the non-equilibrium dynamics of rigid-plastic, spinning, prolate asteroids to examine the simultaneous histories of shape and spin rate for rubble piles. We have succeeded in recovering most results of Richardson et al. [Richardson, D.C., Elankumaran, P., Sanderson, R.E., 2005. Icarus 173, 349-361], who obtained equilibrium shapes by studying numerically the passage into equilibrium of aggregates containing discrete, interacting, frictionless, spherical particles. Our mainly analytical approach aids in understanding and quantifying previous numerical simulations.

Effective collision strengths for fine-structure forbidden transitions among the 3s^23p^3 levels of K V

NASA Astrophysics Data System (ADS)

Bell, Kenneth; Wilson, Nigel

2001-05-01

Electron temperatures and densities are difficult to determine in many astrophysical plasmas. However, it is well known that diagnostics on forbidden line intensity ratios for ions in the phosphorous isoelectronic sequence are of great importance in astrophysics, particularly for nebulae. A key element in the analysis is highly accurate atomic data. In this work we extend the earlier calculations of Butler, Zeippen and Le Bourlot (Astron. Astrophys. 203 189 (1988)) on electron scattering by K v. We have obtained effective collision strengths for a wide range of electron temperatures using the R-matrix method. Twenty-two LS target eigenstates are included in the expansion of the total wavefunction, consisting of the seven n=3 states with configuration 3s^23p^3 and 3s3p^4, twelve n=3 states with configuration 3s^23p^23d, and three n=4 states with configuration 3s^23p^24s. The fine-structure collision strengths have been obtained by transforming to a jj-coupling scheme using the JAJOM program of Saraph (Comp. Phys. Commun. 15 247 (1978)) and have been determined at a sufficiently fine energy mesh to delineate properly the resonance structure. Results for both collision strengths and for effective collision strengths will be presented at the conference and comparison will be made with the earlier work.

Observations of the new Camelopardalids meteor shower using a 38.9 MHz radar at Mohe, China

NASA Astrophysics Data System (ADS)

Younger, J. P.; Reid, I. M.; Li, G.; Ning, B.; Hu, L.

2015-06-01

The Camelopardalids meteor shower was predicted to occur for the first time on 24 May 2014, based on optical observations of the comet 209P/LINEAR. Using a 38.9 MHz meteor radar located at Mohe, China, we were able to detect approximately 590 shower meteors originating from an average pre-infall radiant of R.A. = 129.1° ± 9.8°, declination = 79.4° ± 1.6° (J2000) with a geocentric velocity of 16.0 ± 1.6 km s-1. Measurements of the shower duration, direction, velocity, and individual meteor detection heights facilitated a detailed analysis of the parent debris stream. Orbital parameters were calculated including a semi-major axis of 2.86 AU, eccentricity of 0.659, and inclination of 21.1°. Combining orbital parameters with the shower activity duration FWHM of 5.09 h, it was found that the stream has a FWHM of at least 211,000 km at 1 AU, as measured perpendicular to the direction of orbital motion. A comparison of shower meteor detection heights and diffusion coefficient estimates with the sporadic background is consistent the prediction of Ye and Wiegert (Ye, Q., Wiegert, P. [2014]. Mon. Not. R. Astron. Soc. 437, 3283-3287) that Camelopardalid meteoroids are biased towards larger sizes or that Cameloppardalid meteoroids are less fragile than sporadic background meteoroids.

The Kinematics of the Permitted C II λ6578 Line in a Large Sample of Planetary Nebulae

NASA Astrophysics Data System (ADS)

Richer, Michael G.; Suárez, Genaro; López, José Alberto; García Díaz, María Teresa

2017-03-01

We present spectroscopic observations of the C II λ6578 permitted line for 83 lines of sight in 76 planetary nebulae at high spectral resolution, most of them obtained with the Manchester Echelle Spectrograph on the 2.1 m telescope at the Observatorio Astronómico Nacional on the Sierra San Pedro Mártir. We study the kinematics of the C II λ6578 permitted line with respect to other permitted and collisionally excited lines. Statistically, we find that the kinematics of the C II λ6578 line are not those expected if this line arises from the recombination of C2+ ions or the fluorescence of C+ ions in ionization equilibrium in a chemically homogeneous nebular plasma, but instead its kinematics are those appropriate for a volume more internal than expected. The planetary nebulae in this sample have well-defined morphology and are restricted to a limited range in Hα line widths (no large values) compared to their counterparts in the Milky Way bulge; both these features could be interpreted as the result of young nebular shells, an inference that is also supported by nebular modeling. Concerning the long-standing discrepancy between chemical abundances inferred from permitted and collisionally excited emission lines in photoionized nebulae, our results imply that multiple plasma components occur commonly in planetary nebulae.

Relativistic H-theorem and nonextensive kinetic theory

NASA Astrophysics Data System (ADS)

Silva, R.; Lima, J. A. S.

2003-08-01

In 1988 Tsallis proposed a striking generalization of the Boltzmann-Gibbs entropy functional form given by [1] (1) where kB is Boltzmann's constant, pi is the probability of the i-th microstate, and the parameter q is any real number. Nowadays, the q-thermostatistics associated with Sq is being hailed as the possible basis of a theoretical framework appropriate to deal with nonextensive settings. There is a growing body of evidence suggesting that Sq provides a convenient frame for the thermostatistical analysis of many physical systems and processes ranging from the laboratory scale to the astrophysical domain [2]. However, all the basic results, including the proof of the H-theorem has been worked in the classical non-relativistic domain [3]. In this context we discuss the relativistic kinetic foundations of the Tsallis' nonextensive approach through the full Boltzmann's transport equation. Our analysis follows from a nonextensive generalization of the "molecular chaos hypothesis". For q > 0, the q-transport equation satisfies a relativistic H-theorem based on Tsallis entropy. It is also proved that the collisional equilibrium is given by the relativistic Tsallis' q-nonextensive velocity distribution. References [1] C. Tsallis, J. Stat. Phys. 52, 479 (1988). [2] J. A. S. Lima, R. Silva, and J. Santos, Astron. and Astrophys. 396, 309 (2002). [3] J. A. S. Lima, R. Silva, and A. R. Plastino, Phys. Rev. Lett. 86, 2938 (2001).

Exploración del catálogo de objetos en emisión H de Henize y All Sky Automated Survey: nuevas variables y tipos espectrales

NASA Astrophysics Data System (ADS)

Jaque Arancibia, M.; Barbá, R. H.; Collado, A.; Gamen, R.; Arias, J. I.

2016-08-01

Large astronomical surveys allow us to do systematic studies of stellar populations with significant statistical weight. In this study, we have cross-correlated the Henize's (1976) catalog of stellar sources with H emission-line with “The All Sky Automated Survey'' database. After the positional cross-matching we have found that 1402 of 1926 H sources have ASAS light-curves. From that number, more than 50 (723 sources) are periodic variables with amplitude larger than 0.05 magnitudes, while 276 sources show photometric variations without a clear periodicity. Variable stars that we have found are of many different types, among them Miras, eclipsing binaries, bursting stars, etc. Also, only 133 stars are known previously as variable sources in ASAS catalogue, and 93 of them were studied previously in detail. In order to characterize the nature of the sources, we have started a medium-resolution spectroscopic survey of the unstudied variable emission-line objects using the 2.15-m Jorge Sahade Telescope at Complejo Astronómico El Leoncito (Argentina). At the moment, we have observed a set of 67 blue stars selected using 2MASS colors, being almost all of them Be-type stars. This set of bright new variable Be-type stars is ideal for follow-up monitoring for the study of the Be-phenomenon.

Brightness temperature - obtaining the physical properties of a non-equipartition plasma

NASA Astrophysics Data System (ADS)

Nokhrina, E. E.

2017-06-01

The limit on the intrinsic brightness temperature, attributed to `Compton catastrophe', has been established being 1012 K. Somewhat lower limit of the order of 1011.5 K is implied if we assume that the radiating plasma is in equipartition with the magnetic field - the idea that explained why the observed cores of active galactic nuclei (AGNs) sustained the limit lower than the `Compton catastrophe'. Recent observations with unprecedented high resolution by the RadioAstron have revealed systematic exceed in the observed brightness temperature. We propose means of estimating the degree of the non-equipartition regime in AGN cores. Coupled with the core-shift measurements, the method allows us to independently estimate the magnetic field strength and the particle number density at the core. We show that the ratio of magnetic energy to radiating plasma energy is of the order of 10-5, which means the flow in the core is dominated by the particle energy. We show that the magnetic field obtained by the brightness temperature measurements may be underestimated. We propose for the relativistic jets with small viewing angles the non-uniform magnetohydrodynamic model and obtain the expression for the magnetic field amplitude about two orders higher than that for the uniform model. These magnetic field amplitudes are consistent with the limiting magnetic field suggested by the `magnetically arrested disc' model.

Mineralogical analysis of the Eos family from near-infrared spectra

NASA Astrophysics Data System (ADS)

Mothé-Diniz, T.; Carvano, J. M.; Bus, S. J.; Duffard, R.; Burbine, T. H.

2008-05-01

The aim of this work is to analyze the mineralogy of the Eos family, which exhibits considerable taxonomic diversity. Its biggest fragment, (221) Eos has previously been associated, through direct spectral comparisons, with such diverse mineralogies as CV/CO and achondrite meteorites [Burbine, T.H., Binzel, R.P., Bus, S.J., Clark, B.E., 2001. Meteorit. Planet. Sci. 36, 245-253; Mothé-Diniz, T., Carvano, J.M., 2005. Astron. Astrophys. 174, 54-80]. In order to perform such analysis we obtained spectra of 30 family members in the 0.8-2.5 μm range, and used three different methods of mineralogical inference: direct spectral comparison with meteorites, intimate mixing using Hapke's theory, and fitting absorption features with the MGM. Although the direct comparison failed to yield good matches—the best candidates being R-chondrites—both mixing model and MGM analysis suggest that the bulk of the family is dominated by forsteritic ( Fa) olivine, with a minor component of orthopyroxene. This composition can be compatible with what would be expected from the partial differentiation of a parent-body with an original composition similar to ordinary chondrites, which probably formed and differentiated closer to the Sun than the present location of the family. A CK-like composition is also possible, from the inferred mineralogy, as well as from the similarities of the spectra in the NIR.

Evolving coma abundances and detection of hypervolatiles in Jupiter-family comet 45P/Honda-Mrkos-Pajdusakova

NASA Astrophysics Data System (ADS)

Dello Russo, Neil; DiSanti, Michael A.; Kawakita, Hideyo; Shinnaka, Yoshiharu; Vervack, Ronald J.; Bonev, Boncho P.; Gibb, Erika L.; Roth, Nathan; McKay, Adam J.; Weaver, Harold A.; Cochran, Anita L.

2017-10-01

Two major shortcomings in chemically classifying comets at infrared wavelengths are a lack of hypervolatile (CO and CH4) detections in Jupiter-family comets and incomplete temporal coverage of comet chemistry, particularly at small heliocentric distances (Rh). We report post-perihelion volatile abundances in comet 45P/Honda-Mrkos-Pajdusakova with the high-resolution infrared spectrometer iSHELL at the NASA/IRTF on UT 6 - 8 January when Rh = 0.55 AU (DiSanti et al. 2017, Astron. J., in press), and with NIRSPEC at the Keck Observatory on UT 13 and 19 February when Rh = 1.0 and 1.1 AU, respectively. Favorable comet geocentric velocities enabled the detection of CO and CH4 in early January and 19 February. The relative abundance of CO is severely depleted whereas CH4 is typical to enriched in 45P when compared to comets from the Oort cloud. Significant differences are seen in relative abundances of species between January and February, notably in the ratio of C2H2/HCN. We explore whether the heliocentric distances of the measurements or seasonal changes primarily cause these differences by comparing to observations of C/2012 S1 ISON obtained over a similar range of heliocentric distances. NASA and NSF research grants support this work. We also acknowledge the expert support of the IRTF and Keck support staffs during these observations.

Secular resonances between bodies on close orbits II: prograde and retrograde orbits for irregular satellites

NASA Astrophysics Data System (ADS)

Li, Daohai; Christou, Apostolos A.

2017-09-01

In extending the analysis of the four secular resonances between close orbits in Li and Christou (Celest Mech Dyn Astron 125:133-160, 2016) (Paper I), we generalise the semianalytical model so that it applies to both prograde and retrograde orbits with a one-to-one map between the resonances in the two regimes. We propose the general form of the critical angle to be a linear combination of apsidal and nodal differences between the two orbits b_1 Δ π + b_2 Δ Ω, forming a collection of secular resonances in which the ones studied in Paper I are among the strongest. Test of the model in the orbital vicinity of massive satellites with physical and orbital parameters similar to those of the irregular satellites Himalia at Jupiter and Phoebe at Saturn shows that {>}20 and {>}40% of phase space is affected by these resonances, respectively. The survivability of the resonances is confirmed using numerical integration of the full Newtonian equations of motion. We observe that the lowest order resonances with b_1+|b_2|≤ 3 persist, while even higher-order resonances, up to b_1+|b_2|≥ 7, survive. Depending on the mass, between 10 and 60% of the integrated test particles are captured in these secular resonances, in agreement with the phase space analysis in the semianalytical model.

Relativistic dust accretion of charged particles in Kerr-Newman spacetime

NASA Astrophysics Data System (ADS)

Schroven, Kris; Hackmann, Eva; Lämmerzahl, Claus

2017-09-01

We describe a new analytical model for the accretion of particles from a rotating and charged spherical shell of dilute collisionless plasma onto a rotating and charged black hole. By assuming a continuous injection of particles at the spherical shell and by treating the black hole and a featureless accretion disk located in the equatorial plane as passive sinks of particles, we build a stationary accretion model. This may then serve as a toy model for plasma feeding an accretion disk around a charged and rotating black hole. Therefore, our new model is a direct generalization of the analytical accretion model introduced by E. Tejeda, P. A. Taylor, and J. C. Miller [Mon. Not. R. Astron. Soc. 429, 925 (2013), 10.1093/mnras/sts316]. We use our generalized model to analyze the influence of a net charge of the black hole, which will in general be very small, on the accretion of plasma. Within the assumptions of our model we demonstrate that already a vanishingly small charge of the black hole may in general still have a non-negligible effect on the motion of the plasma, as long as the electromagnetic field of the plasma is still negligible. Furthermore, we argue that the inner and outer edges of the forming accretion disk strongly depend on the charge of the accreted plasma. The resulting possible configurations of accretion disks are analyzed in detail.

Optical low-dispersion spectroscopic observations of Comet 103P/Hartley 2 at Koyama Astronomical Observatory during the EPOXI flyby

NASA Astrophysics Data System (ADS)

Shinnaka, Yoshiharu; Kawakita, Hideyo; Kobayashi, Hitomi; Naka, Chiharu; Arai, Akira; Arasaki, Takayuki; Kitao, Eiji; Taguchi, Gaku; Ikeda, Yuji

2013-02-01

We performed low-dispersion spectroscopic observations of Comet 103P/Hartley 2 in optical wavelengths using the LOSA/F2 mounted on the 1.3 m-Araki telescope at Koyama Astronomical Observatory on UT 2010 November 4 during the close approach of the Deep Impact spacecraft to the nucleus of Comet 103P/Hartley 2 in the EPOXI mission flyby. Our observations have revealed the chemistry of the coma at optical wavelengths; including CN, C3, C2 and NH2 along with H2O from [OI] emission at 6300 Å. Resultant mixing ratios of these radicals put the comet into the normal group in chemical composition. The mixing ratios with respect to H2O obtained in our observations are basically consistent with the previous optical spectro-photometric observations of Comet 103P/Hartley 2 in 1991 by A'Hearn et al. (A'Hearn, M.F., Millis, R.L., Schleicher, D.G., Osip, D.J., Birch, P.V. [1995]. Icarus 118, 223-270), the optical spectroscopic observations in 1998 by Fink (Fink, U. [2009]. Icarus 201, 311-334) and also consistent with the observations on UT 2010 October 27 and 29 by Lara et al. (Lara, L.M., Lin, Z.-Y., Meech, K. [2011]. Astron. Astrophys. 532, A87) (but only for the ratio relative to CN).

An analytical method to compute comet cloud formation efficiency and its application

NASA Astrophysics Data System (ADS)

Brasser, Ramon; Duncan, Martin J.

2008-01-01

A quick analytical method is presented for calculating comet cloud formation efficiency in the case of a single planet or multiple-planet system for planets that are not too eccentric ( e p ≲ 0.3). A method to calculate the fraction of comets that stay under the control of each planet is also presented, as well as a way to determine the efficiency in different star cluster environments. The location of the planet(s) in mass-semi-major axis space to form a comet cloud is constrained based on the conditions developed by Tremaine (1993) together with estimates of the likelyhood of passing comets between planets; and, in the case of a single, eccentric planet, the additional constraint that it is, by itself, able to accelerate material to relative encounter velocity U ~ 0.4 within the age of the stellar system without sweeping up the majority of the material beforehand. For a single planet, it turns out the efficiency is mainly a function of planetary mass and semi-major axis of the planet and density of the stellar environment. The theory has been applied to some extrasolar systems and compared to numerical simulations for both these systems and the Solar System, as well as a diffusion scheme based on the energy kick distribution of Everhart (Astron J 73:1039 1052, 1968). The analytic results are in good agreement with the simulations.

The shell spectrum of HD 94509

NASA Astrophysics Data System (ADS)

Cowley, Charles R.; Przybilla, Norbert; Hubrig, Swetlana

2015-01-01

HD 94509 is a 9th magnitude Be star with an unusually rich metallic-lined shell. The absorption spectrum is rich, comparable to that of an A or F supergiant, but Mg II (4481A), and the Si II (4128 and 4130A), are weak, indicating a dilute radiation field, as described by Otto Struve. The H-alpha emission is double with components of equal intensity and an absorption core that dips well below the stellar continuum. H-beta is weaker, but with a similar structure. H-gamma through H-epsilon have virtually black cores, indicating that the shell covers the stellar disk. The stronger metallic absorption lines are wide near the continuum, but taper to very narrow cores. This line shape is unexplained. However, the total absorption can be modeled to reveal an overall particle densities of 10^{10}-10^{12} cm^{-3}. An electron density log(n_e) = 11.2 is obtained from the Paschen-line convergence and the Inglis-Tellar relation. Column densities are obtained with the help of curves of growth by assuming uniform conditions in the cloud. These indicate a nearly solar composition. The CLOUDY code (Ferland, et al. Rev. Mex. Astron. Astroph. 49, 137, 213) is used to produce a model that predicts matching column densities of the dominant ions, the n = 3 level of hydrogen, the H-alpha strength, and the electron density (± 0.5 dex).

Monitoring Light Pollution on the Starlight Reserve of Montsec

NASA Astrophysics Data System (ADS)

Ribas, S. J.; Paricio, S.; Canal-Domingo, R.; Gustems, L.; Calvo, C. O.

2015-05-01

Montsec Mountains are a special protected place in Catalonia (NE of Iberian Peninsula). Since 2013 the site has been declared Starlight Reserve and Touristic Destination. In the last three years different projects took place in Montsec to evaluate the quality of night sky and the effects of Light Pollution of nearby (and not so nearby) municipalities. Using SQM techniques in RoadRunner configuration (installed on a car) we have evaluated all the region (1 600 km^2) and we determined the distribution of night sky brightness detecting some excellent areas with values around 21.5--22.0 mags. In addition we have evaluated the effects of the closest big city (Lleida with around 200 000 inhabitants) and we have estimated long distance effects of this city on the natural sky. The effect is detected on zenith up to 25 km away from the city. These data show the critical problem of the long-distance effects of LP on protected areas. To complete the monitoring of the region, a new SQM network is ongoing in cooperation with Parc Astronòmic Montsec and Catalan Service against Light Pollution. During 2014 six SQM permanent detectors are starting their measurements around the area of Montsec and major cities that affects this protected area. This data could be combined with meteorological data (clouds, humidity, etc) in some of the evaluation sites.

An Initial Meteoroid Stream Survey in the Southern Hemisphere Using the Southern Argentina Agile Meteor Radar (SAAMER)

NASA Technical Reports Server (NTRS)

Janches, D.; Hormaechea, J. L.; Brunini, C.; Hocking, W.; Fritts, D. C.

2013-01-01

We present in this manuscript a 4 year survey of meteor shower radiants utilizing the Southern Argentina Agile Meteor Radar (SAAMER). SAAMER, which operates at the southern most region of South America, is a new generation SKiYMET system designed with significant differences from typical meteor radars including high transmitted power and an 8-antenna transmitting array enabling large detected rates at low zenith angles. We applied the statistical methodology developed by Jones and Jones (Jones, J., Jones, W. [2006]. Month. Not. R. Astron. Soc. 367, 1050-1056) to the data collected each day and compiled the results into 1 composite representative year at 1 resolution in Solar Longitude. We then search for enhancements in the activity which last for at least 3 days and evolve temporally as is expected from a meteor shower. Using this methodology, we have identified in our data 32 shower radiants, two of which were not part of the IAU commission 22 meteor shower working list. Recently, SAAMER's capabilities were enhanced by adding two remote stations to receive meteor forward scatter signals from meteor trails and thus enable the determination of meteoroid orbital parameters. SAAMER started recording orbits in January 2012 and future surveys will focus on the search for unknown meteor streams, in particular in the southern ecliptic sky.

Gravastars in f (R ,T ) gravity

NASA Astrophysics Data System (ADS)

Das, Amit; Ghosh, Shounak; Guha, B. K.; Das, Swapan; Rahaman, Farook; Ray, Saibal

2017-06-01

We propose a unique stellar model under the f (R ,T ) gravity by using the conjecture of Mazur-Mottola [P. Mazur and E. Mottola, Report No. LA-UR-01-5067, P. Mazur and E. Mottola, Proc. Natl. Acad. Sci. USA 101, 9545 (2004), 10.1073/pnas.0402717101] which is known as gravastar and a viable alternative to the black hole as available in literature. This gravastar is described by the three different regions, viz., (I) Interior core region, (II) Intermediate thin shell, and (III) Exterior spherical region. The pressure within the interior region is equal to the constant negative matter density which provides a repulsive force over the thin spherical shell. This thin shell is assumed to be formed by a fluid of ultrarelativistic plasma and the pressure, which is directly proportional to the matter-energy density according to Zel'dovich's conjecture of stiff fluid [Y. B. Zel'dovich, Mon. Not. R. Astron. Soc. 160, 1 (1972), 10.1093/mnras/160.1.1P], does counterbalance the repulsive force exerted by the interior core region. The exterior spherical region is completely vacuum and assumed to be de Sitter spacetime which can be described by the Schwarzschild solution. Under this specification we find out a set of exact and singularity-free solution of the gravastar which presents several other physically valid features within the framework of alternative gravity.

Modeling Saturnshine in Cassini Images of the Rings

NASA Astrophysics Data System (ADS)

Dones, Henry C.; Weiss, J. W.; Porco, C. C.; DiNino, D.; Skinner, R.

2013-10-01

In some viewing geometries, such as large solar phase angles or small solar elevation angles, the light reflected by or transmitted through Saturn's rings can be dominated by Saturnshine, i.e., illumination of the rings by the planet. Saturnshine results in longitudinal variations in the reflectivity of the rings. In addition, Saturn's A Ring and, to a lesser extent, B Ring, show intrinsic longitudinal variations ("azimuthal asymmetry") due to self-gravity wakes. Any attempt to infer physical properties of ring particles and their spatial distribution using ring photometry must consider both Saturnshine and self-gravity wakes. "Ringshine," in turn, complicates photometry of Saturn itself [1]. We have improved the Saturnshine model in [2], which applies a ray-tracing code to N-body simulations of a patch of Saturn's rings, by incorporating measurements of the planet's reflectivity in Cassini images taken in a range of viewing geometries through a number of broadband filters. We will compare the results of our photometric model with measurements of the I/F of the main rings, and will attempt to constrain the intrinsic properties of ring particles, such as their coefficients of restitution in collisions and internal densities. We thank the Cassini project for support. [1] Skinner, R.W., and Weiss, J.W. (2011). http://serc.carleton.edu/cismi/undergrad_research/posters/52679.html [2] Porco, C.C., et al. (2008). Astron J. 136, 2172-2200

Rayleigh-Taylor Instability as the Reason for the Particle Acceleration and Plasma Heating in Solar Chromosphere

NASA Astrophysics Data System (ADS)

Stepanov, Alexander; Zaitsev, Valerii

New mechanism of electron acceleration in the solar chromosphere and chromospheric plasma heating is proposed. The main role in acceleration and heating belongs to the Rayleigh-Tailor instability. Ballooning mode of the instability develops at the chromospheric footpoints of a flare loop and deforms here the magnetic field. Thus the electric current flowing in the loop changes and an inductive electric field appears. This electric field is the reason for the acceleration of 300-500 keV electrons which do not escape from the chromosphere, providing the excitation of plasma waves and the heating of chromospheric plasma in situ. Observations with New Solar Telescope at Big Bear Solar Observatory (Ji et al. ApJ 750, L25, 2012) give us good evidences on the heating of chromospheric footpoints of coronal loops to the coronal temperatures as well as upward injection of hot plasma that excite the fine loops from the photosphere to the base of the corona. We discuss also other consequences of the Rayleigh-Taylor instability: non-thermal plasma emission at 212 and 405 GHz from the ionized chromosphere with the electron density as high as 10 (15) cm (-3) (Zaitsev et al. Astron.Lett. 39, 650, 2013), and the model of sub-second pulsations at THz observed by Kaufmann et al. (ApJ 697, 420, 2009).

On the correlation between the recent star formation rate in the Solar Neighbourhood and the glaciation period record on Earth

NASA Astrophysics Data System (ADS)

de la Fuente Marcos, R.; de la Fuente Marcos, C.

2004-11-01

Shaviv [New Astron. 8 (2003) 39; J. Geophys. Res. 108 (2003) 3] has shown evidence for a correlation between variations in the Galactic cosmic ray flux reaching Earth and the glaciation period record on Earth during the last 2 Gyr. If the flux of cosmic rays is mainly the result of Type II supernovae, an additional correlation between the star formation history of the Solar Neighbourhood and the timing of past ice ages is expected. Higher star formation rate implies increased cosmic ray flux and this may translate into colder climate through a rise in the average low altitude cloud cover. Here we reanalyze the correlation between this star formation history and the glaciation period record on Earth using a volume limited open cluster sample. Numerical modeling and recent observational data indicate that the correlation is rather strong but only if open clusters within 1.5 kpc from the Sun are considered. Under this constraint, our statistical analysis not only suggests a strong correlation in the timing of the events (enhanced star formation and glaciation episodes), but also in the severity and length of the episodes. In particular, the snowball Earth scenario appears to be connected with the strongest episode of enhanced star formation recorded in the Solar Neighbourhood during the last 2 Gyr.

Speckle interferometry at the OAN-SPM México: astrometry of double stars measured in 2011

NASA Astrophysics Data System (ADS)

Guerrero, C. A.; Orlov, V. G.; Borges Fernandes, M.; Ángeles, F.

2018-04-01

We present speckle interferometric measurements of binary stars performed during 2011 February and April with the 1.5-m telescope and during 2011 July and November with the 2.1-m telescope of the Observatorio Astronómico Nacional, San Pedro Mártir, México, focusing on objects from the Washington Double Star Catalog with separations less than 1 arcsec. Among these objects, we have been interested in performing a follow-up observation of new double stars discovered by Hipparcos. For these observations, we developed a new detector, which is a combination of CCD Watec 120N with a third generation image intensifier. This image intensifier allows us to perform near-infrared speckle interferometric observations for the first time. In this paper, we report 761 astrometric measurements of 478 pairs, with angular separations ranging from 0.09 to 2.61 arcsec. We found that 722 of our measured separations are smaller than 1 arcsec. We estimated a mean error in separation of 16 mas and 1.29° in position angle. In order to overcome the usual 180° ambiguity inherent to speckle measurements, we created a shift-and-add reconstructed image of each source, to establish the true quadrant of the secondary star. We confirmed 40 double stars discovered by Hipparcos and found 4 field stars resolved as interferometric pairs for the first time, with separations smaller than 0.60 arcsec.

The evolution of a Pluto-like system during the migration of the ice giants

NASA Astrophysics Data System (ADS)

Pires, Pryscilla; Giuliatti Winter, Silvia M.; Gomes, Rodney S.

2015-01-01

The planetary migration of the Solar System giant planets in the framework of the Nice model (Tsiganis, K., Gomes, R., Morbidelli, A., Levison, H.F. [2005]. Nature 435,459-461; Morbidelli, A., Levison, H.F., Tsiganis, K., Gomes, R. [2005]. Nature 435, 462-465; Gomes, R., Levison, H.F., Tsiganis, K., Morbidelli, A. [2005]. Nature 435, 466-469) creates a dynamical mechanism which can be used to explain the distribution of objects currently observed in the Kuiper belt (e.g., Levison, H.F., Morbidelli, A., Vanlaerhoven, C., Gomes, R., Tsiganis, K. [2008]. Icarus 196, 258-273). Through this mechanism the planetesimals within the disk, heliocentric distance ranging from beyond Neptune's orbit to approximately 34 AU, are delivered to the belt after a temporary eccentric phase of Uranus and Neptune's orbits. We reproduced the mechanism proposed by Levison et al. to implant bodies into the Kuiper belt. The capture of Pluto into the external 3:2 mean motion resonance with Neptune is associated with this gravitational scattering model. We verified the existence of several close encounters between the ice giants and the planetesimals during their outward radial migration, then we believe that the analysis of the dynamical history of the plutonian satellites during this kind of migration is important, and would provide some constrains about their place of formation - within the primordial planetesimal disk or in situ. We performed N-body simulations and recorded the trajectories of the planetesimals during close approaches with Uranus and Neptune. Close encounters with Neptune are the most common, reaching approximately 1200 in total. A Pluto similarly sized body assumed the hyperbolic trajectories of the former primordial planetesimal with respect to those giant planets. We assumed the current mutual orbital configuration and sizes for Pluto's satellites, then we found that the rate of destruction of systems similar to that of Pluto with closest approaches to Uranus or Neptune <0.10 AU is 40%, i.e. these close approaches can lead to ejections of satellites or to changes in the satellites eccentricities at least 1 order of magnitude larger than the currently observed. However, we also found that the number of closest approaches which the minimum separation to Uranus or Neptune <0.10 AU is negligible, reaching 6%. In the other 60% of close encounter histories with closest approaches >0.10 AU, none of the systems have been destroyed. The latter sample concentrates 94% of closest approaches with the ice giants. Recall that throughout the early history of the Solar System giant impacts were common (McKinnon, W.B. [1989]. Astrophys. J. 344, L41-L44; Stern, A. [1991]. Icarus 90; Canup, R.M. [2005]. Science 307, 546-550). Also, impacts capable of forming a binary like Pluto-Charon can occur possibly prior to 0.5-1 Gyr (Kenyon, S.J., Bromley, B.C. [2014]. Astron. J. 147, 8), and small satellites such as Nix and Hydra can grow in debris from the giant impact (e.g., Canup, R.M. [2011]. Astron. J. 141, 35). Thus, we conclude that if Pluto and its satellites were emplaced into the KB from lower heliocentric orbits, then the Pluto system could survive the encounters that may have happened for emplacement of the Plutinos through the mechanism proposed by Levison et al.

Kinematic and chemical study of planetary nebulae and H II regions in NGC 3109

NASA Astrophysics Data System (ADS)

Flores-Durán, S. N.; Peña, M.; Ruiz, M. T.

2017-05-01

Aims: We present high-resolution spectroscopy of a number of planetary nebulae (PNe) and H II regions distributed along the dwarf irregular galaxy NGC 3109 and compare their kinematical behavior with that of H I data. We aim to determine if there is a kinematical connection among these objects. We also aim to determine the chemical composition of some PNe and H II regions in this galaxy and discuss it in comparison with stellar evolution models. Methods: Data for eight PNe and one H II region were obtained with the high-resolution spectrograph Magellan Inamori Kyocera Echelle (MIKE) at Las Campanas Observatory, Chile. Data for three PNe, six compact H II regions, and nine knots or clumps in extended H II regions were obtained with the high-resolution spectrograph Manchester Echelle Spectrometer (MES) attached to the 2.1m telescope at the Observatorio Astronómico Nacional, SPM, B.C., Mexico. An additional object was obtained from The SPM Catalogue of Extragalactic Planetary Nebulae. Thus, in total we have high-quality data for nine of the 20 PNe detected in this galaxy, and many H II regions. In the wavelength calibrated spectra, the heliocentric radial velocities were measured with a precision better than 7.8 km s-1. Data for blue supergiant stars were collected from the literature to be included in the analysis. The heliocentric radial velocities of the different objects were compared to the velocities of the H I disk at the same position. Physical conditions and ionic abundances of PNe and H II regions were obtained from the emission lines, and we used recent ionization correction factors to derive the total chemical abundances. Results: From the analysis of radial velocities we found that H II regions in NGC 3109 share the kinematics of the H I disk at the same projected position with very low dispersion in velocities. Blue supergiant stars and PNe rotate in the same direction as the H I disk but these objects have much larger dispersion; this larger dispersion is possibly because these objects belong to a different population that is located in the central stellar bar reported for this galaxy. From the chemical abundance determinations we demonstrate that PNe are enriched in O and Ne. The average O abundance in H II regions is 12 + log O/H = 7.74 ± 0.09 and PNe show significantly higher oxygen abundance by 0.43 dex in average. Ne abundance are about three times larger in PNe than in H II regions. This is a very important result showing that because of the low metallicity in the galaxy, O and Ne in PNe have been enriched by their progenitors in nucleosynthesis processes and brought to the surface during third dredge-up events. Our PN abundances are better reproduced by some nonstandard stellar evolution models for a metallicity of Z = 0.001, similar to the metallicity of H II regions. Abundances in H II regions show no metallicity gradient in this galaxy. We discuss a possible connection between the kinematics and chemistry. Based on data obtained at Las Campanas Observatory, Carnegie Institution, Chile.Based on data collected at the Observatorio Astronómico Nacional, SPM, B.C., Mexico.

Analysis on establishing Chang'E-3 landing site as a reflectance calibration target

NASA Astrophysics Data System (ADS)

Liu, Bin; Fu, Xiaohui; Zeng, Xingguo; Yao, Meijuan; Zhang, Hongbo; Su, Yan; Zhao, Shu; Xue, Xiping; Li, Chunlai; Zou, Yongliao

2015-04-01

Recent lunar orbital observations suggested that the surface reflectance calculated based on the Apollo 16 standard area and Apollo 16 sample laboratory measurement is significantly different from its true value [1-3], one reason is the composition and maturity differences between the 62231 sampling site and the Apollo 16 standard site existed, the other reason is the physical properties of the returned lunar sample, such as porosity, have been changed during the sampling operations. So more new standard targets on the Moon, besides the widely used Apollo 16 area, are needed for imaging spectrometers on lunar missions to improve their reflectance calibration accuracies. The Chang'E-3 VIS/NIR Imaging Spectrometer (VNIS), which is just fixed at the front of the Yutu rover [4], equipped with a white spectralon panel as reflectance calibration standard, can perform in situ multispectral observations around the Chang'E-3 landing site without altering the physical and mineralogical natures of lunar soils. Therefore, it provides an opportunity to establish a new reliable standard target for in-flight reflectance calibration. The reflectance calibration target should be compositional homogeneous, the topography of which must be flat, and the reflectance should be identical with no nearby units of other different materials. As we have known, Chang'e-3 probe landed on the Mare Imbrium basin in the east part of Sinus Iridum, the landing site is relatively flat at a spatial coverage of ~660km2, and this region belongs to Eratosthenian low-Ti/high-Ti mare basalts [5-6]. According to much higher resolution topography data, elemental data and reflectance data of Chang'E-2 and Chang'E-3[7-8], we preliminary analyse the possibility on establishing Chang'E-3 landing site as a reflectance calibration target. Firstly, the overall terrain of the 4 km×4 km area around the landing site is flat, but there are still three bigger craters existed. Secondly, the composition on Chang'E-3 landing site is homogeneous according to the two detection results of APXS on elements in lunar soil. At last, we compare and scale the four detection points' reflectance of VNIS, which demonstrate that the reflectance of the landing site are quite similar at the spectral range 450nm-1750nm, but differences still existed beyond 1750nm. Future work is still needed, such as photometric calibration of VNIS data, and errors estimation on reflectance calculation. Besides, the location and spatial coverage of the reflectance calibration target should be determined and its calibration accuracy should be evaluated. Acknowledgements: This work was supported by the National Natural Science Foundation of China (No.11403049 and 41490633). References: [1] J. K. Hillier et al., (1999) Icarus, 141, 205-225. [2] M. Ohtake et al., (2010) Space Sci. Rev., 154, 57-77. [3] M. Ohtake et al., (2010) Icarus, 226, 364-374. [4] B. Liu et al., (2014) RAA, 14, 1674. [5] L. Qiao et al., (2013) Sci Sin-Phys Mech Astron, 43, 1370-1386. [6] J. N. Zhao et al., (2014) Sci China-Phys Mech Astron, 57, 569-576. [7] C. L. Li et al., (2014) RAA, 14, 1514. [8] X. H. Fu et al., (2014) RAA, 14, 1595.

Eventos de Desconexão no Cometa P/Halley sob a Ótica do Modelo de Reconexão Magnética

NASA Astrophysics Data System (ADS)

Voelzke, M. R.; Matsuura, O. T.

1998-08-01

531 imagens contidas no The International Halley Watch Atlas of Large-Scale Phenomena (Brandt et al., 1992) cobrindo o período de setembro de 1985 a julho de 1986 foram analisadas visando identificar, caracterizar as propriedades e correlacionar estruturas morfológicas da cauda de plasma do cometa P/Halley. A análise revelou 47 eventos de desconexão (DEs) (Niedner & Brandt, 1979; Jockers, 1985; Celnik et al., 1988; Delva et al., 1991). A análise completa de todas as imagens encontra-se publicada em Voelzke & Matsuura, 1998. A distribuição dos DEs na distância heliocêntrica apresenta um caráter bimodal possivelmente associado com a distribuição espacial das fronteiras de setor magnético do meio interplanetário. Os 47 DEs fotografados em 47 imagens distintas permitiram determinar 19 origens de DEs, ou seja, o instante em que supostamente o cometa cruzou a fronteira entre setores magnéticos do vento solar. Tais dados cometários foram comparados com dados do vento solar provenientes de medidas realizadas in situ pelas sondas IMP-8, ICE e PVO, que mediram a variação da velocidade do vento solar, da densidade e da pressão dinâmica durante o intervalo analisado. Os dados destas sondas espaciais em conjunto com os da sonda Vega 1 foram usados para determinar o tempo das passagens do lençol de corrente. Com base nos dados das sondas foram calculadas as coordenadas heliográficas retroativas do lençol de corrente na "superfície fonte" dos mapas sinóticos do campo magnético de Hoeksema, 1989. O cálculo retroativo é feito através de um modelo simples de expressão do vento solar com velocidade uniforme, sendo considerada a co-rotação da magnetosfera com o Sol. Este trabalho apresenta os resultados desta comparação e a análise cinemática da origem dos DEs, determinada sob a hipótese que o plasma desconectado de um dado DE afasta-se com velocidade constante do núcleo cometário (Voelzke & Matsuura, 1998) e compara esta análise com outras que determinam o tempo de desconexão a partir de um movimento linear constantemente acelerado (Yi et al., 1994). A velocidade de um DE para outro varia enormemente. - Brandt, J.C., Niedner, M.B.Jr. and Rahe, J., (1992) The International Halley Watch Atlas of Large-Scale Phenomena (printed by: Johnson Printing Co., Boulder, CO), University of Colorado-Boulder. - Celnik, W.E., Koczet, P., Schlosser, W., Schulz, R., Svejda, P. and Weissbauer, K., (1988) Astron. Astrophys. Suppl. Ser. 72, 89. - Delva, M., Schwingenschuh, K., Niedner, M.B.Jr. and Gringauz, K.I., (1991) Planet. Space Sci. 39, Number 5, 697. - Hoeksema, J.T., (1989) Adv. Space Res. 9, 141. - Jockers, K., (1985) Astron. Astrophys. Suppl. Ser. 62, 791. - Niedner, M.B.Jr. and Brandt, J.C., (1979) Astrophys. J. 234, 723. - Voelzke, M.R. and Matsuura, O.T., (1988) Planet. Space Sci. 46, 835. - Yi, Y., Caputo, M.F. and Brandt, J.C., (1994) Planet. Space Sci. 42, Number 9, 705.

To Mercury dynamics

NASA Astrophysics Data System (ADS)

Barkin, Yu. V.; Ferrandiz, J. M.

Present significance of the study of rotation of Mercury considered as a core-mantle system arises from planned Mercury missions. New high accurate data on Mercury's structure and its physical fields are expected from BepiColombo mission (Anselmi et al., 2001). Investigation of resonant rotation of Mercury, begun by Colombo G. (1966), will play here main part. New approaches to the study of Mercury dynamics and the construction of analytical theory of its resonant rotation are suggested. Within these approaches Mercury is considered as a system of two non-spherical interacting bodies: a core and a mantle. The mantle of Mercury is considered as non-spherical, rigid (or elastic) layer. Inner shell is a liquid core, which occupies a large ellipsoidal cavity of Mercury. This Mercury system moves in the gravitational field of the Sun in resonant traslatory-rotary regime of the resonance 3:2. We take into account only the second harmonic of the force function of the Sun and Mercury. For the study of Mercury rotation we have been used specially designed canonical equations of motion in Andoyer and Poincare variables (Barkin, Ferrandiz, 2001), more convenient for the application of mentioned methods. Approximate observational and some theoretical evaluations of the two main coefficients of Mercury gravitational field J_2 and C22 are known. From observational data of Mariner-10 mission were obtained some first evaluations of these coefficients: J_2 =(8± 6)\\cdot 10-5(Esposito et al., 1977); J_2 =(6± 2)\\cdot 10-5and C22 =(1.0± 0.5)\\cdot 10-5(Anderson et al., 1987). Some theoretical evaluation of ratio of these coefficients has been obtained on the base of study of periodic motions of the system of two non-spherical gravitating bodies (Barkin, 1976). Corresponding values of coefficients consist: J_2 =8\\cdot 10-5and C22 =0.33\\cdot 10-5. We have no data about non-sphericity of inner core of Mercury. Planned missions to Mercury (BepiColombo and Messenger) promise to obtain new and accurate data about dynamics and structure of this planet (Anselmi et al., 2001). There are also some evaluations of moments of inertia Mercury and its core: C/(mR^2)=0.35, C_m /C=0.5± 0.07, (Peal, 1996). Here C and C_m are the moments of inertia of the full Mercury and of its core, m and R is a mass and a mean radius of Mercury. Based on two methods, we consider the rotation of Mercury in the gravitational field of the Sun. First method of perturbation has been effectively applied to the construction of a rotational theory of the Earth for its models as two or three layer celestial body moving in gravitational fields of the Moon, Sun and planets in wide set of papers ranging in 1999-2001 years of Ferrandiz J.M. and Getino J.(2001). Some generalization of this Hamiltonian formalism on the case of cavity (core) with arbitrary dynamical and geometrical oblateness has been obtained in a paper (Barkin, Ferrandiz, 2001). Another method is an analytical method of construction of the resonant rotational motion of synchronous satellites and Mercury, considered as non-spherical rigid bodies. This method has been applied earlier to construction of an analytical theory of rotation of the Moon considered as rigid non-spherical body (Barkin, 1989). Here we modified these methods to apply them to the study of the resonant rotation of a two-layer Mercury. By this we use very effective for the application of perturbation methods and dynamical geometrical illustration of canonical equations in Andoyer and Poincare variables. Main resonant properties of Mercury motion were been described first as generalized Cassini's laws (Colombo, 1966). But Colombo and some anothers scientists (Peal, 1969; Beletskii, 1972; Ward, 1975 and oth.) considered Mercury as rigid non-spherical body sometimes taking into account tidal deformation. Here we have been obtained and formulated these laws and their generalization for a two-layer model of Mercury. On the next step we have evaluated frequencies of free oscillations of core-mantle system of Mercury. Based on the mentioned data about Mercury (Barkin, 1976) we have been obtained the following model values of moments of inertia of the Mercury and for its core:A=0.3499534, B=0.3499667, C=0.35; A_c =B_c =0.1749767, C_c =0.175000 (1quad unit=mR^2, m and R is a mass and a mean radius of the Mercury). Here we used model values for moments of inertia of the core using also some analogy with axysimmetrical model of the core of the Moon from paper Williams et al. (2003). Corresponding periods of free oscillations were determined on the base specially constructed equations of developed theory. They are equal: T_1 =260543\\cdot Trot years and T_2 =0.999468\\cdot Trot (Trot =58.6462 days is a period of Mercury rotation). Last period determines long period of relative oscillation of the core and mantleT_r . The mentioned periods are equal: T_1 =713years and T_r =302years. Barkin's work was accepted by grant SAB2000-0235 of Ministry of Education of Spain and partially by grants AYA2001-0787 and ESP2001-4533 is also aknowledged. References Anderson J.D., Colombo G., Esposito P.B., Lau E.L., Trager G.B.: 1987. The mass, gravity field and ephemeris of Mercury. Icarus, pp. 337-349. Anselmi A., Scoon G.E.N.: 2001. BepiColombo, ESA's Mercury Cornerstone mission. Planetary and Space Science, 49, pp. 1409-1420. Barkin Yu.V.: 1976. About plane periodic motions of a rigid body in gravitational field of a sphere. Astron. J., v. 53, pp. 1110-1119. In Russian. Barkin Yu.V.: 1987. An analytical theory of the lunar rotational motion. Proc. Int. Symp. ``Figure and Dynamics of Earth, Moon and Planets'' (September 1986, Prague). Monograph series of VUGTK. Prague. Pp. 657-677. Beletskij V.V.: 1972. Resonance rotation of celestial bodies and Cassini's laws. Celestial Mechanics, v.6, N3, pp. 356-378. Colombo G.: 1966. Cassini's second and third laws, Astron. J., 71, p. 891. Esposito P.B., Anderson J.D., Ng A.T.Y.: 1977. Experimental determination of Mercury's mass and oblateness. Space Res., v. 17, pp. 639-644. Getino J., Ferrandiz J.M.: 2001. Forced nutations of a two-layer earth model. Monthly Notices of the Royal Astronomical Society, v. 322, Iss. 4, pp. 785-799. Ferrandiz J.M., Barkin Yu.V.: 2001. Dynamics of the rotational motion of the planet with the elastic mantle, liquid core and with the changeable external shell. Proc. of Intern. Conf. ``AstroKazan-2001''. Astronomy and geodesy in new millennium (24-29 September 2001), Kazan State University: Publisher ``DAS'', 2001, p. 123-129. Peal S.J.: 1969. Generalized Cassini's laws, Astron. J., 74, p. 483. Peal S.J.: 1996. Characterizing the core of Mercury. LPS XXVII, 1168. Ward W.R.: 1975. Tidal friction and generalized Cassini's laws in the solar system. Astron. Journal, Vol. 80, N 1, pp. 64-70.

Determinacion de Caracteristicas Opticas del Telescopio OAN150

NASA Astrophysics Data System (ADS)

Galan, M. J.; Cobos, F. J.

1987-05-01

En el Observatorio de Calar Alto, en Almería, España, está ubicado un telescopio de 15O-cms de diámetro -construído por REOSC- perteneciente al Observatorio Astronómico Nacional, con sede en Madrid, España. La infraestructura técnica del OAN ha sido tradicionalmente débil y actualmente se está haciendo un esfuerzo por fortalecerla. Existe una información muy limitada del telescopio en general; de su óptica en particular se conocían los valores de los parámetros principales pero sin saber si éstos corresponden a valores teóricos ó de construcción. Por ello se consideró necesario iniciar una investigación para conocer en detalle los valores reales de las componentes ópticas del telescopio, obteniéndose algunos resultados de interés. El primario del telescopio OANl5O es aproximadamente F/3 y el siste ma en su conjunto es F/8.2, con su sistema corrector de campo. En términos generales, la imagen es satisfactoria en todo el campo y, sin sistema corrector, la imagen axial también es buena. En un futuro muy cercano se piensa diseñar instrumentación adicional para este telescopio. Conocer con mayor precisión sus características puede ser de gran utilidad para tal fin, pues se efectúan los cálculos considerando conjuntamente al telescopio y al instrumento.

Inclined asymmetric librations in exterior resonances

NASA Astrophysics Data System (ADS)

Voyatzis, G.; Tsiganis, K.; Antoniadou, K. I.

2018-04-01

Librational motion in Celestial Mechanics is generally associated with the existence of stable resonant configurations and signified by the existence of stable periodic solutions and oscillation of critical (resonant) angles. When such an oscillation takes place around a value different than 0 or π , the libration is called asymmetric. In the context of the planar circular restricted three-body problem, asymmetric librations have been identified for the exterior mean motion resonances (MMRs) 1:2, 1:3, etc., as well as for co-orbital motion (1:1). In exterior MMRs the massless body is the outer one. In this paper, we study asymmetric librations in the three-dimensional space. We employ the computational approach of Markellos (Mon Not R Astron Soc 184:273-281, https://doi.org/10.1093/mnras/184.2.273, 1978) and compute families of asymmetric periodic orbits and their stability. Stable asymmetric periodic orbits are surrounded in phase space by domains of initial conditions which correspond to stable evolution and librating resonant angles. Our computations were focused on the spatial circular restricted three-body model of the Sun-Neptune-TNO system (TNO = trans-Neptunian object). We compare our results with numerical integrations of observed TNOs, which reveal that some of them perform 1:2 resonant, inclined asymmetric librations. For the stable 1:2 TNO librators, we find that their libration seems to be related to the vertically stable planar asymmetric orbits of our model, rather than the three-dimensional ones found in the present study.

Discovery of a [WO] central star in the planetary nebula Th 2-A

NASA Astrophysics Data System (ADS)

Weidmann, W. A.; Gamen, R.; Díaz, R. J.; Niemela, V. S.

2008-09-01

Context: About 2500 planetary nebulae are known in our Galaxy but only 224 have central stars with reported spectral types in the Strasbourg-ESO Catalogue of Galactic Planetary Nebulae (Acker et al. 1992; Acker et al. 1996). Aims: We have started an observational program aiming to increase the number of PN central stars with spectral classification. Methods: By means of spectroscopy and high resolution imaging, we identify the position and true nature of the central star. We carried out low resolution spectroscopic observations at CASLEO telescope, complemented with medium resolution spectroscopy performed at Gemini South and Magellan telescopes. Results: As a first outcome of this survey, we present for the first time the spectra of the central star of the PN Th 2-A. These spectra show emission lines of ionized C and O, typical in Wolf-Rayet stars. Conclusions: We identify the position of that central star, which is not the brightest one of the visual central pair. We classify it as of type [WO 3]pec, which is consistent with the high excitation and dynamical age of the nebula. Based on data collected at (i) the Complejo Astronómico El Leoncito (CASLEO), which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina y Universidades Nacionales de La Plata, Córdoba y San Juan, Argentina; (ii) the 6.5 m Magellan Telescopes at Las Campanas Observatory, Chile; (iii) the 8 m Gemini South Telescope, Chile.

Venus Cloud Morphology and Motions from Ground-based Images at the Time of the Akatsuki Orbit Insertion

NASA Astrophysics Data System (ADS)

Sánchez-Lavega, A.; Peralta, J.; Gomez-Forrellad, J. M.; Hueso, R.; Pérez-Hoyos, S.; Mendikoa, I.; Rojas, J. F.; Horinouchi, T.; Lee, Y. J.; Watanabe, S.

2016-12-01

We report Venus image observations around the two maximum elongations of the planet at 2015 June and October. From these images we describe the global atmospheric dynamics and cloud morphology in the planet before the arrival of JAXA’s Akatsuki mission on 2015 December 7. The majority of the images were acquired at ultraviolet wavelengths (380-410 nm) using small telescopes. The Venus dayside was also observed with narrowband filters at other wavelengths (890 nm, 725-950 nm, 1.435 μm CO2 band) using the instrument PlanetCam-UPV/EHU at the 2.2 m telescope in Calar Alto Observatory. In all cases, the lucky imaging methodology was used to improve the spatial resolution of the images over the atmospheric seeing. During the April-June period, the morphology of the upper cloud showed an irregular and chaotic texture with a well-developed equatorial dark belt (afternoon hemisphere), whereas during October-December the dynamical regime was dominated by planetary-scale waves (Y-horizontal, C-reversed, and ψ-horizontal features) formed by long streaks, and banding suggesting more stable conditions. Measurements of the zonal wind velocity with cloud tracking in the latitude range from 50°N to 50°S shows agreement with retrievals from previous works. Partially based on observations obtained at Centro Astronómico Hispano Alemán, Observatorio de Calar Alto MPIA-CSIC, Almería, Spain.

Torques on Sedna by a Putative Massive Body in the Oort Cloud

NASA Astrophysics Data System (ADS)

Matese, J. J.; Lissauer, J. J.

2004-11-01

Morbidelli and Levison (arXiv:astro-ph/0403358) consider various scenarios for the origin of the orbits of Sedna-like objects. The only one which they find to give satisfactory results is the passage of a low-velocity solar-mass star at about 800 AU during the early solar environment. They observe that creating ``extended scattered disk objects" (in which the largest orbits also have the largest q) requires a perturbation ``from the outside", but do not discuss the possibility that the external perturbation could come from a Jovian-mass wide-binary solar companion. We investigate the parameter space of such an object which would adiabatically detach Sedna from Neptune's dominance with qS (0) ≈ 30 AU, aS = 531 AU. Demanding that the detached osculating orbit satisfy qmin>15 AU, qmax >75 AU, the companion's mass and orbit parameters (m, a, e) that can produce n osculation cycles in a time Δ t are $(m)/(MJup)≈ n/tssΔ t (a)/(6000 AU)3(1-e^2)3/2. A wide-binary companion could also be the source of the 7^° misalignment of the ecliptic plane normal with the solar spin axis (Hogg, Quinlan and Tremaine 1991, Astron. J. 101(6), 2274), but only if n≈ 100$. The solar impulse considered by Morbidelli and Levison would produce an ecliptic plane tilt only 1/100 of that observed. J.J.L. received support from Planetary Geology and Geophysics Grant 344-30-1L.

Modern Paradigm of Star Formation in the Galaxy

NASA Astrophysics Data System (ADS)

Sobolev, A. M.

2017-06-01

Understanding by the scientific community of the star formation processes in the Galaxy undergone significant changes in recent years. This is largely due to the development of the observational basis of astronomy in the infrared and submillimeter ranges. Analysis of new observational data obtained in the course of the Herschel project, by radio interferometer ALMA and other modern facilities significantly advanced our understanding of the structure of the regions of star formation, young stellar object vicinities and provided comprehensive data on the mass function of proto-stellar objects in a number of star-forming complexes of the Galaxy. Mapping of the complexes in molecular radio lines allowed to study their spatial and kinematic structure on the spatial scales of tens and hundreds of parsecs. The next breakthrough in this field can be achieved as a result of the planned project “Spektr-MM” (Millimetron) which implies a significant improvement in angular resolution and sensitivity. The use of sensitive interferometers allowed to investigate the details of star formation processes at small spatial scales - down to the size of the solar system (with the help of the ALMA), and even the Sun (in the course of the space project “Spektr-R” = RadioAstron). Significant contribution to the study of the processes of accretion is expected as a result of the project “Spektr-UV” (WSO-UV = “World Space Observatory - Ultraviolet”). Complemented with significant theoretical achievements obtained observational data have greatly promoted our understanding of the star formation processes.

Observações no âmbito dos "additional programs" do satélite COROT

NASA Astrophysics Data System (ADS)

Janot Pacheco, E.

2003-08-01

O satélite Fraco-europeu COROT fará fotometria de altissima precisão (pretende-se atingir uma parte em um milhão), grande campo (3x3 graus) e por longos períodos, de duas regiões pré-determinadas do céu, com 10 graus de raio. Suas finalidades básicas serão estudos em sismologia estelar e a procura de exoplanetas. A comunidade astronômica brasileira participará dessa missão espacial, com direitos iguais aos dos parceiros europeus. Isso se deve a que o satélite utilizará a estação de recepção de dados de Natal (INPE), 5 a 6 brasileiros participarão das equipes de software e cientistas do país atuarão na fase de pré-lançamento. Apresentamos nesta comunicação sugestões para a preparação de propostas de observações com COROT, no âmbito dos Programas Adicionais, que contemplam outros projetos que não de sismologia ou exoplanetas. As últimas definições técnicas e decisões tomadas na 4th Corot Week de junho último serão igualmente apresentadas, em particular quanto às regiões de observação escolhidas e quanto aos procedimentos a seguir para se propor observações.

Espectroscopía Espacial en el IR-Lejano

NASA Astrophysics Data System (ADS)

Goicoechea, Javier R.; Cernicharo, J.

Debido a la opacidad atmosférica, el dominio IR--lejano del espectro electromagnético ha sido la última ventana en ser utilizada por la Astrofísica Molecular. El potencial que supone abrir este nuevo rango de frecuencias a través de la espectroscopía molecular ha comenzado a ser explotado con el Infrared Space Observatory (ISO). La sensibilidad de la instrumentación embarcada en dicho satélite no tiene comparación alguna con las escasas misiones espaciales, o a bordo de aviones, realizadas con anterioridad a su lanzamiento. En particular, casi todo el rango operativo de ISO en el IR--lejano no había sido explorado. El espectro IR--lejano de las fuentes más representativas de la galaxia era desconocido y los principales emisores de radiación, las moléculas, estaban por identificar. Las observaciones en el IR--lejano están especialmente indicadas para el estudio del gas caliente en las nubes moleculares del medio interestelar y en el interior de las envolturas circunestelares alrededor de estrellas evolucionadas. Algunas de estas fuentes; Sgr B2 en el Centro Galáctico y las Proto--Nebulosas Planetarias, constituyen uno de los objetos más paradigmáticos en nuestra comprensión de la complejidad química de La Galaxia. En esta contribución se presentan los resultados espectroscópicos más importantes de algunas de estas fuentes astronómicas.

L^1 -optimality conditions for the circular restricted three-body problem

NASA Astrophysics Data System (ADS)

Chen, Zheng

2016-11-01

In this paper, the L^1 -minimization for the translational motion of a spacecraft in the circular restricted three-body problem (CRTBP) is considered. Necessary conditions are derived by using the Pontryagin Maximum Principle (PMP), revealing the existence of bang-bang and singular controls. Singular extremals are analyzed, recalling the existence of the Fuller phenomenon according to the theories developed in (Marchal in J Optim Theory Appl 11(5):441-486, 1973; Zelikin and Borisov in Theory of Chattering Control with Applications to Astronautics, Robotics, Economics, and Engineering. Birkhäuser, Basal 1994; in J Math Sci 114(3):1227-1344, 2003). The sufficient optimality conditions for the L^1 -minimization problem with fixed endpoints have been developed in (Chen et al. in SIAM J Control Optim 54(3):1245-1265, 2016). In the current paper, we establish second-order conditions for optimal control problems with more general final conditions defined by a smooth submanifold target. In addition, the numerical implementation to check these optimality conditions is given. Finally, approximating the Earth-Moon-Spacecraft system by the CRTBP, an L^1 -minimization trajectory for the translational motion of a spacecraft is computed by combining a shooting method with a continuation method in (Caillau et al. in Celest Mech Dyn Astron 114:137-150, 2012; Caillau and Daoud in SIAM J Control Optim 50(6):3178-3202, 2012). The local optimality of the computed trajectory is asserted thanks to the second-order optimality conditions developed.

The stability of stratified spatially periodic shear flows at low Péclet number

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garaud, Pascale, E-mail: pgaraud@ucsc.edu; Gallet, Basile; Bischoff, Tobias

2015-08-15

This work addresses the question of the stability of stratified, spatially periodic shear flows at low Péclet number but high Reynolds number. This little-studied limit is motivated by astrophysical systems, where the Prandtl number is often very small. Furthermore, it can be studied using a reduced set of “low-Péclet-number equations” proposed by Lignières [“The small-Péclet-number approximation in stellar radiative zones,” Astron. Astrophys. 348, 933–939 (1999)]. Through a linear stability analysis, we first determine the conditions for instability to infinitesimal perturbations. We formally extend Squire’s theorem to the low-Péclet-number equations, which shows that the first unstable mode is always two-dimensional. Wemore » then perform an energy stability analysis of the low-Péclet-number equations and prove that for a given value of the Reynolds number, above a critical strength of the stratification, any smooth periodic shear flow is stable to perturbations of arbitrary amplitude. In that parameter regime, the flow can only be laminar and turbulent mixing does not take place. Finding that the conditions for linear and energy stability are different, we thus identify a region in parameter space where finite-amplitude instabilities could exist. Using direct numerical simulations, we indeed find that the system is subject to such finite-amplitude instabilities. We determine numerically how far into the linearly stable region of parameter space turbulence can be sustained.« less

Polarimetric purity and the concept of degree of polarization

NASA Astrophysics Data System (ADS)

Gil, José J.; Norrman, Andreas; Friberg, Ari T.; Setälä, Tero

2018-02-01

The concept of degree of polarization for electromagnetic waves, in its general three-dimensional version, is revisited in the light of the implications of the recent findings on the structure of polarimetric purity and of the existence of nonregular states of polarization [J. J. Gil et al., Phys Rev. A 95, 053856 (2017), 10.1103/PhysRevA.95.053856]. From the analysis of the characteristic decomposition of a polarization matrix R into an incoherent convex combination of (1) a pure state Rp, (2) a middle state Rm given by an equiprobable mixture of two eigenstates of R, and (3) a fully unpolarized state Ru -3 D, it is found that, in general, Rm exhibits nonzero circular and linear degrees of polarization. Therefore, the degrees of linear and circular polarization of R cannot always be assigned to the single totally polarized component Rp. It is shown that the parameter P3 D proposed formerly by Samson [J. C. Samson, Geophys. J. R. Astron. Soc. 34, 403 (1973), 10.1111/j.1365-246X.1973.tb02404.x] takes into account, in a proper and objective form, all the contributions to polarimetric purity, namely, the contributions to the linear and circular degrees of polarization of R as well as to the stability of the plane containing its polarization ellipse. Consequently, P3 D constitutes a natural representative of the degree of polarimetric purity. Some implications for the common convention for the concept of two-dimensional degree of polarization are also analyzed and discussed.

Integrated spectral properties of 7 galactic open clusters

NASA Astrophysics Data System (ADS)

Ahumada, A. V.; Clariá, J. J.; Bica, E.; Piatti, A. E.

2000-01-01

This paper presents flux-calibrated integrated spectra in the range 3600-9000 Ä for 7 concentrated, relatively populous Galactic open clusters. We perform simultaneous estimates of age and foreground interstellar reddening by comparing the continuum distribution and line strengths of the cluster spectra with those of template cluster spectra with known parameters. For five clusters these two parameters have been determined for the first time (Ruprecht 144, BH 132, Pismis 21, Lyng\\aa 11 and BH 217), while the results here derived for the remaining two clusters (Hogg 15 and Melotte 105) show very good agreement with previous studies based mainly on colour-magnitude diagrams. We also provide metallicity estimates for six clusters from the equivalent widths of CaII triplet and TiO features. The present cluster sample improves the age resolution around solar metal content in the cluster spectral library for population synthesis. We compare the properties of the present sample with those of clusters in similar directions. Hogg 15 and Pismis 21 are among the most reddened clusters in sectors centered at l = 270o and l = 0o, respectively. Besides, the present results would favour an important dissolution rate of star clusters in these zones. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina.

Near infrared photometric and optical spectroscopic study of 22 low mass star clusters embedded in nebulae

NASA Astrophysics Data System (ADS)

Soares, J. B.; Bica, E.; Ahumada, A. V.; Clariá, J. J.

2008-02-01

Aims:Among the star clusters in the Galaxy, those embedded in nebulae represent the youngest group, which has only recently been explored. The analysis of a sample of 22 candidate embedded stellar systems in reflection nebulae and/or HII environments is presented. Methods: We employed optical spectroscopic observations of stars in the directions of the clusters carried out at CASLEO (Argentina) together with near infrared photometry from the 2MASS catalogue. Our analysis is based on source surface density, colour-colour diagrams and on theoretical pre-main sequence isochrones. We take into account the field star contamination by carrying out a statistical subtraction. Results: The studied objects have the characteristics of low mass systems. We derive their fundamental parameters. Most of the cluster ages are younger than 2 Myr. The studied embedded stellar systems in reflection nebulae and/or HII region complexes do not have stars of spectral types earlier than B. The total stellar masses locked in the clusters are in the range 20-220 M⊙. They are found to be gravitationally unstable and are expected to dissolve in a timescale of a few Myr. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina.

Photometric and spectroscopic study of low mass embedded star clusters in reflection nebulae

NASA Astrophysics Data System (ADS)

Soares, J. B.; Bica, E.; Ahumada, A. V.; Clariá, J. J.

2005-02-01

An analysis of the candidate embedded stellar systems in the reflection nebulae vdBH-RN 26, vdBH-RN} 38, vdBH-RN} 53a, GGD 20, ESO 95-RN 18 and NGC 6595 is presented. Optical spectroscopic data from CASLEO (Argentina) in conjunction with near infrared photometry from the 2MASS Point Source Catalogue were employed. The analysis is based on source surface density, colour-colour and colour-magnitude diagrams together with theoretical pre-main sequence isochrones. We take into account the field population affecting the analysis by carrying out a statistical subtraction. The fundamental parameters for the stellar systems were derived. The resulting ages are in the range 1-4 Myr and the objects are dominated by pre-main sequence stars. The observed masses locked in the clusters are less than 25 M⊙. The studied systems have no stars of spectral types earlier than B, indicating that star clusters do not necessarily evolve through an HII region phase. The relatively small locked mass combined with the fact that they are not numerous in catalogues suggests that these low mass clusters are not important donors of stars to the field populations. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina.

Reddening and age for 13 southern Galactic open clusters determined from integrated spectra

NASA Astrophysics Data System (ADS)

Ahumada, A. V.; Clariá, J. J.; Bica, E.; Dutra, C. M.; Torres, M. C.

2001-10-01

In this study we present flux-calibrated integrated spectra in the range 3800-6800 Å for 13 concentrated open clusters with Galactic longitudes between 219deg and 316deg, nine of which have not been previously studied. Using the equivalent widths of the Balmer lines and comparing the cluster spectra with template spectra of Magellanic Clouds and Galactic star clusters with known parameters, we derive both foreground interstellar reddening values and age. For nine clusters these two parameters have been determined for the first time, while for the rest of the sample the results show good agreement with previous studies. The present analysis indicates four very young (Hogg 11, NGC 5606, vdB-RN 80 and Pismis 17), seven moderately young (ESO 429-SC13, Hogg 3, Hogg 12, Haffner 7, BH 87, NGC 2368 and Bochum 12) and two intermediate-age (Berkeley 75 and NGC 2635) open clusters. The derived foreground interstellar reddening values are in the range 0.00 <= E(B-V) <= 0.38. The age and reddening distributions of the present sample of relatively faint open clusters match those of open clusters with known parameters in a 90deg sector centered at l = 270deg. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, Argentina.

Determinación de miembros, binaridad y metalicidad de gigantes rojas en el cúmulo abierto de edad intermedia NGC 2354

NASA Astrophysics Data System (ADS)

Clariá, J. J.; Mermilliod, J. C.; Piatti, A. E.

We present new Coravel radial-velocity observations and photoelectric photometry in the UBV, DDO and Washington systems for a sample of red giant candidates in the field of the intermediate-age open cluster NGC 2354. Photometric membership probabilities show very good agrement with those obtained from Coravel radial velocities. The analysis of the photometric and kinematical data allow us to confirm cluster membership for 9 red giants, one of them being a spectroscopic binary, while 4 confirmed spectroscopic binaries appear to be probable members. We have also discovered 4 spectroscopic binaries not belonging to the cluster. A mean radial velocity of (33.40±0.27)km s-1 and a mean reddening E(B-V)= 0.13±0.03 were derived for the cluster giants. NGC 2354 has a mean ultraviolet excess <δ(U-B)>=-0.03±0.01, relative to the field K giants, and a mean new cyanogen anomaly ΔCN=-0.035±0.007, both implying [Fe/H]≈-0.3. The moderately metal-poor character of NGC 2354 is confirmed using five different metal abundance indicators of the Washington system. The cluster giant branch is formed by a well defined clump of 7 stars and 4 stars with high membership probabilities seem to define an ascending giant branch. The whole red giant locus cannot be reproduced by any theoretical track. This paper will appear in Astron. & Astrophys. Suppl. (1999).

Searching for New Yellow Symbiotic Stars: Positive Identification of StHα63

NASA Astrophysics Data System (ADS)

Baella, N. O.; Pereira, C. B.; Miranda, L. F.; Alvarez-Candal, A.

2016-04-01

Yellow symbiotic stars are useful targets for probing whether mass transfer has happened in their binary systems. However, the number of known yellow symbiotic stars is very scarce. We report spectroscopic observations of five candidate yellow symbiotic stars that were selected by their positions in the 2MASS (J - H) versus (H - Ks) diagram and which were included in some emission-line catalogs. Among the five candidates, only StHα63 is identified as a new yellow symbiotic star because of its spectrum and its position in the [TiO]1-[TiO]2 diagram, which indicates a K4-K6 spectral type. In addition, the derived electron density (˜108.4 cm-3) and several emission-line intensity ratios provide further support for that classification. The other four candidates are rejected as symbiotic stars because three of them actually do not show emission lines and the fourth one only Balmer emission lines. We also found that the WISE W3-W4 index clearly separates normal K-giants from yellow symbiotic stars and therefore can be used as an additional tool for selecting candidate yellow symbiotic stars. Based on observations collected at the Centro Astronómico Hispano-Alemán, Calar Alto, jointly operated by the Max-Planck-Institut für Astronomie (Heidelberg) and the Instituto de Astrofísica de Andalucía (CSIC), and at the 4.1 m telescope at Cerro Pachón Observatory, Chile.

Where is the fuzz? Undetected Lyman α nebulae around quasars at z ~ 2.3

NASA Astrophysics Data System (ADS)

Herenz, Edmund Christian; Wisotzki, Lutz; Roth, Martin; Anders, Friedrich

2015-04-01

We observed a small sample of five radio-quiet quasars with integral field spectroscopy to search for possible extended emission in the Lyα line. We subtracted the quasar point sources using a simple point spread function (PSF) self-calibration technique that takes advantage of the simultaneous availability of spatial and spectral information. In four of the five objects we find no significant traces of extended Lyα emission beyond the contribution of the quasar nuclei itself, while in UM 247 there is evidence for a weak and spatially quite compact excess in the Lyα line at several kpc outside the nucleus. For all objects in our sample we estimated detection limits for extended, smoothly distributed Lyα emission by adding fake nebulosities into the datacubes and trying to recover them after PSF subtraction. Our observations are consistent with other studies showing that giant Lyα nebulae such as those found recently around some quasars are very rare. Lyα fuzz around typical radio-quiet quasars is fainter and less extended and is therefore much harder to detect. The faintness of these structures is consistent with the idea that radio-quiet quasars typically reside in dark matter haloes of modest masses. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).

A wide and collimated radio jet in 3C84 on the scale of a few hundred gravitational radii

NASA Astrophysics Data System (ADS)

Giovannini, G.; Savolainen, T.; Orienti, M.; Nakamura, M.; Nagai, H.; Kino, M.; Giroletti, M.; Hada, K.; Bruni, G.; Kovalev, Y. Y.; Anderson, J. M.; D'Ammando, F.; Hodgson, J.; Honma, M.; Krichbaum, T. P.; Lee, S.-S.; Lico, R.; Lisakov, M. M.; Lobanov, A. P.; Petrov, L.; Sohn, B. W.; Sokolovsky, K. V.; Voitsik, P. A.; Zensus, J. A.; Tingay, S.

2018-06-01

Understanding the formation of relativistic jets in active galactic nuclei remains an elusive problem1. This is partly because observational tests of jet formation models suffer from the limited angular resolution of ground-based very-long-baseline interferometry that has thus far been able to probe the structure of the jet acceleration and collimation region in only two sources2,3. Here, we report observations of 3C84 (NGC 1275)—the central galaxy of the Perseus cluster—made with an interferometric array including the orbiting radio telescope of the RadioAstron4 mission. The data transversely resolve the edge-brightened jet in 3C84 only 30 μas from the core, which is ten times closer to the central engine than was possible in previous ground-based observations5 and allows us to measure the jet collimation profile from 102 to 104 gravitational radii (rg) from the black hole. The previously found5, almost cylindrical jet profile on scales larger than a few thousand rg is seen to continue at least down to a few hundred rg from the black hole, and we find a broad jet with a transverse radius of ≳250 rg at only 350 rg from the core. This implies that either the bright outer jet layer goes through a very rapid lateral expansion on scales ≲102 rg or it is launched from the accretion disk.

Cassini ISS Observations of Jupiter: An Exoplanet Perspective

NASA Astrophysics Data System (ADS)

West, Robert A.; Knowles, Benjamin

2017-10-01

Understanding the optical and physical properties of planets in our solar system can guide our approach to the interpretation of observations of exoplanets. Although some work has already been done along these lines, there remain low-hanging fruit. During the Cassini Jupiter encounter, the Imaging Science Subsystem (ISS) obtained an extensive set of images over a large range of phase angles (near-zero to 140 degrees) and in filters from near-UV to near-IR, including three methane bands and nearby continuum. The ISS also obtained images using polarizers. Much later in the mission we also obtained distant images while in orbit around Saturn. Some of these data have already been studied to reveal phase behavior (Dyudina et al., Astrophys. J.822, DOI: 10.3847/0004-637X/822/2/76; Mayorga et al., 2016, Astron. J. 152, DOI: 10.3847/0004-6256/152/6/209). Here we examine rotational modulation to determine wavelength and phase angle dependence, and how these may depend on cloud and haze vertical structure and optical properties. The existence of an optically thin forward-scattering and longitudinally-homogeneous haze overlying photometrically-variable cloud fields tends to suppress rotational modulation as phase angle increases, although in the strong 890-nm methane band cloud vertical structure is important. Cloud particles (non-spherical ammonia ice, mostly) have very small polarization signatures at intermediate phase angles and rotational modulation is not apparent above the noise level of our instrument. Part of this work was performed by the Jet Propulsion Lab, Cal. Inst. Of Technology.

Análisis del futuro marco de referencia internacional

NASA Astrophysics Data System (ADS)

Cionco, G. R.; Arias, E. F.

La técnica de interferometría de muy larga línea de base (VLBI) se aplica hoy a la astrometría para el cálculo de posiciones precisas de radiofuentes extragalácticas. Por tratarse de objetos lejanos, sus movimientos propios aparentes pueden considerarse nulos; esta propiedad hace que los catálogos de radiofuentes extragalácticas VLBI constituyan la mejor materialización de un sistema de referencia celeste inercial definido cinemáticamente. La Unión Astronómica Internacional (IAU) recomendó la adopción de un nuevo sistema de referencia celeste internacional materializado por las coordenadas ecuatoriales de objetos extragalácticos observados con le técnica VLBI. Para superar la precisión astrométrica actual es necesaria una mejora en la modelización de aquellos fenómenos que pueden introducir desviaciones sistemáticas en el marco de referencia celeste. El objetivo de este trabajo es poner de manifiesto las sistematicidades presentes en los distintos marcos de referencia elaborados con el próposito de materializar el nuevo sistema de referencia celeste de la IAU. Para la comparación de los distintos marcos de referencia se propone un modelo de tres rotaciones diferenciales más un término lineal que procura absorber los efectos sistemáticos presentes en las coordenadas. Se analiza igualmente la estabilidad de la solución cuando se utilizan distintos conjuntos de objetos de definición.

A wide and collimated radio jet in 3C84 on the scale of a few hundred gravitational radii

NASA Astrophysics Data System (ADS)

Giovannini, G.; Savolainen, T.; Orienti, M.; Nakamura, M.; Nagai, H.; Kino, M.; Giroletti, M.; Hada, K.; Bruni, G.; Kovalev, Y. Y.; Anderson, J. M.; D'Ammando, F.; Hodgson, J.; Honma, M.; Krichbaum, T. P.; Lee, S.-S.; Lico, R.; Lisakov, M. M.; Lobanov, A. P.; Petrov, L.; Sohn, B. W.; Sokolovsky, K. V.; Voitsik, P. A.; Zensus, J. A.; Tingay, S.

2018-04-01

Understanding the formation of relativistic jets in active galactic nuclei remains an elusive problem1. This is partly because observational tests of jet formation models suffer from the limited angular resolution of ground-based very-long-baseline interferometry that has thus far been able to probe the structure of the jet acceleration and collimation region in only two sources2,3. Here, we report observations of 3C84 (NGC 1275)—the central galaxy of the Perseus cluster—made with an interferometric array including the orbiting radio telescope of the RadioAstron4 mission. The data transversely resolve the edge-brightened jet in 3C84 only 30 μas from the core, which is ten times closer to the central engine than was possible in previous ground-based observations5 and allows us to measure the jet collimation profile from 102 to 104 gravitational radii (rg) from the black hole. The previously found5, almost cylindrical jet profile on scales larger than a few thousand rg is seen to continue at least down to a few hundred rg from the black hole, and we find a broad jet with a transverse radius of ≳250 rg at only 350 rg from the core. This implies that either the bright outer jet layer goes through a very rapid lateral expansion on scales ≲102 rg or it is launched from the accretion disk.

Europa: Characterization and interpretation of global spectral surface units

USGS Publications Warehouse

Nelson, M.L.; McCord, T.B.; Clark, R.N.; Johnson, T.V.; Matson, D.L.; Mosher, J.A.; Soderblom, L.A.

1986-01-01

The Voyager global multispectral mosaic of the Galilean satellite Europa (T. V. Johnson, L. A. Soderblom, J. A. Mosher, G. E. Danielson, A. F. Cook, and P. Kupferman, 1983, J. Geophys. Res. 88, 5789-5805) was analyzed to map surface units with similar optical properties (T. B. McCord, M. L. Nelson, R. N. Clark, A. Meloy, W. Harrison, T. V. Johnson, D. L. Matson, J. A. Mosher, and L. Soderblom, 1982, Bull Amer. Astron. Soc. 14, 737). Color assignments in the unit map are indicative of the spectral nature of the unit. The unit maps make it possible to infer extensions of the geologic units mapped by B. K. Lucchitta and L. A. Soderblom (1982, in Satellites of Jupiter, pp. 521-555, Univ. of Arizona Press, Tucson) beyond the region covered in the high-resolution imagery. The most striking feature in the unit maps is a strong hemispheric asymmetry. It is seen most clearly in the ultraviolet/violet albedo ratio image, because the asymmetry becomes more intense as the wavelength decreases. It appears as if the surface has been darkened, most intensely in the center of the trailing hemisphere and decreasing gradually, essentially as the cosine of the angle from the antapex of motion, to a minimum in the center of the leading hemisphere. The cosine pattern suggests that the darkening is exogenic in origin and is interpreted as evidence of alteration of the surface by ion bombardment from the Jovian magnetosphere. ?? 1986.

Simple models of SL-9 impact plumes in flight

NASA Astrophysics Data System (ADS)

Harrington, J.; Deming, D.

1998-09-01

We have extended our ballistic Monte-Carlo model of the Shoemaker-Levy 9 impact plumes (J. Harrington and D. Deming 1996. Simple models of SL9 impact plumes, Bull. Am. Astron. Soc. 28 1150--1151) to calculate the appearance of the plumes in flight. We compare these synthetic images to the data taken by the Hubble Space Telescope of plumes on the limb of Jupiter during impacts A, E, G, and W. The model uses a parameterized version of the final power-law velocity distribution from the impact models of Zahnle and Mac Low. The observed plume heights, lightcurve features, and debris patterns fix the values of model parameters. The parameters that best reproduce the debris patterns dictate an approximately conic plume geometry, with the apex of the cone initially near the impact site, the cone's axis pointed in the direction from which the impactor came, and an opening angle >45sp ° from the axis. Since material of a given velocity is, at any given time, a certain distance from the cone apex, the geometry spreads high-velocity material much thinner than low-velocity material. The power law exponent of -1.55 combines with this effect to make mass density fall off as the -3.55 power of the velocity (or distance from the plume base). However, the outer shell of highest-velocity material, corresponding to the atmospheric shock wave, carries considerably elevated mass density. We are currently studying the range of reasonable optical properties to determine whether the visible plume tops corresponded to the physical top of this shell, or to a lower density contour.

El Sistema de Referencia Celeste convencional de la IAU

NASA Astrophysics Data System (ADS)

Arias, E. F.

La Unión Astronómica Internacional (IAU) recomendó la adopción de un nuevo sistema de referencia celeste baricéntrico cuyo plano fundamental y origen de ascensiones rectas estén próximos, respectivamente, al ecuador y equinoccio dinámicos J2000.0. El nuevo sistema de referencia estará materializado por las posiciones J2000.0 de radiofuentes extragalácticas determinadas con la técnica de interferometría de larga línea de base (VLBI). El Working Group on Reference Frames de la IAU (WGRF) decidió adoptar (Grasse, 1995) al sistema de referencia celeste extragaláctico del Servicio Internacional de la Rotación Terrestre (IERS) como futuro sistema de referencia celeste convencional bajo el nombre International Celestial Reference System (ICRS) y encomendó su mantenimiento futuro al IERS. El marco de referencia que materializará al ICRS contiene posiciones precisas J2000.0 de más de 600 radiofuentes extragalácticas. Las coordenadas fueron ajustadas en una única solución VLBI en la cual se incluyeron todas las observaciones realizadas hasta octubre de 1995 con la técnica de adquisición de datos VLBI Mark III. Para minimizar los errores sistemáticos que pueden afectar la calidad del marco de referencia se introdujeron mejoras sustanciales en la modelización y en la selección de datos. Un subconjunto de objetos del marco de referencia se utilizó para referir las posiciones estelares determinadas con el satélite astrométrico Hipparcos al ICRS.

Giga-year evolution of Jupiter Trojans and the asymmetry problem

NASA Astrophysics Data System (ADS)

Di Sisto, Romina P.; Ramos, Ximena S.; Beaugé, Cristián

2014-11-01

We present a series of numerical integrations of observed and fictitious Jupiter Trojan asteroids, under the gravitational effects of the four outer planets, for time-spans comparable with the age of the Solar System. From these results we calculate the escape rate from each Lagrange point, and construct dynamical maps of ;permanence; time in different regions of the phase space. Fictitious asteroids in L4 and L5 show no significant difference, showing almost identical dynamical maps and escape rates. For real Trojans, however, we found that approximately 23% of the members of the leading swarm escaped after 4.5 Gyrs, while this number increased to 28.3% for L5 . This implies that the asymmetry between the two populations increases with time, indicating that it may have been smaller at the time of formation/capture of these asteroids. Nevertheless, the difference in chaotic diffusion cannot, in itself, account for the current observed asymmetry (∼40%), and must be primarily primordial and characteristic of the capture mechanism of the Trojans. Finally, we calculate new proper elements for all the numbered Trojans using the semi-analytical approach of Beaugé and Roig (Beaugé, C., Roig, F.V. [2001]. Icarus, 153, 391-415), and compare the results with the numerical estimations by Brož and Rosehnal (Brož, M., Rosehnal, J. [2011]. Mon. Not. R. Astron. Soc. 414, 565-574). For asteroids that were already numbered in 2011, both methods yield very similar results, while significant differences were found for those bodies that became numbered after 2011.

Optical polarization observations in Hogg 22 and NGC 6204

NASA Astrophysics Data System (ADS)

Martínez, R.; Vergne, M. M.; Feinstein, C.

2004-06-01

We present new (UBVRI) multicolor linear polarimetric data for 22 of the brightest stars in the area of the open clusters Hogg 22 and NGC 6204 to study the properties of the ISM (interstellar medium) toward these clusters and between them. The new data were incorporated in our data set of previous observations (Waldhausen et al. \\cite{waldhausen}), resulting in 28 observed stars in the region. Our data yield for NGC 6204 a mean polarization percentage of Pλ_max˜1.8%, close to the polarization value produced by the ISM with normal efficiency (Pλ_max ˜ 5 EB-V) with a color excess of EB-V =0.51. Meanwhile for Hogg 22, located behind NGC 6204, the mean polarization is Pλ_max˜ 2.15%, lower than the expected value for the observed color excess of EB-V =0.68 (Forbes et al. 1996) and the average efficiency of polarization for the interstellar dust. The mean angle of the polarization vectors of Hogg 22 is θ=44.9 °, which agrees with the expected angle produce by dust particles aligned in the direction of the Galactic Plane (θ=48°), while for NGC 6204 a lower value, θ=33.7 °, was found. Therefore, we believe that Hogg 22 is depolarized by the same dust that is polarizing NGC 6204, due to different orientations of the dust particles (and magnetic fields) that polarize the starlight. Based on observations obtanined at Complejo Astronómico El Leoncito (CASLEO), operated under agreement between the CONICET and the National Universities of La Plata, Córdoba, and San Juan, Argentina.

Detoxification of Benzoxazolinone Allelochemicals from Wheat by Gaeumannomyces graminis var. tritici, G. graminis var. graminis, G. graminis var. avenae, and Fusarium culmorum

PubMed Central

Friebe, A.; Vilich, V.; Hennig, L.; Kluge, M.; Sicker, D.

1998-01-01

The ability of phytopathogenic fungi to overcome the chemical defense barriers of their host plants is of great importance for fungal pathogenicity. We studied the role of cyclic hydroxamic acids and their related benzoxazolinones in plant interactions with pathogenic fungi. We identified species-dependent differences in the abilities of Gaeumannomyces graminis var. tritici, Gaeumannomyces graminis var. graminis, Gaeumannomyces graminis var. avenae, and Fusarium culmorum to detoxify these allelochemicals of gramineous plants. The G. graminis var. graminis isolate degraded benzoxazolin-2(3H)-one (BOA) and 6-methoxy-benzoxazolin-2(3H)-one (MBOA) more efficiently than did G. graminis var. tritici and G. graminis var. avenae. F. culmorum degraded BOA but not MBOA. N-(2-Hydroxyphenyl)-malonamic acid and N-(2-hydroxy-4-methoxyphenyl)-malonamic acid were the primary G. graminis var. graminis and G. graminis var. tritici metabolites of BOA and MBOA, respectively, as well as of the related cyclic hydroxamic acids. 2-Amino-3H-phenoxazin-3-one was identified as an additional G. graminis var. tritici metabolite of BOA. No metabolite accumulation was detected for G. graminis var. avenae and F. culmorum by high-pressure liquid chromatography. The mycelial growth of the pathogenic fungi was inhibited more by BOA and MBOA than by their related fungal metabolites. The tolerance of Gaeumannomyces spp. for benzoxazolinone compounds is correlated with their detoxification ability. The ability of Gaeumannomyces isolates to cause root rot symptoms in wheat (cultivars Rektor and Astron) parallels their potential to degrade wheat allelochemicals to nontoxic compounds. PMID:9647804

A search for transit timing variations and orbital decay in WASP-46b

NASA Astrophysics Data System (ADS)

Petrucci, R.; Jofré, E.; Ferrero, L. V.; Cúneo, V.; Saker, L.; Lovos, F.; Gómez, M.; Mauas, P.

2018-02-01

We present 12 new transit observations of the exoplanet WASP-46b obtained with the 1.54-m telescope at Estación Astrofísica de Bosque Alegre (EABA, Argentina) and the 0.40-m Horacio Ghielmetti and 2.15-m Jorge Sahade telescopes at Complejo Astronómico El Leoncito (CASLEO, Argentina). We analyse them together with 37 light curves from the literature to re-determine the physical parameters and search for additional planets via transit timing variations (TTVs). We consider the 31 transits with uncertainties in their mid-transit times (e_T0) < 1 min, to perform the first homogeneous study of TTVs for the system, finding a dispersion of σ = 1.66 min over a 6 yr baseline. Since no periodic variations are found, our interpretation for this relatively high value of σ is that the stellar activity could be affecting the measured mid-transit times. This value of dispersion allows us to rule out the presence of additional bodies with masses larger than 2.3, 4.6, 7 and 9.3 M_{\\oplus} at the first-order mean-motion resonances 2:1, 3:2, 4:3 and 5:4 with the transiting planet, respectively. Despite the 6 yr baseline and a typical light-curve precision of 2 × 10-3, we find that we cannot significantly demonstrate a slow decrease of the orbital period of WASP-46b. We place a lower limit of Q⋆ > 7 × 103 on the tidal quality factor and determine that an additional 6 yr baseline is required to rule out Q⋆ < 105.

South American regional ionospheric maps computed by GESA: A pilot service in the framework of SIRGAS

NASA Astrophysics Data System (ADS)

Brunini, C.; Meza, A.; Gende, M.; Azpilicueta, F.

2008-08-01

SIRGAS (Geocentric Reference Frame for the Americas) is an international enterprise of the geodetic community that aims to realize the Terrestrial Reference Frame in the America's countries. In order to fulfill this commitment, SIRGAS manages a network of continuously operational GNSS receivers totalling around one hundred sites in the Caribbean, Central, and South American region. Although the network was not planed for ionospheric studies, its potential to be used for such a purpose was recently recognized and SIRGAS started a pilot experiment devoted to establish a regular service for computing and releasing regional vertical TEC (vTEC) maps based on GNSS data. Since July, 2005, the GESA (Geodesia Espacial y Aeronomía) laboratory belonging to the Facultad de Ciencias Astronómicas y Geofísicas of the Universidad Nacional de La Plata computes hourly maps of vertical Total Electron Content (vTEC) in the framework of the SIRGAS pilot experiment. These maps exploit all the GNSS data available in the South American region and are computed with the LPIM (La Plata Ionospheric Model). LPIM implements a de-biasing procedure that improves data calibration in relation to other procedures commonly used for such purposes. After calibration, slant TEC measurements are converted to vertical and mapped using local-time and modip latitude. The use of modip latitude smoothed the spatial variability of vTEC, especially in the South American low latitude region and hence allows for a better vTEC interpolation. This contribution summarizes the results obtained by GESA in the framework of the SIRGAS pilot experiment.

Dwarf planet Ceres: Ellipsoid dimensions and rotational pole from Keck and VLT adaptive optics images

NASA Astrophysics Data System (ADS)

Drummond, J. D.; Carry, B.; Merline, W. J.; Dumas, C.; Hammel, H.; Erard, S.; Conrad, A.; Tamblyn, P.; Chapman, C. R.

2014-07-01

The dwarf planet (1) Ceres, the largest object between Mars and Jupiter, is the target of the NASA Dawn mission, and we seek a comprehensive description of the spin-axis orientation and dimensions of Ceres in order to support the early science operations at the rendezvous in 2015. We have obtained high-angular resolution images using adaptive optics cameras at the W.M. Keck Observatory and the ESO VLT over ten dates between 2001 and 2010, confirming that the shape of Ceres is well described by an oblate spheroid. We derive equatorial and polar diameters of 967 ± 10 km and 892 ± 10 km, respectively, for a model that includes fading of brightness towards the terminator, presumably linked to limb darkening. These dimensions lie between values derived from a previous analysis of a subset of these images obtained at Keck by Carry et al. (Carry et al. [2008]. Astron. Astrophys. 478 (4), 235-244) and a study of Hubble Space Telescope observations (Thomas et al. [2005]. Nature 437, 224-226). Although the dimensions are 1-2% smaller than those found from the HST, the oblateness is similar. We find the spin-vector coordinates of Ceres to lie at (287°, +64°) in equatorial EQJ2000 reference frame (346°, +82° in ecliptic ECJ2000 coordinates), yielding a small obliquity of 3°. While this is in agreement with the aforementioned studies, we have improved the accuracy of the pole determination, which we set at a 3° radius.

Uranus' Persistent Patterns and Features from High-SNR Imaging in 2012-2014

NASA Astrophysics Data System (ADS)

Fry, Patrick M.; Sromovsky, Lawrence A.; de Pater, Imke; Hammel, Heidi B.; Marcus, Phillip

2015-11-01

Since 2012, Uranus has been the subject of an observing campaign utilizing high signal-to-noise imaging techniques at Keck Observatory (Fry et al. 2012, Astron. J. 143, 150-161). High quality observing conditions on four observing runs of consecutive nights allowed longitudinally-complete coverage of the atmosphere over a period of two years (Sromovsky et al. 2015, Icarus 258, 192-223). Global mosaic maps made from images acquired on successive nights in August 2012, November 2012, August 2013, and August 2014, show persistent patterns, and six easily distinguished long-lived cloud features, which we were able to track for long periods that ranged from 5 months to over two years. Two at similar latitudes are associated with dark spots, and move with the atmospheric zonal flow close to the location of their associated dark spot instead of following the flow at the latitude of the bright features. These features retained their morphologies and drift rates in spite of several close interactions. A second pair of features at similar latitudes also survived several close approaches. Several of the long-lived features also exhibited equatorward drifts and latitudinal oscillations. Also persistent are a remarkable near-equatorial wave feature and global zonal band structure. We will present imagery, maps, and analyses of these phenomena.PMF and LAS acknowledge support from NASA Planetary Astronomy Program; PMF and LAS acknowledge funding and technical support from W. M. Keck Observatory. We thank those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests. Without their generous hospitality none of our groundbased observations would have been possible.

Precision mechanisms for optics in a vacuum cryogenic environment

NASA Astrophysics Data System (ADS)

Navarro, R.; Elswijk, E.; Tromp, N.; Kragt, J.; Kroes, G.; Hanenburg, H.; de Haan, M.; Schuil, M.; Teuwen, M.; Janssen, H.; Venema, L.

2017-11-01

To achieve superb stability in cryogenic optical systems, NOVA-ASTRON generally designs optical instruments on the basis of a 'no adjustments' philosophy. This means that in principle no corrections are possible after assembly. The alignment precision and consequently the performance of the instrument is guaranteed from the design, the tolerance analysis and the detailed knowledge of the material behavior and manufacturing process. This resulted in a higher degree of integrated optomechanical-cryogenic design with fewer parts, but with a higher part complexity. The 'no adjustments' strategy is successful because in the end the risk on instrument performance and project delays is much reduced. Astronomical instrument specifications have become more challenging over the years. Recent designs of the European Southern Observatory Very Large Telescope Interferometer (ESO VLTI) 4 Telescope combiner MATISSE include hundreds of optical components in a cryogenic environment. Despite the large number of optical components the alignment accuracy and stability requirements are in the order of nanometers. The 'no adjustments' philosophy would be too costly in this case, because all components would need to meet extremely tight manufacturing specifications. These specifications can be relaxed dramatically if cryogenic mechanisms are used for alignment. Several mechanisms have been developed: a tip-tilt mirror mechanism, an optical path distance mechanism, a slider mechanism, a bistable cryogenic shutter and a mirror mounting clip. Key aspects of these mechanisms are that the optical element and mechanism are combined in a compact single component, driven by e.g. self braking piezo actuators in order to hold position without power. The design, realization and test results of several mechanisms are presented in this paper.

Candidate counterparts to the soft gamma-ray flare in the direction of LS I +61 303

NASA Astrophysics Data System (ADS)

Muñoz-Arjonilla, A. J.; Martí, J.; Combi, J. A.; Luque-Escamilla, P.; Sánchez-Sutil, J. R.; Zabalza, V.; Paredes, J. M.

2009-04-01

Context: A short duration burst reminiscent of a soft gamma-ray repeater/anomalous X-ray pulsar behaviour was detected in the direction of LS I +61 303 by the Swift satellite. While the association with this well known gamma-ray binary is likely, a different origin cannot be excluded. Aims: We explore the error box of this unexpected flaring event and establish the radio, near-infrared and X-ray sources in our search for any peculiar alternative counterpart. Methods: We carried out a combined analysis of archive Very Large Array radio data of LS I +61 303 sensitive to both compact and extended emission. We also reanalysed previous near infrared observations with the 3.5 m telescope of the Centro Astronómico Hispano Alemán and X-ray observations with the Chandra satellite. Results: Our deep radio maps of the LS I +61 303 environment represent a significant advancement on previous work and 16 compact radio sources in the LS I +61 303 vicinity are detected. For some detections, we also identify near infrared and X-ray counterparts. Extended emission features in the field are also detected and confirmed. The possible connection of some of these sources with the observed flaring event is considered. Based on these data, we are unable to claim a clear association between the Swift-BAT flare and any of the sources reported here. However, this study represents the most sophisticated attempt to determine possible alternative counterparts other than LS I +61 303.

The nature of 50 Palermo Swift-BAT hard X-ray objects through optical spectroscopy

NASA Astrophysics Data System (ADS)

Rojas, A. F.; Masetti, N.; Minniti, D.; Jiménez-Bailón, E.; Chavushyan, V.; Hau, G.; McBride, V. A.; Bassani, L.; Bazzano, A.; Bird, A. J.; Galaz, G.; Gavignaud, I.; Landi, R.; Malizia, A.; Morelli, L.; Palazzi, E.; Patiño-Álvarez, V.; Stephen, J. B.; Ubertini, P.

2017-06-01

We present the nature of 50 hard X-ray emitting objects unveiled through an optical spectroscopy campaign performed at seven telescopes in the northern and southern hemispheres. These objects were detected with the Burst Alert Telescope (BAT) instrument onboard the Swift satellite and listed as of unidentified nature in the 54-month Palermo BAT catalogue. In detail, 45 sources in our sample are identified as active galactic nuclei of which, 27 are classified as type 1 (with broad and narrow emission lines) and 18 are classified as type 2 (with only narrow emission lines). Among the broad-line emission objects, one is a type 1 high-redshift quasi-stellar object, and among the narrow-line emission objects, one is a starburst galaxy, one is a X-ray bright optically normal galaxy, and one is a low ionization nuclear emission line region. We report 30 new redshift measurements, 13 confirmations and 2 more accurate redshift values. The remaining five objects are galactic sources: three are Cataclismic Variables, one is a X-ray Binary probably with a low mass secondary star, and one is an active star. Based on observations obtained from the following observatories: Cerro Tololo Interamerican Observatory (Chile); Astronomical Observatory of Bologna in Loiano (Italy); Observatorio Astronómico Nacional (San Pedro Mártir, Mexico); Radcliffe telescope of the South African Astronomical Observatory (Sutherland, South Africa); Sloan Digital Sky Survey; Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias (Canary Islands, Spain) and New Technology Telescope (NTT) of La Silla Observatory, Chile.

Primary Self-EXPANDing Nitinol Stenting vs Balloon Angioplasty With Optional Bailout Stenting for the Treatment of Infrapopliteal Artery Disease in Patients With Severe Intermittent Claudication or Critical Limb Ischemia (EXPAND Study).

PubMed

Schulte, Karl-Ludwig; Pilger, Ernst; Schellong, Sebastian; Tan, Kong Ten; Baumann, Frederic; Langhoff, Ralf; Torsello, Giovanni; Zeller, Thomas; Amendt, Klaus; Brodmann, Marianne

2015-10-01

To compare primary placement of a self-expanding nitinol stent to percutaneous transluminal angioplasty (PTA) with bailout stenting in infrapopliteal arteries of patients with severe intermittent claudication or critical limb ischemia (CLI). In the EXPAND trial (ClinicalTrials.gov; identifier NCT00906022), 92 patients (mean age 72.9±9.5 years; 62 men) undergoing treatment for infrapopliteal stenosis in 11 European centers were randomized 1:1 to either self-expanding nitinol stenting with the Astron Pulsar/Pulsar-18 nitinol stent or PTA with bailout stenting. The primary endpoint was sustainable clinical improvement after 12 months, defined as a ≥1-category increase for Rutherford category 3 patients or a ≥2-category increase for CLI patients (Rutherford categories 4/5) compared with baseline. Furthermore, target lesion revascularization (TLR), mortality, and amputation were assessed after 12 months. Sustained clinical improvement at 1 year was observed in 74.3% of the patients treated with primary stenting and in 68.6% of the patients treated with PTA and bailout stenting (p>0.05). Kaplan-Meier estimates of freedom from TLR (76.6% and 77.6%), mortality (7.4% vs 2.1%), and amputation [8.9% (major 6.7%) vs 13.2% (major 8.7%)] at 1 year were not significantly different. Primary self-expanding nitinol stenting did not show statistically different clinical outcomes compared to angioplasty with bailout stenting for infrapopliteal lesions. © The Author(s) 2015.

Applicability of meteor radiant determination methods depending on orbit type. I. High-eccentric orbits

NASA Astrophysics Data System (ADS)

Svoren, J.; Neslusan, L.; Porubcan, V.

1993-07-01

It is evident that there is no uniform method of calculating meteor radiants which would yield reliable results for all types of cometary orbits. In the present paper an analysis of this problem is presented, together with recommended methods for various types of orbits. Some additional methods resulting from mathematical modelling are presented and discussed together with Porter's, Steel-Baggaley's and Hasegawa's methods. In order to be able to compare how suitable the application of the individual radiant determination methods is, it is necessary to determine the accuracy with which they approximate real meteor orbits. To verify the accuracy with which the orbit of a meteoroid with at least one node at 1 AU fits the original orbit of the parent body, we applied the Southworth-Hawkins D-criterion (Southworth, R.B., Hawkins, G.S.: 1963, Smithson. Contr. Astrophys 7, 261). D<=0.1 indicates a very good fit of orbits, 0.10.2 the fit is rather poor and the change of orbit unrealistic. The optimal methods with the smallest values of D for given types of orbits are shown in two series of six plots. The new method of rotation around the line of apsides we propose is very appropriate in the region of small inclinations. There is no doubt that Hasegawa's omega-adjustment method (Hasegawa, I.: 1990, Publ. Astron. Soc. Japan 42, 175) has the widest application. A comparison of the theoretical radiants with the observed radiants of seven known meteor showers is also presented.

12th European VLBI Network Symposium and Users Meeting

NASA Astrophysics Data System (ADS)

Tarchi, Andrea; Giroletti, Marcello; Feretti, Luigina

The Istituto di Radioastronomia (IRA) di Bologna and the Osservatorio Astronomico di Cagliari (OAC), on behalf of the European VLBI Consortium, hosted the 12th European VLBI Network (EVN) Symposium and Users Meeting. The Conference was held from 7th to 10th of October at the Hotel Regina Margherita, in the center of Cagliari. The latest scientific results and technical developments from VLBI, and, in particular, e-VLBI and space-VLBI (RadioAstron) outcomes were reported. The timing of this meeting coincided with the first successful observational tests of the Sardinia Radio Telescopes within the EVN, and with a number of results from new and upgraded radio facilities around the globe, such as e-MERLIN, ALMA, and the SKA pathfinders. The symposium was attended by 133 participants from all over the world, with the Asian community represented by more than 20 colleagues. The program of the meeting consisted of 70 oral contributions (including 8 invited speakers) and 50 poster that covered a very wide range of VLBI topics both in galactic and extragalactic astrophysics (e.g., AGN, stellar evolution from birth to death, astrometry, and planetary science) as well as technological developments and future international collaborations. The scientific program also included a visit to the 64-m Sardinia Radio Telescope (SRT) and the EVN Users Meeting, where astronomers have provided useful feedback on various matters regarding EVN operations. The research leading to these results has received funding from the European Commission Seventh Framework Programme (FP/2007-2013) under grant agreement No 283393 (RadioNet3). EDITORIAL BOARD: Andrea Tarchi, Marcello Giroletti, Luigina Feretti

VESPA: Developing the Planetary Science Virtual Observatory in H2020

NASA Astrophysics Data System (ADS)

Erard, S.; Cecconi, B.; Le Sidaner, P.; Capria, M. T.; Rossi, A. P.; Schmitt, B.; Andre, N.; Vandaele, A. C.; Scherf, M.; Hueso, R.; Maattanen, A. E.; Thuillot, W.; Achilleos, N.; Marmo, C.; Santolik, O.; Benson, K.

2015-12-01

In the frame of the Europlanet-RI program, a prototype Virtual Observatory dedicated to Planetary Science has been set up. Most of the activity was dedicated to the definition of standards to handle data in this field. The aim was to facilitate searches in big archives as well as sparse databases, to make on-line data access and visualization possible, and to allow small data providers to make their data available in an interoperable environment with minimum effort. This system makes intensive use of studies and developments led in Astronomy (IVOA), Solar Science (HELIO), and space archive services (IPDA). A general standard has been devised to handle the specific complexity of Planetary Science, e.g. in terms of measurement types and coordinate frames [1]. A procedure has been identified to install small data services, and several hands-on sessions have been organized already. A specific client (VESPA) has been developed at VO-Paris (http://vespa.obspm.fr), using a resolver for target names. Selected data can be sent to VO visualization tools such as TOPCAT or Aladin though the SAMP protocol. The Europlanet H2020 program started in Sept 2015 will provide support to new data services in Europe (30 to 50 expected), and focus on the improvement of the infrastructure. Future steps will include the development of a connection between the VO world and GIS tools, and integration of heliophysics, planetary plasma and reference spectroscopic data. The Europlanet H2020 project is funded by the European Commission under the H2020 Program, grant 654208. [1] Erard et al Astron & Comp 2014

Realistic estimation for the detectability of dark matter subhalos using Fermi-LAT catalogs

NASA Astrophysics Data System (ADS)

Calore, Francesca; De Romeri, Valentina; Di Mauro, Mattia; Donato, Fiorenza; Marinacci, Federico

2017-09-01

Numerical simulations of structure formation have made remarkable progress in recent years, in particular due to the inclusion of baryonic physics evolving with the dark matter component. We generate Monte Carlo realizations of the dark matter subhalo population based on the results of the recent hydrodynamical simulation suite of Milky Way-sized galaxies [F. Marinacci, R. Pakmor, and V. Springel, Mon. Not. R. Astron. Soc. 437, 1750 (2014)., 10.1093/mnras/stt2003]. We then simulate the gamma-ray sky for both the setup of the 3FGL and 2FHL Fermi Large Area Telescope (LAT) catalogs, including the contribution from the annihilation of dark matter in the subhalos. We find that the flux sensitivity threshold strongly depends on the particle dark matter mass and, more mildly, also on its annihilation channel and the observation latitude. The results differ for the 3FGL and 2FHL catalogs, given their different energy thresholds. We also predict that the number of dark matter subhalos among the unassociated sources is very small. A null number of detectable subhalos in the Fermi-LAT 3FGL catalog would imply upper limits on the dark matter annihilation cross section into b b ¯ of 2 ×10-26(5 ×10-25) cm3 /s with MDM=50 (1000 ) GeV . We find less than one extended subhalo in the Fermi-LAT 3FGL catalog. As a matter of fact, the differences in the spatial and mass distribution of subhalos between hydrodynamic and dark matter-only runs do not have significant impact on the detectability of dark subhalos in gamma rays.

Tidal effects in differentiated viscoelastic bodies: a numerical approach

NASA Astrophysics Data System (ADS)

Walterová, M.; Běhounková, M.

2017-09-01

The majority of confirmed terrestrial exoplanets orbits close to their host stars and their evolution was likely altered by tidal interaction. Nevertheless, due to their viscoelastic properties on the tidal frequencies, their response cannot be described exactly by standardly employed constant-lag models. We therefore introduce a tidal model based on the numerical evaluation of a continuum mechanics problem describing the deformation of viscoelastic (Maxwell or Andrade) planetary mantles subjected to external force. We apply the method on a model Earth-size planet orbiting a low-mass star and study the effect of the orbital eccentricity, the mantle viscosity and the chosen rheology on the tidal dissipation, the complex Love numbers and the tidal torque. The number of stable spin states (i.e., zero tidal torque) grows with increasing mantle viscosity, similarly to the analytical model of Correia et al. (Astron Astrophys 571:A50, 2014) for homogeneous bodies. This behavior is only slightly influenced by the rheology used. Similarly, the Love numbers do not distinctly depend on the considered rheological model. The increase in viscosity affects the amplitude of their variations. The tidal heating described by the Maxwell rheology attains local minima associated with low spin-orbit resonances, with depth and shape depending on both the eccentricity and the viscosity. For the Andrade rheology, the minima at low resonances are very shallow and the tidal heating for all viscosities resembles a "fluid limit." The tidal heating is the quantity influenced the most by the rheology, having thus possible impact on the internal thermal evolution.

Solaris: a global network of autonomous observatories in the southern hemisphere

NASA Astrophysics Data System (ADS)

Kozłowski, S. K.; Sybilski, P.; Konacki, Maciej; Pawłaszek, R. K.; Ratajczak, Milena; Helminiak, K. G.

2014-07-01

We present Project Solaris, a network of four autonomous observatories in the Southern Hemisphere. The Project's primary goal is to detect and characterize circumbinary planets using the eclipse timing approach. This method requires high-cadence and long time-span photometric coverage of the binaries' eclipses, hence the observatories are located at sites having similar separation in longitude and nearly identical latitudes: South African Astronómical Observatory, Republic of South Africa (Solaris-1 and -2), Siding Spring Observatory, Australia (Solaris-3) and Complejo Astronomico El Leoncito, Argentina (Solaris-4). The headquarters coordinating and monitoring the network is based in Toruń, Poland. All four sites are operational as of December 2013. The instrument and hardware configurations are nearly identical. Each site is equipped with a 0.5-m Ritchey-Chrétien or Schmidt-Cassegrain optical tube assembly mounted on a direct-drive modified German equatorial mount along with a set of instruments. Computer, power and networking components are installed in rack cabinets. Everything is housed in sandwiched fiberglass clamshell 3.5-m diameter robotized domes. The Argentinian site is additionally equipped with a 20-ft office container. We discuss the design requirements of robotic observatories aimed to operate autonomously as a global network with concentration on efficiency, robustness and modularity. We also present a newly introduced spectroscopic mode of operation commissioned on the Solaris-1 telescope. Using a compact échelle spectrograph (20 000 resolution) mounted directly on the imaging train of the telescope, we are able to remotely acquire spectra. A fully robotic spectroscopic mode is planned for 2015.

Constraints on Bose-Einstein-condensed axion dark matter from the Hi nearby galaxy survey data

NASA Astrophysics Data System (ADS)

Li, Ming-Hua; Li, Zhi-Bing

2014-05-01

One of the leading candidates for dark matter is the axion or axionlike particle in the form of a Bose-Einstein condensate (BEC). In this paper, we present an analysis of 17 high-resolution galactic rotation curves from the Hi nearby galaxy survey (THINGS) data [F. Walter et al., Astron. J. 136, 2563 (2008)] in the context of the axionic Bose-Einstein condensed dark matter model. Assuming a repulsive two-body interaction, we solve the nonrelativistic Gross-Pitaevskii equation for N gravitationally trapped bosons in the Thomas-Fermi approximation. We obtain the maximum possible radius R and the mass profile M(r) of a dilute axionic Bose-Einstein condensed gas cloud. A standard least- χ2 method is employed to find the best-fit values of the total mass M of the axion BEC and its radius R. The local mass density of BEC axion dark matter is ρa ≃0.02 GeV /cm3, which agrees with that presented by Beck [C. Beck, Phys. Rev. Lett. 111, 231801 (2013)]. The axion mass ma we obtain depends not only on the best-fit value of R, but also on the s-wave scattering length a (ma∝a1/3). The transition temperature Ta of an axion BEC on galactic scales is also estimated. Comparing the calculated Ta with the ambient temperature of galaxies and galaxy clusters implies that a ˜10-3 fm. The corresponding axion mass is ma≃0.58 meV. We compare our results with others.

OPTICAL SPECTROSCOPIC OBSERVATIONS OF GAMMA-RAY BLAZAR CANDIDATES. VI. FURTHER OBSERVATIONS FROM TNG, WHT, OAN, SOAR, AND MAGELLAN TELESCOPES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Álvarez Crespo, N.; Massaro, F.; Milisavljevic, D.

Blazars, one of the most extreme classes of active galaxies, constitute so far the largest known population of γ-ray sources, and their number is continuously growing in the Fermi catalogs. However, in the latest release of the Fermi catalog there is still a large fraction of sources that are classified as blazar candidates of uncertain type (BCUs) for which optical spectroscopic observations are necessary to confirm their nature and their associations. In addition, about one-third of the γ-ray point sources listed in the Third Fermi-LAT Source Catalog (3FGL) are still unassociated and lacking an assigned lower-energy counterpart. Since 2012 wemore » have been carrying out an optical spectroscopic campaign to observe blazar candidates to confirm their nature. In this paper, the sixth of the series, we present optical spectroscopic observations for 30 γ-ray blazar candidates from different observing programs we carried out with the Telescopio Nazionale Galileo, William Herschel Telescope, Observatorio Astronómico Nacional, Southern Astrophysical Research Telescope, and Magellan Telescopes. We found that 21 out of 30 sources investigated are BL Lac objects, while the remaining targets are classified as flat-spectrum radio quasars showing the typical broad emission lines of normal quasi-stellar objects. We conclude that our selection of γ-ray blazar candidates based on their multifrequency properties continues to be a successful way to discover potential low-energy counterparts of the Fermi unidentified gamma-ray sources and to confirm the nature of BCUs.« less

CALIFA, the Calar Alto Legacy Integral Field Area survey. III. Second public data release

NASA Astrophysics Data System (ADS)

García-Benito, R.; Zibetti, S.; Sánchez, S. F.; Husemann, B.; de Amorim, A. L.; Castillo-Morales, A.; Cid Fernandes, R.; Ellis, S. C.; Falcón-Barroso, J.; Galbany, L.; Gil de Paz, A.; González Delgado, R. M.; Lacerda, E. A. D.; López-Fernandez, R.; de Lorenzo-Cáceres, A.; Lyubenova, M.; Marino, R. A.; Mast, D.; Mendoza, M. A.; Pérez, E.; Vale Asari, N.; Aguerri, J. A. L.; Ascasibar, Y.; Bekeraitė, S.; Bland-Hawthorn, J.; Barrera-Ballesteros, J. K.; Bomans, D. J.; Cano-Díaz, M.; Catalán-Torrecilla, C.; Cortijo, C.; Delgado-Inglada, G.; Demleitner, M.; Dettmar, R.-J.; Díaz, A. I.; Florido, E.; Gallazzi, A.; García-Lorenzo, B.; Gomes, J. M.; Holmes, L.; Iglesias-Páramo, J.; Jahnke, K.; Kalinova, V.; Kehrig, C.; Kennicutt, R. C.; López-Sánchez, Á. R.; Márquez, I.; Masegosa, J.; Meidt, S. E.; Mendez-Abreu, J.; Mollá, M.; Monreal-Ibero, A.; Morisset, C.; del Olmo, A.; Papaderos, P.; Pérez, I.; Quirrenbach, A.; Rosales-Ortega, F. F.; Roth, M. M.; Ruiz-Lara, T.; Sánchez-Blázquez, P.; Sánchez-Menguiano, L.; Singh, R.; Spekkens, K.; Stanishev, V.; Torres-Papaqui, J. P.; van de Ven, G.; Vilchez, J. M.; Walcher, C. J.; Wild, V.; Wisotzki, L.; Ziegler, B.; Alves, J.; Barrado, D.; Quintana, J. M.; Aceituno, J.

2015-04-01

This paper describes the Second Public Data Release (DR2) of the Calar Alto Legacy Integral Field Area (CALIFA) survey. The data for 200 objects are made public, including the 100 galaxies of the First Public Data Release (DR1). Data were obtained with the integral-field spectrograph PMAS/PPak mounted on the 3.5 m telescope at the Calar Alto observatory. Two different spectral setups are available for each galaxy, (i) a low-resolution V500 setup covering the wavelength range 3745-7500 Å with a spectral resolution of 6.0 Å (FWHM); and (ii) a medium-resolution V1200 setup covering the wavelength range 3650-4840 Å with a spectral resolution of 2.3 Å (FWHM). The sample covers a redshift range between 0.005 and 0.03, with a wide range of properties in the color-magnitude diagram, stellar mass, ionization conditions, and morphological types. All the cubes in the data release were reduced with the latest pipeline, which includes improvedspectrophotometric calibration, spatial registration, and spatial resolution. The spectrophotometric calibration is better than 6% and the median spatial resolution is 2.̋4. In total, the second data release contains over 1.5 million spectra. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck-Institut für Astronomie (MPIA) and the Instituto de Astrofísica de Andalucía (CSIC).The second data release is available at http://califa.caha.es/DR2

Integral field spectroscopy of H II regions in M33

NASA Astrophysics Data System (ADS)

López-Hernández, Jesús; Terlevich, Elena; Terlevich, Roberto; Rosa-González, Daniel; Díaz, Ángeles; García-Benito, Rubén; Vílchez, José; Hägele, Guillermo

2013-03-01

Integral field spectroscopy is presented for star-forming regions in M33. A central area of 300 × 500 pc2 and the external H II region IC 132, at a galactocentric distance ˜19 arcmin (4.69 kpc), were observed with the Potsdam Multi-Aperture Spectrophotometer instrument at the 3.5-m telescope of the Centro Astronómico Hispano-Alemán (CAHA, aka Calar Alto Observatory). The spectral coverage goes from 3600 Å to 1 μm to include from [O II] λ3727 Å to the near-infrared lines required for deriving sulphur electron temperature and abundance diagnostics. Local conditions within individual H II regions are presented in the form of emission-line fluxes and physical conditions for each spatial resolution element (spaxel) and for segments with similar Hα surface brightness. A clear dichotomy is observed when comparing the central to outer disc H II regions. While the external H II region has higher electron temperature plus larger Hβ equivalent width, size and excitation, the central region has higher extinction and metal content. The dichotomy extends to the Baldwin-Phillips-Terlevich (BPT) diagnostic diagrams that show two orthogonal broad distributions of points. By comparing with pseudo-3D photoionization models, we conclude that the bulk of observed differences are probably related to a different ionization parameter and metallicity. Wolf-Rayet (WR) features are detected in IC 132, and resolved into two concentrations whose integrated spectra were used to estimate the characteristic number of WR stars. No WR features were detected in the central H II regions despite their higher metallicity.

The NGC 7771+NGC 7770 minor merger: harassing the little one?

NASA Astrophysics Data System (ADS)

Alonso-Herrero, Almudena; Rosales-Ortega, F. Fabián.; Sánchez, Sebastián. F.; Kennicutt, Robert C.; Pereira-Santaella, Miguel; Díaz, Ángeles I.

2012-09-01

Numerical simulations of minor mergers, typically having mass ratios greater than 3:1, predict little enhancement in the global star formation activity. However, these models also predict that the satellite galaxy is more susceptible to the effects of the interaction than the primary. We use optical integral field spectroscopy and deep optical imaging to study the NGC 7771+NGC 7770 interacting system (˜10:1 stellar mass ratio) to test these predictions. We find that the satellite galaxy NGC 7770 is currently experiencing a galaxy-wide starburst with most of the optical light being from young and post-starburst stellar populations (<1 Gyr). This galaxy lies off the local star-forming sequence for composite galaxies with an enhanced integrated specific star formation rate. We also detect in the outskirts of NGC 7770 Hα emitting gas filaments. This gas appears to have been stripped from one of the two galaxies and is being excited by shocks. All these results are consistent with a minor-merger-induced episode(s) of star formation in NGC 7770 after the first close passage. Such effects are not observed on the primary galaxy NGC 7771. Based on observations collected at the Centro Astronómico Hispano-Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck-Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC). The data presented here were obtained (in part) with ALFOSC, which is provided by the Instituto de Astrofísica de Andalucía (IAA) under a joint agreement with the University of Copenhagen and NOTSA.

Frozen-wave instability in near-critical hydrogen subjected to horizontal vibration under various gravity fields.

PubMed

Gandikota, G; Chatain, D; Amiroudine, S; Lyubimova, T; Beysens, D

2014-01-01

The frozen-wave instability which appears at a liquid-vapor interface when a harmonic vibration is applied in a direction tangential to it has been less studied until now. The present paper reports experiments on hydrogen (H2) in order to study this instability when the temperature is varied near its critical point for various gravity levels. Close to the critical point, a liquid-vapor density difference and surface tension can be continuously varied with temperature in a scaled, universal way. The effect of gravity on the height of the frozen waves at the interface is studied by performing the experiments in a magnetic facility where effective gravity that results from the coupling of the Earth's gravity and magnetic forces can be varied. The stability diagram of the instability is obtained. The experiments show a good agreement with an inviscid model [Fluid Dyn. 21 849 (1987)], irrespective of the gravity level. It is observed in the experiments that the height of the frozen waves varies weakly with temperature and increases with a decrease in the gravity level, according to a power law with an exponent of 0.7. It is concluded that the wave height becomes of the order of the cell size as the gravity level is asymptotically decreased to zero. The interface pattern thus appears as a bandlike pattern of alternate liquid and vapor phases, a puzzling phenomenon that was observed with CO2 and H2 near their critical point in weightlessness [Acta Astron. 61 1002 (2007); Europhys. Lett. 86 16003 (2009)].

Structure of Cometary Dust Particles

NASA Astrophysics Data System (ADS)

Levasseur-Regourd, A. C.; Hadamcik, E.; Lasue, J.

2004-11-01

The recent encounter of Stardust with comet 81P/Wild 2 has provided highly spatially resolved data about dust particles in the coma. They show intense swarms and bursts of particles, suggest the existence of fragmenting low-density particles formed of higher density sub-micrometer components [1], and definitely confirm previous results (inferred from Giotto encounter with comet Grigg-Skjellerup [2] and remote light scattering observations [3]). The light scattering properties (mostly polarization, which does not depend upon disputable normalizations) of dust in cometary comae will be summarized, with emphasis on the spatial changes and on the wavelength and phase angle dependence. Experimental and numerical simulations are needed to translate these observed light scattering properties in terms of physical properties of the dust particles (e.g. size, morphology, albedo, porosity). New experimental simulations (with fluffy mixtures of sub-micron sized silica and carbon grains) and new numerical simulations (with fractal aggregates of homogeneous or core-mantled silicate and organic grains) will be presented. The results are in favor of highly porous particles built up (by ballistic-cluster-cluster agglomeration) from grains of interstellar origin. The perspectives offered by laboratory simulations with aggregates built under conditions representative of the early solar system on board the International Space Station will be presented, together with the perspectives offered by future experiments on board the Rosetta cometary probe. Supports from CNES and ESA are acknowledged [1] Tuzzolino et al., Science, 304, 1776, 2004, [2] N. McBride et al., Mon. Not. R. Astron. Soc., 289, p. 535-553, 1997, [3] Levasseur-Regourd and Hadamcik, J. Quant. Spectros. Radiat. Transfer, 79-80, 903-910, 2003.

Prediction and Confirmation of V-type Asteroids Beyond 2.5 AU Based on SDSS Colors

NASA Astrophysics Data System (ADS)

Binzel, Richard P.; Masi, G.; Foglia, S.

2006-09-01

We apply a taxonomic classification system developed by Masi et al. (2006, submitted to Icarus) to identify C-, S-, and V-type asteroids present within the 3rd Release of the Sloan Digital Sky Survey Moving Object Catalog (SDSS MOC3). The classifications deduced by Masi et al. for 43,000 asteroids using SDSS colors are based on the taxonomy of Bus (1999; MIT Ph.D. thesis). To link SDSS colors to the Bus taxonomy, Masi et al. (2006) use 149 objects measured in common by both SDSS and the Small Main-Belt Asteroid Spectroscopic Survey (SMASS) (Bus and Binzel 2002, Icarus 158, 106). We report results of direct testing of SDSS V-type classification predictions for six objects, where the tests were performed by visible wavelength spectroscopy (Lazzaro et al. 2004, Icarus 172, 179) and target of opportunity near-infrared spectroscopy obtained using the NASA Infrared Telescope Facility (IRTF). Vesta-like spectra and a V-type taxonomy are confirmed for five of the six predicted V-type objects sampled. Most interestingly, the SDSS taxonomy correctly predicted the V-type spectral characteristics for asteroid (21238) 1995 WV7, a 6 km asteroid located far from Vesta across the 3:1 mean motion resonance at 2.54 AU. (Proper elements a,e,i: 2.54 AU, 0.14, and 10.8 deg.) Given the 2 km/sec ejection velocity required from Vesta to reach the current orbit, and the difficulty of migrating across the 3:1 resonance (at 2.5 AU) by a process such as Yarkovsky drift or via secular resonances (Carruba et al. 2005, Astron. Astrophys. 441, 819), asteroid 21238 may be a new candidate for a basaltic asteroid having no relationship to Vesta.

The eccentric Kozai-Lidov effect as a resonance phenomenon

NASA Astrophysics Data System (ADS)

Sidorenko, Vladislav V.

2018-01-01

Exploring weakly perturbed Keplerian motion within the restricted three-body problem, Lidov (Planet Space Sci 9:719-759, 1962) and, independently, Kozai (Astron J 67:591-598, 1962) discovered coupled oscillations of eccentricity and inclination (the KL cycles). Their classical studies were based on an integrable model of the secular evolution, obtained by double averaging of the disturbing function approximated with its first non-trivial term. This was the quadrupole term in the series expansion with respect to the ratio of the semimajor axis of the disturbed body to that of the disturbing body. If the next (octupole) term is kept in the expression for the disturbing function, long-term modulation of the KL cycles can be established (Ford et al. in Astrophys J 535:385-401, 2000; Naoz et al. in Nature 473:187-189, 2011; Katz et al. in Phys Rev Lett 107:181101, 2011). Specifically, flips between the prograde and retrograde orbits become possible. Since such flips are observed only when the perturber has a nonzero eccentricity, the term "eccentric Kozai-Lidov effect" (or EKL effect) was proposed by Lithwick and Naoz (Astrophys J 742:94, 2011) to specify such behavior. We demonstrate that the EKL effect can be interpreted as a resonance phenomenon. To this end, we write down the equations of motion in terms of "action-angle" variables emerging in the integrable Kozai-Lidov model. It turns out that for some initial values the resonance is degenerate and the usual "pendulum" approximation is insufficient to describe the evolution of the resonance phase. Analysis of the related bifurcations allows us to estimate the typical time between the successive flips for different parts of the phase space.

The ultraviolet reflectance of Enceladus: Implications for surface composition

NASA Astrophysics Data System (ADS)

Hendrix, Amanda R.; Hansen, Candice J.; Holsclaw, Greg M.

2010-04-01

The reflectance of Saturn's moon Enceladus has been measured at far ultraviolet (FUV) wavelengths (115-190 nm) by Cassini's Ultraviolet Imaging Spectrograph (UVIS). At visible and near infrared (VNIR) wavelengths Enceladus' reflectance spectrum is very bright, consistent with a surface composed primarily of H 2O ice. At FUV wavelengths, however, Enceladus is surprisingly dark - darker than would be expected for pure water ice. Previous analyses have focused on the VNIR spectrum, comparing it to pure water ice (Cruikshank, D.P., Owen, T.C., Dalle Ore, C., Geballe, T.R., Roush, T.L., de Bergh, C., Sandford, S.A., Poulet, F., Benedix, G.K., Emery, J.P. [2005] Icarus, 175, 268-283) or pure water ice plus a small amount of NH 3 (Emery, J.P., Burr, D.M., Cruikshank, D.P., Brown, R.H., Dalton, J.B. [2005] Astron. Astrophys., 435, 353-362) or NH 3 hydrate (Verbiscer, A.J., Peterson, D.E., Skrutskie, M.F., Cushing, M., Helfenstein, P., Nelson, M.J., Smith, J.D., Wilson, J.C. [2006] Icarus, 182, 211-223). We compare Enceladus' FUV spectrum to existing laboratory measurements of the reflectance spectra of candidate species, and to spectral models. We find that the low FUV reflectance of Enceladus can be explained by the presence of a small amount of NH 3 and a small amount of a tholin in addition to H 2O ice on the surface. The presence of these three species (H 2O, NH 3, and a tholin) appears to satisfy not only the low FUV reflectance and spectral shape, but also the middle-ultraviolet to visible wavelength brightness and spectral shape. We expect that ammonia in the Enceladus plume is transported across the surface to provide a global coating.

Anisotropic extinction distortion of the galaxy correlation function

NASA Astrophysics Data System (ADS)

Fang, Wenjuan; Hui, Lam; Ménard, Brice; May, Morgan; Scranton, Ryan

2011-09-01

Similar to the magnification of the galaxies’ fluxes by gravitational lensing, the extinction of the fluxes by comic dust, whose existence is recently detected by [B. Ménard, R. Scranton, M. Fukugita, and G. Richards, Mon. Not. R. Astron. Soc.MNRAA40035-8711 405, 1025 (2010)DOI: 10.1111/j.1365-2966.2010.16486.x.], also modifies the distribution of a flux-selected galaxy sample. We study the anisotropic distortion by dust extinction to the 3D galaxy correlation function, including magnification bias and redshift distortion at the same time. We find the extinction distortion is most significant along the line of sight and at large separations, similar to that by magnification bias. The correction from dust extinction is negative except at sufficiently large transverse separations, which is almost always opposite to that from magnification bias (we consider a number count slope s>0.4). Hence, the distortions from these two effects tend to reduce each other. At low z (≲1), the distortion by extinction is stronger than that by magnification bias, but at high z, the reverse holds. We also study how dust extinction affects probes in real space of the baryon acoustic oscillations (BAO) and the linear redshift distortion parameter β. We find its effect on BAO is negligible. However, it introduces a positive scale-dependent correction to β that can be as large as a few percent. At the same time, we also find a negative scale-dependent correction from magnification bias, which is up to percent level at low z, but to ˜40% at high z. These corrections are non-negligible for precision cosmology, and should be considered when testing General Relativity through the scale-dependence of β.

Comets 169P/NEAT and P/2003 T12 (SOHO): Two possible fragments of a common ancestor?

NASA Astrophysics Data System (ADS)

Sosa, Andrea; Fernández, Julio Angel

2015-08-01

In a recent work we analyzed the orbit evolution of Jupiter family comets in near-Earth orbits, and found some comets moving on highly stable orbits, like the near-Earth asteroids (Fernández & Sosa 2015). Two of them actually show almost identical orbits; they are the comets 169P/NEAT and P/2003 T12 (SOHO). Comet 169P seems to be a few km-sized, almost inactive body, while P/2003 T12 would be a very small comet, with a sub-km radius nucleus. We performed extended orbital integrations for the past 100,000 yr to further study their dynamical evolution. We found that the orbital parameters remain stable for several thousand years, with a well defined absolute minimum of their relative spatial distance around 2900 yr in the past, coincident with a low value of the relative velocity. This spatial minimum is in a remarkable good agreement with the results obtained by means of other methods to study common origins between pairs of asteroids (Vokrouhlicky & Nesvorny 2008, Southworth & Hawkins 1963), and to test a comet-meteor shower association (Drummond 1981). Our results support the hypothesis of a breakup of a parent body, that ocurred about 2900 yr ago, as the most probable origin for the studied pair of comets. Possible fragmentation mechanisms, like thermal stress, rotational instability, or colisions, are briefly discussed.References:Drumond J.D. 1981. Icarus 45, 545-553.Fernández J.A., & Sosa A. 2015. Submitted to Planetary & Space Science.Southworth R.B., & Hawkins, G.S. 1963. Smithson. Contrib. Astrophys. 7, 261-285Vokrouhlicky D., & Nesvorny D. 2008. Astron. J. 136, 280-290.

LM1-64: a Newly Reported Lmc-Pn with WR Nucleus

NASA Astrophysics Data System (ADS)

Pena, M.; Olguin, L.; Ruiz, M. T.; Torres-Peimbert, S.

1993-05-01

The object LM1-64 was reported by Lindsay & Mullan (1963, Irish Astron. J., 5, 51) as a probable PN in the LMC. Optical and UV spectra taken by us confirm that suggestion. LM1-64 is a high excitation planetary nebulae which shows evidence of having a WC central star. Broad stellar emission at lambda 4650 is detected in the optical spectrum obtained with the CTIO 4m telescope, in 1989. A UV spectrum in the range from 1200 Angstroms to 2000 Angstroms was obtained with IUE in 1990. We have measured all the emission line fluxes available and determined values for the physical conditions and chemical abundances of the nebular ionized gas. The derived values are T(OIII) = 14000K, log He/H = 11.05, log C/H = 9.48, log O/H = 8.55 and log Ne/H = 7.94. LM1-64 shows a large C enhancement in the envelope as result of the central star activity, while He, O and Ne are comparable to the average values reported for the LMC-PNe (Monk, Barlow & Clegg, 1988, MNRAS, 234, 583). We have estimated the He II Zanstra temperature of the central star to be ~ 80,000 K. This temperature is much higher than the values reported for the known LMC-PNe with WR nucleus that Monk et al. have classified as W4 to W8. The only other high temperature WR nucleus in a LMC-PN is N66 which recently showed evidence of undergoing a WR episode (Torres-Peimbert, Ruiz, Peimbert & Pe\\ na, 1993, IAU Symp. 155, eds. A. Acker & R. Weinberger, in press).

Structure and Electronic Properties of Ionized PAH Clusters

NASA Astrophysics Data System (ADS)

Joblin, Christine; Kokkin, Damian L.; Sabbah, Hassan; Bonnamy, Anthony; Dontot, Leo; Rapacioli, Mathias; Simon, Aude; Spiegelman, Fernand; Parneix, Pascal; Pino, Thomas; Pirali, Olivier; Falvo, Cyril; Gamboa, Antonio; Brechignac, Philippe; Garcia, Gustavo A.; Nahon, Laurent

2014-06-01

Polycyclic aromatic hydrocarbon (PAH) clusters have been proposed as candidates for evaporating very small grains that are revealed by their mid-IR emission at the surface of UV-irradiated clouds in interstellar space. This suggestion is a motivation for further characterization of the properties of these clusters in particular when they are ionized. We have used a molecular beam coupled to the photoelectron-photoion coincidence spectrometer DELICIOUS II/ III at the VUV beamline DESIRS of the synchrotron SOLEIL to characterize the electronic properties of cationic coronene (C24H12) and pyrene (C16H10) clusters up to the pentamer and heptamer, respectively. These experimental results are analysed in the light of electronic structure calculations. Simulations of the properties of ionized PAH clusters are faced with the difficulty of describing charge delocalization in these large systems. We will show that recent developments combining a Density Functional Tight Binding method with Configuration Interaction scheme is successful in simulating the ionization potential, which gives strong confidence into the predicted structures for these PAH clusters. We will also present current effort to study charge transfer states by performing complementary measurements with the PIRENEA ion trap set-up. Joint ANR project GASPARIM, ANR-10-BLAN-501 M. Rapacioli, C. Joblin and P. Boissel Astron. & Astrophys., 429 (2005), 193-204. G. Garcia, H. Soldi-Lose and L. Nahon Rev. Sci. Instrum., 80 (2009), 023102; G. Garcia, B. Cunha de Miranda, M. Tia, S. Daly, L. Nahon, Rev. Sci. Instrum., 84 (2013), 053112 M. Rapacioli, A. Simon, L. Dontot and F. Spiegelman Phys. Status Solidi B, 249 (2) (2012), 245-258; L. Dontot, M. Rapacioli and F. Spiegelman (2014) submitted

Spectroscopic and photometric variability of the O9.5 Vp star HD 93521

NASA Astrophysics Data System (ADS)

Rauw, G.; De Becker, M.; van Winckel, H.; Aerts, C.; Eenens, P.; Lefever, K.; Vandenbussche, B.; Linder, N.; Nazé, Y.; Gosset, E.

2008-08-01

Aims: The line profile variability and photometric variability of the O9.5 Vp star HD 93521 are examined in order to establish the properties of the non-radial pulsations in this star. Methods: Fourier techniques are used to characterize the modulations of the He i λλ 5876, 6678 and H α lines in several spectroscopic time series and to search for variations in a photometric time series. Results: Our spectroscopic data confirm the existence of two periods of 1.75 and 2.89 h. The line profiles, especially those affected by emission wings, exhibit also modulations on longer time scales, but these are epoch-dependent and change from line to line. Unlike previous claims, we find no unambiguous signature of the rotational period in our data, nor of a third pulsation period (corresponding to a frequency of 2.66 d-1). Conclusions: HD 93521 very likely exhibits non-radial pulsations with periods of 1.75 and 2.89 h with l ≃ 8 ± 1 and l ≃ 4 ± 1 respectively. No significant signal is found in the first harmonics of these two periods. The 2.89 h mode is seen at all epochs and in all lines investigated, while the visibility of the 1.75 h mode is clearly epoch-dependent. Whilst light variations are detected, their connection to these periodicities is not straightforward. Based on observations collected at the Observatoire de Haute Provence (France), the Flemish 1.2 m Mercator telescope at the Roque de los Muchachos observatory (La Palma, Spain) and the Observatorio Astronómico Nacional of San Pedro Mártir (Mexico).

Migration of Frosts from High-Albedo Regions of Pluto: what New Horizons Reveals

NASA Astrophysics Data System (ADS)

Buratti, Bonnie J.; Stern, S. A.; Weaver, Hal A.; Young, Leslie A.; Olkin, Cathy B.; Ennico, Kimberly; Binzel, Richard P.; Zangari, Amanda; Earle, Alissa M.

2015-11-01

With its high eccentricity and obliquity, Pluto should exhibit seasonal volatile transport on its surface. Several lines of evidence support this transport: doubling of Pluto’s atmospheric pressure over the past two decades (Young et al., 2013, Ap. J. 766, L22; Olkin et al., 2015, Icarus 246, 230); changes in its historical rotational light curve, once all variations due to viewing geometry have been modelled (Buratti et al., 2015; Ap. J. 804, L6); and changes in HST albedo maps (Buie et al., 2010, Astron. J. 139, 1128). New Horizons LORRI images reveal that the region of greatest albedo change is not the polar cap(s) of Pluto, but the feature informally named Tombaugh Regio (TR). This feature has a normal reflectance as high as ~0.8 in some places, and it is superposed on older, lower-albedo pre-existing terrain with an albedo of only ~0.10. This contrast is larger than any other body in the Solar System, except for Iapetus. This albedo dichotomy leads to a complicated system of cold-trapping and thermal segregation, beyond the simple picture of seasonal volatile transport. Whatever the origin of TR, it initially acted as a cold trap, as the temperature differential between the high and low albedo regions could be enormous, possibly approaching 20K, based on their albedo differences and assuming their normalized phase curves are similar. This latter assumption will be refined as the full New Horizons data set is returned.Over six decades of ground-based photometry suggest that TR has been decreasing in albedo over the last 25 years. Possible causes include changing insolation angles, or sublimation from the edges where the high-albedo material impinges on a much warmer substrate.Funding by the NASA New Horizons Project acknowledged.

Contribution of astrology in medicine -- a review.

PubMed

Sharma, Bhuvnesh Kumar; Prasad, P V V; Narayana, A

2007-01-01

Astrology is the art of predicting or determining the influence of the planets and stars on human affairs. The origin of this word is from Greek word astron, star + logos (discourse). Both Ayurveda and Astrology have established a way of life in India since time immemorial. Highly advanced knowledge related to Astrology on medicine is preserved in Indian Holy scriptures and transmitted from generation to generation. Although both Astrology and medicine were developed as a part of religion in ancient India, astrological principles related to prevention, health care and relief from illness were applied as rituals (religious ceremonies). An astrologer gives guidance for taking medicines at suitable time for the best remedy of ailments. Even the medicinal herbs were collected and used at appropriate times for their efficacy. Astrology and Ayurveda are inseparable in human life. Role of the Astrology in healthy life and pathogenesis of the disease is well known to Indians. When a physician knows etiology of the disease, he attempts to treat the disease with specific medication, diet and life style and also avoiding causative factors. In a case where a physician is unable to understand the pathogenesis of the disease and to treat, the patient depends upon Astrology. Account of good and bad deeds during this life and previous lives, their consequences of health or ill health during this life which orderly, when, what and how will be clearly known through Astrology. It gives guidelines about welfare not only to human being but also to whole creation and also indicates about calamities and their solutions as possible extent. Hence a concise astrological evaluation related to prevention, health care, diagnosis and treatment of diseases is being presented in this article.

Gravitational wave transient signal emission via Ekman pumping in neutron stars during post-glitch relaxation phase

NASA Astrophysics Data System (ADS)

Singh, Avneet

2017-01-01

Glitches in the rotational frequency of a spinning neutron star could be promising sources of gravitational wave signals lasting between a few microseconds to a few weeks. The emitted signals and their properties depend upon the internal properties of the neutron star. In neutron stars, the most important physical properties of the fluid core are the viscosity of the fluid, the stratification of flow in the equilibrium state, and the adiabatic sound speed. Such models were previously studied [C. A. van Eysden and A. Melatos, Classical Quantum Gravity 25, 225020 (2008, 10.1088/0264-9381/25/22/225020); M. F. Bennett, C. A. van Eysden, and A. Melatos, Mon. Not. R. Astron. Soc. 409, 1705 (2010), 10.1111/j.1365-2966.2010.17416.x] following simple assumptions on all contributing factors, in which the post-glitch relaxation phase could be driven by the well-known process of Ekman pumping [G. Walin, J. Fluid Mech. 36, 289 (1969, 10.1017/S0022112069001662); M. Abney and R. I. Epstein, J. Fluid Mech. 312, 327 (1996), 10.1017/S0022112096002030]. We explore the hydrodynamic properties of the flow of fluid during this phase following more relaxed assumptions on the stratification of flow and the pressure-density gradients within the neutron star than previously studied. We calculate the time scales of duration as well as the amplitudes of the resulting gravitational wave signals, and we detail their dependence on the physical properties of the fluid core. We find that it is possible for the neutron star to emit gravitational wave signals in a wide range of decay time scales and within the detection sensitivity of aLIGO for selected domains of physical parameters.

Sun-sized Water Vapor Masers in Cepheus A

NASA Astrophysics Data System (ADS)

Sobolev, A. M.; Moran, J. M.; Gray, M. D.; Alakoz, A.; Imai, H.; Baan, W. A.; Tolmachev, A. M.; Samodurov, V. A.; Ladeyshchikov, D. A.

2018-03-01

We present the first VLBI observations of a Galactic water maser (in Cepheus A) made with a very long baseline interferometric array involving the RadioAstron Earth-orbiting satellite station as one of its elements. We detected two distinct components at ‑16.9 and 0.6 km s‑1 with a fringe spacing of 66 μas. In total power, the 0.6 km s‑1 component appears to be a single Gaussian component of strength 580 Jy and width of 0.7 km s‑1. Single-telescope monitoring showed that its lifetime was only eight months. The absence of a Zeeman pattern implies the longitudinal magnetic field component is weaker than 120 mG. The space–Earth cross power spectrum shows two unresolved components smaller than 15 μas, corresponding to a linear scale of 1.6 × 1011 cm, about the diameter of the Sun, for a distance of 700 pc, separated by 0.54 km s‑1 in velocity and by 160 ± 35 μas in angle. This is the smallest angular structure ever observed in a Galactic maser. The brightness temperatures are greater than 2 × 1014 K, and the line widths are 0.5 km s‑1. Most of the flux (about 87%) is contained in a halo of angular size of 400 ± 150 μas. This structure is associated with the compact H II region HW3diii. We have probably picked up the most prominent peaks in the angular size range of our interferometer. We discuss three dynamical models: (1) Keplerian motion around a central object, (2) two chance overlapping clouds, and (3) vortices caused by flow around an obstacle (i.e., von Kármán vortex street) with a Strouhal number of about 0.3.

Ozone Production in Irradiated Laboratory Ices Relevant to Europa and Ganymede

NASA Astrophysics Data System (ADS)

Cooper, P. D.; Moore, M. H.; Hudson, R. L.

2005-08-01

Observations suggest ozone (O3) is present on the icy surfaces of Ganymede (1), and Rhea and Dione (2). Molecular oxygen (O2) has also been observed on Europa (3) and Ganymede (4). The formation and trapping of such molecules in ice and their subsequent transportation to a sub-surface ocean may be potentially important for sustaining astrobiological life (5). It is assumed that ozone is produced in these icy surfaces by the addition of an oxygen atom to molecular oxygen, with the latter formed by prior irradiation of the water ice. The infrared absorption band of ozone in ice at 1037 cm-1 is strong and thus makes ozone a good tracer for the presence of molecular oxygen which is difficult to detect. We will present results of water/oxygen ices irradiated with 800 keV protons and show the band position and growth of ozone with increasing radiation dose. The thermal stability of this radiolytically-produced ozone has also been measured and comparisons made to the Jovian satellites. P. Cooper is grateful for the support from the National Academies Research Associateship Program. (1) Noll, K.S., Johnson, R.E., Lane, A.L., Domingue, D.L., Weaver, H.A., Science, 273, 341-343, (1996). (2) Noll, K.S., Roush, T.L., Cruikshank, D.P., Johnson, R.E., Pendleton, Y.J., Nature, 388, 45-47, (1997). (3) Spencer, J.R., Calvin, W.M., Astron. J., 124, 3400-3403, (2002). (4) Spencer, J.R., Calvin, W.M., Person, M. J., J. Geo. Res. 100 (E9), 19049-19056 (1995). (5) Chyba, C.F., Hand, K.P., Science, 292, 2026-2027, (2001).

Volatile Transport on Pluto: First Results from the 2013 Observing Season

NASA Astrophysics Data System (ADS)

Buratti, B. J.; Dalba, P. A.; Hicks, M.; Chu, D.; O'Neill, A.; Chesley, J. P.

2013-12-01

With the New Horizons spacecraft due to encounter Pluto in slightly less than two years, close scrutiny of this dwarf ice planet has begun in earnest. Ground-based observations are especially critical for context and for a larger temporal excursion. Seasonal transport of volatiles should occur on Pluto, and this transport should be detectable through changes in its rotational light curve, once all variations due to viewing geometry have been modeled. Giving the steady increase observed in Pluto's atmospheric pressure over the past two decades, associated sublimation of frost from the surface has likely occurred, as predicted by volatile transport models. Rotational light curves of Pluto through time have been created for static frost models based on images from the Hubble Space Telescope. These models, which account for changes in viewing geometry, have been compared with observed light curves obtained between 1950 and 2013. No evidence for transport was evident prior to 2000. Observations from 2002 (Buie et al., 2010, Astron. J. 139, 1128) and 2007-2008 (Hicks et al. 2008, B.A.A.S. 40, 460) suggest changes in the frost pattern on Pluto's surface. New observations of Pluto's light curve from the 2013 season from Table Mountain Observatory show no evidence for the large transport of volatiles on Pluto's surface. Our data are the first measurement of a large opposition surge on Pluto similar to that seen on other icy bodies. Both Buie et al. (2010) and our observations from the 2012-2013 seasons show that Pluto is becoming more red in color. This observation makes sense if nitrogen is being removed from the surface to uncover a red, photolyzed substrate of methane. Funded by NASA.

On the calibration of the COBE/IRAS dust emission reddening maps

NASA Astrophysics Data System (ADS)

Dutra, C. M.; Ahumada, A. V.; Clariá, J. J.; Bica, E.; Barbuy, B.

2003-09-01

In this work we study the spectral properties (3600-6800 Å) of the nuclear region of early-type galaxies at low (|b|<25deg), intermediate (including surroundings of the Magellanic Clouds) and high (South Polar Cap) Galactic latitudes. We determine the E(B-V) reddening values of the galaxies by matching their continuum distribution with respect to those of reddening-free spectral galaxy templates with similar stellar populations. We also compare the spectroscopic reddening value of each galaxy with that derived from 100 mu m dust emission (E(B-V)FIR) in its line of sight, and we find that there is agreement up to E(B-V)=0.25. Beyond this limit E(B-V)FIR values are higher. Taking into account the data up to E(B-V) ~ 0.7, we derive a calibration factor of 0.016 between the spectroscopic E(B-V) values and Schlegel et al.'s (\\cite{Schlegel1998}) opacities. By combining this result with an AK extinction map built within ten degrees of the Galactic centre using Bulge giants as probes (Dutra et al. \\cite{Dutra2003}), we extended the calibration of dust emission reddening maps to low Galactic latitudes down to |b|=4deg and E(B-V)= 1.6 (AV ~ 5). According to this new calibration, a multiplicative factor of ~0.75 must be applied to the COBE/IRAS dust emission reddening maps. Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Pata, Córdoba and San Juan, Argentina.

Photometric and integrated spectral study of the young open clusters Pismis 22, NGC 6178, NGC 6216 and Ruprecht 130

NASA Astrophysics Data System (ADS)

Piatti, A. E.; Clariá, J. J.; Bica, E.

2000-08-01

We present CCD observations in the B, V , and I passbands obtained for stars in the fields of the open clusters Pismis 22, NGC 6178, NGC 6216, and Ruprecht 130, projected not far from the Galactic centre (|l| < 30̂, |b| < 2̂). The sample consists of about 790 stars reaching down to V ~ 18-19 mag. From the analysis of the colour magnitude diagrams, we confirmed the physical reality of the clusters and derived their reddening, distance and age. In addition, we obtained flux-calibrated integrated spectra in the range 3500-9200 Å for the cluster sample. The equivalent widths of the Balmer lines provided us with age estimates, while the comparison with template spectra allowed us to derive both foreground reddening and age. The photometric and spectroscopic results reveal that the four studied objects are young open clusters with ages ranging between 35 and 50 Myr. The clusters, located between 1.0 kpc and 4.3 kpc from the Sun, are affected by different amounts of interstellar visual absorption (0.6 ≃ Av ≃ 6.0). Based on observations made at Complejo Astronómico El Leoncito, which is operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la Repúbica Argentina and the National Universities of La Plata, Córdoba, and San Juan, Argentina, and at the University of Toronto (David Dunlap Observatory) 24-inch telescope, Las Campanas, Chile. Tables 3-6 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html

Protective effects of biodegradable collagen implants on thinned sclera after strabismus surgery: a paired-eye study.

PubMed

Yoo, Tae Keun; Han, Sueng-Han; Han, Jinu

2017-12-01

To determine the efficacy of a biodegradable Ologen (Aeon Astron Europe BV, Leiden, The Netherlands) collagen matrix in reducing the blue color change due to exposed thinned sclera after strabismus surgery. Fourteen patients with intermittent exotropia undergoing symmetric bilateral lateral rectus recession surgery were included in this prospective, randomized, paired-eye controlled study. In each patient, Ologen was implanted at the original rectus insertion site in one randomly selected eye; the other eye underwent conventional surgery. Ologen was inserted under the conjunctiva without suturing, covering the muscle insertion site. Conjunctival color change was analyzed using computer-based image analysis immediately and 1 week, 1 month, and 3 months postoperatively. Slit-lamp photographs of each eye were evaluated using contrast limited adaptive histogram equalization (CLAHE), Canny edge, and the RGB (red-green-blue) model. Secondary outcomes were conjunctival and sclera thickness 3 months postoperatively determined by anterior segment optical coherence tomography. Immediately and 1 week postoperatively all color models showed no significant differences between Ologen-implanted and control eyes. Three months postoperatively, Ologen-implanted eyes exhibited significantly lower CLAHE (P = 0.041) and RGB model blue color (P = 0.008) values than control eyes. Canny edge (P = 0.061) and RGB model red color (P = 0.152) values did not differ between eyes. Conjunctival stroma and episcleral complex thickness was greater in Ologen-implanted eyes than in controls (P = 0.001). Blue color change was significantly less noticeable in Ologen-implanted eyes than in controls. Thus, Ologen implantation helps prevent visible blue sclera at the original rectus insertion site after lateral rectus recession. Copyright © 2017 American Association for Pediatric Ophthalmology and Strabismus. Published by Elsevier Inc. All rights reserved.

Applicability of meteor radiant determination methods depending on orbit type. II. Low-eccentric orbits

NASA Astrophysics Data System (ADS)

Svoren, J.; Neslusan, L.; Porubcan, V.

1994-08-01

All known parent bodies of meteor showers belong to bodies moving in high-eccentricity orbits (e => 0.5). Recently, asteroids in low-eccentricity orbits (e < 0.5) approaching the Earth's orbit, were suggested as another population of possible parent bodies of meteor streams. This paper deals with the problem of calculation of meteor radiants connected with the bodies in low-eccentricity orbits from the point of view of optimal results depending on the method applied. The paper is a continuation of our previous analysis of high-eccentricity orbits (Svoren, J., Neslusan, L., Porubcan, V.: 1993, Contrib. Astron. Obs. Skalnate Pleso 23, 23). Some additional methods resulting from mathematical modelling are presented and discussed together with Porter's, Steel-Baggaley's and Hasegawa's methods. In order to be able to compare how suitable the application of the individual radiant determination methods is, it is necessary to determine the accuracy with which they approximate real meteor orbits. To verify the accuracy with which the orbit of a meteoroid with at least one node at 1 AU fits the original orbit of the parent body, the Southworth-Hawkins D-criterion (Southworth, R.B., Hawkins, G.S.: 1963, Smithson. Contr. Astrophys. 7, 261) was applied. D <= 0.1 indicates a very good fit of orbits, 0.1 < D <= 0.2 is considered for a good fit and D > 0.2 means that the fit is rather poor and the change of orbit unrealistic. The optimal method, i.e. the one which results in the smallest D values for the population of low-eccentricity orbits, is that of adjusting the orbit by varying both the eccentricity and perihelion distance. A comparison of theoretical radiants obtained by various methods was made for typical representatives from each group of the NEA (near-Earth asteroids) objects.

Complex dynamics in a simple model of pulsations for super-asymptotic giant branch stars.

PubMed

Munteanu, Andreea; Garcia-Berro, Enrique; Jose, Jordi; Petrisor, Emilia

2002-06-01

When intermediate mass stars reach their last stages of evolution they show pronounced oscillations. This phenomenon happens when these stars reach the so-called asymptotic giant branch (AGB), which is a region of the Hertzsprung-Russell diagram located at about the same region of effective temperatures but at larger luminosities than those of regular giant stars. The period of these oscillations depends on the mass of the star. There is growing evidence that these oscillations are highly correlated with mass loss and that, as the mass loss increases, the pulsations become more chaotic. In this paper we study a simple oscillator which accounts for the observed properties of this kind of stars. This oscillator was first proposed and studied in Icke et al. [Astron. Astrophys. 258, 341 (1992)] and we extend their study to the region of more massive and luminous stars -the region of super-AGB stars. The oscillator consists of a periodic nonlinear perturbation of a linear Hamiltonian system. The formalism of dynamical systems theory has been used to explore the associated Poincare map for the range of parameters typical of those stars. We have studied and characterized the dynamical behavior of the oscillator as the parameters of the model are varied, leading us to explore a sequence of local and global bifurcations. Among these, a tripling bifurcation is remarkable, which allows us to show that the Poincare map is a nontwist area preserving map. Meandering curves, hierarchical-islands traps and sticky orbits also show up. We discuss the implications of the stickiness phenomenon in the evolution and stability of the super-AGB stars. (c) 2002 American Institute of Physics.

New relativistic effective interaction for finite nuclei, infinite nuclear matter, and neutron stars

NASA Astrophysics Data System (ADS)

Kumar, Bharat; Patra, S. K.; Agrawal, B. K.

2018-04-01

We carry out the study of finite nuclei, infinite nuclear matter, and neutron star properties with the newly developed relativistic force, the Institute of Physics Bhubaneswar-I (IOPB-I). Using this force, we calculate the binding energies, charge radii, and neutron-skin thickness for some selected nuclei. From the ground-state properties of superheavy nuclei (Z =120 ), it is noticed that considerable shell gaps appear at neutron numbers N =172 , 184, and 198, manifesting the magicity at these numbers. The low-density behavior of the equation of state for pure neutron matter is compatible with other microscopic models. Along with the nuclear symmetry energy, its slope and curvature parameters at the saturation density are consistent with those extracted from various experimental data. We calculate the neutron star properties with the equation of state composed of nucleons and leptons in β -equilibrium, which are in good agreement with the x-ray observations by Steiner [Astrophys. J. 722, 33 (2010), 10.1088/0004-637X/722/1/33] and Nättilä [Astron. Astrophys. 591, A25 (2016), 10.1051/0004-6361/201527416]. Based on the recent observation of GW170817 with a quasi-universal relation, Rezzolla et al. [Astrophys. J. Lett. 852, L25 (2018), 10.3847/2041-8213/aaa401] have set a limit for the maximum mass that can be supported against gravity by a nonrotating neutron star in the range 2.01 ±0.04 ≲M (M⊙)≲2.16 ±0.03 . We find that the maximum mass of the neutron star for the IOPB-I parametrization is 2.15 M⊙ . The radius and tidal deformability of a canonical neutron star of mass 1.4 M⊙ are 13.2 km and 3.9 ×1036g cm2s2 , respectively.

Metrics in Keplerian orbits quotient spaces

NASA Astrophysics Data System (ADS)

Milanov, Danila V.

2018-03-01

Quotient spaces of Keplerian orbits are important instruments for the modelling of orbit samples of celestial bodies on a large time span. We suppose that variations of the orbital eccentricities, inclinations and semi-major axes remain sufficiently small, while arbitrary perturbations are allowed for the arguments of pericentres or longitudes of the nodes, or both. The distance between orbits or their images in quotient spaces serves as a numerical criterion for such problems of Celestial Mechanics as search for common origin of meteoroid streams, comets, and asteroids, asteroid families identification, and others. In this paper, we consider quotient sets of the non-rectilinear Keplerian orbits space H. Their elements are identified irrespective of the values of pericentre arguments or node longitudes. We prove that distance functions on the quotient sets, introduced in Kholshevnikov et al. (Mon Not R Astron Soc 462:2275-2283, 2016), satisfy metric space axioms and discuss theoretical and practical importance of this result. Isometric embeddings of the quotient spaces into R^n, and a space of compact subsets of H with Hausdorff metric are constructed. The Euclidean representations of the orbits spaces find its applications in a problem of orbit averaging and computational algorithms specific to Euclidean space. We also explore completions of H and its quotient spaces with respect to corresponding metrics and establish a relation between elements of the extended spaces and rectilinear trajectories. Distance between an orbit and subsets of elliptic and hyperbolic orbits is calculated. This quantity provides an upper bound for the metric value in a problem of close orbits identification. Finally the invariance of the equivalence relations in H under coordinates change is discussed.

The Problem of Longitude in the 18th Century: Jorge Juan, Antonio de Ulloa and the Expedition of the Paris Academy of Sciences to the Kingdom of Peru

NASA Astrophysics Data System (ADS)

Gutiérrez, Manuel Pérez

2015-05-01

Jorge Juan and Antonio de Ulloa, naval officers of the Spanish Navy in the Midshipmen's Royal Academy were appointed to take part in one of the most important scientific expeditions of the 18th century. The question of the shape of the Earth, of vital importance for navigation, was solved by the Paris Academy of Sciences by request of Louis XV of France in 1735. The aim was to determine the form of the ellipsoid that Newton had described in the 17th century for any spherical and homogeneous body in rotation about an axis. Two expeditions were prepared for the geodetic measures of meridian arc both in high latitudes (Lapland, Finland) and in the equatorial zone (the Kingdom of Peru); Pierre Louis Maupertuis took charge of the northern expedition whereas the second one was charged to La Condamine, along with Jorge Juan and Antonio de Ulloa. The results obtained by the Spaniards were gathered in a publication: Observaciones astronómicas y físicas hechas en los Reinos del Perú. In it, they dedicate a chapter to the determination of astronomic longitude with the only technology that was providing certain precision at the moment: the simultaneous observation of the same astronomic phenomenon in two different places. Specifically, they explain in detail in Book III: Las Observaciones de la Inmersiones y Emersiones de los satélites de Júpiter, como asimismo de los eclipses de Luna; de las cuales de deduce la Longitud de los Lugares, incluyendo las correcciones a efectuar por la variación de la declinación diaria del Sol.

An analysis of the convergence of Newton iterations for solving elliptic Kepler's equation

NASA Astrophysics Data System (ADS)

Elipe, A.; Montijano, J. I.; Rández, L.; Calvo, M.

2017-12-01

In this note a study of the convergence properties of some starters E_0 = E_0(e,M) in the eccentricity-mean anomaly variables for solving the elliptic Kepler's equation (KE) by Newton's method is presented. By using a Wang Xinghua's theorem (Xinghua in Math Comput 68(225):169-186, 1999) on best possible error bounds in the solution of nonlinear equations by Newton's method, we obtain for each starter E_0(e,M) a set of values (e,M) \\in [0, 1) × [0, π ] that lead to the q-convergence in the sense that Newton's sequence (E_n)_{n ≥ 0} generated from E_0 = E_0(e,M) is well defined, converges to the exact solution E^* = E^*(e,M) of KE and further \\vert E_n - E^* \\vert ≤ q^{2^n -1} \\vert E_0 - E^* \\vert holds for all n ≥ 0. This study completes in some sense the results derived by Avendaño et al. (Celest Mech Dyn Astron 119:27-44, 2014) by using Smale's α -test with q=1/2. Also since in KE the convergence rate of Newton's method tends to zero as e → 0, we show that the error estimates given in the Wang Xinghua's theorem for KE can also be used to determine sets of q-convergence with q = e^k \\widetilde{q} for all e \\in [0,1) and a fixed \\widetilde{q} ≤ 1. Some remarks on the use of this theorem to derive a priori estimates of the error \\vert E_n - E^* \\vert after n Kepler's iterations are given. Finally, a posteriori bounds of this error that can be used to a dynamical estimation of the error are also obtained.

Distribution functions for a family of general-relativistic hypervirial models in the collisionless regime

NASA Astrophysics Data System (ADS)

Gauy, Henrique Matheus; Ramos-Caro, Javier

2018-03-01

By considering the Einstein-Vlasov system for static spherically symmetric distributions of matter, we show that configurations with constant anisotropy parameter β , leading to asymptotically flat spacetimes, have necessarily a distribution function (DF) of the form F =l-2 βξ (ɛ ) , where ɛ =E /m and l =L /m are the relativistic energy and angular momentum per unit rest mass, respectively. We exploit this result to obtain DFs for the general relativistic extension of the hypervirial family introduced by Nguyen and Lingam [Mon. Not. R. Astron. Soc. 436, 2014 (2013), 10.1093/mnras/stt1719], which Newtonian potential is given by ϕ (r )=-ϕo/[1 +(r /a )n]1 /n (a and ϕo are positive free parameters, n =1 ,2 ,… ). Such DFs can be written in the form Fn=ln -2ξn(ɛ ) . For odd n , we find that ξn is a polynomial of order 2 n +1 in ɛ , as in the case of the Hernquist model (n =1 ), for which F1∝l-1(2 ɛ -1 ) (ɛ-1 ) 2 . For even n , we can write ξn in terms of incomplete beta functions (Plummer model, n =2 , is an example). Since we demand that F ≥0 throughout the phase space, the particular form of each ξn leads to restrictions for the values of ϕo. For example, for the Hernquist model we find that 0 ≤ϕo≤2 /3 , i.e., an upper bounding value less than the one obtained for Nguyen and Lingam (0 ≤ϕo≤1 ), based on energy conditions.

North-south asymmetry of Ca II K regions determined from OAUC spectroheliograms: 1996 - 2006

NASA Astrophysics Data System (ADS)

Dorotovič, I.; Rybák, J.; Garcia, A.; Journoud, P.

2010-12-01

The solar activity (SA) evolution levels are not identical in the northern and southern Sun's hemispheres. This fact was repeatedly confirmed in the past by the analysis of a number of long-term observations of various SA indices in individual atmospheric layers of the Sun and in different bandwidths. The north-south asymmetry (NSA) is thus a significant tool in investigation of long-term SA variations. This paper presents a software tool to determine the NSA of the area of bright chromospheric plages, as measured in the Ca II K3 spectroheliograms registered since 1926 in the Observatário Astronómico da Universidade de Coimbra, Portugal, as well as evolution of sizes of these areas in the period 1996 - 2006. The algorithm of the program is limited to determining the total area of bright features in the Ca II K3 emission line based on the definition of the threshold value for relative brightness and, therefore, it does not resolve brightness of individual chromospheric features. A comparison and cross-correlation of this NSA with the NSAs found for the sunspots and coronal green line brightness have been added. In the near future we intend to 1) determine the NSA of the area of bright chromospheric Ca II K3 regions back to the year 1926, and 2) compare the evolution of the surface area of these regions in the period 1970-2006 with the evolution of the magnetic index obtained at Mt. Wilson Observatory, which would also help in setting up a proxy reconstruction of the magnetic index back to 1926. Since 2007 new spectroheliograms have been recorded using a CCD camera and, therefore, in the future we will also address this issue for the period 2007 - present.

Color-magnitude Diagrams for the Stellar Open Cluster M 67 in theVilnius Photometric System

NASA Astrophysics Data System (ADS)

Boyle, Richard P.; Janusz, Robert

2015-01-01

Stellar photometry in the Vilnius Photometric System requires one percent quality for deriving luminosity class and spectral type subclass. We use such existing photometry of the open cluster M 67 to calibrate new CCD observations at the Vatican Advanced Technology Telescope (VATT) for correcting the flat-fielding zero-point and deriving the color-transformation in this intermediate-band, seven filter system (Boyle et al., BAAS 37 #4, 2005).Recently we have developed a "tie-in" observational practice to apply the zero-point and color transformation of the M 67 observations to neighboring starfields of interest that have no existing photometry. Sky transparency must remain constant to better than one percent during a round of short exposures in a filter between the field having calibrated photometry and the new field having no photometry as if the new field was exposed simultaneously with the master field.Proof of success for this "tie-in" method is shown with the master field being M 67 and the "tie-in" field being the nearby extended "corona" area. The distinctive color-magnitude diagrams of the old open clusterM 67 reveal the sensitivity to having constant sky transparency during the round of short exposures on M 67 and its extended area. For the extended area has the same form in its color-magnitude diagram as M 67. So variation in sky transparency shows displacement on the color-magnitude diagrams at the one percent quality.We will attempt new analysis concerning evolution of this very old open cluster (2.56 Gyr, WEBDA, http://www.univie.ac.at/webda/) and the surrounding "coronal" extent with reference to previous work by Chupina and Vereshchagin (Astron. Astrophys, 334, 552, 1998).

Polarimetry of the Highly Reddened Open Clusters HOGG 15 and Lyngå 14

NASA Astrophysics Data System (ADS)

Orsatti, A. M.; Vega, E.; Marraco, H. G.

1998-07-01

We present UBVRI polarimetric observations of stars belonging to the highly reddened open clusters Hogg 15 and Lyngå 14. The wavelength of maximum polarization is computed and then analyzed in the context of its relation to the optical properties and characteristic particle size distribution of the grains responsible for the polarization in each case. The amount and direction of the linear polarization are also computed. Results indicate that the polarization efficiency is relatively low in both cases, compared with the values attributed to the interstellar medium, and probably due to depolarization effects. Only one out of the 12 observed members in Hogg 15, and none in Lyngå 14, presents indications of intrinsic polarization in its measures. There exists some ``intracluster'' dust in association with Hogg 15, with a slightly different grain size distribution when compared with the Coalsack dust itself. For Lyngå 14, we conclude that the polarization detected in this case possibly comes from dust present in a nearby cloud located along the line of sight to the cluster, with some dust related to the cluster itself. The magnetic field in the direction to Hogg 15 follows the general trend of the polarization directions in the region, but this is not true for Lyngå 14, where differences seem to exist. Based on observations at the Complejo Astronómico El Leoncito, operated under agreement among the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina, Secretaría de Ciencia y Tecnología de la Nación, and the National Universities of La Plata, Córdoba, and San Juan.

Integral field spectroscopy of selected areas of the Bright bar and Orion-S cloud in the Orion nebula

NASA Astrophysics Data System (ADS)

Mesa-Delgado, A.; Núñez-Díaz, M.; Esteban, C.; López-Martín, L.; García-Rojas, J.

2011-10-01

We present integral field spectroscopy of two selected zones in the Orion nebula obtained with the Potsdam Multi-Aperture Spectrophotometer, covering the optical spectral range from 3500 to 7200 Å and with a spatial resolution of 1 arcsec. The observed zones are located on the prominent Bright bar and on the brightest area at the north-east of the Orion south cloud, both containing remarkable ionization fronts. We obtain maps of emission-line fluxes and ratios, electron density and temperatures, and chemical abundances. We study the ionization structure and morphology of both fields, whose ionization fronts show different inclination angles with respect to the plane of the sky. We find that the maps of electron density, O+/H+ and O/H ratios show a rather similar structure. We interpret this as produced by the strong dependence on density of the [O II] lines used to derive the O+ abundance, and that our nominal values of electron density - derived from the [S II] line ratio - may be slightly higher than the appropriate value for the O+ zone. We measure the faint recombination lines of O II in the field at the north-east of the Orion south cloud, allowing us to explore the so-called abundance discrepancy problem. We find a rather constant abundance discrepancy across the field and a mean value similar to that determined in other areas of the Orion nebula, indicating that the particular physical conditions of this ionization front do not contribute to this discrepancy. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).

High-precision photometry of WASP-12 b transits

NASA Astrophysics Data System (ADS)

Maciejewski, G.; Errmann, R.; Raetz, St.; Seeliger, M.; Spaleniak, I.; Neuhäuser, R.

2011-04-01

Aims: The transiting extrasolar planet WASP-12 b was found to be one of the most intensely irradiated exoplanets. It is unexpectedly bloated and is losing mass that may accrete into the host star. Our aim was to refine the parameters of this intriguing system and search for signs of transit timing variations. Methods: We gathered high-precision light curves for two transits of WASP-12 b. Assuming various limb-darkening laws, we generated best-fitting models and redetermined the parameters of the system. Error estimates were derived by the prayer-bead method and Monte Carlo simulations. Results: System parameters obtained by us are found to agree with previous studies within one sigma. Use of the non-linear limb-darkening laws results in the best-fitting models. With two new mid-transit times, the ephemeris was refined to BJDTDB = (2 454 508.97682 ± 0.00020) + (1.09142245 ± 0.00000033)E. Interestingly, indications of transit timing variation are detected at the level of 3.4 sigma. This signal can be induced by an additional planet in the system. Simplified numerical simulations show that a perturber could be a terrestrial-type planet if both planets are in a low-order orbital resonance. However, we emphasise that further observations are needed to confirm variation and to constrain properties of the perturber. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA), operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofisica de Andalucia (CSIC).Photometric data are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/528/A65

The AstraLux Large M-dwarf Multiplicity Survey

NASA Astrophysics Data System (ADS)

Janson, Markus; Hormuth, Felix; Bergfors, Carolina; Brandner, Wolfgang; Hippler, Stefan; Daemgen, Sebastian; Kudryavtseva, Natalia; Schmalzl, Eva; Schnupp, Carolin; Henning, Thomas

2012-07-01

We present the results of an extensive high-resolution imaging survey of M-dwarf multiplicity using the Lucky Imaging technique. The survey made use of the AstraLux Norte camera at the Calar Alto 2.2 m telescope and the AstraLux Sur camera at the ESO New Technology Telescope in order to cover nearly the full sky. In total, 761 stars were observed (701 M-type and 60 late K-type), among which 182 new and 37 previously known companions were detected in 205 systems. Most of the targets have been observed during two or more epochs, and could be confirmed as physical companions through common proper motion, often with orbital motion being confirmed in addition. After accounting for various bias effects, we find a total M-dwarf multiplicity fraction of 27% ± 3% within the AstraLux detection range of 0farcs08-6'' (semimajor axes of ~3-227 AU at a median distance of 30 pc). We examine various statistical multiplicity properties within the sample, such as the trend of multiplicity fraction with stellar mass and the semimajor axis distribution. The results indicate that M-dwarfs are largely consistent with constituting an intermediate step in a continuous distribution from higher-mass stars down to brown dwarfs. Along with other observational results in the literature, this provides further indications that stars and brown dwarfs may share a common formation mechanism, rather than being distinct populations. Based on observations collected at the European Southern Observatory, Chile, under observing programs 081.C-0314(A), 082.C-0053(A), and 084.C-0812(A), and on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institute for Astronomy and the Instituto de Astrofísica de Andalucía (CSIC).

The AstraLux Multiplicity Survey: Extension to Late M-dwarfs

NASA Astrophysics Data System (ADS)

Janson, Markus; Bergfors, Carolina; Brandner, Wolfgang; Kudryavtseva, Natalia; Hormuth, Felix; Hippler, Stefan; Henning, Thomas

2014-07-01

The distribution of multiplicity among low-mass stars is a key issue to understanding the formation of stars and brown dwarfs, and recent surveys have yielded large enough samples of nearby low-mass stars to study this issue statistically to good accuracy. Previously, we have presented a multiplicity study of ~700 early/mid M-type stars observed with the AstraLux high-resolution Lucky Imaging cameras. Here, we extend the study of multiplicity in M-type stars through studying 286 nearby mid/late M-type stars, bridging the gap between our previous study and multiplicity studies of brown dwarfs. Most of the targets have been observed more than once, allowing us to assess common proper motion to confirm companionship. We detect 68 confirmed or probable companions in 66 systems, of which 41 were previously undiscovered. Detections are made down to the resolution limit of ~100 mas of the instrument. The raw multiplicity in the AstraLux sensitivity range is 17.9%, leading to a total multiplicity fraction of 21%-27% depending on the mass ratio distribution, which is consistent with being flat down to mass ratios of ~0.4, but cannot be stringently constrained below this value. The semi-major axis distribution is well represented by a log-normal function with μa = 0.78 and σa = 0.47, which is narrower and peaked at smaller separations than for a Sun-like sample. This is consistent with a steady decrease in average semi-major axis from the highest-mass binary stars to the brown dwarf binaries. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institute for Astronomy and the Instituto de Astrofísica de Andalucía (CSIC).

Orbital Monitoring of the AstraLux Large M-dwarf Multiplicity Sample

NASA Astrophysics Data System (ADS)

Janson, Markus; Bergfors, Carolina; Brandner, Wolfgang; Bonnefoy, Mickaël; Schlieder, Joshua; Köhler, Rainer; Hormuth, Felix; Henning, Thomas; Hippler, Stefan

2014-10-01

Orbital monitoring of M-type binaries is essential for constraining their fundamental properties. This is particularly useful in young systems, where the extended pre-main-sequence evolution can allow for precise isochronal dating. Here, we present the continued astrometric monitoring of the more than 200 binaries of the AstraLux Large Multiplicity Survey, building both on our previous work, archival data, and new astrometric data spanning the range of 2010-2012. The sample is very young overall—all included stars have known X-ray emission, and a significant fraction (18%) of them have recently also been identified as members of young moving groups in the solar neighborhood. We identify ~30 targets that both have indications of being young and for which an orbit either has been closed or appears possible to close in a reasonable time frame (a few years to a few decades). One of these cases, GJ 4326, is, however, identified as probably being substantially older than has been implied from its apparent moving group membership, based on astrometric and isochronal arguments. With further astrometric monitoring, these targets will provide a set of empirical isochrones, against which theoretical isochrones can be calibrated, and which can be used to evaluate the precise ages of nearby young moving groups. Based on observations collected at the European Southern Observatory, Chile, under observing programs 081.C-0314(A), 082.C-0053(A), and 084.C-0812(A), and on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institute for Astronomy and the Instituto de Astrofísica de Andalucía (CSIC).

Discovery of the X-ray selected galaxy cluster XMMU J0338.8+0021 at z = 1.49. Indications of a young system with a brightest galaxy in formation

NASA Astrophysics Data System (ADS)

Nastasi, A.; Fassbender, R.; Böhringer, H.; Šuhada, R.; Rosati, P.; Pierini, D.; Verdugo, M.; Santos, J. S.; Schwope, A. D.; de Hoon, A.; Kohnert, J.; Lamer, G.; Mühlegger, M.; Quintana, H.

2011-08-01

We report the discovery of a galaxy cluster at z = 1.490 originally selected as an extended X-ray source in the XMM-Newton Distant Cluster Project. Further observations carried out with the VLT-FORS2 spectrograph allowed the spectroscopic confirmation of seven secure cluster members, providing a median system redshift of z = 1.490 ± 0.009. The color-magnitude diagram of XMMU J0338.8+0021 reveals the presence of a well-populated red sequence with z - H ≈ 3, albeit with an apparent significant scatter in color. Since we do not detect indications of any strong star formation activity in these objects, the color spread could represent the different stellar ages of the member galaxies. In addition, we found the brightest cluster galaxy in a very active dynamical state, with an interacting, merging companion located at a physical projected distance of d ≈ 20 kpc. From the X-ray luminosity, we estimate a cluster mass of M200 ~ 1.2 × 1014 M⊙. The data appear to be consistent with a scenario in which XMMU J0338.8+0021 is a young system, possibly caught in a moment of active ongoing mass assembly. Based on observations under programme ID 084.A-0844 collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, and observations collected at the Centro Astronómico Hispano Alemán at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).Tables 1, 2 and Figs. 3-6 are available in electronic form at http://www.aanda.org

Structure coefficients for different initial metallicities for use in stellar analysis

NASA Astrophysics Data System (ADS)

Inlek, Gulay; Budding, Edwin; Demircan, Osman

2017-09-01

Internal structure coefficients for zero age Main Sequence (ZAMS) model stars with different initial metallicities are presented. A series of (Eggleton) stellar models with masses between 1-40 M_{⊙} and metallicities Z=0.0001, Z=0.001, Z=0.004, Z=0.01, Z=0.02, and Z=0.03 were used. We have also calculated the same coefficients for a recommended solar metallicity value Z=0.0134 (Asplund et al. in Annu. Rev. Astron. Astrophys. 47:481, 2009). For each model, values of the internal structure constants k2, k3, k4 and related coefficients have been derived by numerically integrating Radau's equation with the (FORTRAN) program RADAU. The (Eggleton) stellar models used come from the ` EZ-Web' compilation of the Dept. of Astronomy, University of Wisconsin, Madison. The calculations follow the procedure given by Inlek and Budding (Astrophys. Space Sci. 342:365, 2012). These new results were compared with others in the literature. We deduce that the current state of theoretical evaluation of structure coefficients is generally in sufficient agreement with data obtained from apsidal advance rates of selected well-observed eccentric eclipsing binary stars at the present time, given the probable errors of the latter. However, new results coming from more precise and extensive data sets in the wake of the Kepler Mission, or similar future surveys, may call for further theoretical specification or refinement. The derivation of structure coefficients from observations of apsidal motion in close eccentric binary systems requires specification of relevant parameters from light curve analysis. A self-consistent treatment then implies inclusion of the structure coefficients within the fitting function of such analysis.

The effects of the WISE/ GALEX photometry for the SED-fitting with M31 star clusters and candidates

NASA Astrophysics Data System (ADS)

Fan, Zhou; Wang, Song

2017-10-01

Spectral energy distribution (SED) fitting of stellar population synthesis models is an important and popular way to constrain the physical parameters—e.g., the ages, metallicities, masses for stellar population analysis. The previous works suggest that both blue-bands and red-bands photometry works for the SED-fitting. Either blue-domained or red-domained SED-fitting usually lead to the unreliable or biased results. Meanwhile, it seems that extending the wavelength coverage could be helpful. Since the Galaxy Evolution Explorer ( GALEX) and Wide-field Infrared Survey Explorer (WISE) provide the FUV/NUV and mid-infrared W1/W2 band data, we extend the SED-fitting to a wider wavelength coverage. In our work, we analyzed the effect of adding the FUV/NUV and W1/W2 band to the optical and near-infrared UBVRIJHK bands for the fitting with the (Bruzual and Charlot in Mon. Not. R. Astron. Soc. 344, 1000, 2003) (BC03) models and galev models. It is found that the FUV/NUV bands data affect the fitting results of both ages and metallicities much more significantly than that of the WISE W1/W2 band with the BC03 models. While for the galev models, the effect of the WISE W1/W2 band for the metallicity fitting seems comparable to that of GALEX FUV/NUV bands, but for age the effect of the W1/W2 band seems less crucial than that of the FUV/NUV bands. Thus we conclude that the GALEX FUV/NUV bands are more crucial for the SED-fitting of ages and metallicities, than the other bands, and the high-quality UV data (with high photometry precision) are required.

Cosmic Rays in Thunderstorms

NASA Astrophysics Data System (ADS)

Buitink, Stijn; Scholten, Olaf; van den Berg, Ad; Ebert, Ute

2013-04-01

Cosmic Rays in Thunderstorms Cosmic rays are protons and heavier nuclei that constantly bombard the Earth's atmosphere with energies spanning a vast range from 109 to 1021 eV. At typical altitudes up to 10-20 km they initiate large particle cascades, called extensive air showers, that contain millions to billions of secondary particles depending on their initial energy. These particles include electrons, positrons, hadrons and muons, and are concentrated in a compact particle front that propagates at relativistic speed. In addition, the shower leaves behind a trail of lower energy electrons from ionization of air molecules. Under thunderstorm conditions these electrons contribute to the electrical and ionization processes in the cloud. When the local electric field is strong enough the secondary electrons can create relativistic electron run-away avalanches [1] or even non-relativistic avalanches. Cosmic rays could even trigger lightning inception. Conversely, strong electric fields also influence the development of the air shower [2]. Extensive air showers emit a short (tens of nanoseconds) radio pulse due to deflection of the shower particles in the Earth's magnetic field [3]. Antenna arrays, such as AERA, LOFAR and LOPES detect these pulses in a frequency window of roughly 10-100 MHz. These systems are also sensitive to the radiation from discharges associated to thunderstorms, and provide a means to study the interaction of cosmic ray air showers and the electrical processes in thunderstorms [4]. In this presentation we discuss the involved radiation mechanisms and present analyses of thunderstorm data from air shower arrays [1] A. Gurevich et al., Phys. Lett. A 165, 463 (1992) [2] S. Buitink et al., Astropart. Phys. 33, 1 (2010) [3] H. Falcke et al., Nature 435, 313 (2005) [4] S. Buitink et al., Astron. & Astrophys. 467, 385 (2007)

A 3D tomographic reconstruction method to analyze Jupiter's electron-belt emission observations

NASA Astrophysics Data System (ADS)

Santos-Costa, Daniel; Girard, Julien; Tasse, Cyril; Zarka, Philippe; Kita, Hajime; Tsuchiya, Fuminori; Misawa, Hiroaki; Clark, George; Bagenal, Fran; Imai, Masafumi; Becker, Heidi N.; Janssen, Michael A.; Bolton, Scott J.; Levin, Steve M.; Connerney, John E. P.

2017-04-01

Multi-dimensional reconstruction techniques of Jupiter's synchrotron radiation from radio-interferometric observations were first developed by Sault et al. [Astron. Astrophys., 324, 1190-1196, 1997]. The tomographic-like technique introduced 20 years ago had permitted the first 3-dimensional mapping of the brightness distribution around the planet. This technique has demonstrated the advantage to be weakly dependent on planetary field models. It also does not require any knowledge on the energy and spatial distributions of the radiating electrons. On the downside, it is assumed that the volume emissivity of any punctual point source around the planet is isotropic. This assumption becomes incorrect when mapping the brightness distribution for non-equatorial point sources or any point sources from Juno's perspective. In this paper, we present our modeling effort to bypass the isotropy issue. Our approach is to use radio-interferometric observations and determine the 3-D brightness distribution in a cylindrical coordinate system. For each set (z, r), we constrain the longitudinal distribution with a Fourier series and the anisotropy is addressed with a simple periodic function when possible. We develop this new method over a wide range of frequencies using past VLA and LOFAR observations of Jupiter. We plan to test this reconstruction method with observations of Jupiter that are currently being carried out with LOFAR and GMRT in support to the Juno mission. We describe how this new 3D tomographic reconstruction method provides new model constraints on the energy and spatial distributions of Jupiter's ultra-relativistic electrons close to the planet and be used to interpret Juno MWR observations of Jupiter's electron-belt emission and assist in evaluating the background noise from the radiation environment in the atmospheric measurements.

The tidally-modulated plume of Enceladus: an update

NASA Astrophysics Data System (ADS)

Nimmo, F.; Porco, C.; Mitchell, C. J.; Van Hoolst, T.; Hedman, M. M.

2016-12-01

The brightness of the ice grain plume of Enceladus is observed to vary on a diurnal timescale [1,2], consistent with predictions that the plume's mass is modulated by normal tidal stresses, which open and close cracks that reach the ocean [3]. Here we extend our previous analysis [2] to a larger set of ISS plume observations, including images taken since 2010, extending the temporal baseline by more than a factor of two. The observations were reduced using the same approach as in [2]. Fits were performed as in [2] but now include two different assumptions of how plume brightness responds to stresses [4] plus an updated calculation of the effects of long-period librations [5]. An apparent phase lag of 30-60 degrees between the modelled and observed response is robustly present, irrespective of the data set and assumptions used. This phase lag may be the result of the viscosity structure of the ice shell [2,4], an eruptive delay caused by the hydrodynamics within tidally-pumped cracks [6], or other as yet unknown processes. An earlier suggestion [2], that the phase lag is caused by the additional stresses arising from an 0.8 degree 1:1 physical libration in the moon's ice shell, can be rejected now that this libration has been measured with an amplitude of 0.12 degrees [7]. We also find in ISS images a secular decrease in plume brightness over the ten years of Cassini observations; this decrease may be due to long-period (forced) librations of Enceladus. [1] Hedman et al., Nature 2013 [2] Nimmo et al., Astron. J. 2014 [3] Hurford et al., Nature 2007 [4] Behounkova et al., Nature Geosci. 2015 [5] Yseboodt & Van Hoolst, Fall AGU, 2015 [6] Kite & Rubin, PNAS 2016 [7] Thomas et al., Icarus 2016

Search for volatiles on icy satellites. I. Europa

USGS Publications Warehouse

Brown, R.H.; Cruikshank, D.P.; Tokunaga, A.T.; Smith, R.G.; Clark, R.N.

1988-01-01

New reflectance spectra have been obtained for both the leading and trailing sides of Europa, using the Cooled Grating Array Spectrometer (CGAS) of the NASA Infrared Telescope Facility (IRTF). The spectra are of higher precision than any yet obtained. Spectra of Europa's trailing side (central meridian longitude ???300??) obtained in 1985 show two weak absorptions near 2.2 and 2.3 ??m. Both of these features as well as others are seen in spectra obtained by R. N. Clark, R. B. Singer, P. D. Owensby, and F.P. Fanale (1980a, Bull. Amer. Astron. Soc. 12, 713-714) at similar central meridian longitude. Data obtained with an improved detector array in 1986, however, do not show the absorptions seen in the 1980 and 1985 spectra. It is not clear why the newest data do not show the apparent absorptions seen in previous years, but the suggestion is that either the 1980 and 1985 data are spurious or that the material responsible for the weak absorptions is no longer detectable. Analysis of the 1980 and 1985 data did not reveal any obvious source of systematic error capable of introducing spurious features, but we are skeptical of any explanation that cites transient deposition, movement, and/or destruction of material on Europa's trailing side to account for the nondetection of the features in the 1986 data. If the weak absorptions seen in the 1980 and 1985 data are real, they can be interpreted as indicating the transient spectroscopic presence of a molecular component on Europa's trailing side different from the water ice that is known to be the dominant surface constituent. Further monitoring is required to determine if the apparent absorptions are real. ?? 1988.

Quasi-biennial modulation of solar neutrino flux: connections with solar activity

NASA Astrophysics Data System (ADS)

Vecchio, A.; Laurenza, M.; D'alessi, L.; Carbone, V.; Storini, M.

2011-12-01

A quasi-biennial periodicity has been recently found (Vecchio et al., 2010) in the solar neutrino flux, as detected at the Homestake experiment, as well as in the flux of solar energetic protons, by means of the Empirical Modes Decomposition technique. Moreover, both fluxes have been found to be significantly correlated at the quasi-biennial timescale, thus supporting the hypothesis of a connection between solar neutrinos and solar activity. The origin of this connection is investigated, by modeling how the standard Mikheyev-Smirnov-Wolfenstein (MSW) effect (the process for which the well-known neutrino flavor oscillations are modified in passing through the material) could be influenced by matter fluctuations. As proposed by Burgess et al., 2004, by introducing a background magnetic field in the helioseismic model, density fluctuations can be excited in the radiative zone by the resonance between helioseismic g-modes and Alfvén waves. In particular, with reasonable values of the background magnetic field (10-100 kG), the distance between resonant layers could be of the same order of neutrino oscillation length. We study the effect over this distance of a background magnetic field which is variable with a ~2 yr period, in agreement with typical variations of solar activity. Our findings suggest that the quasi-biennial modulation of the neutrino flux is theoretically possible as a consequence of the magnetic field variations in the solar interior. A. Vecchio, M. Laurenza, V. Carbone, M. Storini, The Astrophysical Journal Letters, 709, L1-L5 (2010). C. Burgess, N. S. Dzhalilov, T. I. Rashba, V., B.Semikoz, J. W. F. Valle, Mon. Not. R. Astron. Soc., 348, 609-624 (2004).

The LOFAR Multifrequency Snapshot Sky Survey (MSSS): Status and Results

NASA Astrophysics Data System (ADS)

Heald, George; LOFAR Collaboration

2014-01-01

The Multifrequency Snapshot Sky Survey (MSSS) is the first large-area survey of the northern sky with the Low Frequency Array (LOFAR). By producing images of the sky at 16 frequencies from 30 to 160 MHz, MSSS probes the low-frequency sky at a sensitivity of order 10 mJy/beam, and angular resolution of 1-2 arcmin or better. It thus dramatically expands the frequency range sampled in high-resolution radio surveys, and, crucially, provides low-frequency spectral information about the detected sources. Using LOFAR's unique multi-beaming mode, the survey requires only a rather modest investment in observing time. MSSS began observations in late 2011, and has nearly completed observations in both frequency components (8 frequencies spanning the 30 to 74 MHz range, and another 8 spanning 120 to 160 MHz). MSSS has driven the initial development of the first production version of LOFAR's automatic Imaging Pipeline and spearheaded efforts aimed at solving some of the ongoing low-frequency calibration challenges. In this contribution, I will briefly review the survey design, including an overview of MSSS science topics. I will also present a status update, highlighting early results from the survey such as an in-depth look at the 100 square degree “MSSS Verification Field,” new sources discovered in MSSS images, and a sneak peek at the full survey area. I will conclude by describing plans for the future of MSSS, including the possibility of reprocessing the data to obtain enhanced data products such as higher resolution imaging and polarization. LOFAR, the Low Frequency Array designed and constructed by ASTRON, has facilities in several countries, that are owned by various parties (each with their own funding sources), and that are collectively operated by the International LOFAR Telescope (ILT) foundation under a joint scientific policy.

Analogies between Jovian magnetodisk and heliospheric current sheet

NASA Astrophysics Data System (ADS)

Kislov, Roman; Khabarova, Olga; Malova, Helmi

Recently due to the development of spatial missions the famous model by E. Parker [1] faced with some problems, such as the effect of magnetic flux excess and the existence of latitude component of magnetic field [2]. Thus the incomplete knowledge about large scale current system of heliospheric current sheet (HCS) motivated us to construct and investigate the self-consistent axisymmetric stationary MHD model of HCS and to compare it with earlier presented model of Jupiterian magnetodisk [3]. Both HCS and magnetodisk have inner plasma sources (i.e. the Sun in case of HCS and satellite Io in case of Jupiter); also they depend on the centrifugal force at small distances and on corotation processes. They both have strong radial component of current density, thin elongated structure etc. Thus in the frame of the MHD model we have calculated for HCS the parallel currents (analogous to Jovian Birkeland currents) and we obtained the latitude component of the magnetic field. The results of the model allowed us to explain the magnetic flux excess by the existence of the self-consistent HCS magnetic field. The decrease of radial magnetic field from the distance from the Sun as the power -5/3 obtained by numerical calculations is in good agreement with experimental data. Generally this model can be applied for the quiet period of the low solar activity when the perturbation of HCS structure named “ballerina skirt” does not play any role. References: 1. Parker E. N., Astrophys. J., V. 128, 664, pp. 664-676, 1958. 2. Khabarova O. V., V. 90, No.11, pp. 919-935, 2013. 3. Kislov R.A. et al., Bull. MSU, Physics and Astron., 2013

Over a thousand new periodic orbits of a planar three-body system with unequal masses

NASA Astrophysics Data System (ADS)

Li, Xiaoming; Jing, Yipeng; Liao, Shijun

2018-05-01

The three-body problem is common in astronomy, examples of which are the solar system, exoplanets, and stellar systems. Due to its chaotic characteristic, discovered by Poincaré, only three families of periodic three-body orbits were found in 300 years, until 2013 when Šuvakov and Dmitrašinović (2013, Phys. Rev. Lett., 110, 114301) found 13 new periodic orbits of a Newtonian planar three-body problem with equal mass. Recently, more than 600 new families of periodic orbits of triple systems with equal mass were found by Li and Liao (2017, Sci. China-Phys. Mech. Astron., 60, 129511). Here, we report 1349 new families of planar periodic orbits of the triple system where two bodies have the same mass and the other has a different mass. None of the families have ever been reported, except the famous "figure-eight" family. In particular, 1223 among these 1349 families are entirely new, i.e., with newly found "free group elements" that have been never reported, even for three-body systems with equal mass. It has been traditionally believed that triple systems are often unstable if they are non-hierarchical. However, all of our new periodic orbits are in non-hierarchical configurations, but many of them are either linearly or marginally stable. This might inspire the long-term astronomical observation of stable non-hierarchical triple systems in practice. In addition, using these new periodic orbits as initial guesses, new periodic orbits of triple systems with three unequal masses can be found by means of the continuation method, which is more general and thus should have practical meaning from an astronomical viewpoint.

Looking for blazars in a sample of unidentified high-energy emitting Fermi sources

NASA Astrophysics Data System (ADS)

Marchesini, E. J.; Masetti, N.; Chavushyan, V.; Cellone, S. A.; Andruchow, I.; Bassani, L.; Bazzano, A.; Jiménez-Bailón, E.; Landi, R.; Malizia, A.; Palazzi, E.; Patiño-Álvarez, V.; Rodríguez-Castillo, G. A.; Stephen, J. B.; Ubertini, P.

2016-11-01

Context. Based on their overwhelming dominance among associated Fermi γ-ray catalogue sources, it is expected that a large fraction of the unidentified Fermi objects are blazars. Through crossmatching between the positions of unidentified γ-ray sources from the First Fermi Catalog of γ-ray sources emitting above 10 GeV (1FHL) and the ROSAT and Swift/XRT catalogues of X-ray objects and between pointed XRT observations, a sample of 36 potential associations was found in previous works with less than 15 arcsec of positional offset. One-third of them have recently been classified; the remainder, though believed to belong to the blazar class, still lack spectroscopic classifications. Aims: We study the optical spectrum of the putative counterparts of these unidentified gamma-ray sources in order to find their redshifts and to determine their nature and main spectral characteristics. Methods: An observational campaign was carried out on the putative counterparts of 13 1FHL sources using medium-resolution optical spectroscopy from the Osservatorio Astronomico di Bologna in Loiano, Italy; the Telescopio Nazionale Galileo and the Nordic Optical Telescope, both in the Canary Islands, Spain; and the Observatorio Astronómico Nacional San Pedro Mártir in Baja California, Mexico. Results: We were able to classify 14 new objects based on their continuum shapes and spectral features. Conclusions: Twelve new blazars were found, along with one new quasar and one new narrow line Seyfert 1 (NLS1) to be potentially associated with the 1FHL sources of our sample. Redshifts or lower limits were obtained when possible alongside central black hole mass and luminosity estimates for the NLS1 and the quasar.

More chips off of Asteroid (4) Vesta: Characterization of eight Vestoids and their HED meteorite analogs

NASA Astrophysics Data System (ADS)

Hardersen, Paul S.; Reddy, Vishnu; Roberts, Rachel; Mainzer, Amy

2014-11-01

Vestoids are generally considered to be fragments from Asteroid (4) Vesta that were ejected by past collisions that document Vesta's collisional history. Dynamical Vestoids are defined by their spatial proximity with Vesta (Zappala, V., Bendjoya, Ph., Cellino, A., Farinella, P., Froeschle', C. [1995]. Icarus 116, 291-314; Nesvorny, D. [2012]. Nesvorny HCM Asteroid Families V2.0. EAR-A-VARGBDET-5-NESVORNYFAM-V2.0. NASA Planetary Data System.). Taxonomic Vestoids are defined as V-type asteroids that have a photometric, visible-wavelength spectral, or other observational relationship with Vesta (Tholen, D.J., 1984. Asteroid Taxonomy from Cluster Analysis of Photometry. Ph.D. Thesis, University of Arizona, Tucson; Bus, S.J., Binzel, R.P. [2002]. Icarus 158, 106-145; Carvano, J., Hasselmann, P.H., Lazzaro, D., Mothe'-Diniz, T. [2010]. Astron. Astrophys. 510, A43). We define 'genetic Vestoids' as V-type asteroids that are probable fragments ejected from (4) Vesta based on the supporting combination of dynamical, near-infrared (NIR) spectral, and taxonomic evidence. NIR reflectance spectroscopy is one of the primary ground-based techniques to constrain an asteroid's major surface mineralogy (Burns, R.G. [1993a]. Mineralogical Applications of Crystal Field Theory. Cambridge University Press, Cambridge, UK, 551 p). Despite the reasonable likelihood that many dynamical and taxonomic Vestoids likely originate from Vesta, ambiguity exists concerning the fraction of these populations that are from Vesta as compared to the fraction of asteroids that might not be related to Vesta. Currently, one of the most robust techniques to identify the genetic Vestoid population is through NIR reflectance spectroscopy from ∼0.7 to 2.5 μm. The derivation of spectral band parameters, and the comparison of those band parameters with those from representative samples from the Howardite-Eucrite-Diogenite (HED) meteorite types, allows a direct comparison of their primary mineralogies. Establishing tighter constraints on the genetic Vestoid population will better inform mass estimates for the current population of probable Vestoids, will provide more accurate orbital information of Vestoid migration through time that will assist dynamical models, and will constrain the overall current abundance of basaltic material in the main asteroid belt (Moskovitz, N.A., Jedicke, R., Gaidos, E., Willman, M., Nesvorny, D., Fevig, R. [2008]. Icarus 198, 77-90). This work reports high-quality NIR spectra, and their respective interpretations, for eight Vp-type asteroids, as defined by Carvano et al. (Carvano, J., Hasselmann, P.H., Lazzaro, D., Mothe'-Diniz, T. [2010]. Astron. Astrophys. 510, A43), that were observed at the NASA Infrared Telescope Facility on January 14, 2013 UT. They include: (3867) Shiretoko, (5235) Jean-Loup, (5560) Amytis, (6331) 1992 FZ1, (6976) Kanatsu, (17469) 1991 BT, (29796) 1999 CW77, and (30872) 1992 EM17. All eight asteroids exhibit the broad ∼0.9- and ∼1.9-μm mineral absorption features indicative of pyroxene on each asteroid's surface. Data reduction and analysis via multiple techniques produced consistent results for the derived spectral absorption band centers and average pyroxene surface chemistries for all eight asteroids (Reddy, V., Sanchez, J.A., Nathues, A., Moskovitz, N.A., Li, J.-Y, Cloutis, E.A., Archer, K., Tucker, R.A., Gaffey, M.J., Mann, P.J., Sierks, H., Schade, U. [2012c]. Icarus 217, 153-168; Lindsay, S.S., Emery, J.P., Marchis, F., Enriquez, J., Assafin, M. [2013]. A spectroscopic and mineralogic study of multiple asteroid systems. American Astronomical Society, DPS Meeting #45, #112.04; Lindsay, S.S., Marchis, F., Emery, J.P., Enriquez, J.E., Assafin, M. [2014]. Icarus, submitted for publication; Gaffey, M.J., Cloutis, E.A., Kelley, M.K., Reed, K.L. [2002]. Mineralogy of asteroids. In: Bottke Jr., W.F., Cellino, A., Paolicchi, P., Binzel, R.P. (Eds.), Asteroids III. The University of Arizona Press, Tucson, pp. 183-204; Burbine, T.H., Buchanan, P.C., Dolkar, T., Binzel, R.P. [2009]. Met. Planet. Sci. 44, 1331-1341.). (3867) Shiretoko is most consistent with the eucrite meteorites while the remaining seven asteroids are most consistent with the howardite meteorites. The existing evidence suggests that all eight of these Vp-type asteroids are genetic Vestoids that probably originated from Vesta's surface.

Similarities Between Cometary, Meteoritic, and Laboratory Analog Dust: Hints from the Attribution of the 10-micrometer Band

NASA Astrophysics Data System (ADS)

Colangeli, L.; Mennella, V.; Bussoletti, E.; Merluzzi, P.; Rotundi, A.; Palumbo, P.; di Marino, C.

1993-07-01

It is well known that the infrared emission of many comets is characterized by a broad feature at 10 micrometers, that has been attributed to a Si-O stretching resonance in amorphous and/or hydrated silicate grains. In the case of comets Halley [1,2], Bradfield [3] and Levy [4] two spectral components have been observed: the wide peak centered at 9.8 micrometers and a sharp feature at 11.3 micrometers. This last band has been interpreted with crystalline olivine silicatic grains [1,2,5]. However, recently, it has been pointed out [6] that the laboratory data frequently used in the fits refer to grains embedded in a matrix, which should produce a significant shift of the peak position, according to Mie computations. We have performed laboratory experiments on various silicatic samples with the perspective of determining their optical properties, to study experimentally the influence of matrix effects, and to use the final spectra to perform comparisons with observations. The samples are four terrestrial materials, olivine forsterite, jadeite pyroxene, andesite feldspar and impactite glass, and two meteoritic samples, chondrite (Zacatecas, Mexico) and pallasite (Atacama, Chile). Fine powders of the bulk materials were obtained by grinding calibrated mass amounts of the various samples in an agata mill. The morphological characterization of the samples was performed by means of S.E.M. (scanning electron microscopy) technique. EDX analysis was also performed to determine elemental composition. IR transmission spectra were obtained by using a double beam spectrophotometer that covers the spectral range 2.5-50 micrometers. The standard pellet technique was used by embedding dust samples in KBr or CsI matrices. For comparison, measurements were also performed by depositing small amounts of dust onto KBr windows. In this last case, dust-matrix interaction should be practically absent as grains are simply sitting onto the matrix. The data obtained from the spectroscopic analysis have allowed us to evidence the following main results. Matrix effects do not appear as relevant as suggested by computations performed by the Mie theory. In particular, the peak shift observed for crystalline olivine is from 11.3 micrometers in CsI (n(sub)o = 1.7) to 11.2 micrometers in vacuum (n(sun)o = 1.0). On the other hand, jadeite and andesite grains present main peaks around 10 micrometers, in contrast to cometary spectra. We can, therefore, conclude that crystalline olivine grains are good candidates to simulate the cometary 11.3 micrometer sharp feature, even when matrix effects are accounted for. The impactite sample presents a main broad band around 9.2 micrometers, due to its mainly amorphous composition. This band could resemble the broad 10 micron cometary band; however, its profile is rather broader than that observed for cometary dust. Concerning the meteoritic samples, both chondrite and pallasite show a well defined main peak at 11.3-11.4 micrometers, comparable to cometary spectra. Again, chondrite band profile is too broad. On the contrary, pallasite appears to be a good candidate to reproduce observations. This result appears reasonable if one considers that the sample is formed by small olivine crystals embedded in a iron matrix. In conclusion, the comparison between the spectra of olivine-rich meteoritic grains and cometary dust could suggest either a common origin of the two classes of materials or, at least, a similarity in the processes experienced by them during past evolution. This result appears very relevant because it could imply that the systematic study in the laboratory of meteoritic materials can provide information about the past history of comets. Acknowledgements: This work was partly supported by ASI, CNR, and MURST 40% and 60%. References: [1] Bregman J. D. et al. (1987) Astron. Astrophys., 187, 616. [2] Campins H. and Ryan E. V. (1989) Ap. J., 341, 1059. [3] Hanner M. S. et al. (1990) Ap. J., 348, 312. [4] Lynch D. K. et al. (1990) 22nd annual meeting of the division for planetary sciences, Charlottesville, Virginia. [5] Sandford S. A. and Walker R. M. (1985) Ap. J., 291, 838. [6] Orofino V. et al. (1993) Astron. Astrophys., submitted.

Disciplines and Professors of Astronomy in Undergraduate Physics Teachers Formation Courses in Brazilian Universities. (Spanish Title: Disciplinas y Profesores de Astronomia en los Cursos de Licenciatura en Física en Las Universidades Brasileñas.) Disciplinas e Professores de Astronomia Nos Cursos de Licenciatura em Física das Universidades Brasileiras

NASA Astrophysics Data System (ADS)

Roberto, Artur Justiniano, Jr.; Reis, Thiago Henrique; dos Reis Germinaro, Daniel

2014-12-01

This article is the result of a research on basic training in Astronomy in physics degrees that performed the ENADE 2011 national examination. The objective was to identify whether there are disciplines of Astronomy in these courses, whether are mandatory or optional, its workload and when it is offered. The relationship between astronomers, physics degrees and disciplines of Astronomy was investigated. To perform this research we examined the results of ENADE 2011 and also the census of Brazilian Astronomical Society. As a result it is observed that in only 15% of the courses there is a mandatory subject of Astronomy, and therefore there is a high probability that 85% of physics teachers trained in 2011 have not had any discipline of Astronomy during their graduation. In addition, the data collected in this study shows a low number of members of SAB (Sociedade Astronômica Brasileira) among the surveyed courses. We have verified that the presence of astronomers in a given university does not imply to have a mandatory discipline of Astronomy in physics degrees at the same university. Este artículo es el resultado de una investigación sobre la formación básica en Astronomía en los cursos de Profesorado en Física que hicieron el examen nacional ENADE 2011. El objetivo del trabajo fue identificar se existen disciplinas de Astronomía en estos cursos, si son obligatorias u optativas, cuál es su carga horaria y el semestre en que son ofrecidas. Se investigó también la correlación entre astrónomos, los cursos de licenciatura en Física y las disciplinas de Astronomía. Para realizar esta investigación se utilizaron los datos del ENADE 2011 y también del censo de la Astronomía brasileña. Como resultado, se observó que en solo 15% de los cursos existe una disciplina obligatoria de Astronomía y que existe una grande probabilidad de que 85% de los profesores de Física formados en el año de 2011 no hayan cursado ninguna disciplina de Astronomía durante su formación. Aparte de eso, los datos levantados en este trabajo apuntan para un número bajo de afiliados a la SAB (Sociedade Astronômica Brasileira) en los cursos investigados. Se verificó que tener astrónomos en una institución no implica tener una disciplina obligatoria de Astronomía en el curso de licenciatura en Física. Este artigo é o resultado de uma pesquisa sobre a formação básica em Astronomia nos cursos de Licenciatura em Física que fizeram o exame nacional ENADE 2011. O objetivo do trabalho foi identificar se há disciplinas de Astronomia nesses cursos, se ela é obrigatória ou optativa/eletiva, qual a sua carga horária e o período em que é oferecida. Pesquisou-se também a relação entre astrônomos, cursos de Licenciatura em Física e disciplinas de Astronomia. Para realizar essa pesquisa utilizamos os dados do ENADE 2011 e também do censo da Astronomia brasileira. Como resultado, se observa que em apenas 15% dos cursos existe uma disciplina obrigatória de Astronomia e que há uma grande probabilidade de que 85% dos professores de Física formados em 2011 não cursaram nenhuma disciplina de Astronomia durante a graduação. Além disso, os dados levantados nesse trabalho apontam um baixo número de filiados à SAB nos cursos pesquisados. Identifica-se que ter astrônomos na instituição não implica em disciplina obrigatória de Astronomia no curso de Licenciatura em Física.

Photometric properties of Ceres from telescopic observations using Dawn Framing Camera color filters

NASA Astrophysics Data System (ADS)

Reddy, Vishnu; Li, Jian-Yang; Gary, Bruce L.; Sanchez, Juan A.; Stephens, Robert D.; Megna, Ralph; Coley, Daniel; Nathues, Andreas; Le Corre, Lucille; Hoffmann, Martin

2015-11-01

The dwarf planet Ceres is likely differentiated similar to the terrestrial planets but with a water/ice dominated mantle and an aqueously altered crust. Detailed modeling of Ceres' phase function has never been performed to understand its surface properties. The Dawn spacecraft began orbital science operations at the dwarf planet in April 2015. We observed Ceres with flight spares of the seven Dawn Framing Camera color filters mounted on ground-based telescopes over the course of three years to model its phase function versus wavelength. Our analysis shows that the modeled geometric albedos derived from both the IAU HG model and the Hapke model are consistent with a flat and featureless spectrum of Ceres, although the values are ∼10% higher than previous measurements. Our models also suggest a wavelength dependence of Ceres' phase function. The IAU G-parameter and the Hapke single-particle phase function parameter, g, are both consistent with decreasing (shallower) phase slope with increasing wavelength. Such a wavelength dependence of phase function is consistent with reddening of spectral slope with increasing phase angle, or phase-reddening. This phase reddening is consistent with previous spectra of Ceres obtained at various phase angles archived in the literature, and consistent with the fact that the modeled geometric albedo spectrum of Ceres is the bluest of all spectra because it represents the spectrum at 0° phase angle. Ground-based FC color filter lightcurve data are consistent with HST albedo maps confirming that Ceres' lightcurve is dominated by albedo and not shape. We detected a positive correlation between 1.1-μm absorption band depth and geometric albedo suggesting brighter areas on Ceres have absorption bands that are deeper. We did not see the "extreme" slope values measured by Perna et al. (Perna, D., et al. [2015]. Astron. Astrophys. 575 (L1-6)), which they have attributed to "resurfacing episodes" on Ceres.

The Thermal Structure of Triton's Atmosphere: Results from the 1993 and 1995 Occultations

NASA Astrophysics Data System (ADS)

Olkin, C. B.; Elliot, J. L.; Hammel, H. B.; Cooray, A. R.; McDonald, S. W.; Foust, J. A.; Bosh, A. S.; Buie, M. W.; Millis, R. L.; Wasserman, L. H.; Dunham, E. W.; Young, L. A.; Howell, R. R.; Hubbard, W. B.; Hill, R.; Marcialis, R. L.; McDonald, J. S.; Rank, D. M.; Holbrook, J. C.; Reitsema, H. J.

1997-09-01

This paper presents new results about Triton's atmospheric structure from the analysis of all ground-based stellar occultation data recorded to date, including one single-chord occultation recorded on 1993 July 10 and nine occultation lightcurves from the double-star event on 1995 August 14. These stellar occultation observations made both in the visible and in the infrared have good spatial coverage of Triton, including the first Triton central-flash observations, and are the first data to probe the altitude level 20-100 km on Triton. The small-planet lightcurve model of J. L. Elliot and L. A. Young (1992,Astron. J.103,991-1015) was generalized to include stellar flux refracted by the far limb, and then fitted to the data. Values of the pressure, derived from separate immersion and emersion chords, show no significant trends with latitude, indicating that Triton's atmosphere is spherically symmetric at ∼50-km altitude to within the error of the measurements; however, asymmetry observed in the central flash indicates the atmosphere is not homogeneous at the lowest levels probed (∼20-km altitude). From the average of the 1995 occultation data, the equivalent-isothermal temperature of the atmosphere is 47 ± 1 K and the atmospheric pressure at 1400-km radius (∼50-km altitude) is 1.4 ± 0.1 μbar. Both of these are not consistent with a model based on Voyager UVS and RSS observations in 1989 (D. F. Strobel, X. Zhu, M. E. Summers, and M. H. Stevens, 1996,Icarus120,266-289). The atmospheric temperature from the occultation is 5 K colder than that predicted by the model and the observed pressure is a factor of 1.8 greater than the model. In our opinion, the disagreement in temperature and pressure is probably due to modeling problems at the microbar level, since measurements at this level have not previously been made. Alternatively, the difference could be due to seasonal change in Triton's atmospheric structure.

Identifying OH Imposters in the ALFALFA HI Survey

NASA Astrophysics Data System (ADS)

Suess, Katherine; Darling, Jeremiah K.; Haynes, Martha P.; Giovanelli, Riccardo

2015-01-01

OH megamasers (OHMs) are rare, luminous molecular masers that are typically observed in (ultra) luminous infrared galaxies and serve as markers of major galaxy mergers. In blind emission line surveys such as the ALFALFA (Arecibo Legacy Fast Arecibo L-Band Feed Array) survey for neutral hydrogen (HI) in the local universe, OHMs at z~0.2 can mimic z~0.05 HI lines. We present the results of optical spectroscopy of ambiguous HI detections in the ALFALFA 40% data release [1] detected by WISE but with uncertain optical counterparts. The optical redshifts, obtained from observations at the Apache Point Observatory 3.5m telescope, identified 127 HI optical counterparts and discovered five new OHMs. Fifty-six candidates remain ambiguous. The new OHMs are the first detected in a blind spectral line survey.The number of OHMs in ALFALFA matches predictions based on the OH luminosity function [2]. Additionally, the OHMs found in a blind survey do not seem to differ from those found in previous targeted surveys. This provides validation of the methods used in previous IR-selected OHM surveys and indicates there is no previously unknown OHM-producing population at z~0.2. We also provide a method for future surveys to separate OH and HI lines without expensive spectral observations. This method utilizes infrared colors and magnitudes, such as WISE mid-IR data. Since the fraction of OHMs found in flux-limited HI surveys is expected to increase with the redshift of the survey [3], this analysis can be applied to future flux-limited high-redshift hydrogen surveys.We thank the ALFALFA team for observing and producing the survey dataset. The ALFALFA team at Cornell is supported by NSF AST-1107390 and the Brinson Foundation.[1] Haynes, M. P., R. Giovanelli, A. M. Martin, K. M. Hess, A. Saintonge, et al. 2011, Astron J, 142, 142[2] Darling, J. & R. Giovanelli 2002, Astrophys J, 572, 810[3] Briggs, F. H. 1998, A&A, 336, 815

Which processes form the volcanic sands on Mars?

NASA Astrophysics Data System (ADS)

Grégoire, M.; Baratoux, D.; Mangold, N.; Arnalds, O.; Platvoet, B.; Bardinzeff, J.; Pinet, P.

2007-12-01

Volcanic sands are common at the surface of Mars. They are usually of basaltic composition. Occurrence of sands, mostly recognized as dark dune fields include numerous impact craters in the southern hemisphere [1], several volcanic provinces such as Cerberus and Syrtis Major[2], several impact craters in the northern hemisphere, the large basins (Hellas and Argyre), Valles Marineris, and the poles [3]. In most cases, the sands are of basaltic composition [2,4], at the exception of the polar dunes which are made of sulfates [3]. It is interesting to note that dunes have been found on the Hesperian volcanic plateau of Systis Major, while they are not reported on Tyrrhena Terra, a volcanic province similar in age and morphology to Syrtis. It seems thus that the formation of sand from volcanic material is not systematic and thus requires particular conditions. These different situations which will be presented raise the following questions. When did these volcanic sands form in the Martian history? Did they result from a long-standing and slow process operating in the present cold conditions or did they result from several episodes associated for instant to climate changes? We review several mechanisms which could account for the formation of volcanic sand on Mars from the volcanic material. In particular, we focus on the role of cold-climate processes from an analysis of terrestrial analogs in Iceland. In this case, the advance and retreat of glaciers over a recent erupted shield volcano associated with the strong catabatic winds have resulted in the rapid formation (less than few thousands years) of large volumes of sands. [1] Fenton, L. K. (2005), Potential sand sources for the dune fields in Noachis Terra, Mars, J. Geophys. Res. 110, E11004, doi :10.1029/2005JE002436. [2] Vaucher et. al, in revision for Icarus [3] Langevin et. al, (2005), Science, 307, 1584-1586 [4] Poulet F., Mangold N. and Erard S. (2003), Astron. & Astrophys. 412, L19-L23.

High Resolution Spectrum of the 13C12C12C Lowest Bending Mode

NASA Astrophysics Data System (ADS)

Endres, C. P.; Lutter, V.; Kötting, J.; Krieg, J.; Thorwirth, S.; Schlemmer, S.; Giesen, T. F.; Harding, M. E.; Vazquez, J.

2012-06-01

Linear C_3 is a floppy molecule which possesses an extremely low lying bending mode, ν_2, at roughly 60 cm-1 or 1.9 THz. Based on highly accurate laboratory data C_3 has been detected in various astronomical sources most recently with the HIFI instrument aboard the Herschel satellite. Although C_3 turns out to be quite abundant in interstellar environments which makes a search for 13C substituted isotopologs feasible, other isotopologs could not be detected so far, because no accurate transition frequencies have been available for these species in this frequency range. Relative abundance ratios of C_3 isotopologs might give important hints on its building mechanism and further constraints for chemical networks. In this work, the spectrum of the ν_2 lowest bending mode of 13CCC has been investigated. We used laser ablation of 13C enriched carbon samples to record absorption spectra in a supersonic jet expansion. The radiation in our setup is generated by a synthesizer referenced to a Rubidium standard in combination with a frequency multiplier chain and detected by a liquid Helium cooled InSb bolometer. The laboratory search has been supported by high-level coupled-cluster calculations, which turns out to compare very favorably with obtained experimental molecular parameters. Schmuttenmaer, C. A., Cohen, R. C., Pugliano, N., Heath, et al., Science 249, 897-900 (1990) Giesen, T. F., van Orden, A. O., Cruzan, J. D., and Provencal, R. A., et al., Astrophys. J. 551, L181-L184 (2001) Gendriesch, R. and Pehl, K. and Giesen, T. and Winnewisser, G. and Lewen, F., Z. Naturforsch. 58a, 129-138 (2003) Van Orden, A., Cruzan, J. D., Provencal, R. A., et al. in Proc. Airborne Astronomy Symp., ASP Conf. Ser. 73, 67 (1995) ernicharo, J. and Goicoechea, J. R. and Caux, E., Astrophys. J. Lett. 534, L199-L202 (2000) Mookerjea, B., Giesen, T., Stutzki, J., Cernicharo, J., et al., Astron. Astrophys. 521, L13 (2010)

OPTICAL SPECTROSCOPIC OBSERVATIONS OF GAMMA-RAY BLAZAR CANDIDATES. V. TNG, KPNO, AND OAN OBSERVATIONS OF BLAZAR CANDIDATES OF UNCERTAIN TYPE IN THE NORTHERN HEMISPHERE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Álvarez Crespo, N.; Massaro, F.; Masetti, N.

The extragalactic γ-ray sky is dominated by emission from blazars, a peculiar class of active galactic nuclei. Many of the γ-ray sources included in the Fermi-Large Area Telescope Third Source catalog (3FGL) are classified as blazar candidates of uncertain type (BCUs) because there are no optical spectra available in the literature to confirm their nature. In 2013, we started a spectroscopic campaign to look for the optical counterparts of the BCUs and of the unidentified γ-ray sources to confirm their blazar nature. Whenever possible we also determine their redshifts. Here, we present the results of the observations carried out inmore » the northern hemisphere in 2013 and 2014 at the Telescopio Nazionale Galileo, Kitt Peak National Observatory, and Observatorio Astronómico Nacional in San Pedro Mártir. In this paper, we describe the optical spectra of 25 sources. We confirmed that all of the 15 BCUs observed in our campaign and included in our sample are blazars and we estimated the redshifts for three of them. In addition, we present the spectra for three sources classified as BL Lacs in the literature but with no optical spectra available to date. We found that one of them is a quasar (QSO) at a redshift of z = 0.208 and the other two are BL Lacs. Moreover, we also present seven new spectra for known blazars listed in the Roma-BZCAT that have an uncertain redshift or are classified as BL Lac candidates. We found that one of them, 5BZB J0724+2621, is a “changing look” blazar. According to the spectrum available in the literature, it was classified as a BL Lac, but in our observation we clearly detected a broad emission line that led us to classify this source as a QSO at z = 1.17.« less

The role of partial ionization effects in the chromosphere

PubMed Central

Martínez-Sykora, Juan; De Pontieu, Bart; Hansteen, Viggo; Carlsson, Mats

2015-01-01

The energy for the coronal heating must be provided from the convection zone. However, the amount and the method by which this energy is transferred into the corona depend on the properties of the lower atmosphere and the corona itself. We review: (i) how the energy could be built in the lower solar atmosphere, (ii) how this energy is transferred through the solar atmosphere, and (iii) how the energy is finally dissipated in the chromosphere and/or corona. Any mechanism of energy transport has to deal with the various physical processes in the lower atmosphere. We will focus on a physical process that seems to be highly important in the chromosphere and not deeply studied until recently: the ion–neutral interaction effects in the chromosphere. We review the relevance and the role of the partial ionization in the chromosphere and show that this process actually impacts considerably the outer solar atmosphere. We include analysis of our 2.5D radiative magnetohydrodynamic simulations with the Bifrost code (Gudiksen et al. 2011 Astron. Astrophys. 531, A154 (doi:10.1051/0004-6361/201116520)) including the partial ionization effects on the chromosphere and corona and thermal conduction along magnetic field lines. The photosphere, chromosphere and transition region are partially ionized and the interaction between ionized particles and neutral particles has important consequences on the magneto-thermodynamics of these layers. The partial ionization effects are treated using generalized Ohm's law, i.e. we consider the Hall term and the ambipolar diffusion (Pedersen dissipation) in the induction equation. The interaction between the different species affects the modelled atmosphere as follows: (i) the ambipolar diffusion dissipates magnetic energy and increases the minimum temperature in the chromosphere and (ii) the upper chromosphere may get heated and expanded over a greater range of heights. These processes reveal appreciable differences between the modelled atmospheres of simulations with and without ion–neutral interaction effects. PMID:25897096

Unveiling the nature of INTEGRAL objects through optical spectroscopy. VI. A multi-observatory identification campaign

NASA Astrophysics Data System (ADS)

Masetti, N.; Mason, E.; Morelli, L.; Cellone, S. A.; McBride, V. A.; Palazzi, E.; Bassani, L.; Bazzano, A.; Bird, A. J.; Charles, P. A.; Dean, A. J.; Galaz, G.; Gehrels, N.; Landi, R.; Malizia, A.; Minniti, D.; Panessa, F.; Romero, G. E.; Stephen, J. B.; Ubertini, P.; Walter, R.

2008-04-01

Using 8 telescopes in the northern and southern hemispheres, plus archival data from two on-line sky surveys, we performed a systematic optical spectroscopic study of 39 putative counterparts of unidentified or poorly studied INTEGRAL sources in order to determine or at least better assess their nature. This was implemented within the framework of our campaign to reveal the nature of newly-discovered and/or unidentified sources detected by INTEGRAL. Our results show that 29 of these objects are active galactic nuclei (13 of which are of Seyfert 1 type, 15 are Seyfert 2 galaxies and one is possibly a BL Lac object) with redshifts between 0.011 and 0.316, 7 are X-ray binaries (5 with high-mass companions and 2 with low-mass secondaries), one is a magnetic cataclysmic variable, one is a symbiotic star and one is possibly an active star. Thus, the large majority (74%) of the identifications in this sample belongs to the AGN class. When possible, the main physical parameters for these hard X-ray sources were also computed using the multiwavelength information available in the literature. These identifications further underscore the importance of INTEGRAL in studying the hard X-ray spectra of all classes of X-ray emitting objects, and the effectiveness of a strategy of multi-catalogue cross-correlation plus optical spectroscopy to securely pinpoint the actual nature of still unidentified hard X-ray sources. Based on observations collected at the following observatories: ESO (La Silla, Chile), partly under program 079.A-0171(A); Astronomical Observatory of Bologna in Loiano (Italy); Astronomical Observatory of Asiago (Italy); Cerro Tololo Interamerican Observatory (Chile); Complejo Astronómico El Leoncito (San Juan, Argentina); South African Astronomical Observatory (Sutherland, South Africa); Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias (Canary Islands, Spain); Anglo-Australian Observatory (Siding Spring, Australia); Apache Point Observatory (New Mexico, USA).

VISIR upgrade overview and status

NASA Astrophysics Data System (ADS)

Kerber, Florian; Käufl, Hans Ulrich; Baksai, Pedro; Dobrzycka, Danuta; Finger, Gert; Ives, Derek; Jakob, Gerd; Lagadec, Eric; Lundin, Lars; Mawet, Dimitri; Mehrgan, Leander; Moerchen, Margaret; Momany, Yazan; Moreau, Vincent; Pantin, Eric; Riquelme, Miguel; Siebenmorgen, Ralf; Silber, Armin; Smette, Alain; Taylor, Julian; van den Ancker, Mario; Venema, Lars; Weilenmann, Ueli; Yegorova, Irina

2012-09-01

We present an overview of the VISIR upgrade project. VISIR is the mid-infrared imager and spectrograph at ESO's VLT. The project team is comprised of ESO staff and members of the original VISIR consortium: CEA Saclay and ASTRON. The project plan is based on input from the ESO user community with the goal of enhancing the scientific performance and efficiency of VISIR by a combination of measures: installation of improved hardware, optimization of instrument operations and software support. The cornerstone of the upgrade is the 1k by 1k Si:As Aquarius detector array (Raytheon) which has demonstrated very good performance (sensitivity, stability) in the laboratory IR detector test facility (modified TIMMI 2 instrument). A prism spectroscopic mode will cover the N-band in a single observation. New scientific capabilities for high resolution and high-contrast imaging will be offered by sub-aperture mask (SAM) and phase-mask coronagraphic (4QPM/AGPM) modes. In order to make optimal use of favourable atmospheric conditions a water vapour monitor has been deployed on Paranal, allowing for real-time decisions and the introduction of a userdefined constraint on water vapour. Improved pipelines based on the ESO Reflex concept will provide better support to astronomers. The upgraded VISIR will be a powerful instrument providing background limited performance for diffraction-limited observations at an 8-m telescope. It will offer synergy with facilities such as ALMA, JWST, VLTI and SOFIA, while a wealth of targets is available from survey work (e.g. VISTA, WISE). In addition it will bring confirmation of the technical readiness and scientific value of several aspects of potential mid-IR instrumentation at Extremely Large Telescopes. The intervention on VISIR and installation of hardware has been completed in July and commissioning will take place during July and August. VISIR is scheduled to be available to the users starting Oct 2012.

Precessing rotating flows with additional shear: stability analysis.

PubMed

Salhi, A; Cambon, C

2009-03-01

We consider unbounded precessing rotating flows in which vertical or horizontal shear is induced by the interaction between the solid-body rotation (with angular velocity Omega(0)) and the additional "precessing" Coriolis force (with angular velocity -epsilonOmega(0)), normal to it. A "weak" shear flow, with rate 2epsilon of the same order of the Poincaré "small" ratio epsilon , is needed for balancing the gyroscopic torque, so that the whole flow satisfies Euler's equations in the precessing frame (the so-called admissibility conditions). The base flow case with vertical shear (its cross-gradient direction is aligned with the main angular velocity) corresponds to Mahalov's [Phys. Fluids A 5, 891 (1993)] precessing infinite cylinder base flow (ignoring boundary conditions), while the base flow case with horizontal shear (its cross-gradient direction is normal to both main and precessing angular velocities) corresponds to the unbounded precessing rotating shear flow considered by Kerswell [Geophys. Astrophys. Fluid Dyn. 72, 107 (1993)]. We show that both these base flows satisfy the admissibility conditions and can support disturbances in terms of advected Fourier modes. Because the admissibility conditions cannot select one case with respect to the other, a more physical derivation is sought: Both flows are deduced from Poincaré's [Bull. Astron. 27, 321 (1910)] basic state of a precessing spheroidal container, in the limit of small epsilon . A Rapid distortion theory (RDT) type of stability analysis is then performed for the previously mentioned disturbances, for both base flows. The stability analysis of the Kerswell base flow, using Floquet's theory, is recovered, and its counterpart for the Mahalov base flow is presented. Typical growth rates are found to be the same for both flows at very small epsilon , but significant differences are obtained regarding growth rates and widths of instability bands, if larger epsilon values, up to 0.2, are considered. Finally, both flow cases are briefly discussed in view of a subsequent nonlinear study using pseudospectral direct numerical simulations, which is a natural continuation of RDT.

The slowly pulsating B-star 18 Pegasi: A testbed for upper main sequence stellar evolution

NASA Astrophysics Data System (ADS)

Irrgang, A.; Desphande, A.; Moehler, S.; Mugrauer, M.; Janousch, D.

2016-06-01

The predicted width of the upper main sequence in stellar evolution models depends on the empirical calibration of the convective overshooting parameter. Despite decades of discussions, its precise value is still unknown and further observational constraints are required to gauge it. Based on a photometric and preliminary asteroseismic analysis, we show that the mid B-type giant 18 Peg is one of the most evolved members of the rare class of slowly pulsating B-stars and, thus, bears tremendous potential to derive a tight lower limit for the width of the upper main sequence. In addition, 18 Peg turns out to be part of a single-lined spectroscopic binary system with an eccentric orbit that is greater than 6 years. Further spectroscopic and photometric monitoring and a sophisticated asteroseismic investigation are required to exploit the full potential of this star as a benchmark object for stellar evolution theory. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programmes 265.C-5038(A), 069.C-0263(A), and 073.D-0024(A). Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC), proposals H2005-2.2-016 and H2015-3.5-008. Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, proposal W15BN015. Based on observations obtained with telescopes of the University Observatory Jena, which is operated by the Astrophysical Institute of the Friedrich-Schiller-University.

Studies of cosmic plasma using radioastron VLBI observations of giant pulses of the pulsar B0531+21

NASA Astrophysics Data System (ADS)

Rudnitskii, A. G.; Karuppusamy, R.; Popov, M. V.; Soglasnov, V. A.

2016-02-01

The structure of the interstellar plasma in the direction of the pulsar in the Crab Nebula is studied using several sets of space-VLBI observations obtained with networks of ground telescopes and the RadioAstron space antenna at 18 and 92 cm. Six observing sessions spanning two years are analyzed. Giant pulses are used to probe the cosmic plasma, making it possible to measure the scattering parameters without averaging. More than 4000 giant pulses were detected. The interferometer responses (visibility functions) on ground and ground-space baselines are analyzed. On the ground baselines, the visibility function as a function of delay is dominated by a narrow feature at zero delay with a width of δ τ ~ 1/B, where B is the receiver bandwidth. This is typical for compact continuum sources. On the ground-space baselines, the visibility function contains a set of features superposed on each other and distributed within a certain interval of delays, which we identify with the scattering time for the interfering rays τ. The amplitude of the visibility function on ground baselines falls with increasing baseline; the scattering disk is partially resolved at 18 cmand fully resolved at 92 cm. Estimates of the scattering angle ? give 0.5-1.3mas at 18 cm and 14.0 mas at 92 cm. The measured values of ? and τ are compared to estimate the distance from the source to the effective scattering screen, which is found at various epochs to be located at distances from 0.33 to 0.96 of the distance from the observer to the pulsar, about 2 kpc. The screen is close to the Crab Nebula at epochs of strong scattering, confirming that scattering on inhomogeneities in the plasma in the vicinity of the nebula itself dominates at these epochs.

A deep search for the release of volcanic gases on Mars using ground-based high-resolution infrared and submillimeter spectroscopy: Sensitive upper limits for OCS and SO2

NASA Astrophysics Data System (ADS)

Khayat, A.; Villanueva, G. L.; Mumma, M. J.; Tokunaga, A. T.

2017-11-01

Recent volcanic activity has long been considered a distinct possibility that would place major constraints on the evolution of Mars' interior. Volcanic activity would result in the outgassing of sulfur-bearing species. As part of our multi-band search for active release of volcanic gases on Mars, we looked for carbonyl sulfide (OCS) at its combination band (ν1 +ν3) at 3.42 μ m (2924 cm-1), and sulfur dioxide (SO2) at 346.652 GHz, in two successive Mars years during its late Northern spring and mid Northern summer seasons (Ls= 43°-144°). The targeted volcanic districts, Tharsis and Syrtis Major, were observed during the two intervals, 15 Dec. 2011 to 6 Jan. 2012 in the first year, and 23 May 2014 to 12 June 2014 in the second year using the high resolution infrared spectrometer CSHELL on the NASA Infrared Telescope Facility, and the high resolution heterodyne receiver HARP at the James Clerk Maxwell Telescope atop Maunakea, Hawaii. No active release of such gases was detected, and we report 2σ upper limits of 1.8 ppbv and 3.1 ppbv for OCS and SO2, respectively, compared to 0.3 ppbv for SO2 (Encrenaz, T. et al. [2011] Astron. & Astrophys. 530, A37; Krasnopolsky, V.A. [2012] Icarus 217, 144-152) over the disk of Mars. Our retrieved upper limit on the SO2 outgassing rate of 156 tons/day (1.8 kg/s), corresponds to a mass rate of magma that is able to degas the SO2 of 104 kilotons/day (1200 kg/s), or 40,000 m3/day (0.46 m3/s). Our campaign places stringent limits on the concentration of sulfur-bearing species into the atmosphere of Mars.

Health promotion, preventive and curative aspects of diseases in astrology.

PubMed

Sharma, Bhuvnesh Kumar; Subhakta, P K J P; Narayana, A

2007-01-01

The whole universe is intermingling into a unit in the period of globalization. Different cultures, life-styles and sciences are co-operating with each other in this situation. World Health Organization is working towards collaborating all prevalent medical sciences for attainment of good health and family welfare for each and every individual by 2020. Astrology is a part of Indian heritage. Astrology means the art of predicting or determining the influence of the planets and stars on human affairs. The origin of this word is from Greek word astron, star + logos (discourse). The account of deeds of good and bad during the present life and previous lives, their consequences of health or ill health during this life i.e. what, when and how the things takes place will be clearly known through Astrology. Highly advanced knowledge related to Astrology on medicine is preserved in Indian scriptures and the knowledge was transmitted from generation to generation. It is also a good source for health promotion, preventive, curative and other medical aspects. Brief direction related to astrological medical aspects is also available in Ayurvedic literature (Carakasamhită, Suśrutasamhhită, Aşţăngasangraha, Aşţăngahŗdaya, Sărngadharasamhită , Băvaprakăśa etc.) Some Ayurvedic practitioners, scholars and scientists realize the need of astrological knowledge related to medicine in the present time. In ancient times physician, astrologer and purŏhita (Hindu priest) simultaneously looked after the health and family welfare of individual, families and country. Astrologer guides medication and suitable time for the better cure of ailments. Even the medicinal herbs were collected and treated at appropriate time for their efficacy. Astrology and Ayurvĕda are inseparable sciences of life. Hence, in this article, a concise astrological evaluation related to health promotion, preventive and curative aspects of Astrology is being presented.

Looking a gift horse in the mouth: Evaluation of wide-field asteroid photometric surveys

NASA Astrophysics Data System (ADS)

Harris, Alan W.; Pravec, Petr; Warner, Brian D.

2012-09-01

It has recently become possible to do a photometric survey of many asteroids at once, rather than observing single asteroids one (or occasionally a couple) at a time. We evaluate two such surveys. Dermawan et al. (Dermawan et al. [2011]. Publ. Astron. Soc. Jpn. 63, S555-S576) observed one night on the Subaru 8.2 m telescope, and Masiero et al. (Masiero, J., Jedicke, R., Durech, J., Gwen, S., Denneau, L., Larsen, J. [2009]. Icarus 204, 145-171) observed six nights over 2 weeks with the 3.6 m CFHT. Dermawan claimed 83 rotation periods from 127 detected asteroids; Masiero et al. claimed 218 rotation periods from 828 detections. Both teams claim a number of super-fast rotators (P < 2.2 h) among main belt asteroids larger than 250 m diameter, some up to several km in diameter. This would imply that the spin rate distribution of main belt asteroids differs from like-sized NEAs, that there are larger super-fast rotators (monolithic asteroids) in the main belt than among NEAs. Here we evaluate these survey results, applying the same criteria for reliability of results that we apply to all results listed in our Lightcurve Database (Warner, B.D., Harris, A.W., Pravec, P. [2009a]. Icarus 202, 134-146). In doing so, we assigned reliability estimates judged sufficient for inclusion in statistical studies for only 27 out of 83 (33%) periods claimed by Dermawan, and only 87 out of 218 (40%) periods reported by Masiero et al.; none of the super-fast rotators larger than about 250 m diameter claimed by either survey received a reliability rating judged sufficient for analysis. We find no reliable basis for the claim of different rotation properties between main belt and near-Earth asteroids. Our analysis presents a cautionary message for future surveys.

Polarimetry in the Outskirts of NGC 6611

NASA Astrophysics Data System (ADS)

Orsatti, Ana M.; Vega, E. Irene; Marraco, Hugo G.

2006-11-01

We present new polarimetric UBVRI observations of 25 stars in the direction of the halo of NGC 6611, the rich stellar open cluster embedded in an ionized hydrogen complex (M16). Our plan is to characterize the interstellar material (ISM) associated with halo stars in order to make a comparison with the ISM dusty core characteristics that resulted from a previous investigation by the same authors. Of the halo stars, 47% (8 out of 17) show indications of intrinsic polarization in their light, similar to what was found for core stars (50%). We have identified the presence of nearby dust clouds located on the Local arm that produce a mean polarization of about 1%; a value λmax=0.61+/-0.07 μm, which is slightly larger than that of the average ISM; and a mean direction of the polarization vectors of θV=81.9d+/-1.8d. The ISM associated with the halo region has λmax similar to the general interstellar medium (0.55+/-0.07 μm). The observed polarizations show a gradual increase from halo (Pmax=1.93%+/-0.3%) to core (Pmax=3.19%+/-0.63%). Position angles of the e-vector for both groups are generally similar, but there exists a slight difference in mean direction between them that is within the errors. We have also found that the halo stars are possibly represented by Whittet & van Breda's relationship, while in the cluster's core the dust does not fulfill the above-mentioned relationship. As a conclusion, we cannot find any clear difference between core and halo dust characteristics, with the exception of λmax, which may suggest a change in dust size. Based on observations obtained at Complejo Astronómico El Leoncito, operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the Universities of La Plata, Córdoba, and San Juan.

The spectroscopic binary system Gl 375. I. Orbital parameters and chromospheric activity

NASA Astrophysics Data System (ADS)

Díaz, R. F.; González, J. F.; Cincunegui, C.; Mauas, P. J. D.

2007-11-01

Aims:We study the spectroscopic binary system Gl 375 to characterise its orbit and the spectral types and chromospheric activity levels of the components. Methods: We employed medium-resolution echelle spectra obtained at the 2.15 m telescope at the Argentinian observatory CASLEO and photometric observations obtained from the ASAS database. Results: We have separated the composite spectra into those corresponding to both components. The separated spectra allow us to confirm that the spectral types of both components are similar (dMe3.5) and to obtain precise measurements of the orbital period (P = 1.87844 days), minimum masses (M_1 sin3 i = 0.35 {M}_⊙ and M_2 sin3 i =0.33 {M}_⊙), and other orbital parameters. The photometric observations exhibit a sinusoidal variation with the same period as the orbital period. We interpreted this as signs of active regions carried along with rotation in a tidally synchronised system, and studied the evolution of the amplitude of the modulation on longer timescales. Together with the mean magnitude, the modulation exhibits a roughly cyclic variation with a period of around 800 days. This periodicity is also found in the flux of the Ca II K lines of both components, which seem to be in phase. Conclusions: The periodic changes in the three observables are interpreted as a sign of a stellar activity cycle. Both components appear to be in phase, which implies that they are magnetically connected. The measured cycle of ≈2.2 years (≈800 days) is consistent with previous determinations of activity cycles in similar stars. The authors are visiting astronomers of the Complejo Astronómico El Leoncito, operated under an agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba, and San Juan.

Developing the Planetary Science Virtual Observatory

NASA Astrophysics Data System (ADS)

Erard, Stéphane; Cecconi, Baptiste; Le Sidaner, Pierre; Henry, Florence; Chauvin, Cyril; Berthier, Jérôme; André, Nicolas; Génot, Vincent; Schmitt, Bernard; Capria, Teresa; Chanteur, Gérard

2015-08-01

In the frame of the Europlanet-RI program, a prototype Virtual Observatory dedicated to Planetary Science has been set up. Most of the activity was dedicated to the definition of standards to handle data in this field. The aim was to facilitate searches in big archives as well as sparse databases, to make on-line data access and visualization possible, and to allow small data providers to make their data available in an interoperable environment with minimum effort. This system makes intensive use of studies and developments led in Astronomy (IVOA), Solar Science (HELIO), and space archive services (IPDA).The current architecture connects existing data services with IVOA or IPDA protocols whenever relevant. However, a more general standard has been devised to handle the specific complexity of Planetary Science, e.g. in terms of measurement types and coordinate frames. This protocol, named EPN-TAP, is based on TAP and includes precise requirements to describe the contents of a data service (Erard et al Astron & Comp 2014). A light framework (DaCHS/GAVO) and a procedure have been identified to install small data services, and several hands-on sessions have been organized already. The data services are declared in standard IVOA registries. Support to new data services in Europe will be provided during the proposed Europlanet H2020 program, with a focus on planetary mission support (Rosetta, Cassini…).A specific client (VESPA) has been developed at VO-Paris (http://vespa.obspm.fr). It is able to use all the mandatory parameters in EPN-TAP, plus extra parameters from individual services. A resolver for target names is also available. Selected data can be sent to VO visualization tools such as TOPCAT or Aladin though the SAMP protocol.Future steps will include the development of a connection between the VO world and GIS tools, and integration of heliophysics, planetary plasma and reference spectroscopic data.The EuroPlaNet-RI project was funded by the European Commission under the 7th Framework Program, grant 228319 "Capacities Specific Programme".

Cassini/CIRS Observations of Water Vapor in Titan's Stratosphere

NASA Technical Reports Server (NTRS)

Bjoraker, Gordon L.; Achterberg, R. K.; Anderson, C. M.; Samuelson, R. E.; Carlson, R. C.; Jennings, D. E.

2008-01-01

The Composite Infrared Spectrometer (CIRS) on the Cassini spacecraft has obtained spectra of Titan during most of the 44 flybys of the Cassini prime mission. Water vapor on Titan was first detected using whole-disk observations from the Infrared Space Observatory (Coustenis et al 1998, Astron. Astrophys. 336, L85-L89). CIRS data permlt the retrieval of the latitudinal variation of water on Titan and some limited information on its vertical profile. Emission lines of H2O on Titan are very weak in the CIRS data. Thus, large spectral averages as well as improvements in calibration are necessary to detect water vapor. Water abundances were retrieved in nadir spectra at 55 South, the Equator, and at 19 North. Limb spectra of the Equator were also modeled to constrain the vertical distribution of water. Stratospheric temperatures in the 0.5 - 4.0 mbar range were obtained by inverting spectra of CH4 in the v4 band centered at 1304/cm. The temperature in the lower stratosphere (4 - 20 mbar) was derived from fitting pure rotation lines of CH4 between 80 and 160/cm. The origin of H2O and CO2 is believed to be from the ablation of micrometeorites containing water ice, followed by photochemistry. This external source of water originates either within the Saturn system or from the interplanetary medium. Recently, Horst et al (J. Geophys. Res. 2008, in press) developed a photochemical model of Titan in which there are two external sources of oxygen. Oxygen ions (probably from Enceladus) precipitate into Titan's atmosphere to form CO at very high altitudes (1100 km). Water ice ablation at lower altitudes (700 km) forms H2O and subsequent chemistry produces CO2. CIRS measurements of CO, CO2, and now of H2O will provide valuable constraints to these photochemical models and - improve our understanding of oxygen chemistry on Titan.

Waldmeier's Rules in the Solar and Stellar Dynamos

NASA Astrophysics Data System (ADS)

Pipin, Valery; Kosovichev, Alexander

2015-08-01

The Waldmeier's rules [1] establish important empirical relations between the general parameters of magnetic cycles (such as the amplitude, period, growth rate and time profile) on the Sun and solar-type stars [2]. Variations of the magnetic cycle parameters depend on properties of the global dynamo processes operating in the stellar convection zones. We employ nonlinear mean-field axisymmetric dynamo models [3] and calculate of the magnetic cycle parameters, such as the dynamo cycle period, total magnetic and Poynting fluxes for the Sun and solar-type stars with rotational periods from 15 to 30 days. We consider two types of the dynamo models: 1) distributed (D-type) models employing the standard α - effect distributed in the whole convection zone, and 2) Babcock-Leighton (BL-type) models with a non-local α - effect. The dynamo models take into account the principal mechanisms of the nonlinear dynamo generation and saturation, including the magnetic helicity conservation, magnetic buoyancy effects, and the feedback on the angular momentum balance inside the convection zones. Both types of models show that the dynamo generated magnetic flux increases with the increase of the rotation rate. This corresponds to stronger brightness variations. The distributed dynamo model reproduces the observed dependence of the cycle period on the rotation rate for the Sun analogs better than the BL-type model. For the solar-type stars rotating more rapidly than the Sun we find dynamo regimes with multiple periods. Such stars with multiple cycles form a separate branch in the variability-rotation diagram.1. Waldmeier, M., Prognose für das nächste Sonnenfleckenmaximum, 1936, Astron. Nachrichten, 259,262. Soon,W.H., Baliunas,S.L., Zhang,Q.,An interpretation of cycle periods of stellar chromospheric activity, 1993, ApJ, 414,333. Pipin,V.V., Dependence of magnetic cycle parameters on period of rotation in nonlinear solar-type dynamos, 2015, astro-ph: 14125284

Origin Of The Near-earth Asteroid Phaethon And The Geminids Meteor Shower

NASA Astrophysics Data System (ADS)

de Leon, Julia; Campins, H.; Tsiganis, K.; Morbidelli, A.; Licandro, J.

2010-10-01

Asteroid (3200) Phaethon is a remarkable Near Earth Asteroid (NEA). It was the first asteroid associated with a meteor shower, namely the Geminid stream1. Phaethon's unusual orbit has a high inclination and a very low perihelion distance (0.14 AU). Its reflectance spectrum suggests a connection with primitive meteorites, best fitting with CI/CM carbonaceous chondrites2, aqueously altered and rich in hydrated silicates. However, its origin is not well determined. Recent studies suggest a connection with the population of main-belt comets3, classifying Phaethon as an activated asteroid. Here we show that the most likely source of Phaethon and the Geminids is the asteroid (2) Pallas, one of the largest asteroids in the main belt, which is surrounded by a collisional family, containing several Phaethon-sized objects. Pallas’ highly inclined orbit and surface composition, also primitive and with evidence of hydration4, support this connection. Our analysis reveals a striking similarity between Phaethon's visual spectrum and those of Pallas family members. Moreover, our numerical simulations show the existence of a robust dynamical pathway, connecting the orbital neighborhood of Pallas with that of Phaethon. In this respect, the Pallas family may constitute a source of primitive NEAs. (The author gratefully acknowledges support from the Spanish "Ministerio de Ciencia e Innovación" projects AYA2005-07808-C03-02 and AYA2008-06202-C03-02.) References 1. Whipple, F. L. 1983, IAU Circular, 3881 2. Licandro, J., Campins, H., Mothe-Diniz, T., Pinilla-Alonso, N. & de Leon, J. 2007, Astron. Astrophys. 461, 751-757 3. Hsieh, H. H., & Jewitt, D. 2006, Science, 312, 561-563 4. Rivkin, A. S., Howell, E. S., Vilas, F. & Lebofsky, L. A. in Asteroids III (eds Bottke, W. F., Cellino, A., Paolicchi, P. & Binzel, R. P.) 235-253 (Univ. Arizona Press, 2002).

Reconstructing the dark sector interaction with LISA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai, Rong-Gen; Yang, Tao; Tamanini, Nicola, E-mail: cairg@itp.ac.cn, E-mail: nicola.tamanini@cea.fr, E-mail: yangtao@itp.ac.cn

We perform a forecast analysis of the ability of the LISA space-based interferometer to reconstruct the dark sector interaction using gravitational wave standard sirens at high redshift. We employ Gaussian process methods to reconstruct the distance-redshift relation in a model independent way. We adopt simulated catalogues of standard sirens given by merging massive black hole binaries visible by LISA, with an electromagnetic counterpart detectable by future telescopes. The catalogues are based on three different astrophysical scenarios for the evolution of massive black hole mergers based on the semi-analytic model of E. Barausse, Mon. Not. Roy. Astron. Soc. 423 (2012) 2533.more » We first use these standard siren datasets to assess the potential of LISA in reconstructing a possible interaction between vacuum dark energy and dark matter. Then we combine the LISA cosmological data with supernovae data simulated for the Dark Energy Survey. We consider two scenarios distinguished by the time duration of the LISA mission: 5 and 10 years. Using only LISA standard siren data, the dark sector interaction can be well reconstructed from redshift z ∼1 to z ∼3 (for a 5 years mission) and z ∼1 up to z ∼5 (for a 10 years mission), though the reconstruction is inefficient at lower redshift. When combined with the DES datasets, the interaction is well reconstructed in the whole redshift region from 0 z ∼ to z ∼3 (5 yr) and z ∼0 to z ∼5 (10 yr), respectively. Massive black hole binary standard sirens can thus be used to constrain the dark sector interaction at redshift ranges not reachable by usual supernovae datasets which probe only the z ∼< 1.5 range. Gravitational wave standard sirens will not only constitute a complementary and alternative way, with respect to familiar electromagnetic observations, to probe the cosmic expansion, but will also provide new tests to constrain possible deviations from the standard ΛCDM dynamics, especially at high redshift.« less

Thz Spectroscopy of 12CH^+, 13CH^+, and 12CD^+

NASA Astrophysics Data System (ADS)

Yu, Shanshan; Drouin, Brian; Pearson, John; Amano, Takayoshi

2015-06-01

In 1937, Dunham detected a couple of unidentified lines in near-UV, and later Douglas and Herzberg identified them based on their laboratory observations to be low-J electronic transitions of CH^+. The electronic spectra, in particular the A^1Π-X^1σ^+ band, have been investigated extensively. On the other hand, the pure rotational transitions have not been studied so extensively. Only the lowest rotational transition, J=1-0, was observed in the laboratory for the normal species, 13CH^+, and CD^+. Based on the laboratory frequency, CH^+ was detected in star forming regions with the Hershel space observatory. Cernicharo et al identified pure rotational transitions from J=2-1 to J=6-5 in the far-infrared region in the ISO spectrum of the planetary nebula NGC 7027. The ISO spectra, however, were of low-resolution, so high-resolution spectroscopic observation is highly desirable. In this presentation, we have extended the measurements to higher-J lines up to 2 THz. For production of CH^+, an extended negative glow discharge in a gas mixture of CH_4 (˜ 0.5 mTorr) diluted in He (˜ 60 mTorr) was used. The optimum discharge current was about 15 mA and the axial magnetic filed to 160 Gauss was applied up. The discharge cell was cooled down to liquid nitrogen temperature. Several frequency multiplier chains, developed at JPL and purchased from Virginia Diodes, were used as THz radiation sources. New THz measurements are not only useful for providing better characterization of spectroscopic properties but also will serve as starting point for astronomical observations. T. Dunham, Publ. Astron. Soc. Pac., 49,~26 (1937) A. E. Douglas and G. Herzberg, Ap. J. 94,~381 (1941) T. Amano, Ap.J.Lett., 716, L1 (2010) T. Amano, J. Chem. Phys., 133, 244305 (2010) J. Cernicharo et al., Ap. J. Lett., 483, L65 (1997)

Espectroscopia de candidatos a remanescentes de aglomerados abertos

NASA Astrophysics Data System (ADS)

Pavani, D. B.; Bica, E.; Ahumada, A. V.; Clariá, J. J.

2003-08-01

A pesquisa sobre remanescentes de aglomerados abertos tem despertado grande interesse. Seguindo esta tendência encontramos estudos teóricos e observacionais. Os primeiros baseiam-se em simulações numéricas buscando determinar fração de binárias e distâncias galatocêntricas, tempo de vida e conteúdo estelar. Estes estão relacionados à função inicial de massa e densidade de estrelas, ou seja, se ricos ou pobremente povoados, compactos ou esparsos. No caso observacional procuram-se identificar os remanescentes considerando-se que trazem estas assinaturas de seus percursores. No presente estudo empregamos espectroscopia para analisar oito concentrações pobremente povoadas, previamente classificadas como aglomerados abertos, sendo sete compactas e uma esparsa. As observações foram obtidas através do telescópio de 2,15 m do CASLEO em San Juan, Argentina, em turnos entre 2001 e 2003. Utilizamos uma câmara CCD contendo um chip Tektronics de 1024X1024 pixeis aliado a um espectrógrafo REOSC. O domínio espectral vai de 3700 a 7000 Å. As reduções foram realizadas no Observatório Astronômico de Córdoba (Argentina) usando pacotes IRAF padrões. Determinamos idades, avermelhamentos e tipos espectrais através de comparações com biblioteca de estrelas e de aglomerados. Em alguns casos nossos espectros estavam dominados por estrelas individuais às quais determinamos seus tipos espectrais. Aos oito objetos adicionamos mais cinco da literatura recente analisados via espectro ou diagrama cor-magnitude. O histograma resultante contém idades típicas entre 0.5 e 3 Ganos. Considerando que predominantemente estes objetos encontram-se na vizinhança solar e, portanto, não cruzaram muitas vezes o plano Galático esperamos que a diferença no tempo necessário para dissolução destes prováveis remanescentes seja em função de diferentes massas iniciais.

Noncircular features in Saturn's rings I: The edge of the B ring

NASA Astrophysics Data System (ADS)

Nicholson, Philip D.; French, Richard G.; Hedman, Matthew M.; Marouf, Essam A.; Colwell, Joshua E.

2014-01-01

A comprehensive investigation of all available radio and stellar occultation data for the outer edge of Saturn's B ring, spanning the period 1980-2010, confirms that the m = 2 distortion due to the strong Mimas 2:1 inner Lindblad resonance circulates slowly relative to Mimas in a prograde direction, with a frequency ΩL = 0.1819° d-1. Our best-fitting model implies that the radial amplitude of this distortion ranges from a minimum of 3 km to a maximum of 71 km, with short-lived minima recurring every 5.42 yrs. In addition to the dominant m = 2 pattern, the edge of the B ring also exhibits at least four other perturbations. An m = 1 component with a radial amplitude of ˜20 km rotates at a rate very close to the expected local apsidal precession rate of ϖ˜5.059° d-1, while smaller perturbations are seen with m = 3 (amplitude 12.5 km), m = 4 (5.9 km), and m = 5 (5.6 km), each of which has a pattern speed consistent with that expected for a spontaneously-generated "normal mode" (French, R.G. et al. [1988]. Icarus 73, 349-378). Our results for m = 1, m = 2 and m = 3 are compatible with those obtained by Spitale and Porco (Spitale, J.N., Porco, C.C. [2010]. Astron. J. 140, 1747-1757), which were based on Cassini imaging data. The pattern speed of each normal mode slightly exceeds that expected at the mean edge radius, supporting their conclusion that they may represent a series of free modes, each of which is trapped in a narrow region between the mode's resonant radius and the ring's edge. However, both our model and that of Spitale and Porco fail to provide complete descriptions of this surprisingly complex feature, with post-fit root-mean-square residuals of ˜8 km considerably exceeding typical measurement errors of 1 km or less.

New Horizons Results at Charon

NASA Astrophysics Data System (ADS)

Buratti, B. J.; Stern, A.; Moore, J. M.; Weaver, H. A., Jr.; Grundy, W. M.; Hofgartner, J. D.; Spencer, J. R.; McKinnon, W. B.; Olkin, C.; Young, L. A.; Verbiscer, A.; Singer, K. N.; Robbins, S. J.; Ennico Smith, K.

2016-12-01

The New Horizons Spacecraft encountered dwarf planet Pluto and its system of moons on July 15, 2015 for the first detailed study of a Kuiper Belt Object (1). Pluto possesses a system of at least 5 moons, including Charon, which is the largest moon in relation to its primary, comprising 12% of the mass of Pluto. The results from the flyby show a world that has undergone a large resurfacing event on at least one of its hemispheres, perhaps from differentiation and subsequent freezing of a subsurface ocean. Charon has a complex system of faults, and regions of various ages based on crater counting statistics. It has no evidence for recent or ongoing geologic activity as Pluto does. Its visible geometric albedo is 0.41±0.02, with normal reflectances ranging from 0.2-0.7. A few isolated brighter areas exist. A northern polar cap of low-albedo red material may be formed from a newly discovered process in the Solar System: the capture of methane from Pluto's atmosphere and subsequent polymerization and accumulation of a complex lag deposit (2). Unlike Pluto, which has a surface covered primarily of methane and nitrogen, Charon's surface is composed of water ice, along with NH3-ice in some form (3). The substantial relief on the moon implies that ice extends below the surface. The bulk density of Pluto and Charon are similar (1). This result implies that if Charon was formed from an impact and reaccretion event involving Pluto and a second body (4), it is unlikely the two bodies were fully differentiated prior to the event. (1) Stern, S. A. et al. (2015). Science 350, 292. (2) Grundy, W. M. et al. (2016). Manuscript accepted at Nature. (3) Grundy, W. M. et al. (2016). Science 351, 1283. (4) Canup, R. M. (2011). Astron. J. 141, 35. Funded by NASA.

Polarimetric imaging of NGC 1068 at high angular resolution in the near infrared. Direct evidence of an extended nuclear torus

NASA Astrophysics Data System (ADS)

Gratadour, D.; Rouan, D.; Grosset, L.; Boccaletti, A.; Clénet, Y.

2015-09-01

Aims: One of the main observational challenges for investigating the central regions of active galactic nuclei (AGN) at short wavelengths, using high angular resolution, and high contrast observations, is to directly detect the circumnuclear optically thick material hiding the central core emission when viewed edge-on. The lack of direct evidence is limiting our understanding of AGN, and several scenarios have been proposed to cope for the diverse observed aspects of activity in a unified approach. Methods: Observations in the near-infrared spectral range have shown themselves to be powerful for providing essential hints to the characterisation of the unified model ingredients because of the reduced optical depth of the obscuring material. Moreover, it is possible to trace this material through light scattered from the central engine's closest environment, so that polarimetric observations are the ideal tool for distinguishing it from purely thermal and stellar emissions. Results: Here we show strong evidence that there is an extended nuclear torus at the center of NGC 1068 thanks to new adaptive-optics-assisted polarimetric observations in the near-infrared. The orientation of the polarization vectors proves that there is a structured hourglass-shaped bicone and a compact elongated (20 × 60 pc) nuclear structure perpendicular to the bicone axis. The linearly polarized emission in the bicone is dominated by a centro-symmetric pattern, but the central compact region shows a clear deviation from the latter with linear polarization aligned perpendicular to the bicone axis. Figure 2 is available in electronic form at http://www.aanda.orgData obtained with the SPHERE an instrument designed and built by a consortium consisting of IPAG (France), MPIA (Germany), LAM (France), LESIA (France), Laboratoire Lagrange (France), INAF - Osservatorio di Padova (Italy), Observatoire de Genève (Switzerland), ETH Zurich (Switzerland), NOVA (Netherlands), ONERA (France), and ASTRON (Netherlands) in collaboration with ESO.

Electron Impact Studies Relevant to Rosetta Coma Measurements of 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Bodewits, D.; Feldman, P. D.; Matejčík, Š.; Országh, J.; Durian, M.

2017-12-01

Auroral emission from electron impact processes can provide a remote window on the physical properties of plasma and neutral gases surrounding small bodies (Galand & Chakrabarti, 2002; Roth et al. 2014). Surprisingly, Rosetta found that outside 2 AU pre-perihelion, atomic and molecular emission features in the inner coma were predominantly caused by dissociative electron impact excitation (Feldman et al. 2015). When the comet came within 2 au of the Sun, fluorescent emission became the dominant process, as water densities in the inner coma could effectively cool the electron population below the appearance energy of the relevant electron impact dissociative excitation processes (Bodewits et al. 2016). Further quantitative interpretation of the Alice and OSIRIS images of the coma is by limited excitation cross sections measured of electron impact reactions with the gases present in cometary comae, including H2O, CO2, CO, O2, and HCN. We will present the first results of a series of experiments dedicated to investigate the emission features seen by the instruments on board Rosetta. The experimental set up is located at the Comenius University in Bratislava, Slovakia, and consists of a crossed-beam configuration combining an electron monochromator and a gas beam (Danko et al. 2013). The electron induced emission spectra are measured using a Czerny-Turner optical monochromator provides a spectral resolution of 0.3 nm FWHM and is equipped with a photomultiplier sensitive between 185 and 710 nm. References: Bodewits, D. et al. The Astronomical Journal 152, 130 (2016). Danko, M. et al. J. Phys. B 46, 045203 (2013). Feldman, P. D. et al. Astron. Astroph. 583, A8 (2015). Galand, M. & Chakrabarti, S. Geophysical Monograph 130. Ed. Michael Mendillo 130, 55- (2002). Roth, L., Saur, J., Retherford, K. D., Strobel, D. F. & Feldman, P. D. Science (2014). doi:10.1126/science.1247051

A New Model for the Seasonal Evolution of Triton

NASA Astrophysics Data System (ADS)

Forget, F.; Decamp, N.; Berthier, J.; Le Guyader, C.

2000-10-01

The seasonal evolution of Triton's surface and atmosphere remains poorly understood. No model [1] has been able to fully reproduce the main characterictics of the Voyager 2 observations in 1989 in combination with the "Global warming" recently inferred from stellar occultations [2]. Within this context, we have developped a new thermal model to study the seasonal nitrogen cycle on Triton. The model is the surface part of a Triton atmosphere General circulation model developped at LMD [3]. The nitrogen cycle was found to be very sensitive to Triton complex seasonal variations of the subsolar point latitude, especially during the current decade (south summer solstice). Since only pre-Voyager formulations were available for such a study, this has motivated some new calculations of Triton's motion based on more recent rotationnal elements combined with a relatively complete dynamic solution [4] adapted to Triton. A new analytic formulation suitable for climate modelling has been derived. On this basis, we wish to suggest a new, realistic scenario to explain Triton's apparence and evolution based on solar-induced variation of the frost albedo. Such variations have been observed in Mars CO2 ice seasonal polar caps [5]. Although they seem to result from complex microphysical behavior, they are likely to occur on Triton since both Triton and Mars polar caps are composed of weakly absorbing ice (N2 or CO2) in vapor pressure equilibrium with the main constituant of the atmosphere. [1] e.g. Hansen and Paige, Icarus 99, 273-288 (1992); Brown and Kirk, J. Geophys. Res. 99, 1965-1981 (1994); Spencer and Moore, Icarus 99, 261-272 (1992). [2] Elliot et al., Nature 393, 765-767 (1998). [3] Forget, Descamp and Hourdin, in ``Pluto and Triton, comparisons and evolution over time", Lowell Observatory's fourth annual workshop, Flagstaff, Arizona. (1999) [4] Le Guyader, Astron. Astrophys. 272, 687-694 (1993). [5] Kieffer et al., J. Geophys. Res. 105, 9653-9700 (2000).

Do cosmological data rule out f (R ) with w ≠-1 ?

NASA Astrophysics Data System (ADS)

Battye, Richard A.; Bolliet, Boris; Pace, Francesco

2018-05-01

We review the equation of state (EoS) approach to dark sector perturbations and apply it to f (R ) gravity models of dark energy. We show that the EoS approach is numerically stable and use it to set observational constraints on designer models. Within the EoS approach we build an analytical understanding of the dynamics of cosmological perturbations for the designer class of f (R ) gravity models, characterized by the parameter B0 and the background equation of state of dark energy w . When we use the Planck cosmic microwave background temperature anisotropy, polarization, and lensing data as well as the baryonic acoustic oscillation data from SDSS and WiggleZ, we find B0<0.006 (95% C.L.) for the designer models with w =-1 . Furthermore, we find B0<0.0045 and |w +1 |<0.002 (95% C.L.) for the designer models with w ≠-1 . Previous analyses found similar results for designer and Hu-Sawicki f (R ) gravity models using the effective field theory approach [Raveri et al., Phys. Rev. D 90, 043513 (2014), 10.1103/PhysRevD.90.043513; Hu et al., Mon. Not. R. Astron. Soc. 459, 3880 (2016), 10.1093/mnras/stw775]; therefore this hints for the fact that generic f (R ) models with w ≠-1 can be tightly constrained by current cosmological data, complementary to solar system tests [Brax et al., Phys. Rev. D 78, 104021 (2008), 10.1103/PhysRevD.78.104021; Faulkner et al., Phys. Rev. D 76, 063505 (2007), 10.1103/PhysRevD.76.063505]. When compared to a w CDM fluid with the same sound speed, we find that the equation of state for f (R ) models is better constrained to be close to -1 by about an order of magnitude, due to the strong dependence of the perturbations on w .

Prospective Work for Alma: the Millimeterwave and Submillimeterwave Spectrum of 13C-GLYCOLALDEHYDE

NASA Astrophysics Data System (ADS)

Haykal, Imane; Margulès, Laurent; Huet, Therese R.; Motiyenko, Roman; Guillemin, J.-C.

2011-06-01

Glycolaldehyde has been identified in interstellar sources. The relative abundance ratios of the three isomers (acetic acid) : (glycolaldehyde) : (methylformate) were estimated . The detection of 13C_1 and 13C_2 isotopomers of methylformate has been recently reported in Orion, as a result of the detailled labororatory spectroscopic study. Therefore the spectroscopy of the 13C isotopomers of glycolaldehyde is investigated in laboratory in order to provide data for an astronomical search. The instrument ALMA will certainly be a good instrument to detect them. Up to now, only the microwave spectra of 13CH_2OH-CHO and of CH_2OH-13CHO have been observed several years ago in the 12-40 GHz range. Spectra of both species are presently recorded in Lille in the 150-950 GHz range with the new submillimetre-wave spectrometer based on harmonic generation of a microwave synthesizer source, using only solid-state devices, and coupled to a cell of 2.2 m length The absolute accuracy of the line positions is better than 30 KHz. The rotational structure of the ground state and of the three first excited vibrational states has been observed. Two 13C enriched samples were used. The analysis is in progress. This work is supported by the Programme National de Physico-Chimie du Milieu Interstellaire (PCMI-CNRS) and by the contract ANR-08-BLAN-0054 J. M. Hollis, S. N. Vogel, L. E. Snyder, et al., Astrophys. J. 554(2001) L81 R. A. H. Butler, F. C. De Lucia, D. T Petkie, et al., Astrophys. J. Supp. 134 (2001) 319 M. T. Beltran, C. Codella, S. Viti, R. Niri, R. Cesaroni, Astrophys. J. 690 (2009) L93. M. Carjaval, L. Margulès, B. Tercero et al., Astron. Astrophys. 500 (2009) 1109. K.-M. Marstokk and H. Møllendal, J. Mol. Struct. 16 (1973) 259. R. A. Motiyenko, L. Margulès, E. A. Alekseev et al., J. Mol. Spectrosc. 264 (2010) 94.

PPAK wide-field Integral Field Spectroscopy of NGC 628 - II. Emission line abundance analysis

NASA Astrophysics Data System (ADS)

Rosales-Ortega, F. F.; Díaz, A. I.; Kennicutt, R. C.; Sánchez, S. F.

2011-08-01

In this second paper of the series, we present the two-dimensional (2D) emission line abundance analysis of NGC 628, the largest object within the PPAK Integral Field Spectroscopy (IFS) Nearby Galaxies Survey, PINGS. We introduce the methodology applied to the 2D IFS data in order to extract and deal with large spectral samples, from which a 2D abundance analysis can be later performed. We obtain the most complete and reliable abundance gradient of the galaxy up to date, by using the largest number of spectroscopic points sampled in the galaxy, and by comparing the statistical significance of different strong-line metallicity indicators. We find features not previously reported for this galaxy that imply a multimodality of the abundance gradient consistent with a nearly flat distribution in the innermost regions of the galaxy, a steep negative gradient along the disc and a shallow gradient or nearly constant metallicity beyond the optical edge of the galaxy. The N/O ratio seems to follow the same radial behaviour. We demonstrate that the observed dispersion in metallicity shows no systematic dependence with the spatial position, signal-to-noise ratio or ionization conditions, implying that the scatter in abundance for a given radius is reflecting a true spatial physical variation of the oxygen content. Furthermore, by exploiting the 2D IFS data, we were able to construct the 2D metallicity structure of the galaxy, detecting regions of metal enhancement and showing that they vary depending on the choice of the metallicity estimator. The analysis of axisymmetric variations in the disc of NGC 628 suggest that the physical conditions and the star formation history of different symmetric regions of the galaxy have evolved in a different manner. Based on observations made at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).

Observations of TeV Gamma Rays from Supernova Remnants

NASA Astrophysics Data System (ADS)

Buckley, James H.

1994-12-01

Measurements of the gamma ray flux from a number of supernova remnants (SNRs) at energies above 250 GeV have been made with the Whipple Imaging air \\v Cerenkov detector. Observation of the gamma ray emission of SNRs at energies above 1 GeV should provide a sensitive test of shock acceleration models of particle acceleration in SNRs. Gamma-ray luminosities of supernova remnants are well constrained by the observed supernova rate and the cosmic ray flux if supernovae are indeed the source of cosmic rays. Drury et al. (Astron. Astrophys. 287, 959 (1994)) predict that the luminosity of nearby Sedov-phase SNRs should be observable by the Whipple telescope. In this model, diffusive shock acceleration produces energetic charged particles which interact with the ambient medium forming gamma rays. There is an indication that a number of unidentified EGRET sources may correspond to supernova remnants (G. Kanbach, private communication), although at these energies (>100 MeV) the diffuse background is somewhat uncertain. Measurements of the gamma-ray flux with the Whipple instrument have a similar sensitivity to the EGRET detector for a source spectral index of 2.15, and less sensitivity to diffuse background. A number of observations of SNRs including: Tycho, W66, IC443, and others have been made. Currently for Tycho an upper limit of 9times 10(-12) cm(-2) sec(-1) is obtained. The status of these observations will be presented, and it will be shown that these measurements combined with the EGRET observations are beginning to provide a useful constraint on models of cosmic ray origin. Gamma-ray observations may also be used to constrain models of particle acceleration in SNRs exhibiting pulser-powered synchrotron nebula (plerions). The status of observations of this class of objects, including the Crab nebula, will also be presented. Supported in part by the U.S. Dept. of Energy.

Follow-up spectroscopic observations of HD 107148 B: A new white dwarf companion of an exoplanet host star

NASA Astrophysics Data System (ADS)

Mugrauer, M.; Dinçel, B.

2016-06-01

We report on our follow-up spectroscopy of HD 1071478 B, a recently detected faint co-moving companion of the exoplanet host star HD 107148 A. The companion is separated from its primary star by about 35 arcsec (or 1790 AU of projected separation) and its optical and near infrared photometry is consistent with a white dwarf, located at the distance of HD 107148 A. In order to confirm the white dwarf nature of the co-moving companion, we obtained follow-up spectroscopic observations of HD 107148 B with CAFOS at the CAHA 2.2 m telescope. According to our CAFOS spectroscopy HD 107148 B is a DA white dwarf with an effective temperature in the range between 5900 and 6400 K. The properties of HD 107148 B can further be constrained with the derived effective temperature and the known visual and infrared photometry of the companion, using evolutionary models of DA white dwarfs. We obtain for HD 107148 B a mass of 0.56±0.05 M_⊙, a luminosity of (2.0±0.2)×10-4 L_⊙, log g [cm s-2])=7.95±0.09, and a cooling age of 2100±270 Myr. With its white dwarf companion the exoplanet host star HD 107148 A forms an evolved stellar system, which hosts at least one exoplanet. So far, only few of these evolved systems are known, which represent only about 5 % of all known exoplanet host multiple stellar systems. HD 107148 B is the second confirmed white dwarf companion of an exoplanet host star with a projected separation to its primary star of more than 1000 AU. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).

Long-term Monitoring of Comet 103P/Hartley 2

NASA Astrophysics Data System (ADS)

Lin, Z.-Y.; Lara, L. M.; Ip, W.-H.

2013-07-01

We report the spectrophotometric, photometric, and imaging monitoring results of comet 103P/Hartley 2 obtained at the Lulin (1 m), Calar Alto (2.2 m), and Beijing Astronomical (2.16 m) observatories from 2010 April to December. We found that a dust feature in the sunward direction was detected starting from the end of September until the beginning of December (our last observation from the Lulin and Calar Alto observatories). Two distinct sunward jet features in the processed images were observed on October 11 and after October 29 until November 2. In parallel, the CN images reveal two asymmetrical jet features which are nearly perpendicular to the Sun-nucleus direction, these asymmetrical features imply that the comet was in a nearly side-on view in late October and early November. In addition to the jet features, the average result of the C2-to-CN production rate ratio ranges from 0.7 to 1.5, consistent with 103P/Hartley 2 being of typical cometary chemistry. We found that the rh dependence for the dust production rate, Afρ (5000 km), is -3.75 ± 0.45 before perihelion and -3.44 ± 1.20 during the post-perihelion period. We detected higher dust reddening around the optocenter and decreased reddening along the sunward jet feature. We concluded that higher dust reddening could be associated with strong jet activity while lower dust reddening could be associated with the outburst or might imply changes in the optical properties. The average dust color did not appear to vary significantly as the comet passed through perihelion. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC), at Lulin Observatory operated by the Institute of Astronomy, National Central University in Taiwan, and at Xinglong Station inaugurated by the National Astronomical Observatory (BAO), Beijing.

Non-LTE spectral models for the gaseous debris-disk component of Ton 345

NASA Astrophysics Data System (ADS)

Hartmann, S.; Nagel, T.; Rauch, T.; Werner, K.

2014-11-01

Context. For a fraction of single white dwarfs with debris disks, an additional gaseous disk was discovered. Both dust and gas are thought to be created by the disruption of planetary bodies. Aims: The composition of the extrasolar planetary material can directly be analyzed in the gaseous disk component, and the disk dynamics might be accessible by investigating the temporal behavior of the Ca ii infrared emission triplet, hallmark of the gas disk. Methods: We obtained new optical spectra for the first helium-dominated white dwarf for which a gas disk was discovered (Ton 345) and modeled the non-LTE spectra of viscous gas disks composed of carbon, oxygen, magnesium, silicon, sulfur, and calcium with chemical abundances typical for solar system asteroids. Iron and its possible line-blanketing effects on the model structure and spectral energy distribution was still neglected. A set of models with different radii, effective temperatures, and surface densities as well as chondritic and bulk-Earth abundances was computed and compared with the observed line profiles of the Ca ii infrared triplet. Results: Our models suggest that the Ca ii emission stems from a rather narrow gas ring with a radial extent of R = 0.44-0.94 R⊙, a uniform surface density Σ = 0.3 g cm-2, and an effective temperature of Teff ≈ 6000 K. The often assumed chemical mixtures derived from photospheric abundances in polluted white dwarfs - similar to a chondritic or bulk-Earth composition - produce unobserved emission lines in the model and therefore have to be altered. We do not detect any line-profile variability on timescales of hours, but we confirm the long-term trend over the past decade for the red-blue asymmetry of the double-peaked lines. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck-Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).

Physical properties, star-spot activity, orbital obliquity and transmission spectrum of the Qatar-2 planetary system from multicolour photometry

NASA Astrophysics Data System (ADS)

Mancini, L.; Southworth, J.; Ciceri, S.; Tregloan-Reed, J.; Crossfield, I.; Nikolov, N.; Bruni, I.; Zambelli, R.; Henning, Th.

2014-09-01

We present 17 high-precision light curves of five transits of the planet Qatar-2 b, obtained from four defocused 2 m-class telescopes. Three of the transits were observed simultaneously in the Sloan g'r'i'z' passbands using the seven-beam Gamma Ray Burst Optical and Near-Infrared Detector imager on the MPG/ESO 2.2-m telescope. A fourth was observed simultaneously in Gunn grz using the Centro Astronómico Hispano Alemán 2.2-m telescope with Bonn University Simultaneous Camera, and in r using the Cassini 1.52-m telescope. Every light curve shows small anomalies due to the passage of the planetary shadow over a cool spot on the surface of the host star. We fit the light curves with the PRISM+GEMC model to obtain the photometric parameters of the system and the position, size and contrast of each spot. We use these photometric parameters and published spectroscopic measurements to obtain the physical properties of the system to high precision, finding a larger radius and lower density for both star and planet than previously thought. By tracking the change in position of one star-spot between two transit observations, we measure the orbital obliquity of Qatar-2 b to be λ = 4.3° ± 4.5°, strongly indicating an alignment of the stellar spin with the orbit of the planet. We calculate the rotation period and velocity of the cool host star to be 11.5 ± 0.2 d and 3.28 ± 0.04 km s-1 at a colatitude of 74°. We assemble the planet's transmission spectrum over the 386-976 nm wavelength range and search for variations of the measured radius of Qatar-2 b as a function of wavelength. Our analysis highlights a possible H2/He Rayleigh scattering in the blue.

Var C: Long-term photometric and spectral variability of a luminous blue variable in M 33

NASA Astrophysics Data System (ADS)

Burggraf, B.; Weis, K.; Bomans, D. J.; Henze, M.; Meusinger, H.; Sholukhova, O.; Zharova, A.; Pellerin, A.; Becker, A.

2015-09-01

Aims: So far the highly unstable phase of luminous blue variables (LBVs) has not been understood well. It is still uncertain why and which massive stars enter this phase. Investigating the variabilities by looking for a possible regular or even (semi-)periodic behaviour could give a hint at the underlying mechanism for these variations and might answer the question of where these variabilities originate. Finding out more about the LBV phase also means understanding massive stars better in general, which have (e.g. by enriching the ISM with heavy elements, providing ionising radiation and kinetic energy) a strong and significant influence on the ISM, hence also on their host galaxy. Methods: Photometric and spectroscopic data were taken for the LBV Var C in M 33 to investigate its recent status. In addition, scanned historic plates, archival data, and data from the literature were gathered to trace Var C's behaviour in the past. Its long-term variability and periodicity was investigated. Results: Our investigation of the variability indicates possible (semi-)periodic behaviour with a period of 42.3 years for Var C. That Var C's light curve covers a time span of more than 100 years means that more than two full periods of the cycle are visible. The critical historic maximum around 1905 is less strong but discernible even with the currently rare historic data. The semi-periodic and secular structure of the light curve is similar to the one of LMC R71. Both light curves hint at a new aspect in the evolution of LBVs. Based on observations collected at the Thüringer Landessternwarte (TLS) Tautenburg.Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).Tables 2-4, and 6 are available in electronic form at http://www.aanda.org

Tides on Self-gravitating, Compressible Bodies

NASA Astrophysics Data System (ADS)

Hurford, T. A.; Greenberg, R.

2001-11-01

Most modern derivations of tidal amplitude follow the approach presented by Love [1]. Love's analysis for a homogeneous sphere assumed an incompressible material, which required introduction of a non-rigorously justified pressure term. We have solved the more general case of arbitrary compressibility, which allows for a more straightforward derivation [2,3]. We find the h2 love number of a body of radius R, density ρ , by solving the deformation equation [4], μ ∇ 2 u = ρ ∇U - (λ + μ ) ∇ (∇ ṡ u) where μ is the rigidity of the body and λ the Lamé constant. The potential U is the sum of (a) the tide raising potential, (b) the potential of surface mass shifted above or below the spherical surface, (c) potential due to the internal density changes and (d) the change in potential of each bit of volume due to its displacement u. A self-consistent solution can be obtained with U = \\sum_{q=0}^{\\infty} b_{(2+2q)} r^{(2+2q)} ( {3}/{2} \\cos2 \\theta - {1}/{2} ). In [1] and [3] only the r2 term was considered, which was valid only if compressibility is small or elasticity governs deformation (i.e. ρ g R << (λ + 2 μ )). The solution with only the r2 term reduces to Love's [1] solution in the limit of zero compressibility (λ = ∞ ). However, for rock μ ~ λ [4], in which case h2 is enhanced by ~ 3 %, and solutions for greater compressibility give up to 8 % enhancement of tidal amplitude. If ρ g R is significant, higher order r(2q+2) terms are important and even greater corrections are required to the classical tidal amplitude. [1] Love, A.E.H., New York Dover Publications, 1944 [2] Hurford, T.A. and R. Greenberg, Lunar Plan. Sci. XXXII 1741, 2001 [3] Hurford, T.A. and R. Greenberg, 2001 DDA meeting, Bull. Amer. Astron. Soc. in press [4] Kaula, W.M., John Wiley & Sons, Inc., 1968

NASA's Astronant Family Support Office

NASA Technical Reports Server (NTRS)

Beven, Gary; Curtis, Kelly D.; Holland, Al W.; Sipes, Walter; VanderArk, Steve

2014-01-01

During the NASA-Mir program of the 1990s and due to the challenges inherent in the International Space Station training schedule and operations tempo, it was clear that a special focus on supporting families was a key to overall mission success for the ISS crewmembers pre-, in- and post-flight. To that end, in January 2001 the first Family Services Coordinator was hired by the Behavioral Health and Performance group at NASA JSC and matrixed from Medical Operations into the Astronaut Office's organization. The initial roles and responsibilities were driven by critical needs, including facilitating family communication during training deployments, providing mission-specific and other relevant trainings for spouses, serving as liaison for families with NASA organizations such as Medical Operations, NASA management and the Astronaut Office, and providing assistance to ensure success of an Astronaut Spouses Group. The role of the Family Support Office (FSO) has modified as the ISS Program matured and the needs of families changed. The FSO is currently an integral part of the Astronaut Office's ISS Operations Branch. It still serves the critical function of providing information to families, as well as being the primary contact for US and international partner families with resources at JSC. Since crews launch and return on Russian vehicles, the FSO has the added responsibility for coordinating with Flight Crew Operations, the families, and their guests for Soyuz launches, landings, and Direct Return to Houston post-flight. This presentation will provide a summary of the family support services provided for astronauts, and how they have changed with the Program and families the FSO serves. Considerations for future FSO services will be discussed briefly as NASA proposes one year missions and beyond ISS missions. Learning Objective: 1) Obtain an understanding of the reasons a Family Support Office was important for NASA. 2) Become familiar with the services provided for astronauts and their families and how they changed with the Program and family needs.

Two Approaches in the Lunar Libration Theory: Analytical vs. Numerical Methods

NASA Astrophysics Data System (ADS)

Petrova, Natalia; Zagidullin, Arthur; Nefediev, Yurii; Kosulin, Valerii

2016-10-01

Observation of the physical libration of the Moon and the celestial bodies is one of the astronomical methods to remotely evaluate the internal structure of a celestial body without using expensive space experiments. Review of the results obtained due to the physical libration study, is presented in the report.The main emphasis is placed on the description of successful lunar laser ranging for libration determination and on the methods of simulating the physical libration. As a result, estimation of the viscoelastic and dissipative properties of the lunar body, of the lunar core parameters were done. The core's existence was confirmed by the recent reprocessing of seismic data Apollo missions. Attention is paid to the physical interpretation of the phenomenon of free libration and methods of its determination.A significant part of the report is devoted to describing the practical application of the most accurate to date the analytical tables of lunar libration built by comprehensive analytical processing of residual differences obtained when comparing the long-term series of laser observations with numerical ephemeris DE421 [1].In general, the basic outline of the report reflects the effectiveness of two approaches in the libration theory - numerical and analytical solution. It is shown that the two approaches complement each other for the study of the Moon in different aspects: numerical approach provides high accuracy of the theory necessary for adequate treatment of modern high-accurate observations and the analytic approach allows you to see the essence of the various kind manifestations in the lunar rotation, predict and interpret the new effects in observations of physical libration [2].[1] Rambaux, N., J. G. Williams, 2011, The Moon's physical librations and determination of their free modes, Celest. Mech. Dyn. Astron., 109, 85-100.[2] Petrova N., A. Zagidullin, Yu. Nefediev. Analysis of long-periodic variations of lunar libration parameters on the basis of analytical theory / // The Russian-Japanese Workshop, 20-25 October, Tokyo (Mitaka) - Mizusawa, Japan. - 2014.

Integrated spectral study of small angular diameter galactic open clusters

NASA Astrophysics Data System (ADS)

Clariá, J. J.; Ahumada, A. V.; Bica, E.; Pavani, D. B.; Parisi, M. C.

2017-10-01

This paper presents flux-calibrated integrated spectra obtained at Complejo Astronómico El Leoncito (CASLEO, Argentina) for a sample of 9 Galactic open clusters of small angular diameter. The spectra cover the optical range (3800-6800 Å), with a resolution of ˜14 Å. With one exception (Ruprecht 158), the selected clusters are projected into the fourth Galactic quadrant (282o < l < 345o) near the Galactic plane (∣b∣ ≤ 9o). We performed simultaneous estimates of foreground interstellar reddening and age by comparing the continuum distribution and line strenghts of the cluster spectra with those of template cluster spectra with known parameters. We thus provide spectroscopic information independent from that derived through color-magnitude diagram studies. We found three clusters (Collinder 249, NGC 4463 and Ruprecht 122) younger than ˜40 Myr, four moderately young ones (BH 92, Harvard 5, Hogg 14 and Pismis 23) with ages within 200-400 Myr, and two intermediate-age ones (Ruprecht 158 and ESO 065-SC07) with ages within 1.0-2.2 Gyr. The derived foreground E(B - V) color excesses vary from around 0.0 in Ruprecht 158 to ˜1.1 in Pismis 23. In general terms, the results obtained show good agreement with previous photometric results. In Ruprecht 158 and BH 92, however, some differences are found between the parameters here obtained and previous values in the literature. Individual spectra of some comparatively bright stars located in the fields of 5 out of the 9 clusters here studied, allowed us to evaluate their membership status. The current cluster sample complements that of 46 open clusters previously studied by our group in an effort to gather a spectral library with several clusters per age bin. The cluster spectral library that we have been building is an important tool to tie studies of resolved and unresolved stellar content.

Influence of the Renner-Teller Coupling in CO+H Collision Dynamics

NASA Astrophysics Data System (ADS)

Ndengue, Steve Alexandre; Dawes, Richard

2017-06-01

Carbon monoxide is after molecular hydrogen the second most abundant molecule in the universe and an important molecule for processes occurring in the atmosphere, hydrocarbon combustion and the interstellar medium. The rate coefficients of CO in collision with dominant species like H, H_2, He, etc are necessary to understand the CO emission spectrum or to model combustion chemistry processes. The inelastic scattering of CO with H has been intensively studied theoretically in the past decades,^1 mostly using the so-called WKS PES^6 developed by Werner et al. or recently a modified version by Song et al.^2 Though the spectroscopic agreement of the WKS surface with experiment is quite good, so far the studies of scattering dynamics have neglected coupling to an electronic excited state. We present new results on a set of HCO surfaces of the ground and the excited Renner-Teller coupled electronic states^3 with the principal objective of studying the influence of the Renner-Teller coupling on the inelastic scattering of CO+H. Our calculations done using the MCTDH^4 algorithm in the 0-2 eV energy range allow evaluation of the contribution of the Renner-Teller coupling on the rovibrationally inelastic scattering and discuss the relevance and reliability of the calculations. References:} 1. N. Balakrishnan, M. Yan and A. Dalgarno, Astrophys. J. 568, 443 (2002); B.C. Shepler et al, Astron. & Astroph. 475, L15 (2007); L. Song et al, J. Chem. Phys. 142, 204303 (2015); K.M. Walker et al, Astroph. J. 811, 27 (2015). 2. L. Song et al, Astrophys. J. 813, 96 (2015). 3. H.-M. Keller et al, J. Chem. Phys. 105, 4983 (1996). 4. S. Ndengue, R. Dawes and H. Guo, J. Chem. Phys. 144, 244301 (2016). 5. M.H. Beck et al., Phys. Rep. 324, 1 (2000).

Two-halo term in stacked thermal Sunyaev-Zel'dovich measurements: Implications for self-similarity

NASA Astrophysics Data System (ADS)

Hill, J. Colin; Baxter, Eric J.; Lidz, Adam; Greco, Johnny P.; Jain, Bhuvnesh

2018-04-01

The relation between the mass and integrated electron pressure of galaxy group and cluster halos can be probed by stacking maps of the thermal Sunyaev-Zel'dovich (tSZ) effect. Perhaps surprisingly, recent observational results have indicated that the scaling relation between integrated pressure and mass follows the prediction of simple, self-similar models down to halo masses as low as 1 012.5 M⊙ . Hydrodynamical simulations that incorporate energetic feedback processes suggest that gas should be depleted from such low-mass halos, thus decreasing their tSZ signal relative to self-similar predictions. Here, we build on the modeling of V. Vikram, A. Lidz, and B. Jain, Mon. Not. R. Astron. Soc. 467, 2315 (2017), 10.1093/mnras/stw3311 to evaluate the bias in the interpretation of stacked tSZ measurements due to the signal from correlated halos (the "two-halo" term), which has generally been neglected in the literature. We fit theoretical models to a measurement of the tSZ-galaxy group cross-correlation function, accounting explicitly for the one- and two-halo contributions. We find moderate evidence of a deviation from self-similarity in the pressure-mass relation, even after marginalizing over conservative miscentering effects. We explore pressure-mass models with a break at 1 014 M⊙, as well as other variants. We discuss and test for sources of uncertainty in our analysis, in particular a possible bias in the halo mass estimates and the coarse resolution of the Planck beam. We compare our findings with earlier analyses by exploring the extent to which halo isolation criteria can reduce the two-halo contribution. Finally, we show that ongoing third-generation cosmic microwave background experiments will explicitly resolve the one-halo term in low-mass groups; our methodology can be applied to these upcoming data sets to obtain a clear answer to the question of self-similarity and an improved understanding of hot gas in low-mass halos.

Black holes in binary stellar systems and galactic nuclei

NASA Astrophysics Data System (ADS)

Cherepashchuk, A. M.

2014-04-01

In the last 40 years, following pioneering papers by Ya B Zeldovich and E E Salpeter, in which a powerful energy release from nonspherical accretion of matter onto a black hole (BH) was predicted, many observational studies of black holes in the Universe have been carried out. To date, the masses of several dozen stellar-mass black holes (M_BH = (4{-}20) M_\\odot) in X-ray binary systems and of several hundred supermassive black holes (M_BH = (10^{6}{-}10^{10}) M_\\odot) in galactic nuclei have been measured. The estimated radii of these massive and compact objects do not exceed several gravitational radii. For about ten stellar-mass black holes and several dozen supermassive black holes, the values of the dimensionless angular momentum a_* have been estimated, which, in agreement with theoretical predictions, do not exceed the limiting value a_* = 0.998. A new field of astrophysics, so-called black hole demography, which studies the birth and growth of black holes and their evolutionary connection to other objects in the Universe, namely stars, galaxies, etc., is rapidly developing. In addition to supermassive black holes, massive stellar clusters are observed in galactic nuclei, and their evolution is distinct from that of supermassive black holes. The evolutionary relations between supermassive black holes in galactic centers and spheroidal stellar components (bulges) of galaxies, as well as dark-matter galactic haloes are brought out. The launch into Earth's orbit of the space radio interferometer RadioAstron opened up the real possibility of finally proving that numerous discovered massive and highly compact objects with properties very similar to those of black holes make up real black holes in the sense of Albert Einstein's General Relativity. Similar proofs of the existence of black holes in the Universe can be obtained by intercontinental radio interferometry at short wavelengths \\lambda \\lesssim 1 mm (the international program, Event Horizon Telescope).

Luminous Infrared Galaxies. III. Multiple Merger, Extended Massive Star Formation, Galactic Wind, and Nuclear Inflow in NGC 3256

NASA Astrophysics Data System (ADS)

Lípari, S.; Díaz, R.; Taniguchi, Y.; Terlevich, R.; Dottori, H.; Carranza, G.

2000-08-01

We report detailed evidence for multiple merger, extended massive star formation, galactic wind, and circular/noncircular motions in the luminous infrared galaxy NGC 3256, based on observations of high-resolution imaging (Hubble Space Telescope, ESO NTT), and extensive spectroscopic data (more than 1000 spectra, collected at Estación Astrofísica de Bosque Alegre, Complejo Astronómico el Leoncito, Cerro Tololo InterAmerican Observatory, and IUE observatories). We find in a detailed morphological study (resolution ~15 pc) that the extended massive star formation process detected previously in NGC 3256 shows extended triple asymmetrical spiral arms (r~5 kpc), emanating from three different nuclei. The main optical nucleus shows a small spiral disk (r~500 pc), which is a continuation of the external one and reaches the very nucleus. The core shows blue elongated structure (50 pc×25 pc) and harbors a blue stellar cluster candidate (r~8 pc). We discuss this complex morphology in the framework of an extended massive star formation driven by a multiple merger process (models of Hernquist et al. and Taniguchi et al.). We study the kinematics of this system and present a detailed Hα velocity field for the central region (40''×40'' rmax~30''~5 kpc), with a spatial resolution of 1" and errors of +/-15 km s-1. The color and isovelocity maps show mainly (1) a kinematic center of circular motion with ``spider'' shape, located between the main optical nucleus and the close (5") mid-IR nucleus and (2) noncircular motions in the external parts. We obtained three ``sinusoidal rotation curves'' (from the Hα velocity field) around position angle (P.A.) ~55°, ~90°, and ~130°. In the main optical nucleus we found a clear ``outflow component'' associated with galactic winds plus an ``inflow radial motion.'' The outflow component was also detected in the central and external regions (r<=5-6 kpc). The main axis of the inflow region (P.A.~80deg) is practically perpendicular to the ouflow axis (at P.A.~160deg). We analyze in detail the physical conditions in the giant H II regions located in the asymmetric spiral arms, the two main optical nuclei, and the outflow component (using long-slit spectroscopy, plus standard models of photoionization, shocks, and starbursts). We present four detailed emission-line ratios (N II/Hα, S II/Hα, S II/S II), and FWHM (Hα) maps for the central region (30''×30'' rmax~22''~4 kpc), with a spatial resolution of 1". In the central region (r~5-6 kpc) we detected that the nuclear starburst and the extended giant H II regions (in the spiral arms) have very similar properties, i.e., high metallicity and low-ionization spectra, with Teff=35,000 K, solar abundance, a range of Te~6000-7000 K, and Ne~100-1000 cm-3. The nuclear and extended outflow shows properties typical of galactic wind/shocks, associated with the nuclear starburst. We suggest that the interaction between dynamical effects, the galactic wind (outflow), low-energy cosmic rays, and the molecular+ionized gas (probably in the inflow phase) could be the possible mechanism that generate the ``similar extended properties in the massive star formation, at a scale of 5-6 kpc!'' We have also studied the presence of the close merger/interacting systems NGC 3256C (at ~150 kpc, ΔV=-100 km s-1) and the possible association between the NGC 3256 and 3263 groups of galaxies. In conclusion, these results suggest that NGC 3256 is the product of a multiple merger, which generated an extended massive star formation process with an associated galactic wind plus a nuclear inflow. Therefore, NGC 3256 is another example in which the relation between mergers and extreme starburst (and the powerful galactic wind, ``multiple'' Type II supernova explosions) play an important role in the evolution of galaxies (the hypothesis of Rieke et al., Joseph et al., Terlevich et al., Heckman et al., and Lípari et al.). Based on observations obtained at the Hubble Space Telescope (HST; Wide Field Planetary Camera 2 [WFPC2] and NICMOS) satellite; International Ultraviolet Explorer (IUE) satellite; European Southern Observatory (ESO, NTT); Chile, Cerro Tololo Inter-American Observatory (CTIO), Chile; Complejo Astronómico el Leoncito (CASLEO), Argentina; Estación Astrofísica de Bosque Alegre (BALEGRE), Argentina.

Resolving the clumpy circumstellar environment of the B[e] supergiant LHA 120-S 35

NASA Astrophysics Data System (ADS)

Torres, A. F.; Cidale, L. S.; Kraus, M.; Arias, M. L.; Barbá, R. H.; Maravelias, G.; Borges Fernandes, M.

2018-05-01

Context. B[e] supergiants are massive post-main-sequence stars, surrounded by a complex circumstellar environment where molecules and dust can survive. The shape in which the material is distributed around these objects and its dynamics as well as the mechanisms that give rise to these structures are not well understood. Aims: The aim is to deepen our knowledge of the structure and kinematics of the circumstellar disc of the B[e] supergiant LHA 120-S 35. Methods: High-resolution optical spectra were obtained in three different years. Forbidden emission lines, that contribute to trace the disc at different distances from the star, are modelled in order to determine the kinematical properties of their line-forming regions, assuming Keplerian rotation. In addition, we used low-resolution near-infrared spectra to explore the variability of molecular emission. Results: LHA 120-S 35 displays an evident spectral variability in both optical and infrared regions. The P-Cygni line profiles of H I, as well as those of Fe II and O I, suggest the presence of a strong bipolar clumped wind. We distinguish density enhancements in the P-Cygni absorption component of the first Balmer lines, which show variations in both velocity and strength. The P-Cygni profile emission component is double-peaked, indicating the presence of a rotating circumstellar disc surrounding the star. We also observe line-profile variations in the permitted and forbidden features of Fe II and O I. In the infrared, we detect variations in the intensity of the H I emission lines as well as in the emission of the CO band-heads. Moreover, we find that the profiles of each [Ca II] and [O I] emission lines contain contributions from spatially different (complete or partial) rings. Globally, we find evidence of detached multi-ring structures, revealing density variations along the disc. We identify an inner ring, with sharp edge, where [Ca II] and [O I] lines share their forming region with the CO molecular bands. The outermost regions show a complex structure, outlined by fragmented clumps or partial-ring features of Ca II and O I. Additionally, we observe variations in the profiles of the only visible absorption features, the He I lines. Conclusions: We suggest that LHA 120-S 35 has passed through the red-supergiant (RSG) phase and evolves back bluewards in the Hertzsprung-Russell diagram. In this scenario, the formation of the complex circumstellar structure could be the result of the wind-wind interactions of the post-RSG wind with the previously ejected material from the RSG. The accumulation of material in the circumstellar environment could be attributed to enhanced mass-loss, probably triggered by stellar pulsations. However, the presence of a binary companion cannot be excluded. Finally, we find that LHA 120-S 35 is the third B[e] supergiant belonging to a young stellar cluster. Based on data acquired using (1) the du Pont Telescope at Las Campanas Observatory, Chile, under the programme CNTAC 2008-02 (PI: Barbá), (2) the MPG 2.2-m Telescope at La Silla Observatory, Chile, under the programme ID.: 094.A-9029(D) and under the agreement MPI-Observatório Nacional/MCTIC, Prog. ID.: 096.A-9030(A), (3) the J. Sahade 2.15-m Telescope at Complejo Astronómico El Leoncito, operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juan, (4) the 8.1-m Telescope at Gemini South Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciěncia, Tecnologia e Inovacão (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), under the programme GS-2013B-Q-6 (PI: L. Cidale), (5) the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the U.S. National Optical Astron. Obs. (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU) and (6) the ESO Science Archive Facility.

Difficulties of First Years Elementary School Teachers with the Teaching of Astronomy. (Breton Title: Dificuldades de Professores dos Anos Iniciais do Ensino Fundamental em Relação ao Ensino da Astronomia. ) Dificultades de LOS Profesores de los Primeros Años de la Escuela Primaria en Relación a la Enseñanza de la Astronomía

NASA Astrophysics Data System (ADS)

Langhi, Rodolfo; Nardi, Roberto

2005-12-01

This paper reports Primary School teachers' discourses analysis about their difficulties related to the teaching of Astronomy. It reports partial data of a master's level research carried out in the last two years, named "An exploratory study for inserting Astronomy in primary school teachers' education" (LANGHI, 2004). The study took into consideration students' and teachers' common sense conceptions about astronomical phenomena, conceptual mistakes in textbooks, and Astronomy's suggestions given by the PCN (Parâmetros Curriculares Nacionais - The Brazilian National Curriculum Standards). The paper aims to characterize teachers' difficulties, in order to provide subsides to the implementation of an initial or continuing education program. This study is justified by the fact that courses plans like these only will be adapted to the teacher's (and students') reality, if there is a primary investigation about what the teachers really need to know about Astronomy. This fact was possible here by the enunciations interpretation of a teachers' sample using semi-structured interviews, according to discourse analysis procedures. The research outcomes show difficulties related to factors like: those of personal order, methodological, on teacher's formation, educational infrastructure and other related to information sources for educators. Este artigo, que relata as dificuldades de professores em relação ao ensino da Astronomia, faz parte de um estudo exploratório para a inserção da Astronomia na formação de professores dos anos iniciais do Ensino Fundamental. Esse estudo leva em consideração as concepções alternativas de alunos e professores sobre fenômenos astronômicos, os erros conceituais em livros didáticos e as sugestões de conteúdos de Astronomia constantes nos PCN (Parâmetros Curriculares Nacionais). Caracterizar as dificuldades dos professores é a questão central deste texto, apontando para o objetivo de contribuir com subsídios para um futuro programa de formação continuada neste tema. O estudo se justifica mediante o fato de que planejamentos de cursos como estes só se adequarão à realidade do professor (e do aluno) se houver uma investigação antecipada sobre o que os docentes precisam saber e saber fazer a respeito da Astronomia, o que se concretizou em nosso caso pela interpretação dos discursos de uma amostra de professores coletados através de entrevistas semi-estruturadas, utilizando para interpretação os princípios e métodos da análise do discurso em sua linha francesa. Os resultados da pesquisa indicaram dificuldades de ordem pessoal, metodológica, de formação, de infra-estrutura e outras relacionadas às fontes de informações para docentes. Este artículo que relata las dificultades de los profesores en relación a la enseñanza da laAstronomía es parte de un estudio preliminar para la implantación dela Astrnomía enla formación de profesores de ls primeros años del ciclo primario.El estudio considera las concepciones alternativas de alumnos y profesores respecto a los fenómenos astronómicos, los errores conceptuales en los libros didácticos y las sugerencias de contenidos de Astronomía que constan en los Parámetros Curriculares Nacionales del Brasil. Caracterizar las dificultades de los profesores constituye la cuestión central de este texto, apuntando para el objetivo de contribuir para un futuro programa de educación contínua en este tema. El estudio se justifica mediante el hecho que la planificación de cursos de este tipo solo se adecuarán a la realidade del profesor (y del alumno) si existe una investigación anterior a respecto de lo que los docentes precisan saber y saber realizar en Astronomía, lo cual se concretó en nuestro caso por medio de la interpretación de los discursos de una muestra de profesores obtenidos através de entrevistas semiestructuradas, utilizand para esta interpretación los principios y métodos de análisis del discurso en su línea francesa. Los resultados mostraron dificultades de orden personal, metodológica, formativa, de infraestructura y otras relacionadas a las fuentes de información para los docentes.

Teaching of Astronomy: Scenarios of Teaching Practice in Elementary Schools. (Spanish Title: Enseñanza de la Astronomía: Semblanzas de la Práctica Docente en Educación Primaria.) Ensino de Astronomia: Cenários da Prática Docente no Ensino Fundamental

NASA Astrophysics Data System (ADS)

Marchi Gonzatti, Sônia Elisa; Spessatto De Maman, Andréia; Fernandes Borragini, Eliana; Kerber, Júlia Cristina; Haetinger, Werner

2013-12-01

The present work presents the main results of a research carried out within the Astronomy Education field with Elementary School teachers from two regions of Rio Grande do Sul. The study aimed to show the regional panorama of teaching Astronomy compared to the national panorama already discussed in several studies in the area. It was divided into three main issues: identifying the main topics of Astronomy developed in class, verifying which were the methodological strategies used, and which were the difficulties teachers faced when developing their practice. Regarding the contents, it was found a wide range of covered topics although Earth motion and astronomical phenomena were cited by most participants. Concerning the strategies used in class, two-dimensional resources such as movies, texts, maps and web searching were mainly used. The most relevant difficulties were the lack of specific education related to Astronomy contents and abstraction level, which complicated the understanding for both students and teachers. In general, the indicators met the results already found in other studies that investigated Astronomy teaching practice, in which the teacher's original education deficiency - or even the lack of it - hampers the proper development of Astronomy contents in class. En este trabajo se presentan los principales resultados de una investigación hecha en el campo de la Educación en Astronomía, con profesores de la Enseñanza Fundamental de dos regiones de Rio Grande do Sul. El presente estudio tuvo como objetivo caracterizar el panorama regional de la enseñanza de Astronomía, estableciendo una comparación con el panorama nacional ya presentado en trabajos de referencia en el área. Ese estudio abordó tres cuestiones: identificar los principales temas de astronomía trabajados, las estrategias metodológicas y cuáles fueron las dificultades sufridas por los profesores al presentar su práctica. Con relación a los contenidos, se encontró una atomización de los asuntos, aunque temas como movimientos de la Tierra y fenómenos astronómicos hayan sido citados por la mayoría de los participantes. En cuanto a las estrategias, se verifico que se emplean principalmente clases con el apoyo de recursos bidimensionales, como películas, textos, mapas y búsqueda en internet. Las principales dificultades fueron la falta de formación específica con respecto a los contenidos de Astronomía, y el nivel de abstracción exigido por los contenidos. De modo general, esos indicadores convergen para los resultados ya encontrados en otros estudios, en el que las deficiencias de la formación inicial de los profesores, o incluso su ausencia, dificulta el adecuado abordaje de la Astronomía en las clases. Neste trabalho são apresentados os principais resultados de uma investigação realizada no campo da Educação em Astronomia, com professores do ensino fundamental de duas regiões do Rio Grande do Sul. O objetivo do estudo foi caracterizar o cenário regional do ensino de Astronomia, estabelecendo um comparativo com o cenário nacional. Esse estudo abordou três questões: identificar os principais temas de astronomia trabalhados em sala de aula, as estratégias metodológicas e quais as dificuldades apresentadas pelos professores ao desenvolver sua prática. Quanto aos conteúdos, encontrouse uma pulverização dos assuntos abordados, embora temas como movimentos da Terra e fenômenos astronômicos tenham sido citados pela maioria dos participantes. Sobre estratégias, são utilizadas principalmente aulas com apoio de recursos bidimensionais, como filmes, textos, mapas e pesquisa na internet. As principais dificuldades foram: falta de formação específica em relação a conteúdos de Astronomia; nível de abstração dos conteúdos, que dificultam sua compreensão, tanto pelos alunos quanto pelos próprios professores. De maneira geral, esses indicadores convergem para resultados já encontrados em outros estudos que investigam a prática docente em Astronomia, em que as deficiências da formação inicial dos professores, ou mesmo a falta dela, dificulta a adequada abordagem da Astronomia em sala de aula.

Interconexión de la Estación Astrofísica de Bosque Alegre y la red local de datos del Observatorio Astronómico de Córdoba

NASA Astrophysics Data System (ADS)

Nicotra, M. A.; Anun, S.; Montes, M.; Goldes, G.; Carranza, G.

We describe the outlines of a project for the interconnection between the Astrophysical Station of Bosque Alegre and the wide area network of the University of Córdoba. The Astrophysical Station is located 38.55 km (23.96 milles) from the Observatory of Córdoba. This location is suitable for radio links in the range of centimeters wavelenghts. In the last years, Spread-Spectrum technology equipments has become popular. Spread-Spectrum signals, contrary to narrow band radio signals, operates within a widthband 20 to 200 times broader than the widthband of the modulated information. Signals are modulated by special spreading codes, in such a way that emulates noisy signals. These codes are known under the generic designation of pseudo-random or pseudo-noise. In addition, the wide band is correlated with a low power density in the emitted signals. Spread-Spectrum equipment links are stable, exhibits low interferences with conventional radio transmitters, and their commercial prices are remarkably lower than those for the conventional microwave devices. Data links are compliant with Ethernet protocol networks and operates with data tramsmition rates up to 4 Mbits per second. The described equipment will enable the access to full-Internet services for visitor astronomers in Bosque Alegre. Also, it will be possible fast transfer for the observational data from telescope to computers in the local area network at Córdoba. This project must be considered as the second stage of another wide purpose project, which has the main purpose in transforming the Bosque Alegre Station as a fully robotic station controlled from the computational center at the Observatory in Cordoba. The advantages of robotic telescopes has recently been the subject of several discussions. However, it is now widely accepted that an automatic station enables some important options in the use of the astronomical instruments, such us the possibility of performing parallel programs, one of which is selected accordingly to environmental conditions in the instant of the observation.

R&D at JIVE: transforming the way VLBI is done

NASA Astrophysics Data System (ADS)

Szomoru, Arpad; van Langevelde, Huib

2015-08-01

Arpad Szomoru, Huib van Langevelde and the JIVE staffFor many years, the heart of operations at JIVE has been the MkIV hardware correlator, a custom-built high-performance data processor. At this time the MkIV has been replaced by the locally developed EVN software correlator (SFXC).This development has vastly improved the science capacity of the EVN, by providing higher spectral resolution and polarization accuracy, but most notably, by enabling completely new observing modes. Observing multiple simultaneous field centers has enabled wide-field imaging, while a phased-array mode has made it possible to do pulsar time series with the EVN. New algorithms have been developed for near-field VLBI, making it possible to focus on objects within our solar system. This has been used to track the RadioAstron satellite, and by applying the derived orbital parameters to improve subsequent space VLBI observations.New digital baseband convertors will allow higher observing bandwidths in the EVN. In anticipation of this, and of the even higher bandwidths of future mm-VLBI observations, added to the deployment of much larger arrays (including the AVN, the SKA precursors and the SKA itself), we are investigating more powerful and economical solutions. The JIVE UniBoard Correlator is the first FPGA-based EVN correlator; its scalability and flexibility are now under assessment. The new UniBoard2 project, also sponsored by the EC, will skip two generations of FPGA technology and deliver enormous processing power at lower power consumption.Maybe just as importantly, research is ongoing into software tools to enable the efficient handling of the vast data sets that the EVN and other current and future instruments will produce. New data processing pipelines are being designed that will be able to cache intermediate products, and upon changing parameters only re-calculate what is needed, as opposed to re-starting every time from scratch.Finally, we will discuss the development of time and frequency transfer via public networks, in the context of a new H2020 project aimed at the astronomy, astrophysics and astroparticle physics faciclities within the ESFRI roadmap .

Laboratory Simulations of Space Weathering of Asteroid Surfaces by Solar Wind Ions.

NASA Astrophysics Data System (ADS)

Miller, Kenneth A.; De Ruette, Nathalie; Harlow, George; Domingue, Deborah L.; Savin, Daniel Wolf

2014-06-01

Studies into the formation of the terrestrial planets rely on the analysis of asteroids and meteorites. Asteroids are solar system remnants from the planetary formation period. By characterizing their mineralogical composition we can better constrain the formation and evolution of the inner planets.Remote sensing is the primary means for studying asteroids. Sample return missions, such as Hayabusa, are complex and expensive, hence we rely on asteroid reflectance spectra to determine chemical composition. Links have been made and debated between meteorite classes and asteroid types [1, 2]. If such relationships can be confirmed, then meteorites would provide a low cost asteroid sample set for study. However, a major issue in establishing this link is the spectral differences between meteorite samples and asteroid surfaces. The most commonly invoked explanation for these differences is that the surfaces of asteroids are space weathered [2, 3]. The dominant mechanism for this weathering is believed to be solar-wind ion irradiation [2, 4, 5]. Laboratory simulations of space weathering have demonstrated changes in the general direction required to alter spectra from unweathered meteorite samples to asteroid observations [3, 6 -10], but many open questions remain and we still lack a comprehensive understanding. We propose to explore the alleged connection of ordinary chondrite (OC) meteorites to S-type asteroids through a series of systematic laboratory simulations of solar-wind space weathering of asteroid surface materials. Here we describe the issue in more detail and describe the proposed apparatus. [1] Chapman C. R. (1996) Meteorit. Planet. Sci., 31, 699-725. [2] Chapman C. R. (2004), Annu. Rev. Earth Planet. Sci., 32, 539-567. [3] Hapke B. (2001) J. Ge-ophys. Res., 106, 10039-10074. [4] Pieters C.M. et al. (2000) Meteorit. Planet. Sci., 35, 1101-1107. [5] Ver-nazza P. et al. (2009) Nature, 458, 993-995. [6] Stra-zulla G. et al. (2005) Icarus, 174, 31-35 (2005). [7] Brunetto R and Strazzulla G (2005) Icarus, 179, 265-273. [8] Marchi S et al. (2005) Astron. Astrophys., 443, 769-775. [9] Loeffler M. J. et al. (2009) J. Geo-phys. Res., 114, E03003. [10] Fu X. et al. (2012) Ica-rus, 219, 630-640

A Mobile Asteroid Surface Scout (MASCOT) on board the Hayabusa 2 Mission to the near Earth asteroid (162173) Ryugu

NASA Astrophysics Data System (ADS)

Jaumann, R.; Bibring, J. P.; Glassmeier, K. H.; Grott, M.; Ho, T. M.; Ulamec, S.; Schmitz, N.; Auster, H. U.; Biele, J.; Kuninaka, H.; Okada, T.; Yoshikawa, M.; Watanabe, S.; Spohn, T.; Koncz, A.; Hercik, D.; Michaelis, H.; Fujimoto, M.

2016-12-01

MASCOT is part of JAXA's Hayabusa 2 asteroid sample return mission that has been launched to asteroid (162173) Ryugu (1,2,3) on Dec 3rd, 2014. It is scheduled to arrive at Ryugu in 2018, and return samples to Earth in 2020. The German Aerospace Center (DLR) developed the lander MASCOT with contributions from CNES (France) (2,3). Ryugu has been classified as a Cg-type (4), believed to be a primitive volatile-rich remnant from the early solar system. Its visible geometric albedo is 0.07±0.01with a diameter of 0.87±0.03 km (5). The thermal inertia indicates thick dust with a cm-sized, gravel-dominated surface layer (5,6). Ryugu shows a retrograde rotation with a period of 7.63±0.01h. Spectral observations indicate iron-bearing phyllosilicates (1) on parts of the surface, suggesting compositional heterogeneity. MASCOT will enable to in-situ map the asteroid's geomorphology, the intimate structure, texture and composition of the regolith (dust, soil and rocks), and its thermal, mechanical, and magnetic properties in order to provide ground truth for the orbiter remote measurements, support the selection of sampling sites, and provide context information for the returned samples (2,3). MASCOT comprises a payload of four scientific instruments: camera, radiometer, magnetometer and hyperspectral microscope (2,3). Characterizing the properties of asteroid regolith in-situ will deliver important ground truth for further understanding telescopic and orbital observations as well as samples of asteroids. MASCOT will descend and land on the asteroid and will change its position by hopping (3). (1) Vilas, F., Astro. J. 1101-1105, 2008; (2) Jaumann, R., et al., SSR, DOI 10.1007/s11214-016-0263-2, 2016; (3) Ho, T.-M. et al., SSR, DOI 10.1007/s11214-016-0251-6, 2016; (4) Bus, S.J., Binzel, R.P. Icarus 158, 2002; (5) Hasegawa, T.G., et al., Astron. Soc. Japan 60, 2008; (6) T.G. Müller, T.G., et al., doi 10.1051/0004-6361/201015599, 2011.

A post-Rosetta understanding of polarimetric observations of comets

NASA Astrophysics Data System (ADS)

Levasseur-Regourd, A. Chantal; Ciarletti, Valérie; Hadamcik, Edith; Lasue, Jérémie; Mannel, Thurid

2017-04-01

Numerous polarimetric observations of solar light scattered by dust in cometary comae have been obtained by various teams, providing phase angle and wavelength dependences for many comets and revealing different classes of comets [e.g., 1]. Besides, numerical and experimental simulations have suggested interpretations for such observations. The Rosetta long duration rendezvous with comet 67P/Churyumov-Gerasimenko (thereafter 67P/C-G) now allows us to compare our understanding of the polarimetric properties of cometary dust with the ground-truth provided by the Rosetta mission, at least for two typical results. First, some comets present a highly-polarized positive branch, the most conspicuous case being that of new comet C/1995 O1 Hale-Bopp [2], while other comets suffering a partial fragmentation or a total disruption, such as C/1995 S4 LINEAR [3], present a significant increase in polarization. We will discuss these observations in the context of evidence for changes between the porosity (and possibly the dust/ice ratio) of the subsurface and of the interior of 67P/C-G, a periodic Jupiter Family Comet, as derived from analyses [4] of the CONSERT bi-static radar measurements on board Rosetta and Philae. Secondly, numerical simulations of the phase and wavelength dependence of polarimetric observations of some comets (extensively observed on a wide range of wavelengths and phase angles) have suggested the presence of fractal, likely-porous aggregates and of compact particles within their comae [e.g., 5]. We will review such results in the context of evidence for porous and compact aggregates of submicron-sized grains in the inner coma of 67P/C-G [6], as given by 3D images (with a resolution down to tens of nanometers) of the MIDAS atomic force microscope on board Rosetta. References: [1] Kiselev et al., 2015, In Polarization of stars and planetary systems, CUP 379-404. [2] Levasseur-Regourd & Hadamcik, 2003, JQSRT 79-80, 903-910. [3] Hadamcik & Levasseur-Regourd, 2003, Icarus 166, 188-194. [4] Ciarletti et al., 2015, Astron. Astrophys. 583, A40. [5] Lasue et al., 2009, Icarus 199, 129-144. [6] Mannel et al., 2016, MNRAS 462, S 304-S311.

Antarctic meteor observations using the Davis MST and meteor radars

NASA Astrophysics Data System (ADS)

Holdsworth, David A.; Murphy, Damian J.; Reid, Iain M.; Morris, Ray J.

2008-07-01

This paper presents the meteor observations obtained using two radars installed at Davis (68.6°S, 78.0°E), Antarctica. The Davis MST radar was installed primarily for observation of polar mesosphere summer echoes, with additional transmit and receive antennas installed to allow all-sky interferometric meteor radar observations. The Davis meteor radar performs dedicated all-sky interferometric meteor radar observations. The annual count rate variation for both radars peaks in mid-summer and minimizes in early Spring. The height distribution shows significant annual variation, with minimum (maximum) peak heights and maximum (minimum) height widths in early Spring (mid-summer). Although the meteor radar count rate and height distribution variations are consistent with a similar frequency meteor radar operating at Andenes (69.3°N), the peak heights show a much larger variation than at Andenes, while the count rate maximum-to-minimum ratios show a much smaller variation. Investigation of the effects of the temporal sampling parameters suggests that these differences are consistent with the different temporal sampling strategies used by the Davis and Andenes meteor radars. The new radiant mapping procedure of [Jones, J., Jones, W., Meteor radiant activity mapping using single-station radar observations, Mon. Not. R. Astron. Soc., 367(3), 1050-1056, doi: 10.1111/j.1365-2966.2006.10025.x, 2006] is investigated. The technique is used to detect the Southern delta-Aquarid meteor shower, and a previously unknown weak shower. Meteoroid speeds obtained using the Fresnel transform are presented. The diurnal, annual, and height variation of meteoroid speeds are presented, with the results found to be consistent with those obtained using specular meteor radars. Meteoroid speed estimates for echoes identified as Southern delta-Aquarid and Sextantid meteor candidates show good agreement with the theoretical pre-atmospheric speeds of these showers (41 km s -1 and 32 km s -1, respectively). The meteoroid speeds estimated for these showers show decreasing speed with decreasing height, consistent with the effects of meteoroid deceleration. Finally, we illustrate how the new radiant mapping and meteoroid speed techniques can be combined for unambiguous meteor shower detection, and use these techniques to detect a previously unknown weak shower.

Multi-spectral remote sensing of the vortex formerly known as White Oval BA: Temperature structure and cloud properties

NASA Astrophysics Data System (ADS)

Orton, G.; Parrish, P.; Yanamandra-Fisher, P.; Baines, K.; Mousis, O.; Pantin, E.; Fujiyoshi, T.; Fuse, T.; Simon-Miller, A.

White Oval BA: Temperature structure and cloud properties G. Orton, P. Parrish, P. Yanamandra-Fisher, K. Baines (1), O. Mousis (2), E. Pantin (3), T. Fuse, T. Fujiyoshi (4), A. Simon-Miller (5) (1) Jet Propulsion Laboratory, Calif. Inst. of Technology, USA, (2) Obs. de Besancon, France, (3) C.E.A., France, (4) Subaru National Astron. Obs., Japan, (5) NASA Goddard Space Flight Center, USA. (Glenn.Orton@jpl.nasa.gov) White Oval BA, constituted from 3 predecessor vortices (known as Jupiter's "classical" White Ovals) after successive mergers in 1998 and 2000, became second-largest vortex in the atmosphere of Jupiter (and possibly the solar system) at the time of its formation. While it continues in this distinction, it required a name change after a 2005 December through 2006 February transformation which made it appear visually the same color as the Great Red Spot. Our campaign to understand the changes involved examination of the detailed color and wind field using Hubble Space Telescope instrumentation on several orbits in April. The field of temperatures, ammonia distribution and clouds were also examined using the mid-infrared VISIR camera/spectrometer on ESO's 8.2-m Very Large Telescope (3), the NASA Infrared telescope with the mid-infrared MIRSI instrument and the refurbished near-infrared facility camera NSFCam2. High-resolution images of the Oval were made before the color change with the COMICS mid-infrared facility on the Subaru telescope. We are using these data, and possibly others to be acquired during the summer, to characterize the extent to which changes in storm strength (vorticity, positive vertical motion) influenced (i) the depth from which colored cloud particles may have been "dredged up" from depth or (ii) the altitude to which particles may have been lofted and subject to high-energy UV radiation which caused a color change, as alternative explanations for the phenomenon. Clues to this will provide clues to the chemistry of Jupiter's cloud system and its well-known colors in general.

Accurate PSF-matched photometry for the J-PAS survey

NASA Astrophysics Data System (ADS)

Jimenez-Teja, Yolanda; Benitez, Txitxo; Dupke, Renato a.

2015-08-01

The Javalambre-PAU Astrophysical Survey (J-PAS) is expected to map 8,600 squared-degrees of the sky using 54 narrow and 5 broad band filters. Carried out by a Spanish-Brazilian consortium, the main goal of this survey is to measure Baryon Acoustic Oscillations (BAOs) with photometric redshifts. The expectation is measuring these photometric redshifts with a precision of dz/(1 + z) ~ 0.003 for 100 million galaxies and a few millions of quasars, and reaching an accuracy of dz/(1 + z) ~ 0.01 for other 300 million galaxies. With these numbers, it will be possible to determine w in the Dark Energy (DE) equation of state with an accuracy of < 4%. To achieve such precision and measure the radial BAOs, not only an advanced technical setup but also special data processing tools are required. These tools must be accurate as well as suitable to be implemented in fully automated and computationally efficient algorithms.The factor that most influences the photometric redshift precision is the quality of the photometry. For that reason we have developed a new technique based on the Chebyshev-Fourier bases (CHEFs, Jiménez-Teja & Benítez 2012, ApJ, 745, 150) to obtain a highly precise multicolor photometry without PSF consideration, thus saving a considerable amount of time and circumventing severe problems such as the PSF variability across the images. The CHEFs are a set of mathematical orthonormal bases with different scale and resolution levels, originally designed to fit the surface light distribution of galaxies. They have proved to be able to model any kind of morphology, including spirals, highly elliptical, or irregular galaxies, including isophotal twists and fine substructure. They also fit high signal-to-noise images, lensing arcs and stars with great accuracy. We can calculate optimal, unbiased, total magnitudes directly through these CHEFs models and, thus, colors without needing the PSF.We compare our photometry with widely-used codes such as SExtractor (Bertin & Arnouts 1996, Astron Astrophys Sup, 117, 393) and ColorPro (Coe et al. 2006, AJ, 132, 926), using real data from the COSMOS survey, the HUDF, and the XDF.

Understanding the Effects of Long-duration Space Flight on Astronant Functional Task Performance

NASA Technical Reports Server (NTRS)

Bloomberg, Jacob J.; Batson, Crystal D.; Buxton, Roxanne E.; Feiveson, Al H.; Kofman, Igor S.; Lee, Stuart M. C.; Miller, Chris A.; Mulavara, Ajitkumar P.; Peters, Brian T.; Phillips, Tiffany;

Resistance of Wheat Accessions to the English Grain Aphid Sitobion avenae

PubMed Central

Hu, Xiang-Shun; Liu, Ying-Jie; Wang, Yu-Han; Wang, Zhe; Yu, Xin-lin; Wang, Bo; Zhang, Gai-Sheng; Liu, Xiao-Feng; Hu, Zu-Qing; Zhao, Hui-Yan; Liu, Tong-Xian

2016-01-01

The English grain aphid, Sitobion avenae, is a major pest species of wheat crops; however, certain varieties may have stronger resistance to infestation than others. Here, we investigated 3 classical resistance mechanisms (antixenosis, antibiosis, and tolerance) by 14 wheat varieties/lines to S. avenae under laboratory and field conditions. Under laboratory conditions, alatae given the choice between 2 wheat varieties, strongly discriminated against certain varieties. Specifically, the ‘Amigo’ variety had the lowest palatability to S. avenae alatae of all varieties. ‘Tm’ (Triticum monococcum), ‘Astron,’ ‘Xanthus,’ ‘Ww2730,’ and ‘Batis’ varieties also had lower palatability than other varieties. Thus, these accessions may use antibiosis as the resistant mechanism. In contrast, under field conditions, there were no significant differences in the number of alatae detected on the 14 wheat varieties. One synthetic line (98-10-30, a cross between of Triticum aestivum (var. Chris) and Triticum turgidum (var. durum) hybridization) had low aphid numbers but high yield loss, indicating that it has high antibiosis, but poor tolerance. In comparison, ‘Amigo,’ ‘Xiaoyan22,’ and some ‘186Tm’ samples had high aphid numbers but low yield loss rates, indicating they have low antibiosis, but good tolerance. Aphid population size and wheat yield loss rates greatly varied in different fields and years for ‘98-10-35,’ ‘Xiaoyan22,’ ‘Tp,’ ‘Tam200,’ ‘PI high,’ and other ‘186Tm’ samples, which were hybrid offspring of T. aestivum and wheat related species. Thus, these germplasm should be considered for use in future studies. Overall, S. avenae is best adapted to ‘Xinong1376,’ because it was the most palatable variety, with the greatest yield loss rates of all 14 wheat varieties. However, individual varieties/lines influenced aphid populations differently in different years. Therefore, we strongly recommend a combination of laboratory and long-term field experiments in targeted planting regions to identify varieties/lines that consistently show high resistance to S. avenae infestation. PMID:27249206

Deep multi-frequency rotation measure tomography of the galaxy cluster A2255

NASA Astrophysics Data System (ADS)

Pizzo, R. F.; de Bruyn, A. G.; Bernardi, G.; Brentjens, M. A.

2011-01-01

Aims: By studying the polarimetric properties of the radio galaxies and the radio filaments belonging to the galaxy cluster Abell 2255, we aim to unveil their 3-dimensional location within the cluster. Methods: We performed WSRT observations of A2255 at 18, 21, 25, 85, and 200 cm. The polarization images of the cluster were processed through rotation measure (RM) synthesis, producing three final RM cubes. Results: The radio galaxies and the filaments at the edges of the halo are detected in the high-frequency RM cube, obtained by combining the data at 18, 21, and 25 cm. Their Faraday spectra show different levels of complexity. The radio galaxies lying near by the cluster center have Faraday spectra with multiple peaks, while those at large distances show only one peak, as do the filaments. Similar RM distributions are observed for the external radio galaxies and for the filaments, with much lower average RM values and RM variance than those found in previous works for the central radio galaxies. The 85 cm RM cube is dominated by the Galactic foreground emission, but it also shows features associated with the cluster. At 2 m, no polarized emission from A2255 nor our Galaxy is detected. Conclusions: The radial trend observed in the RM distributions of the radio galaxies and in the complexity of their Faraday spectra favors the interpretation that the external Faraday screen for all the sources in A2255 is the ICM. Its differential contribution depends on the amount of medium that the radio signal crosses along the line of sight. The filaments should therefore be located at the periphery of the cluster, and their apparent central location comes from projection effects. Their high fractional polarization and morphology suggest that they are relics rather than part of a genuine radio halo. Their inferred large distance from the cluster center and their geometry could argue for an association with large-scale structure (LSS) shocks. The RM cubes in gif format are only available in electronic form at http://www.aanda.org. To request the RM cubes in FITS format, please contact R. F. Pizzo at: pizzo@astron.nl

Mimas: Constraints on Origin and Evolution from Libration Data

NASA Astrophysics Data System (ADS)

Neveu, Marc; Rhoden, Alyssa R.

2016-10-01

In stark contrast with its neighbor moon Enceladus, Mimas is surprisingly geologically quiet, despite an orbital configuration prone to levels of tidal dissipation 30 times higher. While Mimas' lack of activity could be due to a stiff, frigid interior, libration data from the Cassini spacecraft suggest its interior is not homogeneous [1]. Here, we present 1-D models of Mimas' thermal and structural evolution under two accretion scenarios: primordial, undifferentiated formation in the Saturnian subnebula [2]; and late, layered formation from a debris ring created by the disruption of one or more previous moons [3]. In the primordial scenario, our simulations yield two possible outcomes. If tidal dissipation proceeds at levels higher than those obtained using an Andrade rheology [4], Mimas differentiates and an ocean persists until the present day. This should quickly circularize its orbit, but the current orbit is eccentric. In addition, Mimas lacks surface fractures that should result from strong tidal stresses in an ice shell atop an ocean [5]. If dissipation proceeds at lower levels obtained using a Maxwell rheology, it is too weak to drive differentiation; this does not match the observed libration [1]. In the late accretion scenario, Mimas forms already differentiated. As a result, even its deepest ice is within only 100 km of the frigid surface, and poorly insulated by overlying thermally conductive crystalline ice. Thus, all ice remains cold and poorly dissipative, even if dissipation is an order of magnitude above that provided by the Andrade rheology [4]. If Mimas' rocky core is slightly non-hydrostatic [1], this matches the observed libration. We conclude that Mimas' libration is compatible with a late origin from a debris ring, but not with primordial accretion. Consistent with findings from many authors (e.g. [6]), these models cannot produce an ocean on Enceladus unless its orbital eccentricity is higher than observed.References:[1] Tajeddine et al. (2014) Science 346, 322[2] Peale (1999) Annu Rev Astron Astrophys 37, 533[3] Charnoz et al. (2011) Icarus 216, 535[4] McCarthy & Cooper (2016) EPSL 443, 185[5] Rhoden et al., JGR: Planets, submitted[6] Roberts & Nimmo (2008) Icarus 194, 675

The nature of HHL 73 from optical imaging and integral field spectroscopy

NASA Astrophysics Data System (ADS)

López, R.; Sánchez, S. F.; García-Lorenzo, B.; Gómez, G.; Estalella, R.; Riera, A.; Busquet, G.

2008-02-01

We present new results on the nature of the Herbig-Haro-like object 73 (HHL 73, also known as [G84b] 11) based on narrow-band CCD Hα and [SII] images of the HHL 73 field, and integral field spectroscopy (IFS) and radio continuum observations at 3.6 cm covering the emission of the HHL 73 object. The CCD images allow us to resolve the HHL 73 comet-shaped morphology into two components and a collimated emission feature of ~4 arcsec long, reminiscent of a microjet. The IFS spectra of HHL 73 showed emission lines characteristic of the spectra of Herbig-Haro objects. The kinematics derived for HHL 73 are complex. The profiles of the [SII] λλ6717, 6731 Å lines were well fitted with a model of three Gaussian velocity components peaking at VLSR ~= -100, -20 and +35 km s-1. We found differences among the spatial distribution of the kinematic components that are compatible with the emission from a bipolar outflow with two blueshifted (low- and high-velocity) components. Extended radio continuum emission at 3.6 cm was detected showing a distribution in close agreement with the HHL 73 redshifted gas. From the results discussed here, we propose HHL 73 to be a true HH object. IRAS 21432+4719, offset 30-arcsec north-east from the HHL 73 apex, is the most plausible candidate to be driving HHL 73, although the evidence is not conclusive. Based on observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC) and in the 2.6-m Nordic Optical Telescope and 2.5-m Isaac Newton Telescope at the Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. E-mail: rosario@am.ub.es (RL); sanchez@caha.es (SFS); bgarcia@iac.es (BG-L); gabriel.gomez@gtc.iac.es (GG); robert.estalella@am.ub.es (RE); angels.riera@upc.edu (AR); gbusquet@am.ub.es (GB)

Conservación de material histórico sobre papel en el Observatorio Astronómico de la Universidad Nacional de Córdoba

NASA Astrophysics Data System (ADS)

Laguzzi, N.; Tonini, A.; Andreoli, G.; Goldes, G.; Paolantonio, S.; Cequeira, F.; Landi, L.; Alba, J.

At the recently created Astronomical Museum ``Pte. Sarmiento - Dr. Benjamin Gould", the task of preventive conservation of historic documents has been faced. These materials include: 1) letters exchanged between national authorities and the directors of the Observatory, during the first decades (1870-1880-1890); b) original observation logs from these very first times, containing astrometrical and photometrical data; c) a variety of ancient books and papers; d) administrative documents. The state of conservation of this patrimony was varied: since well-conserved books and letters, to highly degraded logs. The observation logs written by B. Gould and the astronomers who followed him had been stocked in a safe with a permanent humidity of about 70 %, without any ventilation and exposed to the attack of insects of the family ``dermestidae." These conditions could not be worse for the conservation of paper. In order to stop the proccess of degradation and create a healthy environment for written-paper conservation, a team was formed with personnel belonging to the Cultural Area of the Municipality. The tasks being performed on the observation logs are: 1) an initial, mechanical cleaning, performed once the material is extracted from the contaminated safe: by these means, adult insects and pupas are removed 2) a stage of about two weeks of duration, in which the logs are mantained in a vacuum chamber, in orden to completely eliminate the adult, pupa and egg stage insects by anoxia 3) the final mechanical cleaning 4) storage in a clean location. In order to perform these tasks, we work in collaboration with the Environmental Observatory of the City, and the group of Material-Science Research of Fa.M.A.F. Regarding the letters, a mechanical cleaning was performed. After that, the letters were digitized by means of a scanner, inventoried, put inside acid-free polipropylene envelops and filed for conservation, protected from intense light and external sources of contamination. Copies of these letters will be included as exhibits.

Visible and Near-Infrared Spectroscopy of Seyfert 1 and Narrow-Line Seyfert 1 Galaxies

NASA Astrophysics Data System (ADS)

Rodríguez-Ardila, Alberto; Pastoriza, Miriani G.; Donzelli, Carlos J.

2000-01-01

This paper studies the continuum and emission-line properties of a sample composed of 16 normal Seyfert 1 and seven narrow-line Seyfert 1 (NLS1) galaxies using optical and near-IR CCD spectroscopy. The continuum emission of the galaxies can be described in terms of a combination of stellar population, a nonstellar continuum of power-law form, and Fe II emission. A significative difference in the optical spectral index between NLS1's and normal Seyfert 1's is observed; the latter is steeper. Most NLS1's show Fe II/Hβ ratios larger than those observed in the other Seyfert 1's. In the IRAS band, both groups of galaxies have very similar properties. We have searched for the presence of optically thin gas in the broad-line region (BLR) of the galaxies by comparing the broad O I λ8446 and Hα emission-line profiles. Our analysis show that in the NLS1's, both profiles are similar in shape and width. This result contradicts the hypothesis of thin gas emission in the high-velocity part of the BLR to explain the ``narrowness'' of broad optical permitted lines in these objects. Evidence of narrow O I λ8446 emission is found in six galaxies of our sample, implying that this line is not restricted to a pure BLR phenomenon. In the narrow-line region, we find similar luminosities in the permitted and high-ionization lines of NLS1's and normal Seyfert 1's. However, low-ionization lines such as [O I] λ6300, [O II] λ3727, and [S II] λλ6717, 6731 are intrinsically less luminous in NLS1's. Physical properties derived from density- and temperature-sensitive line ratios suggest that the [O II] and [S II] emitting zones are overlapping in normal Seyfert 1's and separated in NLS1's. Based on observations made at CASLEO. Complejo Astronómico El Leoncito (CASLEO) is operated under agreement between the Consejo Nacional de Investigaciones Científicas y técnicas de la República Argentina and the National Universities of La Plata, Córdoba and San Juán.

Projeto educação em ciências com observatórios virtuais: a participação da Escola Moppe no período 2000-2003

NASA Astrophysics Data System (ADS)

Wuensche, C. A.; Gavioli, E.; Oliveira, A. L. P. R. S.; da Silva, C.; Cardoso, H. P.; Estácio, S.

2003-08-01

O projeto Educação em Ciências com Observatórios Virtuais foi concebido pelo Instituto Astronômico e Geofísico da USP, agregando diversas instituições de ensino e pesquisa no país para desenvolver competências diversas na educação fundamental, média e superior utilizando a astronomia como ferramenta multidisciplinar. Este trabalho descreve a participação da MOPPE, escola-piloto do INPE no projeto, no período de 2000-2003. Serão apresentadas 1) a criação de um clube de ciências (1999 a 2001) cujo tema foi a colonização de Marte e 2) a ementa de astronomia trabalhada com as 7a. e 8a. séries do ensino fundamental. A proposta do projeto Colonizando Marte foi estudar diversos aspectos de uma missão interplanetária e construir experiementos que permitissem quantificar esses aspectos. Os resultados obtidos incluiram apresentações nas SBPC Jovem em 2000 e 2001. Discutiremos também as ementas de astronomia trabalhadas desde 2001 e o envolvimento dos alunos com atividades ligadas a astronomia, fora da aula de ciências. A inclusão de astronomia no currículo das últimas séries motivou a participação de mais alunos culminando com a conquista de duas medalhas para alunos da 7a. série na Olimpiada Brasileira de Astronomia em 2002. Houve também um aumento no número de participantes na OBA 2003 e nos projetos de astronomia mais elaborados nas Feira de Ciências de 2001 e 2002. Destacamos em 2003 a inclusão da MOPPE no projeto TIE - Telescopes in Education - da NASA, que utiliza o telescópio do Observatório de Mount Wilson (EUA) para observações remotas em projetos pedagógicos para o ensino de astronomia.

Laboratory and theoretical work in the service of planetary atmospheric research

NASA Astrophysics Data System (ADS)

Coustenis, Athena

2015-08-01

A large quantity of observations is obtained by instruments onboard space missions exploring our solar system and by large ground-based telescopes observing the planets and also the exoplanets. Spectroscopy plays a major role in this type of investigation. To analyze and exploit these observations, planetary scientists need spectroscopic data covering wide ranges in wavelength but also in temperature, pressure, distance, etc.The outer regions of our solar system in particular, including the giant gaseous planets Jupiter and Saturn and their satellites, have recently been the target of space missions such as Cassini-Huygens and several investigations from the ground. Titan, the largest moon of Saturn, in particular, offers many similarities with our own planet, among which a dense atmosphere whose major component is dinitrogen at about 95%. Combining with methane (at a few percent) and hydrogen, gives rise to a complex organic chemistry with hydrocarbons and nitriles. Oxygen compounds also exist in Titan’s atmosphere. By studying Titan, we learn about our own planet and our Solar system Solar as a whole [1,2,3]. To properly interpret the Cassini-Huygens data and in anticipation of future missions like ESA’s JUICE to the Jupiter system, spectroscopic data are crucially needed. In the field of exoplanets (over 1000 discovered to date), it also becomes urgent to have adequate data of several molecules in order to analyze the observations returned to us every day by major observatories on Earth and in the space [4,5]. I will discuss recent applications from theoretical and experimental studies on the investigation of Titan and exoplanets, with emphasis on methane. I will also present some needs for future analyses.References: [1] Campargue, A., et al. 2012. Icarus 219, 110-128. [2] Coustenis, A., et al. 2013. Astrophys. J. 799, 177, 9p. [3] Hirtzig, et al., 2013. Icarus 226, 470-486 and corrigendum 1182-1182. [4] Tinetti, G., Encrenaz, Th., Coustenis, A., 2013. Astron. Astrophys. Rev. 21, #63. [5] Encrenaz, T., et al., 2014. Experimental Astronomy, DOI: 10.1007/s10686-014-9415-0.

Relative 2-color Photometry Of Neo's

NASA Astrophysics Data System (ADS)

Shelus, P.; Gyorgyey-Ries, J.; Ricklefs, R.; Barker, E.

We have been making Solar System small body positional observations at McDon- ald Observatory since the early 1970's. In 1994 we moved to a CCD-based, almost totally automated, astrometry system (Whipple et al, 1996, Astron. J., Vol. 112, p. 316). Our present observational effort is focussed upon Near Earth Objects (NEOs) as part of NASA's mission to discover and catalogue 90 percent of NEOs with diameters larger than 1 km by 2008. Observing 4 nights per lunation, we conduct observations to confirm newly discovered NEOs, filling in the night on a target-of-opportunnity basis, with observations of under-observed NEOs. Our major intent is to understand the overall hazard that these objects pose to Earth and their dynamical and physical characterization. We recently adopted the USNO-A2.0 catalogue to improve astromet- ric results and a number of up-grades to the end-to-end system have been developed (Barker et al, 2001, Bull. AAS, Vol. 33, p. 1116). The USNO catalog also provides stellar magnitudes in the standard Johnson R and B photometric bands. We have thus taken the opportunity to expand our observational efforts to regularly provide R mag- nitudes, in addition to astrometric positions. Our limiting magnitude in R is near 22. We are now furthering our photometric efforts by including B exposures as part of our standard observation triplet. We have already confirmed that switching filters between exposures on standard fields does not compromise the astrometric accurary. Thus, we plan to provide two color, sequential, relative photometry, (B-R), of newly discov- ered or under observed asteroids, as part of our routine observation process. The time interval between exposures is always less than 20 minutes, short compared to most asteroid rotation times. Consequently, a meaningful color index can be obtained in parallel with the astrometric positions. Although (B-R) is not the usual color index used in asteroid classification studies, we are testing whether we can use it as a quick diagnostic tool to roughly classify newly discovered NEOs. The results so far obtained are presented here. This research is funded by NASA's NEO Observation Program grants NAG5-6863 and NAG5-10183.

Photochemistry in Saturn's Ring-Shadowed Atmosphere: Modulation of Key Molecules and Observations of Dust Content

NASA Astrophysics Data System (ADS)

Edgington, Scott G.; Atreya, Sushil H.; Wilson, Eric H.; Baines, Kevin H.; West, Robert A.; Bjoraker, Gordon L.; Fletcher, Leigh N.; Momary, Tom

2015-04-01

Cassini has been orbiting Saturn for over ten years now. During this epoch, the ring shadow has moved from covering a large portion of the northern hemisphere to covering a large swath south of the equator and continues to move southward. At Saturn Orbit Insertion in 2004, the ring plane was inclined by ~24 degrees relative to the Sun-Saturn vector. The projection of the B-ring onto Saturn reached as far as 40N along the central meridian (~52N at the terminator). At its maximum extent, the ring shadow can reach as far as 48N/S (~58N/S at the terminator). The net effect is that the intensity of both ultraviolet and visible sunlight penetrating into any particular latitude will vary depending on both Saturn's axis relative to the Sun and the optical thickness of each ring system. In essence, the rings act like venetian blinds. Our previous work [1] examined the variation of the solar flux as a function of solar inclination, i.e. ~8 year season at Saturn. Here, we report on the impact of the oscillating ring shadow on the photolysis and production rates of hydrocarbons in Saturn's stratosphere and upper troposphere, including acetylene, ethane, propane, and benzene. Beginning with methane, we investigate the impact on production and loss rates of the long-lived photochemical products leading to haze formation are examined at several latitudes over a Saturn year. Similarly, we assess its impact on phosphine abundance, a disequilibrium species whose presence in the upper troposphere is a tracer of convective processes in the deep atmosphere. We will also present our ongoing analysis of Cassini's CIRS, UVIS, and VIMS datasets that provide an estimate of the evolving haze content of the northern hemisphere and we will begin to assess the implications for dynamical mixing. In particular, we will examine how the now famous hexagonal jet stream acts like a barrier to transport, isolating Saturn's north polar region from outside transport of photochemically-generated molecules and haze. [1] Edgington, S.G., et al., 2012. Photochemistry in Saturn's Ring Shadowed Atmosphere: Modeling, Observations, and Preliminary Analysis. Bull. American. Astron. Soc., 38, 499 (#11.23).

Investigation of the Hydantoin Monomer and its Interaction with Water Molecules

NASA Astrophysics Data System (ADS)

Gruet, Sébastien; Perez, Cristobal; Schnell, Melanie

2017-06-01

Hydantoin (Imidazolidine-2,4-dione, C_3H_4N_2O_2) is a five-membered heterocyclic compound of astrobiological interest. This molecule has been detected in carbonaceous chondrites [1], and its formation can rise from the presence of glycolic acid and urea, two prebiotic molecules [2]. The hydrolysis of hydantoin under acidic conditions can also produce glycine [3], an amino acid actively searched for in the interstellar medium. Spectroscopic data of hydantoin is very limited and mostly dedicated to the solid phase. The high resolution study in gas phase is restricted to the work recently published by Ozeki et al. reporting the pure rotational spectra of the ground state and two vibrational states of the molecule in the millimeter-wave region (90-370 GHz)[4]. Using chirped-pulse Fourier-transform microwave (CP-FTMW) spectroscopy, we recorded the jet-cooled rotational spectra of hydantoin with water between 2 to 8 GHz. We observed the ground state of hydantoin monomer and several water complexes with one or two water molecules. All the observed species exhibit a hyperfine structure due to the two nitrogen atoms present in the molecule, which were fully resolved and analyzed. Additional experiments with a ^{18}O enriched water sample were realized to determine the oxygen-atom positions of the water monomers. These experiments yielded accurate structural information on the preferred water binding sites. The observed complexes and the interactions that hold them together, mainly strong directional hydrogen bonds, will be presented and discussed. [1] Shimoyama, A. and Ogasawara, R., Orig. Life Evol. Biosph., 32, 165-179, 2002. DOI:10.1023/A:1016015319112. [2] Menor-Salván, C. and Marín-Yaseli, M.R., Chem. Soc. Rev., 41(16), 5404-5415, 2012. DOI:10.1039/c2cs35060b. [3] De Marcellus P., Bertrand M., Nuevo M., Westall F. and Le Sergeant d'Hendecourt L., Astrobiology. 11(9), 847-854, 2011. DOI:10.1089/ast.2011.0677. [4] Ozeki, H., Miyahara R., Ihara H., Todaka S., Kobayashi K., and Ohishi M., Astron. Astrophys., Forthcoming article (

Characterizing the population of Asteroids in Cometary Orbits (ACOs)

NASA Astrophysics Data System (ADS)

Tancredi, Gonzalo; Licandro, Javier; Alí-Lagoa, Victor; Martino, Silvia; Vieira Monteiro, Filipe; Silva, Jose Sergio; Lazzaro, Daniela

2015-08-01

The classification criterion between asteroids and comets has evolved in recent decades, but the main phenomenological distinction remains unchanged: comets are active objects as they present gas and dust ejection from the surface at some point of their orbits, while asteroids are inert objects as they do not show any kind of large scale gas and dust ejection.To identify the transitional objects several classification schemes based on the orbital elements have been used. They are usually based on the Tisserand’s parameter (TJ). Tancredi (2014) presents a much more restrictive criterion to identify ACOs that ensured that the objects have a dynamical evolution similar to the population of periodic comets. After applying the criteriaa to the sample of over half a million asteroids already discovered, we obtain 316 ACOs that are further classified in subclasses similar to the cometary classification: 203 objects belong to the Jupiter Family group; 72 objects are classified as Centaurs; and 56 objects have Halley Type Orbits (also known as Damocloids). These are the best-known extinct/dormant comets candidates from a dynamical point of view.We study the physical properties of this sample of ACOs. Two results will be presented:- We look for the ACOs detected by the NASA’s WISE and by fitting a thermal model to their observations, we derive: the effective diameter, beaming parameter and the visible geometric albedo, using the method described in Al-Lagoa et al (2013). We obtain these parameters for 37 of 203 ACOs in JFC orbits and 13 of 56 Damocloids. We also compute the Cumulative Size Distribution (CSDs) of these populations and compare them with the CSDs of JF Comets and Centaurs.- We have been monitoring the observable ACOs since 12/2014 up to 06/2015. Every other month we select all the ACOs with elongations >90deg and estimated magnitudes V<21. We try to observe them with the 1m IMPACTON telescope of the Observatório Astronômico do Sertão de Itaparica (OASI). By comparing the photometric profiles of the ACOs with background stars, we try to detect some hint of cometary activity. Over 20 ACOs have been observed in the six months.

Full Empirical Potential Curves and Improved Dissociation Energies for the X ^1Σ^+ and a ^1Π States of CH^+

NASA Astrophysics Data System (ADS)

Cho, Young-Sang; Le Roy, Robert

2014-06-01

CH^+ has been a species of interest since the dawn of molecular astrophysics,and it is an important intermediate in combustion processes. In the domain of `conventional' spectroscopy there have been a number of studies of low v' and v" portions of the A ^1Π-X ^1Σ^+ band system of various isotopologues, and Amano recently reported microwave measurements of the ground-state R(0) lines of 12CH^+, 13CH^+ and 12CD^+. used photodissociation spectroscopy to observe transitions to very high-J' tunneling-predissociation levels (shape resonances) involving v(A)=0-10, for many of which they also measured the photo-fragment kinetic energy release. More recently Hechtfischer et al. used photodissociation spectroscopy of `Feschbach resonance' levels at very high v'(A) and low J' to obtain the first direct measurement of the 12CH^+ dissociation energy with near-spectroscopic accuracy (± 1.1 cm-1). However, to date, all analyses of the data for this system had been performed using traditional band-constant or Dunham-expansion fits to data for the lowest vibrational levels, and there have been no attempts to combine the `conventional' low-v data with the high-J' and high-v' photodissociation data in a single treatment. The present work has addressed this problem by performing a Direct-Potential-Fit (DPF) analysis that obtains full analytic potential energy functions for the X ^1Σ^+ and A ^1Π states of CH^+ that are able to account for all of the available data (on average) within their uncertainties. A.E. Douglas and G. Herzberg, Astrophys. J. 94, 381 (1941). T. Amano, Astrophys. J. Lett. {716}, L1 (2010) H. Helm, P.C. Crosby, M.M. Graff and J.T. Mosley, Phys. Rev. A 25, 304 (1982) U. Hechtfischer and C. J. Williams, M. Lange, J. Linkemann, D. Schwalm, R. Wester, A. Wolf and D. Zajfman, J.Chem.Phys. 117, 8754 (2002). H.S.P. Müller, Astron. Astrophys. 514, L7 (2010)

Modeling of the Enceladus water vapor jets for interpreting UVIS star and solar occultation observations

NASA Astrophysics Data System (ADS)

Portyankina, Ganna; Esposito, Larry W.; Aye, Klaus-Michael; Hansen, Candice J.

2015-11-01

One of the most spectacular discoveries of the Cassini mission is jets emitting from the southern pole of Saturn’s moon Enceladus. The composition of the jets is water vapor and salty ice grains with traces of organic compounds. Jets, merging into a wide plume at a distance, are observed by multiple instruments on Cassini. Recent observations of the visible dust plume by the Cassini Imaging Science Subsystem (ISS) identified as many as 98 jet sources located along “tiger stripes” [Porco et al. 2014]. There is a recent controversy on the question if some of these jets are “optical illusion” caused by geometrical overlap of continuous source eruptions along the “tiger stripes” in the field of view of ISS [Spitale et al. 2015]. The Cassini’s Ultraviolet Imaging Spectrograph (UVIS) observed occultations of several stars and the Sun by the water vapor plume of Enceladus. During the solar occultation separate collimated gas jets were detected inside the background plume [Hansen et al., 2006 and 2011]. These observations directly provide data about water vapor column densities along the line of sight of the UVIS instrument and could help distinguish between the presence of only localized or also continuous sources. We use Monte Carlo simulations and Direct Simulation Monte Carlo (DSMC) to model the plume of Enceladus with multiple (or continuous) jet sources. The models account for molecular collisions, gravitational and Coriolis forces. The models result in the 3-D distribution of water vapor density and surface deposition patterns. Comparison between the simulation results and column densities derived from UVIS observations provide constraints on the physical characteristics of the plume and jets. The specific geometry of the UVIS observations helps to estimate the production rates and velocity distribution of the water molecules emitted by the individual jets.Hansen, C. J. et al., Science 311:1422-1425 (2006); Hansen, C. J. et al, GRL 38:L11202 (2011); Porco, C.C. et al. Astron. J. 148, 45 (2014); Spitale, J.N. et al. Nature 521, 57-60 (2015)

Formation of interstellar anions

NASA Astrophysics Data System (ADS)

Senent, Maria Luisa

2012-05-01

Formation of interstellar anions: M.L. Senent. The recent detection of negative charged species in the ISM1 has instigated enthusiasm for anions in the astrophysical community2. Many of these species are new and entail characterization. How they are formed in astrophysical sources is a question of major relevance. The anion presence in ISM was first predicted theoretically on the basis of electron affinities and on the negative linear chain molecular stabilities. Although very early, they were considered in astrochemical models3-4, their discovery is so recent because their abundances seem to be relatively low. These have to be understood in terms of molecular stabilities, reaction probabilities and radiative and collisional excitations. Then, we present our theoretical work on even carbon chains type Cn and CnH (n=2,4,6) focused to the understanding of anion abundances. We use highly correlated ab initio methods. We performed spectroscopic studies of various isomers that can play important roles as intermediates5-8. In previous papers9-10, we compared C2H and C2H- collisional rates responsible for observed line intensities. Actually, we study hydrogen attachment (Cn +H → CnH and Cn- +H → CnH-) and associative detachment processes (Cn- +H → CnH +e-) for 2, 4 and 6 carbon atom chains11. [1] M.C.McCarthy, C.A.Gottlieb, H.Gupta, P.Thaddeus, Astrophys.J, 652, L141 (2006) [2] V.M.Bierbaum, J.Cernicharo, R.Bachiller, eds., 2011, pp 383-389. [3] A. Dalgarno, R.A. Mc Cray, Astrophys.J,, 181, 95 (1973) [4] E. Herbst E., Nature, 289, 656 (1981); [5] H.Massó, M.L.Senent, P.Rosmus, M.Hochlaf, J.Chem.Phys., 124, 234304 (2006) [6] M.L.Senent, M.Hochlaf, Astrophys. J. , 708, 1452(2010) [7] H.Massó, M.L.Senent, J.Phys.Chem.A, 113, 12404 (2009) [8] D. Hammoutene, M.Hochlaf, M.L.Senent, submitted. [9] A. Spielfiedel, N. Feautrier, F. Najar, D. ben Abdallah, F. Dayou, M.L. Senent, F. Lique, Mon.Not.R.Astron.Soc., 421, 1891 (2012) [10] F.Dumouchel, A, Spielfieldel , M.L.Senent, N.Feautrier, Chem. Phys. Lett., 533, 6 (2012) [11] M.L.Senent, M.Hochlaf, submitted

Two new pulsating low-mass pre-white dwarfs or SX Phoenicis stars?

NASA Astrophysics Data System (ADS)

Corti, M. A.; Kanaan, A.; Córsico, A. H.; Kepler, S. O.; Althaus, L. G.; Koester, D.; Sánchez Arias, J. P.

2016-03-01

Context. The discovery of pulsations in low-mass stars opens an opportunity to probe their interiors and determine their evolution by employing the tools of asteroseismology. Aims: We aim to analyse high-speed photometry of SDSS J145847.02+070754.46 and SDSS J173001.94+070600.25 and discover brightness variabilities. In order to locate these stars in the Teff - log g diagram, we fit optical spectra (SDSS) with synthetic non-magnetic spectra derived from model atmospheres. Methods: To carry out this study, we used the photometric data we obtained for these stars with the 2.15 m telescope at CASLEO, Argentina. We analysed their light curves and applied the discrete Fourier transform (FT) to determine the pulsation frequencies. Finally, we compare both stars in the Teff - log g diagram, with two known pre-white dwarfs and seven pulsating pre-ELM white dwarf stars, δ Scuti, and SX Phe stars Results: We report the discovery of pulsations in SDSS J145847.02+070754.46 and SDSS J173001.94+070600.25. We determine their effective temperature and surface gravity to be Teff = 7972 ± 200 K, log g = 4.25 ± 0.5 and Teff = 7925 ± 200 K, log g = 4.25 ± 0.5, respectively. With these parameters, these new pulsating low-mass stars can be identified with either ELM white dwarfs (with ~0.17 M⊙) or more massive SX Phe stars. We identified pulsation periods of 3278.7 and 1633.9 s for SDSS J145847.02+070754.46 and a pulsation period of 3367.1 s for SDSS J173001.94+070600.25. These two new objects, together with those of Maxted et al. (2013, 2014), indicate the possible existence of a new instability domain towards the late stages of evolution of low-mass white dwarf stars, although their identification with SX Phe stars cannot be discarded. Visiting Astronomer, Complejo Astronómico El Leoncito operated under agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina and the National Universities of La Plata, Córdoba, and San Juan.

Astronomia cultural e meio ambiente segundo uma abordagem holística

NASA Astrophysics Data System (ADS)

Jafelice, L. C.

2003-08-01

Neste trabalho ampliamos a discussão da abordagem holística para o ensino de astronomia que temos desenvolvido nos últimos anos, analisamos novos resultados e apresentamos exemplos práticos para interessados em experimentá-la. A constatação básica a orientar este enfoque é que cursos introdutórios em astronomia costumam ser excessiva e prematuramente técnicos, além de assumirem uma visão tradicional, muito estreita, do que seja educação científica, herdada da era cartesiana e positivista da ciência. Fundamentamos porque é importante que elementos de astronomia cultural ofereçam o mote e constituam o eixo norteador daqueles cursos e porque é urgente revermos a visão que temos da relação entre astronomia e meio ambiente. Um ponto central nesta abordagem é explorar formas de reativar e atualizar uma relação orgânica com o meio e excitar a consciência de nossa inevitável e profunda interdependência com ele em nível cósmico. Neste trabalho exemplificamos a possibilidade de concretização desta proposta em três diferentes situações: disciplinas de cursos de licenciatura em geografia e em física; escolas de nível fundamental; e, neste caso ainda a ser implementada, comunidades carentes. Estes casos envolvem públicos e espaços diferenciados para educação formal e não-formal. Dos casos já implementados, destacamos os resultados alcançados pelos alunos: enriquecimento cultural, aprendizagem significativa de conteúdos astronômicos tradicionais; mudanças de comportamento, incorporando contato diário com o céu; e freqüentes vivências de sentimentos empáticos que redirecionam a relação com a natureza e a consciência ecológica global. Além disto, para interessados em aplicar esta proposta, também socializamos procedimentos e cuidados para a implementação de ações alternativas consonantes com a mesma. (PPGECNM/UFRN; PRONEX/FINEP; NUPA/USP; Temáticos/FAPESP)

A Statistical Analysis of YORP Coefficients

NASA Astrophysics Data System (ADS)

McMahon, Jay W.; Scheeres, D.

2013-10-01

The YORP (Yarkovsky-O'Keefe-Radzievskii-Paddack) effect is theorized to be a major factor in the evolution of small asteroids (<10 km) in the near-Earth and main belt populations. YORP torques, which originate from absorbed sunlight and subsequent thermal radiation, causes secular changes in an asteroid's spin rate and spin vector orientation (e.g. Rubincam, Journal of Geophysical Research, 1995). This in turn controls the magnitude and direction of the Yarkovsky effect, which causes a drift in an asteroid's heliocentric semi-major axis (Vokrouhlicky and Farinella, Nature, 2000). YORP is also thought to be responsible for the creation of multiple asteroid systems and asteroid pairs through the process of rotational fission (Pravec et al, Nature, 2010). Despite the fact that the YORP effect has been measured on several asteroids (e.g. Taylor et al, Science, 2007 and Kaasalainen et al, Nature, 2007), it has proven very difficult to predict the effect accurately from a shape model due to the sensitivity of the YORP coefficients to shape changes (Statler, Icarus, 2009). This has been especially troublesome for Itokawa, for which a very detailed shape model is available (Scheeres et al, Icarus 2007; Breiter et al, Astronomy & Astrophysics, 2009). In this study, we compute the YORP coefficients for a number asteroids with detailed shape models available on the PDS-SBN. We then statistically perturb the asteroid shapes at the same resolution, creating a family of YORP coefficients for each shape. Next, we analyze the change in YORP coefficients between a shape model of accuracy obtainable from radar with one including small-scale topography on the surface as was observed on Itokawa. The combination of these families of coefficients will effectively give error bars on our knowledge of the YORP coefficients given a shape model of some accuracy. Finally, we discuss the statistical effect of boulder and craters, and the modification of these results due to recent studies on thermal beaming (Rozitis and Green, Mon. Not. R. Astron. Soc., 2012) and "tangential" YORP (Golubov and Krugly, The Astrophysical Journal Letters, 2012).

On the Generation of Hydrodynamic Shocks by Mixed Beams and Occurrence of Sunquakes in Flares

NASA Astrophysics Data System (ADS)

Zharkova, Valentina; Zharkov, Sergei

2015-11-01

Observations of solar flares with sunquakes by space- and ground-based instruments reveal essentially different dynamics of seismic events in different flares. Some sunquakes are found to be closely associated with the locations of hard X-ray (HXR) and white-light (WL) emission, while others are located outside either of them. In this article we investigate possible sources causing a seismic response in a form of hydrodynamic shocks produced by the injection of mixed (electron plus proton) beams, discuss the velocities of these shocks, and the depths where they deposit the bulk of their energy and momentum. The simulation of hydrodynamic shocks in flaring atmospheres induced by electron-rich and proton-rich beams reveals that the linear depth of the shock termination is shifted beneath the level of the quiet solar photosphere on a distance from 200 to 5000 km. The parameters of these atmospheric hydrodynamic shocks are used as initial condition for another hydrodynamic model developed for acoustic-wave propagation in the solar interior (Zharkov, Mon. Not. Roy. Astron. Soc. 431, 3414, 2013). The model reveals that the depth of energy and momentum deposition by the atmospheric shocks strongly affects the propagation velocity of the acoustic-wave packet in the interior. The locations of the first bounces from the photosphere of acoustic waves generated in the vicinity of a flare are seen as ripples on the solar surface, or sunquakes. Mixed proton-dominated beams are found to produce a strong supersonic shock at depths 200 - 300 km under the level of the quiet-Sun photosphere and in this way produce well-observable acoustic waves, while electron-dominated beams create a slightly supersonic shock propagating down to 5000 km under the photosphere. This shock can only generate acoustic waves at the top layers beneath the photosphere since the shock velocity very quickly drops below the local sound speed. The distance Δ of the first bounce of the generated acoustic waves is discussed in relation to the minimal phase velocities of wave packets defined by the acoustic cutoff frequency and the parameters of atmospheric shock termination beneath the photosphere.

Photometry and Spectroscopy of BD+35 1111 in M38

NASA Astrophysics Data System (ADS)

Souza, Steven P.; Kwitter, Karen B.; Sami, Mona; Beltz-Mohrmann, Gillian

2014-06-01

BD+35 1111 is a ~10.5-magnitude star in the field of M38, an open cluster that has been a target of our ongoing study of Hα emission variability in massive stars via narrowband CCD photometry (e.g. Souza, Davis, and Teich 2013, BAAS. 45, PM354.22). BD+35 1111 has no MKK classification in the literature, and is not listed as variable in GCVS, VSX, or NSVS. It is included, with no further characterization, in both the Vatican and Kohoutek catalogs of emission line stars. Using inhomogeneous ensemble photometry (e.g. Bhatti, Richmond, Ford, and Petro 2010, ApJ Supp., 186, 233), we find it to be an irregular variable with a range of ~0.15 mag. To further understand this star we obtained a medium-resolution spectrum using the DIS spectrograph on the ARC 3.5-meter telescope at Apache Point Observatory. We classify BD+35 1111 as B2Ve, the only confirmed Be star in the field of M38. This raises the question of membership, since the age of M38 is likely 250 Ma or greater (Pandey et al. 2007, Publ. Astron. Soc. Japan 59, 547). From published B and V magnitudes we find a nominal distance to BD+35 1111 of 1.6 kpc, but with a range of 1.3 to 2.0 kpc, marginally consistent with distance estimates for M38 ranging from 1.0 to 1.4 kpc. If a member, BD+35 1111 is a candidate blue straggler. If not, it may have escaped from a nearby younger cluster, possibly Kronberger 1 (Kronberger et al. 2006, A&A 447, 921), which has the right heliocentric distance and age. The notion that BD+35 1111 is behind M38 is supported by its reddening of EB-V ~ 0.5, significantly higher than for M38 itself 0.24). We gratefully acknowledge support for student research from NSF grant AST-1005024 to the Keck Northeast Astronomy Consortium, Williams College, and NASA via an American Astronomical Society Small Research Grant.