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Sample records for blue stellar objects

  1. Accurate photometry and variability of First Byurakan Survey blue stellar objects

    NASA Astrophysics Data System (ADS)

    Mickaelian, A. M.; Mikayelyan, G. A.; Sinamyan, P. K.

    2011-08-01

    A new method for the combined calculation of magnitudes based on accurate measurements of Palomar Observatory Sky Survey (POSS) epochs 1 and 2 (POSS1 and POSS2) plates is given. The photometric accuracy of various surveys and catalogues has been estimated and established and statistical weights have been calculated for each one. To achieve the best possible magnitudes, weighted averaging of data from United States Naval Observatory (USNO-A2.0), Automatic Plate Measuring (APM), Minnesota Automated Plate Scanner (MAPS), USNO-B1.0 and Guide Star Catalog (GSC 2.3.2) catalogues has been used. The root-mean-square (rms) accuracy of magnitudes achieved for POSS1 is 0.184 mag for B and 0.173 mag for R, while that for POSS2 is 0.138 mag for B and 0.128 mag for R. We have derived the best POSS1 and POSS2 magnitudes for First Byurakan Survey (FBS) blue stellar objects. We have refined the transformation formulae between POSS1 and POSS2 magnitudes and those for the Sloan Digital Sky Survey (SDSS) and a standard UBV system. Using these accurate magnitudes, we have estimated the variability of FBS blue stellar objects and revealed probable and possible variables. We have worked out methods with which to control and exclude the accidental errors that appear in any survey. We have compared and combined our results with those given in the Northern Sky Variability Survey (NSVS) data base and obtained better candidates for variability. Having excluded variables, we have combined POSS1 and POSS2 data for the remaining objects to achieve even better magnitudes and colours, the rms being smaller than 0.1 mag in both B and R and for B-R colours. This approach has been applied to FBS blue stellar objects containing a significant number of white dwarfs (WDs) or cataclysmic variables (CVs), as well as extragalactic objects (quasars, Seyferts, BL Lac objects). Altogether 336 variable objects have been revealed, with POSS2-POSS1 ≥ 3σ of the errors. An electronic table of these objects is

  2. DSS1/DSS2 astrometry for 1101 First Byurakan Survey blue stellar objects: Accurate positions and other results

    NASA Astrophysics Data System (ADS)

    Mickaelian, A. M.

    2004-10-01

    Accurate measurements of the positions of 1101 First Byurakan Survey (FBS) blue stellar objects (the Second part of the FBS) have been carried out on the DSS1 and DSS2 (red and blue images). To establish the accuracy of the DSS1 and DSS2, measurements have been made for 153 AGN for which absolute VLBI coordinates have been published. The rms errors are: 0.45 arcsec for DSS1, 0.33 arcsec for DSS2 red, and 0.59 arcsec for DSS2 blue in each coordinate, the corresponding total positional errors being 0.64 arcsec, 0.46 arcsec, and 0.83 arcsec, respectively. The highest accuracy (0.42 arcsec) is obtained by weighted averaging of the DSS1 and DSS2 red positions. It is shown that by using all three DSS images accidental errors can be significantly reduced. The comparison of DSS2 and DSS1 images made it possible to reveal positional differences and proper motions for 78 objects (for 62 of these for the first time), including new high-probability candidate white dwarfs, and to find objects showing strong variability, i.e. high-probability candidate cataclysmic variables. Table 1 is 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/cgi-bin/qcat?J/A+A/426/367

  3. VizieR Online Data Catalog: FBS blue stellar objects (Mickaelian+, 1999)

    NASA Astrophysics Data System (ADS)

    Mickaelian, A. M.; Goncalves, A. C.; Veron-Cetty, M. P.; Veron, P.

    2000-02-01

    The second part of the First Byurakan Survey is aimed at detecting all bright (B<16.5) UV-excess starlike objects in a large area of the sky. By comparison with other major surveys such as the ROSAT All Sky Survey (Cat. , the ROSAT WGACAT (Cat. ) catalogue of point sources, the IRAS (Cat. ) survey, the 6cm Green Bank (Cat. , the 1.4GHz NRAO VLA (Cat. , and the 92cm Westerbork Northern sky surveys (Cat. ) and with the catalogue of mean UBV data on stars, we estimate the number of AGNs present in the FBS survey and its completeness. We have made spectroscopic observations of nine of the most promising FBS candidates. We have found six new QSOs, bringing the total number of known QSOs in this survey to 42. By comparison with the Bright Quasar Survey, we found that the completeness of this last survey is of the order of 70% rather than 30-50% as suggested by several authors. (1 data file).

  4. On the nature of the FBS blue stellar objects and the completeness of the bright quasar survey.

    NASA Astrophysics Data System (ADS)

    Mickaelian, A. M.; Gonçalves, A. C.; Véron-Cetty, M. P.; Véron, P.

    1999-02-01

    The second part of the First Byurakan Survey is aimed at detecting all bright (B < 16.5) UV-excess starlike objects in a large area of the sky. By comparison with other major surveys such as the ROSAT All Sky Survey, the ROSAT WGACAT catalogue of point sources, the IRAS survey, the 6 cm Green Bank, the 1.4 GHz NRAO VLA and the 92 cm Westerbork Northern sky surveys and with the catalogue of mean UBV data on stars, the authors estimate the number of AGNs present in the FBS survey and its completeness. The authors have made spectroscopic observations on nine of the most promising FBS candidates. They have found six new QSOs bringing the total number of known QSOs in this survey to 42. By comparison with the Bright Quasar Survey, they found that the completeness of this last survey is of the order of 70% rather than 30 - 50% as suggested by several authors.

  5. On the nature of the FBS blue stellar objects and the completeness of the Bright Quasar Survey

    NASA Astrophysics Data System (ADS)

    Mickaelian, A. M.; Gonçales, A. C.; Véron-Cetty, M. P.; Véron, P.

    1999-01-01

    The second part of the First Byurakan Survey is aimed at detecting all bright (B < 16.5) UV-excess starlike objects in a large area of the sky. By comparison with other major surveys such as the ROSA T All Sky Survey, the ROSAT WGACAT catalogue of point sources, the IRAS survey, the 6cm Green Bank, the 1.4GHz NRAO VLA, and the 92cm Westerbork Northern sky surveys and with the catalogue of mean UBV data on stars, we estimate the number of AGNs present in the FBS survey and its completeness. We have made spectroscopic observations of nine of the most promising FBS candidates. We have found six new QSOs, bringing the total number of known QSOs in this survey to 42. By comparison with the Bright Quasar Survey, we found that the completeness of this last survey is of the order of 70% rather than 30 50% as suggested by several authors.

  6. Truncated accretion discs around stellar mass objects

    NASA Astrophysics Data System (ADS)

    D'Angelo, C. R. M. X.

    2011-03-01

    This thesis explores dynamical and radiative processes that occur in accretion flows around various stellar-mass objects. The work is divided into two separate themes: the interaction between strong stellar magnetic fields and accretion flows (chapters 2, 3, and 4) and radiative processes and accretion flow geometry in black holes at low luminosity (chapter 5).

  7. Stellar Populations in BL Lac type Objects

    NASA Astrophysics Data System (ADS)

    Serote Roos, Margarida

    The relationship between an Active Galactic Nucleus (AGN) and its host galaxy is a crucial question in the study of galaxy evolution. We present an estimate of the stellar contribution in a sample of low luminosity BL Lac type objects. We have performed stellar population synthesis for a sample of 19 objects selected from Marchã et al. (1996, MNRAS 281, 425). The stellar content is quantified using the equivalent widths of all absorption features available throughout the spectrum. The synthesis is done by a variant of the GPG method (Pelat: 1997, MNRAS 284, 365).

  8. Accretion disks in luminous young stellar objects

    NASA Astrophysics Data System (ADS)

    Beltrán, M. T.; de Wit, W. J.

    2016-01-01

    An observational review is provided of the properties of accretion disks around young stars. It concerns the primordial disks of intermediate- and high-mass young stellar objects in embedded and optically revealed phases. The properties were derived from spatially resolved observations and, therefore, predominantly obtained with interferometric means, either in the radio/(sub)millimeter or in the optical/infrared wavelength regions. We make summaries and comparisons of the physical properties, kinematics, and dynamics of these circumstellar structures and delineate trends where possible. Amongst others, we report on a quadratic trend of mass accretion rates with mass from T Tauri stars to the highest mass young stellar objects and on the systematic difference in mass infall and accretion rates.

  9. Young stellar objects close to Sgr A*

    NASA Astrophysics Data System (ADS)

    Jalali, B.; Pelupessy, F. I.; Eckart, A.; Portegies Zwart, S.; Sabha, N.; Borkar, A.; Moultaka, J.; Mužić, K.; Moser, L.

    2014-05-01

    We aim at modeling small groups of young stars such as IRS 13N, 0.1 pc away from Sgr A*, which is suggested to contain a few embedded massive young stellar objects. We perform hydrodynamical simulations to follow the evolution of molecular clumps orbiting around a 4 × 106 M⊙ black hole, to constrain the formation and the physical conditions of such groups.

  10. Blue Stragglers in Clusters and Integrated Spectral Properties of Stellar Populations

    NASA Astrophysics Data System (ADS)

    Xin, Yu; Deng, Licai

    Blue straggler stars are the most prominent bright objects in the colour-magnitude diagram of a star cluster that challenges the theory of stellar evolution. Star clusters are the closest counterparts of the theoretical concept of simple stellar populations (SSPs) in the Universe. SSPs are widely used as the basic building blocks to interpret stellar contents in galaxies. The concept of an SSP is a group of coeval stars which follows a given distribution in mass, and has the same chemical property and age. In practice, SSPs are more conveniently made by the latest stellar evolutionary models of single stars. In reality, however, stars can be more complicated than just single either at birth time or during the course of evolution in a typical environment. Observations of star clusters show that there are always exotic objects which do not follow the predictions of standard theory of stellar evolution. Blue straggler stars (BSSs), as discussed intensively in this book both observationally and theoretically, are very important in our context when considering the integrated spectral properties of a cluster, or a simple stellar population. In this chapter, we are going to describe how important the contribution of BSSs is to the total light of a cluster.

  11. Radio Jets in Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Anglada, Guillem

    Radio continuum emission in the centimeter range has already been detected in association with a large number of the youngest stellar objects. This emission, dominated by a thermal free-free component, is in general weak, but sensitive interferometric observations at these wavelengths have become one of the most important tools to detect and study the objects (particularly those most deeply embedded) that are powering the outflows frequently found in the star forming regions. Observations carried out with high (subarcsecond) angular resolution reveal that these centimeter sources are tracing collimated ionized outflows, i.e. "thermal radio jets". These radio jets constitute, at present, the best evidence for collimated outflow at the smallest scale (~100 AU). For objects of low bolometric luminosity (for which no significant photoionization is expected), there is a correlation between the momentum rate in the large scale outflow and the centimeter continuum luminosity, as expected if the emission is originated in shock-ionized gas, produced when a stellar wind shocks against surrounding high density material. This result provides important evidence favoring a connection between small scale jets and molecular outflows.

  12. Study of transneptunian objects through stellar occultations

    NASA Astrophysics Data System (ADS)

    Benedetti-Rossi, G.; Sicardy, B.; Braga-Ribas, F.

    2014-07-01

    The physical parameters of the transneptunian objects (TNO's) such as size, shape, density, presence of atmosphere, provide important information on their formation and evolution. At more than 30 astronomical units (au) from the Sun, those objects receive low solar radiation and have low mutual collisions so they can be considered as remnants of the primordial outer Solar System. Besides that, information on TNO's is of great relevance when trying to establish a general formation scenario for the recently discovered planetary systems. The problem is that such bodies have a diameter smaller than 2300 km (Eris, one of the largest TNO, has 2326 km) and, when viewed from Earth, they subtend angles smaller than 50 milli-arcseconds, a fact that makes their resolution very poor with current imaging systems. One method to obtain very accurate information on the TNO's is the stellar-occultation technique. Sizes at kilometer accuracies and pressure at nanobar levels can be achieved with this method. Shape, mass, density and other physical parameters can also be derived using this technique. Since 2010, we observed stellar occultations of several TNO's (Varuna in 2010 and 2013; Eris in 2010; 2003 AZ_{84} in 2010 and 2011; Makemake in 2011; Quaoar in 2011 and two in 2012; 2002 KX_{14} in 2013; and finally Sedna in 2013) besides some other occultations of the Pluto system and of the largest Centaurs. We also predicted future events in 2014 and 2015 for the largest 40 TNO's and Centaurs. In this work, we will present new results obtained from recent stellar occultations of TNO's.

  13. Stellar Clusters Forming in the Blue Dwarf Galaxy NGC 5253

    NASA Astrophysics Data System (ADS)

    2004-11-01

    ; it is located at a distance of about 11 million light-years in the direction of the southern constellation Centaurus. Some time ago a group of European astronomers [1] decided to take a closer look at this object and to study star-forming processes in the primordial-like environment of this galaxy. True, NGC 5253 does contains some dust and heavier elements, but significantly less than our own Milky Way galaxy. However, it is quite extreme as a site of intense star formation, a profuse "starburst galaxy" in astronomical terminology, and a prime object for detailed studies of large-scale star formation. ESO PR Photo 31a/04 provides an impressive view of NGC 5253. This composite image is based on a near-infrared exposure obtained with the multi-mode ISAAC instrument mounted on the 8.2-m VLT Antu telescope at the ESO Paranal Observatory (Chile), as well as two images in the optical waveband obtained from the Hubble Space Telescope data archive (located at ESO Garching). The VLT image (in the K-band at wavelength 2.16 μm) is coded red, the HST images are blue (V-band at 0.55 μm) and green (I-band at 0.79 μm), respectively. The enormous light-gathering capability and the fine optical quality of the VLT made it possible to obtain the very detailed near-infrared image (cf. PR Photo 31b/04) during an exposure lasting only 5 min. The excellent atmospheric conditions of Paranal at the time of the observation (seeing 0.4 arcsec) allow the combination of space- and ground-based data into a colour photo of this interesting object. A major dust lane is visible at the western (right) side of the galaxy, but patches of dust are visible all over, together with a large number of colourful stars and stellar clusters. The different colour shades are indicative of the ages of the objects and the degree of obscuration by interstellar dust. The near-infrared VLT image penetrates the dust clouds much better than the optical HST images, and some deeply embedded objects that are not

  14. Spectral evolution of young stellar objects

    NASA Technical Reports Server (NTRS)

    Adams, Fred C.; Lada, Charles J.; Shu, Frank H.

    1987-01-01

    An evolutionary sequence, from protostars to pre-main sequence stars, for the classification of young stellar objects is derived by comparing the predictions of the theoretical protostar models of Adams and Shu (AS, 1986) with the morphological classification scheme of Lada and Wilking (1984). It is shown that the AS models adequately explain the emergent spectral energy distributions of unidentified objects with negative spectral indices in the mid-IR and near-IR in both Taurus and Ophiuchus. If the infalling dust envelope is then completely removed, the spectra of the underlying stars and nebular disks used by AS provide a natural explanation for the near-IR and mid-IR excesses and the positive spectral indices of embedded T Tauri stars. It is found that the addition of a simple physical model for residual dust envelopes can reproduce the far-IR excesses found in some of these T Tauri stars.

  15. Spectral evolution of young stellar objects

    NASA Technical Reports Server (NTRS)

    Adams, F. C.

    1986-01-01

    An evolutionary sequence, from protostars to pre-main-sequence stars, is suggested for the classification of young stellar objects. This sequence is derived by comparing the predictions of the theoretical models of Adams and Shu with the morphological classification scheme of Lada and Wilking. We first define the spectral index in the near- and mid-infrared, n is identical to d log(nu F sub nu)/d log nu, and then interpret the class of sources with negative spectral indices as protostars. The inferred mass infall rates for these objects are generally consistent with the measured gas temperatures of approx. 35 K in Ophiuchus, and of approx. 10 K in Taurus. Fitting the data requires us to adopt cloud rotation rates in Ophiuchus which are typically an order of magnitude greater than in Taurus, and we speculate on the mechanistic origin for this difference. Next, we consider a subclass of T Tauri stars with near- and mid-infrared excesses and positive or zero spectral indices. We find that the objects with the steeper indices can be understood as the post-infall products from the collapse of rotating cloud cores, where the infrared excesses arise from the simple reprocessing of visible stellar photons in optically thick but spatially thin disks. The sources with flatter spectra may require massive accretion disks. Given the existence of protostars and naked star/disk systems, there is a natural interpretation of another subclass of T Tauri stars, those with two peaks in their emergent spectral energy distributions. These are readily explained as intermediate cases in which dust envelopes still surround the stars and disks. Finally, we find that the theory can be extended to explain the spectral energy distribution of FU Orionis, a famous outburst source. Our model suggests that FU Orionis has a disk, but it offers no discrimination between the competing ideas that the outburst took place on the star or in the disk.

  16. The Gaseous Disks of Young Stellar Objects

    NASA Technical Reports Server (NTRS)

    Glassgold, A. E.

    2006-01-01

    Disks represent a crucial stage in the formation of stars and planets. They are novel astrophysical systems with attributes intermediate between the interstellar medium and stars. Their physical properties are inhomogeneous and are affected by hard stellar radiation and by dynamical evolution. Observing disk structure is difficult because of the small sizes, ranging from as little as 0.05 AU at the inner edge to 100-1000 AU at large radial distances. Nonetheless, substantial progress has been made by observing the radiation emitted by the dust from near infrared to mm wavelengths, i.e., the spectral energy distribution of an unresolved disk. Many fewer results are available for the gas, which is the main mass component of disks over much of their lifetime. The inner disk gas of young stellar objects (henceforth YSOs) have been studied using the near infrared rovibrational transitions of CO and a few other molecules, while the outer regions have been explored with the mm and sub-mm lines of CO and other species. Further progress can be expected in understanding the physical properties of disks from observations with sub-mm arrays like SMA, CARMA and ALMA, with mid infrared measurements using Spitzer, and near infrared spectroscopy with large ground-based telescopes. Intense efforts are also being made to model the observations using complex thermal-chemical models. After a brief review of the existing observations and modeling results, some of the weaknesses of the models will be discussed, including the absence of good laboratory and theoretical calculations for essential microscopic processes.

  17. Young stellar objects and their environment

    NASA Astrophysics Data System (ADS)

    Choudhury, Rumpa

    This paper presents the results of a Ph.D thesis emphasizing the studies of various characteristics of Young Stellar Objects (YSOs) and their environment. The main objective of the thesis is to study the effects of mechanical and radiative feedback of massive stars on their surroundings including triggered star formation in Cometary Globules (CGs) and Bright-Rimmed Clouds (BRCs) situated at the borders of Galactic HII regions and time dependent interaction of Pre-Main Sequence (PMS) stars with their circumstellar environment through accretion and outflow processes. Some of the important results of this thesis are (i) star formation in BRC SFO~38 is triggered by massive OB type stars in HII region IC 1396 (ii) distribution of CGs at the border of HII region Gum Nebula is shaped by photoevaporation powered by UV radiation of massive stars in Vela OB2 association (iii) interaction of Herbig Ae star V351 Ori with its circumstellar environment is time-dependent and episodic in nature. Dynamic magnetospheric accretion and disk wind emerge as the most satisfactory model for interpreting the observed line profile variations of V351 Ori. The full version of the thesis is available from the Indian Institute of Astrophysics Repository webpage: http://prints.iiap.res.in/handle/2248/5529

  18. Stellar Collisions and the Interior Structure of Blue Stragglers

    NASA Astrophysics Data System (ADS)

    Lombardi, James C., Jr.; Warren, Jessica S.; Rasio, Frederic A.; Sills, Alison; Warren, Aaron R.

    2002-04-01

    Collisions of main-sequence stars occur frequently in dense star clusters. In open and globular clusters, these collisions produce merger remnants that may be observed as blue stragglers. Detailed theoretical models of this process require lengthy hydrodynamic computations in three dimensions. However, a less computationally expensive approach, which we present here, is to approximate the merger process (including shock heating, hydrodynamic mixing, mass ejection, and angular momentum transfer) with simple algorithms based on conservation laws and a basic qualitative understanding of the hydrodynamics. These algorithms have been fine-tuned through comparisons with the results of our previous hydrodynamic simulations. We find that the thermodynamic and chemical composition profiles of our simple models agree very well with those from recent SPH (smoothed particle hydrodynamics) calculations of stellar collisions, and the subsequent stellar evolution of our simple models also matches closely that of the more accurate hydrodynamic models. Our algorithms have been implemented in an easy-to-use software package, which we are making publicly available.4 This software could be used in combination with realistic dynamical simulations of star clusters that must take into account stellar collisions.

  19. YOUNG STELLAR OBJECTS IN THE GOULD BELT

    SciTech Connect

    Dunham, Michael M.; Allen, Lori E.; Evans II, Neal J.; Harvey, Paul M.; Broekhoven-Fiene, Hannah; Cieza, Lucas A.; Di Francesco, James; Johnstone, Doug; Matthews, Brenda C.; Gutermuth, Robert A.; Hatchell, Jennifer; Heiderman, Amanda; Huard, Tracy L.; Kirk, Jason M.; Miller, Jennifer F.; Peterson, Dawn E.; Young, Kaisa E.

    2015-09-15

    We present the full catalog of Young Stellar Objects (YSOs) identified in the 18 molecular clouds surveyed by the Spitzer Space Telescope “cores to disks” (c2d) and “Gould Belt” (GB) Legacy surveys. Using standard techniques developed by the c2d project, we identify 3239 candidate YSOs in the 18 clouds, 2966 of which survive visual inspection and form our final catalog of YSOs in the GB. We compile extinction corrected spectral energy distributions for all 2966 YSOs and calculate and tabulate the infrared spectral index, bolometric luminosity, and bolometric temperature for each object. We find that 326 (11%), 210 (7%), 1248 (42%), and 1182 (40%) are classified as Class 0 + I, Flat-spectrum, Class II, and Class III, respectively, and show that the Class III sample suffers from an overall contamination rate by background Asymptotic Giant Branch stars between 25% and 90%. Adopting standard assumptions, we derive durations of 0.40–0.78 Myr for Class 0 + I YSOs and 0.26–0.50 Myr for Flat-spectrum YSOs, where the ranges encompass uncertainties in the adopted assumptions. Including information from (sub)millimeter wavelengths, one-third of the Class 0 + I sample is classified as Class 0, leading to durations of 0.13–0.26 Myr (Class 0) and 0.27–0.52 Myr (Class I). We revisit infrared color–color diagrams used in the literature to classify YSOs and propose minor revisions to classification boundaries in these diagrams. Finally, we show that the bolometric temperature is a poor discriminator between Class II and Class III YSOs.

  20. Outflow Collimation in Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Noriega-Crespo, A.; Frank, A.

    1993-05-01

    Recent results of long-slit spectroscopy of the forbidden lines of the outflow in the young star DG Tau [7] suggest that its wind is well collimated very close to it, leading to the formation of its jet. The analysis of the width of stellar jets, on the other hand, seems to indicate that the collimation of the jets takes place at larger scales [5]. In other to understand this discrepancy, we are studying by means of a two dimensional hydrodynamical code [1][3], the collimation driven by the interaction of the stellar wind with the surrounding density structure left by the star formation process [8][9]. We have found in our adiabatic outflow simulations (using physical parameters similar to those for the HH 34 bipolar stellar jet [2]) that a spherical wind is well collimated near the source resembling a de Laval Nozzle [4][6]. ANC research is supported by NSF grant AST-91-14888. \\ References [1] Frank, A. 1992, PhD Thesis, University of Washington. [2] Heathcote, S. & Reipurth, B. 1992, AJ 104, 2193. [3] Icke, V., 1988 A&A 202, 177. [4] Konigl, A. 1982, ApJ 261, 115. [5] Mundt, R., Ray, T.P., & Raga, A.C. 1991, A&A 252, 740. [6] Raga A.C., & Canto, J. 1989, ApJ 344, 404. [7] Solf, J., & Bohm, K.H. 1993, ApJL (in press). [8] Terebey, S., Shu, F.H., & Cassen, P. 1984, ApJ 286, 529. [9] Yorke, H.W., Bodenheimer, P., & Laughlin, G. 1993, ApJ (in press).

  1. Detection of Small Kuiper Belt Objects by Stellar Occultation

    NASA Astrophysics Data System (ADS)

    Georgevits, George

    2006-09-01

    We present here the results for the first attempt to survey the sub-kilometre radius KBO population by stellar occultation. Using the unique capabilities of the 1.2m UK Schmidt Telescope (Anglo Australian Observatory, Australia), in conjunction with the 6df Spectrograph, by simultaneously monitoring 100 suitably selected stars, we were able to embark upon an occultation observation program which yielded 7,000 hours of stellar light curves, with 10 millisecond resolution. Initial data reduction indicates that we have captured many events which resemble occultation events, in so far as the light curves of recorded events typically match that which may be expected when a small KBO occults a distant star. Logged events are spread over many pixels, with 10 pixels (corresponding to 100 milliseconds) being the typical event duration. By simultaneously monitoring many stars in the same field, false events are eliminated. Most runs monitored blue stars located at 2kpcs. As a sanity check, one night's observing monitored close F and G class stars in the same field. The event statistics for the distant and the close star cases are consistent with occultations caused by KBO's. As an additional confirmation, it was found that the observation results at 30o and 60o past opposition give the expected 50% fall in event rate due to the change in observing geometry. It is estimated that many of the events logged correspond to occultations which would be caused by objects down to 300m radius. As the next step, it is hoped to construct a purpose-built 2,000 fibre instrument and to conduct a complete survey of the Kuiper Belt. We wish to express our thanks to the Anglo Australian Observatory for their technical assistance and telescope time.

  2. Young Stellar Objects from Soft to Hard X-rays

    NASA Astrophysics Data System (ADS)

    Güdel, Manuel

    2009-05-01

    Magnetically active stars are the sites of efficient particle acceleration and plasma heating, processes that have been studied in detail in the solar corona. Investigation of such processes in young stellar objects is much more challenging due to various absorption processes. There is, however, evidence for violent magnetic energy release in very young stellar objects. The impact on young stellar environments (e.g., circumstellar disk heating and ionization, operation of chemical networks, photoevaporation) may be substantial. Hard X-ray devices like those carried on Simbol-X will establish a basis for detailed studies of these processes.

  3. STELLAR COLLISIONS AND BLUE STRAGGLER STARS IN DENSE GLOBULAR CLUSTERS

    SciTech Connect

    Chatterjee, Sourav; Rasio, Frederic A.; Sills, Alison; Glebbeek, Evert

    2013-11-10

    Blue straggler stars (BSSs) are abundantly observed in all Galactic globular clusters (GGCs) where data exist. However, observations alone cannot reveal the relative importance of various formation channels or the typical formation times for this well-studied population of anomalous stars. Using a state-of-the-art Hénon-type Monte Carlo code that includes all relevant physical processes, we create 128 models with properties typical of the observed GGCs. These models include realistic numbers of single and binary stars, use observationally motivated initial conditions, and span large ranges in central density, concentration, binary fraction, and mass. Their properties can be directly compared with those of observed GGCs. We can easily identify the BSSs in our models and determine their formation channels and birth times. We find that for central densities above ∼10{sup 3} M{sub ☉} pc{sup –3}, the dominant formation channel is stellar collisions, while for lower density clusters, mass transfer in binaries provides a significant contribution (up to 60% in our models). The majority of these collisions are binary-mediated, occurring during three-body and four-body interactions. As a result, a strong correlation between the specific frequency of BSSs and the binary fraction in a cluster can be seen in our models. We find that the number of BSSs in the core shows only a weak correlation with the collision rate estimator Γ traditionally used by observers, in agreement with the latest Hubble Space Telescope Advanced Camera for Surveys data. Using an idealized 'full mixing' prescription for collision products, our models indicate that the BSSs observed today may have formed several Gyr ago. However, denser clusters tend to have younger (∼1 Gyr) BSSs.

  4. Stellar Collisions and Blue Straggler Stars in Dense Globular Clusters

    NASA Astrophysics Data System (ADS)

    Chatterjee, Sourav; Rasio, Frederic A.; Sills, Alison; Glebbeek, Evert

    2013-11-01

    Blue straggler stars (BSSs) are abundantly observed in all Galactic globular clusters (GGCs) where data exist. However, observations alone cannot reveal the relative importance of various formation channels or the typical formation times for this well-studied population of anomalous stars. Using a state-of-the-art Hénon-type Monte Carlo code that includes all relevant physical processes, we create 128 models with properties typical of the observed GGCs. These models include realistic numbers of single and binary stars, use observationally motivated initial conditions, and span large ranges in central density, concentration, binary fraction, and mass. Their properties can be directly compared with those of observed GGCs. We can easily identify the BSSs in our models and determine their formation channels and birth times. We find that for central densities above ~103 M ⊙ pc-3, the dominant formation channel is stellar collisions, while for lower density clusters, mass transfer in binaries provides a significant contribution (up to 60% in our models). The majority of these collisions are binary-mediated, occurring during three-body and four-body interactions. As a result, a strong correlation between the specific frequency of BSSs and the binary fraction in a cluster can be seen in our models. We find that the number of BSSs in the core shows only a weak correlation with the collision rate estimator Γ traditionally used by observers, in agreement with the latest Hubble Space Telescope Advanced Camera for Surveys data. Using an idealized "full mixing" prescription for collision products, our models indicate that the BSSs observed today may have formed several Gyr ago. However, denser clusters tend to have younger (~1 Gyr) BSSs.

  5. Star-forming galaxies in intermediate-redshift clusters: stellar versus dynamical masses of luminous compact blue galaxies

    NASA Astrophysics Data System (ADS)

    Randriamampandry, S. M.; Crawford, S. M.; Bershady, M. A.; Wirth, G. D.; Cress, C. M.

    2017-10-01

    We investigate the stellar masses of the class of star-forming objects known as luminous compact blue galaxies (LCBGs) by studying a sample of galaxies in the distant cluster MS 0451.6-0305 at z ≈ 0.54 with ground-based multicolour imaging and spectroscopy. For a sample of 16 spectroscopically confirmed cluster LCBGs (colour B - V < 0.5, surface brightness μB < 21 mag arcsec-2 and magnitude MB < -18.5), we measure stellar masses by fitting spectral energy distribution (SED) models to multiband photometry, and compare with dynamical masses [determined from velocity dispersion in the range 10 < σv(km s- 1) < 80] we previously obtained from their emission-line spectra. We compare two different stellar population models that measure stellar mass in star-bursting galaxies, indicating correlations between the stellar age, extinction and stellar mass derived from the two different SED models. The stellar masses of cluster LCBGs are distributed similarly to those of field LCBGs, but the cluster LCBGs show lower dynamical-to-stellar mass ratios (Mdyn/M⋆ = 2.6) than their field LCBG counterparts (Mdyn/M⋆ = 4.8), echoing trends noted previously in low-redshift dwarf elliptical galaxies. Within this limited sample, the specific star formation rate declines steeply with increasing mass, suggesting that these cluster LCBGs have undergone vigorous star formation.

  6. Stellar science from a blue wavelength range. A possible design for the blue arm of 4MOST

    NASA Astrophysics Data System (ADS)

    Hansen, C. J.; Ludwig, H.-G.; Seifert, W.; Koch, A.; Xu, W.; Caffau, E.; Christlieb, N.; Korn, A. J.; Lind, K.; Sbordone, L.; Ruchti, G.; Feltzing, S.; de Jong, R. S.; Barden, S.

    2015-09-01

    From stellar spectra, a variety of physical properties of stars can be derived. In particular, the chemical composition of stellar atmospheres can be inferred from absorption line analyses. These provide key information on large scales, such as the formation of our Galaxy, down to the small-scale nucleosynthesis processes that take place in stars and supernovae. By extending the observed wavelength range toward bluer wavelengths, we optimize such studies to also include critical absorption lines in metal-poor stars, and allow for studies of heavy elements (Z\\ensuremath{g}e 38) whose formation processes remain poorly constrained. In this context, spectrographs optimized for observing blue wavelength ranges are essential, since many absorption lines at redder wavelengths are too weak to be detected in metal-poor stars. This means that some elements cannot be studied in the visual-redder regions, and important scientific tracers and science cases are lost. The present era of large public surveys will target millions of stars. It is therefore important that the next generation of spectrographs are designed such that they cover a wide wavelength range and can observe a large number of stars simultaneously. Only then, we can gain the full information from stellar spectra, from both metal-poor to metal-rich ones, that will allow us to understand the aforementioned formation scenarios in greater detail. Here we describe the requirements driving the design of the forthcoming survey instrument 4MOST, a multi-object spectrograph commissioned for the ESO VISTA 4 m-telescope. While 4MOST is also intended for studies of active galactic nuclei, baryonic acoustic oscillations, weak lensing, cosmological constants, supernovae and other transients, we focus here on high-density, wide-area survey of stars and the science that can be achieved with high-resolution stellar spectroscopy. Scientific and technical requirements that governed the design are described along with a thorough

  7. Young Stellar Objects in NGC 6334

    NASA Astrophysics Data System (ADS)

    Rathborne, Jill; Burton, Michael

    NGC 6334 is a young star forming complex with at least seven distinct sites of ongoing star formation located along a central molecular ridge. These sites range in evolutionary stage and have associated with them many tracers of active star formation including 1-mm peaks far- and near-IR sources CO hot spots molecular outflows H20 OH and methanol maser emission. We obtained L-band observations across the central molecular ridge using the SPIREX/Abu system at the Amundsen-Scott South Pole Station. These data combined with near-IR data from 2MASS reveal the existance of many sources displaying an L-band excess in (J-H) v (K-L) colour-colour diagrams. An excess of emission in the L-band is indicative of the presence of a circumstellar disk the detection of which is greatly facilitated by inclusion of the L-band data. Approximately 18 sources are selected as Class I objects with many more objects likely to also be candidates once optical extinction is accurately determined and removed. The majority of these objects correspond to high-mass stars (A--O type) and represent an ideal list of sources in which to study further (e.g. interferometric mm observations) to gain a better understanding of the nature and role of disks in high-mass star formation.

  8. Young Stellar Objects in the Orion B Cloud

    NASA Astrophysics Data System (ADS)

    Petr-Gotzens, M. G.; Alcalá, J. M.; Spezzi, L.; Jørgensen, J. K.; Stanke, Th.; Lombardi, M.; Alves, J. F.

    2015-12-01

    Wide-field near-infrared imaging surveys offer an excellent opportunity to obtain spatially complete samples of young stars in nearby star-forming regions. By studying their spatial distribution and individual properties, the global star formation characteristics of a region can be established. Near-infrared wide-field imaging observations of a significantly large area in the Orion Molecular Cloud B, obtained with the VISTA telescope on Cerro Paranal are presented. On the basis of photometric selection criteria, we have identified 186 candidate young stellar objects that are associated with the stellar clusters NGC 2068 and NGC 2071, and with the stellar group around HH24-26. Overall, Orion B shows a lot of similarities in its star formation characteristics with other Galactic star-forming regions: a star formation efficiency of a few percent, a stellar mass distribution very similar to that of the Orion Trapezium cluster, and a high observed fraction of circumstellar discs.

  9. Quasi-stellar objects: possible local origin.

    PubMed

    Terrell, J

    1966-12-09

    Many difficulties face the conventional interpretation of the red shift of quasars as a Hubble shift, with associated immense distances. These objects are not of galactic size or nature, and are not associated with galaxies or clusters of galaxies. The continuing energy source for such enormous powers for a period of 10(6) to 10(7) years has not been clearly revealed. The absence of the expected absorption for the Lyman-alpha spectral line of hydrogen is a new difficulty. Because of the relativistic limit on the diameter which can produce rapid fluctuations of light output, there may not be enough surface to radiate the required light.A similar and perhaps more serious difficulty exists for the fluctuating radio output. Calculations given here for synchrotron radiation self-absorption lead to a reasonably accurate formula for the angular diameter of a radio source. For the quasar 3C 273B these relations indicate a conflict with the usually assumed distance. However, the discrepancy may be explained in terms of strong variation of radio diameter with frequency. For CTA 102 the conflict is more serious, and could be explained -for cosmological distance-only by rejecting the data of Sholomitskii. These difficulties are removed by the hypothesis that the observed quasars were ejected from a gravitational collapse at the center of our own galaxy, which may have occurred roughly 5 million years ago. The resultant distances, of the order of a million lightyears, reduce the energy problem by a factor of 10(6) or 10(7). On this basis the optical diameter would be less than a light-hour, about the size of the earth's orbit. A rotating mass of a few thousand solar masses with this diameter would account for the unusual line width, could easily produce the required radiated energy, and could readily account for observed short fluctuation periods and variations in spectrum. It is suggested that the radio output may be produced by high-speed passage of the quasar through

  10. Chemical evolution of circumstellar matter around young stellar objects.

    PubMed

    van Dishoeck, E F; Blake, G A

    1995-01-01

    Recent observational studies of the chemical composition of circumstellar matter around both high- and low-mass young stellar objects are reviewed. The molecular abundances are found to be a strong function of evolutionary state, but not of system mass or luminosity. The data are discussed with reference to recent theoretical models.

  11. The WISE Census of Young Stellar Objects in Canis Major

    NASA Astrophysics Data System (ADS)

    Fischer, W. J.; Padgett, D. L.; Stapelfeldt, K. R.

    2016-01-01

    While searches for young stellar objects (YSOs) with the Spitzer Space Telescope focused on known molecular clouds, photometry from the Wide-field Infrared Survey Explorer (WISE) can be used to extend the search to the entire sky. As a precursor to more expansive searches, we present results for a 100 deg2 region centered on the Canis Major clouds.

  12. Theoretical studies of the outer envelopes of young stellar objects

    NASA Technical Reports Server (NTRS)

    Hartmann, Lee

    1992-01-01

    With the Monte Carlo code developed by Whitney and Hartmann, a series of models was computed of scattering in disks around young stellar objects. The code calculates scattering by dust, including polarization, in arbitrary geometries. By computing model images, it was found that disk, by themselves, around young stellar objects would be very difficult to detect with present day imaging techniques. In comparing these images to observations of young stellar objects which show diffuse structure, little resemblance was found. A flared disk system will only give high polarization when viewed edge-on, and the position angle is always oriented perpendicular to the disk plane. This suggests that an envelope, perhaps the remnant infalling envelope, must be present to scatter more stellar light than a disk can, and obscure the star at many inclinations. A grid was computed of models of scattering in a disk+envelope system. Evidence is presented that the wind of the pre-main sequence object FU Orionis arises from the surface of the luminous prostellar accretion disk. A disk wind model calculated assuming radiative equilibrium explains the differential behavior of the observed asymmetrical absorption line profiles. The model predicts that strong lines should be asymmetric and blueshifted, while weak lines should be symmetric and doubled peaked due to disk rotation, in agreement with observations.

  13. Gravitational effects of condensate dark matter on compact stellar objects

    SciTech Connect

    Li, X.Y.; Wang, F.Y.; Cheng, K.S. E-mail: fayinwang@gmail.com

    2012-10-01

    We study the gravitational effect of non-self-annihilating dark matter on compact stellar objects. The self-interaction of condensate dark matter can give high accretion rate of dark matter onto stars. Phase transition to condensation state takes place when the dark matter density exceeds the critical value. A compact degenerate dark matter core is developed and alter the structure and stability of the stellar objects. Condensate dark matter admixed neutron stars is studied through the two-fluid TOV equation. The existence of condensate dark matter deforms the mass-radius relation of neutron stars and lower their maximum baryonic masses and radii. The possible effects on the Gamma-ray Burst rate in high redshift are discussed.

  14. Model atmospheres of sub-stellar mass objects

    NASA Astrophysics Data System (ADS)

    Hubeny, Ivan

    2017-07-01

    We present an outline of basic assumptions and governing structural equations describing atmospheres of sub-stellar mass objects, in particular the extrasolar giant planets and brown dwarfs. Although most of the presentation of the physical and numerical background is generic, details of the implementation pertain mostly to the code cooltlusty. We also present a review of numerical approaches and computer codes devised to solve the structural equations, and make a critical evaluation of their efficiency and accuracy.

  15. The WISE Census of Young Stellar Objects in Canis Major

    NASA Astrophysics Data System (ADS)

    Fischer, William J.; Padgett, Deborah; Stapelfeldt, Karl

    2015-08-01

    While Spitzer enabled the efficent discovery of thousands of young stellar objects within 1 kpc of the Sun, it focused on known molecular clouds. With WISE, color and magnitude criteria similar to those used in Spitzer studies can identify YSOs in largely unexplored regions. Newly identified YSOs may refine the initial stellar mass function, allow a better characterization of star and planet formation in regions with low initial gas densities, and identify nearby targets for high-resolution follow-up imaging. As a precursor to more expansive searches, we present results for a 100 square degree region centered on the relatively unexplored Canis Major clouds. Our preliminary catalog contains 114 Class I YSOs and 242 Class II YSOs that are mostly concentrated at the sites of known 13CO clouds. We will discuss several newly discovered clusters that are dominated by Class I protostars and explore the ability of WISE to identify even younger Class 0 protostars.

  16. INTERMEDIATE-AGE STELLAR POPULATIONS IN CLASSICAL QUASI-STELLAR OBJECT HOST GALAXIES

    SciTech Connect

    Canalizo, Gabriela; Stockton, Alan E-mail: stockton@ifa.hawaii.edu

    2013-08-01

    Although mergers and starbursts are often invoked in the discussion of quasi-stellar object (QSO) activity in the context of galaxy evolution, several studies have questioned their importance or even their presence in QSO host galaxies. Accordingly, we are conducting a study of z {approx} 0.2 QSO host galaxies previously classified as passively evolving elliptical galaxies. We present deep Keck/LRIS spectroscopy of a sample of 15 hosts and model their stellar absorption spectra using stellar synthesis models. The high signal-to-noise ratio of our spectra allows us to break various degeneracies that arise from different combinations of models, varying metallicities, and contamination from QSO light. We find that none of the host spectra can be modeled by purely old stellar populations and that the majority of the hosts (14/15) have a substantial contribution from intermediate-age populations with ages ranging from 0.7 to 2.4 Gyr. An average host spectrum is strikingly well fit by a combination of an old population and a 2.1 (+0.5, -0.7) Gyr population. The morphologies of the host galaxies suggest that these aging starbursts were induced during the early stages of the mergers that resulted in the elliptical-shaped galaxies that we observe. The current active galactic nucleus activity likely corresponds to the late episodes of accretion predicted by numerical simulations, which occur near the end of the mergers, whereas earlier episodes may be more difficult to observe due to obscuration. Our off-axis observations prevent us from detecting any current star formation or young stellar populations that may be present in the central few kiloparsecs.

  17. Stellar Occultations by Trans-Neptunian Objects and Centaurs

    NASA Astrophysics Data System (ADS)

    Wolf, Juergen

    2015-10-01

    Our solar system beyond Neptune's orbit is populated with numerous small objects, referred to as Trans-Neptunian Objects (TNOs). About 1400 TNOs are known today ranging in size from the most prominent one, Pluto (2370 km diameter), down to a few tens of kilometers. Most diameters have been determined by radiometric methods in the IR/FIR (SPITZER, HERSCHEL) with uncertainties in the 20% range. Only for Pluto and about 12 other objects have the projected diameters been measured more accurately by stellar occultations. A group of objects lingering between the orbits of Jupiter and Neptune, the Centaurs, are believed to have originated from TNOs. Two of them, Chariklo and Chiron, have recently drawn attention, as stellar occultations have revealed rings around them. Our proposed occultation observations with SOFIA shall add to the sparse knowledge on TNOs and Centaurs by determining more projected diameters and albedos. They have the potential of detecting moons, rings and atmospheres. We will use SOFIA's demonstrated capability of measuring occultations (Pluto 2011 & 2015) with its Focal Plane Imager (FPI) to observe up to five events on flight legs of approximately 30 min each. As most of these events cannot be predicted accurately enough more than a few months or weeks ahead of time, we propose these as targets of opportunity.

  18. Exploring the association of Fermi sources with Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Munar-Adrover, P.; Paredes, J. M.; Romero, G. E.

    2011-02-01

    Massive protostars have associated bipolar outflows which can produce strong shocks when interact with the surrounding medium. Some theoretical models predict that particle acceleration at relativistic velocities can occur leading to gamma ray emission. In order to identify young stellar objects (YSO) that might emit gamma rays, we have crossed the Fermi First Year Catalog with catalogs of known YSOs, obtaining a set of candidates by spatial correlation. We have conducted Montecarlo simulations to find the probability of chance coincidence. Our results indicate that ~70% of the candidates should be gamma-ray sources with a confidence of ~5σ.

  19. Search for Exoplanets around Young Stellar Objects by Direct Imaging

    NASA Astrophysics Data System (ADS)

    Uyama, Taichi; Tamura, Motohide; Hashimoto, Jun; Kuzuhara, Masayuki

    2015-12-01

    SEEDS project, exploring exoplanets and protoplanetary disks with Subaru/HiCIAO, has observed about 500 stars by Direct Imaging from 2009 Dec to 2015 Apr. Among these targets we explore around Young Stellar Objects (YSOs; age ≦ 10Myr) which often have the protoplanetary disks where planets are being formed in order to detect young exoplanets and to understand the formation process. We analyzed 66 YSOs (about 100 data in total) with LOCI data reduction. We will report the results (companion candidates and detection limit) of our exploration.

  20. Ultracompact Blue Dwarf Galaxies: Hubble Space Telescope Imaging and Stellar Population Analysis

    NASA Astrophysics Data System (ADS)

    Corbin, Michael R.; Vacca, William D.; Cid Fernandes, Roberto; Hibbard, John E.; Somerville, Rachel S.; Windhorst, Rogier A.

    2006-11-01

    We present deep Hubble Space Telescope (HST) Advanced Camera for Surveys/High Resolution Channel U-, narrow-V-, and I-band images of nine ``ultracompact'' blue dwarf galaxies (UCBDs) selected from the Sloan Digital Sky Survey (SDSS). We define UCBDs as local (z<0.01) star-forming galaxies having angular diameters less than 6" and physical diameters <1 kpc. They are also among the most metal-poor galaxies known, including objects having 12+log(O/H)<7.65, and are found to reside within voids. Both the HST images and the objects' SDSS optical spectra reveal that they are composites of young (~1-10 Myr) populations that dominate their light and older (~10 Gyr) populations that dominate their stellar masses, which we estimate to be ~107-108 Msolar. An intermediate-age (~107-109 yr) population is also indicated in most objects. The objects do not appear to be as dynamically disturbed as the prototype UCBD, POX 186, but the structure of several of them suggests that their current star formation has been triggered by the collisions/mergers of smaller clumps of stars. In one case, HS 0822+3542, the images resolve what may be two small (~100 pc) components that have recently collided, supporting this interpretation. In six of the objects much of the star formation is concentrated in young massive clusters, contributing to their compactness in ground-based images. The evidence that the galaxies consist mainly of ~10 Gyr old stars establishes that they are not protogalaxies, forming their first generation of stars. Their low metallicities are more likely to be the result of the escape of supernova ejecta, rather than youth.

  1. Magnetic confinement of the optical jets in young stellar objects

    NASA Astrophysics Data System (ADS)

    Choe, S.-U.; Jones, T. W.

    1993-03-01

    We discuss a model for collimating plasma outflow from a young stellar object via an axial current initiated by collisionally charged dust grains incorporated in the ionized outflow from the central object. The charged grains generate an electric current in response to their greater reaction to the radiation field of the central star and their large mobility with respect to the plasma. This produces a pinching toroidal magnetic field of about 0.001 G in the base flow. A simple self-similar, steady state MHD solution shows that a well-collimated jet can result, provided this pinch is only marginally overbalanced there by the gas pressure and centrifugal acceleration associated with any rotation of the jet.

  2. Constraining the Stellar Populations and Star Formation Histories of Blue Compact Dwarf Galaxies with SED Fits

    NASA Astrophysics Data System (ADS)

    Janowiecki, Steven; Salzer, John J.; van Zee, Liese; Rosenberg, Jessica L.; Skillman, Evan

    2017-02-01

    We discuss and test possible evolutionary connections between blue compact dwarf galaxies (BCDs) and other types of dwarf galaxies. BCDs provide ideal laboratories to study intense star formation episodes in low-mass dwarf galaxies, and have sometimes been considered a short-lived evolutionary stage between types of dwarf galaxies. To test these connections, we consider a sample of BCDs as well as a comparison sample of nearby galaxies from the Local Volume Legacy (LVL) survey for context. We fit the multi-wavelength spectral energy distributions (SED, far-ultra-violet to far-infrared) of each galaxy with a grid of theoretical models to determine their stellar masses and star formation properties. We compare our results for BCDs with the LVL galaxies to put BCDs in the context of normal galaxy evolution. The SED fits demonstrate that the star formation events currently underway in BCDs are at the extreme of the continuum of normal dwarf galaxies, both in terms of the relative mass involved and in the relative increase over previous star formation rates. Today’s BCDs are distinctive objects in a state of extreme star formation that is rapidly transforming them. This study also suggests ways to identify former BCDs whose star formation episodes have since faded.

  3. ClassLess: A Comprehensive Database of Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Hillenbrand, Lynne A.; baliber, nairn

    2015-08-01

    We have designed and constructed a database intended to house catalog and literature-published measurements of Young Stellar Objects (YSOs) within ~1 kpc of the Sun. ClassLess, so called because it includes YSOs in all stages of evolution, is a relational database in which user interaction is conducted via HTML web browsers, queries are performed in scientific language, and all data are linked to the sources of publication. Each star is associated with a cluster (or clusters), and both spatially resolved and unresolved measurements are stored, allowing proper use of data from multiple star systems. With this fully searchable tool, myriad ground- and space-based instruments and surveys across wavelength regimes can be exploited. In addition to primary measurements, the database self consistently calculates and serves higher level data products such as extinction, luminosity, and mass. As a result, searches for young stars with specific physical characteristics can be completed with just a few mouse clicks. We are in the database population phase now, and are eager to engage with interested experts worldwide on local galactic star formation and young stellar populations.

  4. Explaining Multi-wavelength Photometric Variability in Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Kesseli, Aurora; Whitney, B.; Wood, K.; Plavchan, P.; Terebey, S.; Stauffer, J. R.; Morales-Calderon, M.; YSOVAR

    2013-01-01

    We explore a variety of radiation transfer models to explain multi-wavelength photometric variability of young stellar objects in the Orion Nebula Cluster (Morales-Calderon et al. (2011). Our models include hotspots, warps in the accretion disk, and spiral arms. Variability comes in different types, which have been categorized as periodic or quasi-periodic, narrow or broad dips in the light curves, and rapid flux variations or “wild type” stars. Our models can successfully reproduce these. The optical and near-infrared light curves are sensitive to the stellar variations and obscurations from the circumstellar material. The mid-infrared provides an additional diagnostic because it is sensitive to emission from the inner disk and the inner wall height. Our models make specific predictions as to the shapes and phasing of optical through mid-infrared photometry that can be tested with multi-wavelength time-series data. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. Support for this work was provided by NASA through an award issued by JPL/Caltech and was partially supported by the National Science Foundation's REU program through NSF Award AST-1004881.

  5. MID-INFRARED SPECTRAL VARIABILITY ATLAS OF YOUNG STELLAR OBJECTS

    SciTech Connect

    Kospal, A.; Abraham, P.; Kun, M.; Moor, A.; Acosta-Pulido, J. A.; Henning, Th.; Leinert, Ch.; Turner, N. J.

    2012-08-01

    Optical and near-infrared variability is a well-known property of young stellar objects. However, a growing number of recent studies claim that a considerable fraction of them also exhibit mid-infrared flux changes. With the aim of studying and interpreting variability on a decadal timescale, here we present a mid-infrared spectral atlas containing observations of 68 low- and intermediate-mass young stellar objects. The atlas consists of 2.5-11.6 {mu}m low-resolution spectra obtained with the ISOPHOT-S instrument on board the Infrared Space Observatory (ISO) between 1996 and 1998, as well as 5.2-14.5 {mu}m low-resolution spectra obtained with the Infrared Spectrograph instrument on board the Spitzer Space Telescope between 2004 and 2007. The observations were retrieved from the ISO and Spitzer archives and were post-processed interactively by our own routines. For those 47 objects where multi-epoch spectra were available, we analyze mid-infrared spectral variability on annual and/or decadal timescales. We identify 37 variable candidate sources. Many stars show wavelength-independent flux changes, possibly due to variable accretion rates. In several systems, all exhibiting 10 {mu}m silicate emission, the variability of the 6-8 {mu}m continuum, and the silicate feature exhibit different amplitudes. A possible explanation is variable shadowing of the silicate-emitting region by an inner disk structure of changing height or extra silicate emission from dust clouds in the disk atmosphere. Our results suggest that mid-infrared variability, in particular, the wavelength-dependent changes, is more ubiquitous than was known before. Interpreting this variability is a new possibility for exploring the structure of the disk and its dynamical processes.

  6. Young Stellar Objects in Lynds 1641: Disks and Accretion

    NASA Astrophysics Data System (ADS)

    Fang, Min; Kim, Jinyoung Serena; van Boekel, Roy; Sicilia-Aguilar, Aurora; Henning, Thomas; Flaherty, Kevin

    2013-07-01

    We investigate the young stellar objects (YSOs) in the Lynds 1641 (L1641) cloud using multi-wavelength data including Spitzer, WISE, 2MASS, and XMM covering 1390 YSOs across a range of evolutionary stages. In addition, we targeted a sub-sample of YSOs for optical spectroscopy with the MMT/Hectospec and the MMT/Hectochelle. We use this data, along with archival photometric data, to derive spectral types, masses, ages and extinction values. We also use the H_alpha and H_beta lines to derive accretion rates. We calculate the disk fraction as N(II)/N(II+III), where N(II) and N(III) are numbers of Class\\ II and Class\\ III sources, respectively, and obtain a disk fraction of 50% in L1641. We find that the disk frequency is almost constant as a function of stellar mass with a slight peak at log(M_*/M_sun) -0.25. The analysis of multi-epoch data indicates that the accretion variability of YSOs cannot explain the two orders of magnitude of scatter for YSOs with similar masses in the M_acc vs. M_* plot. Forty-six new transition disk objects are confirmed in our spectroscopic survey and we find that the fraction of transition disks that are actively accreting is lower than for optically thick disks (40-45% vs. 77-79% respectively). We confirm our previous result that the accreting YSOs with transition disks have a similar median accretion rate to normal optically thick disks. Analyzing the age distributions of various populations, we find that the diskless YSOs are statistically older than the YSOs with optically-thick disks and the transition disk objects have a median age which is intermediate between the two populations.

  7. Possible Young Stellar Objects without Detectable CO Emission

    NASA Astrophysics Data System (ADS)

    Iwata, I.; Saitō , M.

    1999-12-01

    We discovered about 20 possible Young Stellar Objects (YSOs) which are invisible both in optical and near-infrared wavelengths, do not have detectable 12CO emission and locate avoiding molecular clouds. Wouterloot and Brand (1989) searched 1302 IRAS point sources with reliable fluxes at 25, 60, and 100 μm near the galactic plane for 12CO(J=1-0) line, and detected CO emission for 83% of them. We checked literature and optical images of their sources without detectable CO emission, and carried out near-infrared imaging observations for 55 objects without CO emission and optical counterpart. We found that at least 18 objects are also invisible at near-infrared wavelengths. These objects are highly concentrated around the galactic plane and dispersely distributed avoiding molecular clouds. The distances are estimated to be 1 kpc and their induced infrared luminosities are 4 96 Lodot (average 27 Lodot). The infrared spectral indices between 2.2 μm and 25 μm correspond to those of Class I YSOs, and the IRAS infrared colors are similar to colors of usual YSOs rather than those of cirrus and cold dust associated with early-type stars. The objects are possible YSOs with unusually low CO abundance in their envelopes.

  8. Possible Young Stellar Objects without Detectable CO Emission

    NASA Astrophysics Data System (ADS)

    Iwata, Ikuru; Okumura, Shin-ichiro; Saitō, Mamoru

    1999-10-01

    Young stellar objects (YSOs) usually appear in molecular clouds as infrared objects associated with a molecular envelope. Wouterloot and Brand (1989, AAA 50.133.012) searched 1302 IRAS point sources with reliable fluxes at 25, 60, and 100 mu m near to the galactic plane for 12CO (J=1-0) emission; 1077 sources were detected. Among their far-infrared sources without detectable CO emission, we found that at least 18 objects are invisible at optical and near-infrared wavelengths. The infrared spectral indices between 2.2 mu m and 25 mu m correspond to those of class I YSOs, and the IRAS colors are similar to those of the usual YSOs. These peculiar far-infrared objects are highly concentrated around the galactic plane and the distances are estimated to be ~ 1 kpc. Although their distribution is away from molecular clouds, some of them seem to be associated with large dark clouds or weak radio sources. These objects are possible YSOs with low CO abundance in the envelopes.

  9. Exploring the association of Fermi sources with young stellar objects

    NASA Astrophysics Data System (ADS)

    Munar-Adrover, P.; Paredes, J. M.; Romero, G. E.

    2011-11-01

    Massive protostars have associated bipolar outflows which can produce strong shocks when interact with the surrounding medium. In these conditions particle acceleration at relativistic velocities can occur leading to gamma ray emission, as some theoretical models predict. To identify young stellar objects (YSO) that may emit gamma rays we have crossed the Fermi First Year Catalog with some catalogs of known YSOs, and we have conducted Montecarlo simulations to find the probability of chance coincidence. With this crossing we obtained a list of YSOs spatially coincident with Fermi sources that may show gamma ray emission. Our results indicate that about 70% of the candidates should be gamma-ray sources with a confidence of 5 sigma. We have studied the coincidences one by one to check the viability of these YSOs as potential counterparts of Fermi sources and plan further detailed observations of few of them.

  10. Collimation and Propagation of Jets from Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Movsessian, T. A.

    2017-06-01

    An overview of our investigations of Herbig-Haro jets using the methods of the spectra-imagery is presented. Observations were carried out with 2.6-m telescope of Byurakan Observatory and 6-m telescope of SAO RAS using scanning Fabry-Perot etalons. The new method to measure proper motions of spectoscopically separated structures using two-epoch observations with Fabry-Perot was developed. This method allows to separate inner structures of various physical nature, such as bow-shocks, Mach disks, and deflection shocks. We suppose that characteristic knotty structures in the jets represent internal working surfaces formed by the episodic velocity variations in the flows from young stellar objects. The compact emission structure near the source of FS Tau B flow system was recognised as jet base with wider opening angle by comparison with the jet itself. This scenario was confirmed by spectropolarimetric observations.

  11. Searching for Young Stellar Objects in CG4

    NASA Astrophysics Data System (ADS)

    Johnson, Chelen H.; Rebull, L. M.; Hoette, V.; Mallory, C.; McCarron, K.; Gartner, C.; VanDerMolen, J.; Gamble, L.; Laher, R.; Legassie, M.; Crump, R.; Laorr, A.; Mork, K.; Steinbergs, E.; Wigley, E.; Caruso, S.; Killingstad, N.; McCanna, T.; Matche, L.; McCartney, A.; Doering, M.; Feig, M.; Mahmud, N.; Selic, T.; Kim, S.

    2011-01-01

    We used archival Spitzer infrared data to look for new young stellar objects (YSOs) in Cometary Globule 4 (CG4) in Puppis. CG4 is approximately 1300 parsecs away and one of about 30 cometary globules in the Gum Nebula, many of which are known to be forming stars. CG4 is dramatic in appearance, and that has brought it to the attention of both scientists and the public. Our team used archival Spitzer InfraRed Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS) data, combined with 2 Micron All Sky Survey (2MASS) data as well as optical data obtained by collaborators. We used infrared excess to investigate the properties of previously known YSOs in this region and identify additional new candidate YSOs in this region. This research was made possible through the NASA/IPAC Teacher Archive Research Project (NITARP) and was funded by NASA Astrophysics Data Program and Archive Outreach funds.

  12. ClassLess: A Comprehensive Database of Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Hillenbrand, Lynne; Baliber, Nairn

    2015-01-01

    We have designed and constructed a database housing published measurements of Young Stellar Objects (YSOs) within ~1 kpc of the Sun. ClassLess, so called because it includes YSOs in all stages of evolution, is a relational database in which user interaction is conducted via HTML web browsers, queries are performed in scientific language, and all data are linked to the sources of publication. Each star is associated with a cluster (or clusters), and both spatially resolved and unresolved measurements are stored, allowing proper use of data from multiple star systems. With this fully searchable tool, myriad ground- and space-based instruments and surveys across wavelength regimes can be exploited. In addition to primary measurements, the database self consistently calculates and serves higher level data products such as extinction, luminosity, and mass. As a result, searches for young stars with specific physical characteristics can be completed with just a few mouse clicks.

  13. Stellar occultations by large Transneptunian Objects (dwarf planets candidates)

    NASA Astrophysics Data System (ADS)

    Müller, Thomas G.

    2013-10-01

    Occultations of stars by Transneptunian Objects (TNOs) had never been observed (except for Pluto-Charon system), but in slightly more than three years, 12 such occultations have been detected. This has been a breakthrough. Stellar occultations allow us to derive accurate diameters, shapes and albedos of TNOs. Besides, the presence of atmospheres can be determined and the orbits can be refined. We request two attempts to observe occultations with SOFIA / HIPO during Cycle 2. Occultations by TNOs are brief and the uncertainties in timing require only around 0.33 hrs of observations per alert. The predictions only become accurate enough around 1 or 2 weeks prior to the occultation. This is why a target of opportunity proposal with SOFIA / HIPO is requested.

  14. Model scattering envelopes of young stellar objects. II - Infalling envelopes

    NASA Technical Reports Server (NTRS)

    Whitney, Barbara A.; Hartmann, Lee

    1993-01-01

    We present scattered light images for models of young stellar objects surrounded by dusty envelopes. The envelopes are assumed to have finite angular momentum and are falling in steady flow onto a disk. The model envelopes include holes, such as might be created by energetic bipolar flows. We calculate images using the Monte Carlo method to follow the light scattered in the dusty envelope and circumstellar disk, assuming that the photons originate from the central source. Adopting typical interstellar medium dust opacities and expected mass infall rates for protostars of about 10 exp -6 solar mass/yr, we find that detectable amounts of optical radiation can escape from envelopes falling into a disk as small as about 10-100 AU, depending upon the viewing angle and the size of the bipolar flow cavity. We suggest that the extended optical and near-IR light observed around several young stars is scattered by dusty infalling envelopes rather than disks.

  15. Model scattering envelopes of young stellar objects. II - Infalling envelopes

    NASA Technical Reports Server (NTRS)

    Whitney, Barbara A.; Hartmann, Lee

    1993-01-01

    We present scattered light images for models of young stellar objects surrounded by dusty envelopes. The envelopes are assumed to have finite angular momentum and are falling in steady flow onto a disk. The model envelopes include holes, such as might be created by energetic bipolar flows. We calculate images using the Monte Carlo method to follow the light scattered in the dusty envelope and circumstellar disk, assuming that the photons originate from the central source. Adopting typical interstellar medium dust opacities and expected mass infall rates for protostars of about 10 exp -6 solar mass/yr, we find that detectable amounts of optical radiation can escape from envelopes falling into a disk as small as about 10-100 AU, depending upon the viewing angle and the size of the bipolar flow cavity. We suggest that the extended optical and near-IR light observed around several young stars is scattered by dusty infalling envelopes rather than disks.

  16. Young Stellar Clusters Containing Massive Young Stellar Objects in the VVV Survey

    NASA Astrophysics Data System (ADS)

    Borissova, J.; Ramírez Alegría, S.; Alonso, J.; Lucas, P. W.; Kurtev, R.; Medina, N.; Navarro, C.; Kuhn, M.; Gromadzki, M.; Retamales, G.; Fernandez, M. A.; Agurto-Gangas, C.; Chené, A.-N.; Minniti, D.; Contreras Pena, C.; Catelan, M.; Decany, I.; Thompson, M. A.; Morales, E. F. E.; Amigo, P.

    2016-09-01

    The purpose of this research is to study the connections of the global properties of eight young stellar clusters projected in the Vista Variables in the Via Lactea (VVV) ESO Large Public Survey disk area and their young stellar object (YSO) populations. The analysis is based on the combination of spectroscopic parallax-based reddening and distance determinations with main-sequence and pre-main-sequence ishochrone fitting to determine the basic parameters (reddening, age, distance) of the sample clusters. The lower mass limit estimations show that all clusters are low or intermediate mass (between 110 and 1800 M ⊙), the slope Γ of the obtained present-day mass functions of the clusters is close to the Kroupa initial mass function. The YSOs in the cluster’s surrounding fields are classified using low resolution spectra, spectral energy distribution fits with theoretical predictions, and variability, taking advantage of multi-epoch VVV observations. All spectroscopically confirmed YSOs (except one) are found to be massive (more than 8 M ⊙). Using VVV and GLIMPSE color-color cuts we have selected a large number of new YSO candidates, which are checked for variability and 57% are found to show at least low-amplitude variations. In few cases it was possible to distinguish between YSO and AGB classifications on the basis of light curves.

  17. INFRARED SPECTROSCOPY OF INTERMEDIATE-MASS YOUNG STELLAR OBJECTS

    SciTech Connect

    Pitann, Jan; Bouwman, Jeroen; Krause, Oliver; Henning, Thomas; Hennemann, Martin

    2011-12-10

    In this paper, we present Spitzer Infrared Spectrograph spectroscopy for 14 intermediate-mass young stellar objects (YSOs). We use Spitzer spectroscopy to investigate the physical properties of these sources and their environments. Our sample can be divided into two types of objects: young isolated, embedded objects with spectra that are dominated by ice and silicate absorption bands, and more evolved objects that are dominated by extended emission from polycyclic aromatic hydrocarbons (PAHs) and pure H{sub 2} rotational lines. We are able to constrain the illuminating FUV fields by classifying the PAH bands below 9 {mu}m. For most of the sources we are able to detect several atomic fine structure lines. In particular, the [Ne II] line appearing in two regions could originate from unresolved photodissociation regions or J-shocks. We relate the identified spectral features to observations obtained from NIR through submillimeter imaging. The spatial extent of several H{sub 2} and PAH bands is matched with morphologies identified in previous Infrared Array Camera observations. This also allows us to distinguish between the different H{sub 2} excitation mechanisms. In addition, we calculate the optical extinction from the silicate bands and use this to constrain the spectral energy distribution fit, allowing us to estimate the masses of these YSOs.

  18. The Stellar Population and Star Formation Properties of Blue Compact Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Zhao, Yinghe; Gu, Qiusheng; Gao, Yu

    2011-02-01

    We study stellar populations, star formation histories (SFHs), and star formation properties for a sample of blue compact dwarf galaxies (BCDs) selected by cross-correlating the Gil de Paz et al. sample with the Sloan Digital Sky Survey Data Release 6. The sample includes 31 BCDs, which span a large range of galactic parameters. Using a stellar population synthesis method, we derive stellar populations and reconstruct SFHs for these BCDs. Our studies confirm that BCDs are not young systems experiencing their first star formation, but old systems undergoing a starburst activity. The stellar mass-weighted ages can be up to 10 Gyr, while the luminosity-weighted ages might be up to approximately three orders of magnitude younger (~10 Myr) for most galaxies. Based on multiwavelength data, we also study the integrated star formation properties. The star formation rate (SFR) for our sample galaxies spans nearly three orders of magnitude, from a few 10-3 to ~1 M sun yr-1, with a median value of ~0.1 M sun yr-1. We find that about 90% of BCDs in our sample have their birthrate parameter (the ratio of the current SFR to the averaged past SFR) b>2-3. We further discuss correlations of the current SFR with the integrated galactic stellar mass and explore the connection between SFR and metallicity.

  19. The inner-disk and stellar properties of the young stellar object WL 16

    NASA Technical Reports Server (NTRS)

    Carr, John S.; Tokunaga, Alan T.; Najita, Joan; Shu, Frank H.; Glassgold, Alfred E.

    1993-01-01

    We present kinematic evidence for a rapidly rotating circumstellar disk around the young stellar object WL 16, based on new high-velocity-resolution data of the v = 2-0 CO bandhead emission. A Keplerian disk provides an excellent fit to the observed profile and requires a projected velocity for the CO-emitting region of roughly 250 km/s at the inner radius and 140 km/s at the outer radius, giving a ratio of the inner to the outer radius of about 0.3. We show that satisfying the constraints imposed by the gas kinematics, the observed CO flux, and the total source luminosity requires the mass of WL 16 to lie between 1.4 and 2.5 solar mass. The inner disk radius for the CO emission must be less than 8 solar radii.

  20. Stellar structure and compact objects before 1940: Towards relativistic astrophysics

    NASA Astrophysics Data System (ADS)

    Bonolis, Luisa

    2017-06-01

    Since the mid-1920s, different strands of research used stars as "physics laboratories" for investigating the nature of matter under extreme densities and pressures, impossible to realize on Earth. To trace this process this paper is following the evolution of the concept of a dense core in stars, which was important both for an understanding of stellar evolution and as a testing ground for the fast-evolving field of nuclear physics. In spite of the divide between physicists and astrophysicists, some key actors working in the cross-fertilized soil of overlapping but different scientific cultures formulated models and tentative theories that gradually evolved into more realistic and structured astrophysical objects. These investigations culminated in the first contact with general relativity in 1939, when J. Robert Oppenheimer and his students George Volkoff and Hartland Snyder systematically applied the theory to the dense core of a collapsing neutron star. This pioneering application of Einstein's theory to an astrophysical compact object can be regarded as a milestone in the path eventually leading to the emergence of relativistic astrophysics in the early 1960s.

  1. A WISE Census of Young Stellar Objects in Canis Major

    NASA Astrophysics Data System (ADS)

    Fischer, William J.; Padgett, Deborah L.; Stapelfeldt, Karl L.; Sewiło, Marta

    2016-08-01

    With the Wide-field Infrared Survey Explorer (WISE), we searched for young stellar objects (YSOs) in a 100 deg2 region centered on the lightly studied Canis Major star-forming region. Applying stringent magnitude cuts to exclude the majority of extragalactic contaminants, we find 144 Class I candidates and 335 Class II candidates. The sensitivity to Class II candidates is limited by their faintness at the distance to Canis Major (assumed as 1000 pc). More than half the candidates (53%) are found in 16 groups of more than four members, including four groups with more than 25 members each. The ratio of Class II to Class I objects, N II/N I, varies from 0.4 to 8.3 in just the largest four groups. We compare our results to those obtainable with combined Two Micron All Sky Survey and post-cryogenic Spitzer Space Telescope data; the latter approach recovers missing Class II sources. Via a comparison to protostars characterized with the Herschel Space Observatory, we propose new WISE color criteria for flat-spectrum and Class 0 protostars, finding 80 and 7 of these, respectively. The distribution of YSOs in CMa OB1 is consistent with supernova-induced star formation, although the diverse N II/N I ratios are unexpected if this parameter traces age and the YSOs are due to the same supernova. Less massive clouds feature larger N II/N I ratios, suggesting that initial conditions play a role in determining this quantity.

  2. Herschel Hi-GAL imaging of massive young stellar objects

    NASA Astrophysics Data System (ADS)

    Olguin, F. A.; Hoare, M. G.; Wheelwright, H. E.; Clay, S. J.; de Wit, W.-J.; Rafiq, I.; Pezzuto, S.; Molinari, S.

    2015-05-01

    We used Herschel Hi-GAL (Herschel infrared Galactic Plane survey) data to determine whether massive young stellar objects (MYSOs) are resolved at 70 μm and to study their envelope density distribution. Our analysis of three relatively isolated sources in the l = 30° and 59° Galactic fields show that the objects are partially resolved at 70 μm. The Herschel Hi-GAL survey data have a high scan velocity which makes unresolved and partially resolved sources appear elongated in the 70 μm images. We analysed the two scan directions separately and examine the intensity profile perpendicular to the scan direction. Spherically symmetric radiative transfer models with a power-law density distribution were used to study the circumstellar matter distribution. Single dish submm data were also included to study how different spatial information affects the fitted density distribution. The density distribution which best fits both the 70 μm intensity profile and spectral energy distribution has an average index of ˜0.5. This index is shallower than expected and is probably due to the dust emission from bipolar outflow cavity walls not accounted for in the spherical models. We conclude that 2D axisymmetric models and Herschel images at low scan speeds are needed to better constrain the matter distribution around MYSOs.

  3. Supernovae from yellow, blue supergiants: origin and consequences for stellar evolution

    NASA Astrophysics Data System (ADS)

    Meynet, Georges; Georgy, Cyril; Saio, Hideyuki; Kudritzki, Rolf-Peter; Groh, Jose

    2015-08-01

    A few core collapse supernovae progenitors have been found to be yellow or blue supergiants. We shall discuss possible scenarios involving single and close binary evolution allowing to explain this kind of core collapse supernova progenitors. According to stellar models for both single and close binaries, blue supergiants, at the end of their nuclear lifetimes and thus progenitors of core collapse supernovae, present very different characteristics for what concerns their surface compositions, rotational surface velocities and pulsational properties with respect to blue supergiants in their core helium burning phase. We discuss how the small observed scatter of the flux-weighted gravity-luminosity (FWGL) relation of blue supergiants constrains the evolution of massive stars after the Main-Sequence phase and the nature of the progenitors of supernovae in the mass range between 12 and 40 solar masses. The present day observed surface abundances of blue supergiants, of their pulsational properties, as well as the small scatter of the FWGL relation provide strong constraints on both internal mixing and mass loss in massive stars and therefore on the end point of their evolution.

  4. CANDIDATES FOR THE YOUNG STELLAR OUTFLOWS: WATER AND METHANOL MASERS FROM YOUNG STELLAR OBJECTS

    SciTech Connect

    Lim, Wanggi; Lyo, A-Ran; Kim, Kee-Tae; Byun, Do-Young

    2012-11-01

    We conducted simultaneous 22 GHz water maser and 44 GHz class I methanol maser surveys of newly identified 282 H{sub 2} emission features from the 2.122 {mu}m H{sub 2} narrowband image survey in the Galactic plane (UWISH2 project) using Korean VLBI Network 21 m radio telescopes. We detected 16 and 13 new water and methanol maser sources, respectively. This result indicates that at least {approx}5% of the H{sub 2} emission features originate from young stellar objects (YSOs) that are in the right physical condition to produce the water and methanol masers. The masers are closely related to the current outflow activities in the Galactic plane. The power sources of these 23 diffused/collimated H{sub 2} emission features (six sources are detected for both masers) are likely to be intermediate- to high-mass YSOs, based on a comparison with the maser luminosities of other well-studied YSOs. Both maser velocities are mostly close to their own systemic velocities within {approx}<5 km s{sup -1}, even though water masers generally show larger variabilities in the intensity, velocity, and shape than methanol masers. We also discovered three new water maser sources with high-velocity components: {approx}25 km s{sup -1} redshifted CMHO 019, {approx}50 km s{sup -1} blueshifted CMHO 132, and {approx}120 km s{sup -1} blueshifted CMHO 182. In particular, we propose that the dominant blueshifted water maser of CHMO 182 can be a unique laboratory for the study of the high-mass young stellar jet and its acceleration.

  5. THE BLUE TIP OF THE STELLAR LOCUS: MEASURING REDDENING WITH THE SLOAN DIGITAL SKY SURVEY

    SciTech Connect

    Schlafly, Edward F.; Finkbeiner, Douglas P.; Juric, Mario; Schlegel, David J.; Ivezic, Zeljko; Gibson, Robert R.; Knapp, Gillian R.; Weaver, Benjamin A.

    2010-12-10

    We present measurements of reddening due to dust using the colors of stars in the Sloan Digital Sky Survey (SDSS). We measure the color of main-sequence turnoff stars by finding the 'blue tip' of the stellar locus: the prominent blue edge in the distribution of stellar colors. The method is sensitive to color changes of order 18, 12, 7, and 8 mmag of reddening in the colors u - g, g - r, r - i, and i - z, respectively, in regions measuring 90' by 14'. We present maps of the blue tip colors in each of these bands over the entire SDSS footprint, including the new dusty southern Galactic cap data provided by the SDSS-III. The results disfavor the best-fit O'Donnell and Cardelli et al. reddening laws, but are described well by a Fitzpatrick reddening law with R{sub V} = 3.1. The Schlegel et al. (SFD) dust map is found to trace the dust well, but overestimates reddening by factors of 1.4, 1.0, 1.2, and 1.4 in u - g, g - r, r - i, and i - z largely due to the adopted reddening law. In select dusty regions of the sky, we find evidence for problems in the SFD temperature correction. A dust map normalization difference of 15% between the Galactic north and south sky may be due to these dust temperature errors.

  6. Imaging polarimetry of class I young stellar objects

    NASA Astrophysics Data System (ADS)

    Lucas, P. W.; Roche, P. F.

    1998-09-01

    We present near-infrared imaging polarimetry of three class I young stellar objects in the Taurus-Auriga dark cloud. We use Monte Carlo simulations to analyse the flux distributions and polarization patterns of these three sources and five others from an earlier paper. In addition, we present high-resolution polarimetry of HL Tau using the shift and add technique. Most young stellar objects in the sample display sharp, unresolved, peaks in the scattered light distribution. This is most simply explained by a strong concentration of matter in the centre, which we model by applying the rho~r^-1.5 power law throughout the envelope. In terms of the Ulrich/Terebey, Shu and Cassen solution for the late stages of contraction of an initially spherical non-magnetic cloud, this corresponds to r_c<10 au. However, this almost spherically symmetric density distribution is inconsistent with observations of flattened, disc-like structures, so we conclude that this solution is not appropriate and different initial conditions apply. The multiple-scattering models with spherical grains do not reproduce some features of the observed polarization patterns, in particular the broad regions of aligned vectors seen in some sources. We interpret this as evidence for elongated aligned grains. The weak wavelength dependence of nebular morphology shows that the dust grains in circumstellar envelopes obey a much shallower extinction law than interstellar grains in the near-infrared, which we describe by the opacity ratio kappa(J/K)=1.8+/-0.3, compared to the interstellar value of 3.25. We place an upper limit on albedo of omega<0.6 from 1.25 to 2.2 μm and we find 0.1<0.4. With the addition of two more observables derived from the observed degrees of linear and circular polarization, we identify five

  7. Extremely high-velocity molecular flows in young stellar objects

    NASA Astrophysics Data System (ADS)

    Koo, Bon-Chul

    1989-02-01

    Very sensitive, wideband CO J = 1-0, J = 2-1, and HCO+ J = 1-0 spectra of several young stellar objects are presented. Extremely weak and very broad extremely high velocity (EHV) wings are found in GL 4909, HH 7-11, S140, and MWC 1080. The line profiles of EHV wings are smooth or flat, quite different from steep HV wings. In L551 and HL Tau, EHV wings as broad as other sources are not found, which would be due to the inclination of the bipolar flows to the line of sight. From the excitation temperature of about 10 K derived for the EHV flows, the estimated column density of CO yields a number density too small to explain the observed ratio of CO J = 2-1 to J = 1-0 intensity. It is concluded that either EHV flows are composed of small dense clumps or most of the carbon in the flow is atomic carbon, unless the kinetic temperature of the flow is much higher than 100 K.

  8. Complex molecule formation around massive young stellar objects.

    PubMed

    Oberg, Karin I; Fayolle, Edith C; Reiter, John B; Cyganowski, Claudia

    2014-01-01

    Interstellar complex organic molecules were first identified in the hot inner regions of massive young stellar objects (MYSOs), but have more recently been found in many colder sources, indicating that complex molecules can form at a range of temperatures. However, individually these observations provide limited constraints on how complex molecules form, and whether the same formation pathways dominate in cold, warm and hot environments. To address these questions, we use spatially resolved observations from the Submillimeter Array of three MYSOs together with mostly unresolved literature data to explore how molecular ratios depend on environmental parameters, especially temperature. Towards the three MYSOs, we find multiple complex organic emission peaks characterized by different molecular compositions and temperatures. In particular, CH3CCH and CH3CN seem to always trace a lukewarm (T = 60 K) and a hot (T > 100 K) complex chemistry, respectively. These spatial trends are consistent with abundance-temperature correlations of four representative complex organics--CH3CCH, CH3CN, CH3OCH3 and CH3CHO--in a large sample of complex molecule hosts mined from the literature. Together, these results indicate a general chemical evolution with temperature, i.e. that new complex molecule formation pathways are activated as a MYSO heats up. This is qualitatively consistent with model predictions. Furthermore, these results suggest that ratios of complex molecules may be developed into a powerful probe of the evolutionary stage of a MYSO, and may provide information about its formation history.

  9. E/S0 GALAXIES ON THE BLUE COLOR-STELLAR MASS SEQUENCE AT z = 0: FADING MERGERS OR FUTURE SPIRALS?

    SciTech Connect

    Kannappan, Sheila J.; Guie, Jocelly M.; Baker, Andrew J. E-mail: jocelly@mail.utexas.edu

    2009-08-15

    We identify a population of morphologically defined E/S0 galaxies lying on the locus of late-type galaxies in color-stellar mass space - the 'blue sequence' -at the present epoch. Using three samples (from the Nearby Field Galaxy Survey or NFGS, a merged HyperLeda/Sloan Digital Sky Survey/Two Micron All Sky Survey catalog, and the NYU Value-Added Galaxy Catalog), we analyze blue-sequence E/S0s with stellar masses {approx}>10{sup 8} M {sub sun}, arguing that individual objects may be evolving either up toward the red sequence or down into the blue sequence. Blue-sequence E/S0 galaxies become more common with decreasing stellar mass, comprising {approx}<2% of E/S0s near the 'shutdown mass' M{sub s} {approx} 1-2 x 10{sup 11} M {sub sun}, increasing to {approx}>5% near the 'bimodality mass' M{sub b} {approx} 3 x 10{sup 10} M {sub sun}, and sharply rising to {approx}> 20%-30% below the 'threshold mass' M{sub t} {approx} 4-6 x 10{sup 9} M {sub sun}, down to our completeness analysis limit at {approx}10{sup 9} M {sub sun}. The strong emergence of blue-sequence E/S0s below M{sub t} coincides with a previously reported global increase in mean atomic gas fractions below M{sub t} for galaxies of all types on both sequences, suggesting that the availability of cold gas may be basic to blue-sequence E/S0s' existence. Environmental analysis reveals that many sub-M{sub b} blue-sequence E/S0s reside in low-to-intermediate density environments. Thus, the bulk of the population we analyze appears distinct from the generally lower-mass cluster dE population; S0 morphologies with a range of bulge sizes are typical. In mass-radius and mass-{sigma} scaling relations, blue-sequence E/S0s are more similar to red-sequence E/S0s than to late-type galaxies, but they represent a transitional class. While some of them, especially in the high-mass range from M{sub b} to M{sub s} , resemble major-merger remnants that will likely fade onto the red sequence, most blue-sequence E/S0s below M{sub b

  10. ISOPHOT observations of circumstellar disks around young stellar objects

    NASA Astrophysics Data System (ADS)

    Robberto, M.; Meyer, M. R.; Natta, A.; Beckwith, S. V. W.

    1999-03-01

    We observed 97 stars in five young clusters at 25 and 60 μm with ISOPHOT to determine the frequency of infrared emission from circumstellar disks. The clusters have ages between 1 and 300 Myr. Most stars (5/6) that have near-infrared excess emission, thought to be indicative of accretion disks, exhibit far-infrared emission; only one object that has no excess emission in the near-infrared exhibits far-infrared excess emission. No stars older than 10 Myr have evidence for optically-thick disks. These results show that dust in the disks between about 0.3 and 3 AU disappears on timescales of ~ 10 Myr, identical within the uncertainties to the timescale for cessation of accretion as indicated by near-infrared observations of similar samples. Detection of one object whose dust optical depth is intermediate between opaque and transparent suggests that the duration of the transition phase between optically-thick and thin disk emission is less than 300,000 yr. Broad-band photometry between 2.5 and 100 μm, low resolution spectra between 2 and 12 μm, and 200 μm maps of 18 young stars (1-3 Myr old) in the Taurus and Chamaeleon dark clouds suggests that the irradiation dominates over viscous dissipation of mass accretion in the heating of the disk. The spectral energy distributions are consistent with those predicted by models of disks heated centrally by the stellar/accretion photosphere or by scattering from a diffuse halo surrounding the disk. The observations demonstrate that heating by accretion through the disks contributes little or no power to the energy budget at distances more than a few tenths AU from the central star.

  11. Populations of Young Stellar Objects in Nearby Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Hsieh, Tien-Hao; Lai, Shih-Ping

    2013-03-01

    We develop a new method for identifying young stellar objects (YSOs) from star-forming regions using the photometry data from Spitzer's c2d Legacy Project. The aim is to obtain YSO lists as complete as possible for studying statistical properties such as the star formation rate (SFR) and lifetimes of YSOs in different evolutionary stages. The largest obstacle in identifying YSOs comes from background galaxies with similar spectral energy distributions to YSOs. Traditionally, selected color-color and color-magnitude criteria are used to separate YSOs and galaxies. However, since there is no obvious boundary between YSOs and galaxies in color-color diagrams and color-magnitude diagrams (CMDs), those criteria may exclude faint YSOs near the boundary. In this paper, we separate the YSOs and galaxies in a multi-dimensional (multi-D) magnitude space, which is equivalent to using all variations of CMDs simultaneously. Comparing sources from molecular clouds to Spitzer's SWIRE data, which have a negligible amount of YSOs, we can naturally identify YSO candidates (YSOc) located outside of the galaxy-populated regions in the multi-D space. In the five c2d surveyed clouds, we select 322 new YSOc and miss/exclude 33 YSOc compared to Evans et al., and this results in 1313 YSOc in total. As a result, SFR increases 28% correspondingly, but the lifetimes of YSOs in different evolutionary stages remain unchanged. Compared to theories by Krumholz & McKee, our derived SFR suggests that star formation at a large scale is dominated by supersonic turbulence rather than magnetic fields. Furthermore, we identify seven new very low luminosity objects.

  12. POPULATIONS OF YOUNG STELLAR OBJECTS IN NEARBY MOLECULAR CLOUDS

    SciTech Connect

    Hsieh, Tien-Hao; Lai, Shih-Ping E-mail: slai@phys.nthu.edu.tw

    2013-03-01

    We develop a new method for identifying young stellar objects (YSOs) from star-forming regions using the photometry data from Spitzer's c2d Legacy Project. The aim is to obtain YSO lists as complete as possible for studying statistical properties such as the star formation rate (SFR) and lifetimes of YSOs in different evolutionary stages. The largest obstacle in identifying YSOs comes from background galaxies with similar spectral energy distributions to YSOs. Traditionally, selected color-color and color-magnitude criteria are used to separate YSOs and galaxies. However, since there is no obvious boundary between YSOs and galaxies in color-color diagrams and color-magnitude diagrams (CMDs), those criteria may exclude faint YSOs near the boundary. In this paper, we separate the YSOs and galaxies in a multi-dimensional (multi-D) magnitude space, which is equivalent to using all variations of CMDs simultaneously. Comparing sources from molecular clouds to Spitzer's SWIRE data, which have a negligible amount of YSOs, we can naturally identify YSO candidates (YSOc) located outside of the galaxy-populated regions in the multi-D space. In the five c2d surveyed clouds, we select 322 new YSOc and miss/exclude 33 YSOc compared to Evans et al., and this results in 1313 YSOc in total. As a result, SFR increases 28% correspondingly, but the lifetimes of YSOs in different evolutionary stages remain unchanged. Compared to theories by Krumholz and McKee, our derived SFR suggests that star formation at a large scale is dominated by supersonic turbulence rather than magnetic fields. Furthermore, we identify seven new very low luminosity objects.

  13. WISE Identified Young Stellar Objects In BRC 38

    NASA Astrophysics Data System (ADS)

    Gibbs, John; Rebull, L. M.; Laurence, W.; Marshall, R.; Murphy, M.; Orr, L.; Whitworth, C.; Burton, A.; Corris, T.; Goodey, S.; McGinnis, S.; Laurence, C.; Aschman, O.; Kikuchi, R.; Prather, J.; Whitley, L.; Billings, C.; Mader, C.

    2014-01-01

    Bright rimmed clouds (BRCs) are dense clumps of gas and dust within HII regions at the edges of molecular clouds; while the BRCs themselves are dark, their rims are optically bright from illumination by nearby O or B stars. Many BRCs show evidence of active star formation possibly triggered by the ionizing radiation from the nearby O or B stars. The large molecular cloud IC1396 is home to eleven BRCs thought to be driven by the O6.5V star HD206267. BRC 38 is located in the north of IC1396, at 21:40:42 +58:16:13. The immediate ~5'x5' region around BRC 38 has been extensively studied in many wavelengths from X-rays to infrared (IR), identifying ~100 young stellar objects (YSOs). We used data from the Wide-field Infrared Survey Explorer (WISE) to expand the search for YSOs to a 20 arcminute radius from the center of BRC 38. Starting with approximately 7000 sources identified in the WISE catalog, we used an updated version of the IR color selection scheme developed by Koenig et al. (2012) to identify ~40 objects having IR colors consistent with those of YSOs; some overlapping with the literature YSO candidates. Combining confirmed and candidate YSOs from literature with those we identified by color selection, we find 115 unique objects of interest. For each of these sources, we analyzed (a) the WISE, 2MASS, and Spitzer images to determine if they were point-like sources; (b) their IR colors to determine if they exhibited a clear IR excess; and (c) their spectral energy distributions (SEDs) to determine if they had an SED shape consistent with their identification as YSO candidates. Our work adds several new YSO candidates to the list of YSOs in and near BRC 38 and newly identifies IR excesses for many of the previously identified YSOs in the region. We looked for evidence of triggered star formation in BRC 38, but are limited in our conclusions by small-number statistics. Support is provided for this work by the NASA/IPAC Teacher Archive Research Program (NITARP

  14. Three quasi-stellar objects acting as strong gravitational lenses

    NASA Astrophysics Data System (ADS)

    Courbin, F.; Faure, C.; Djorgovski, S. G.; Rérat, F.; Tewes, M.; Meylan, G.; Stern, D.; Mahabal, A.; Boroson, T.; Dheeraj, R.; Sluse, D.

    2012-04-01

    We report the discovery of three new cases of quasi-stellar objects (QSOs) acting as strong gravitational lenses on background emission line galaxies: SDSS J0827+5224 (zQSO = 0.293, zs = 0.412), SDSS J0919+2720 (zQSO = 0.209, zs = 0.558), SDSS J1005+4016 (zQSO = 0.230, zs = 0.441). The selection was carried out using a sample of 22,298 SDSS spectra displaying at least four emission lines at a redshift beyond that of the foreground QSO. The lensing nature is confirmed from Keck imaging and spectroscopy, as well as from HST/WFC3 imaging in the F475W and F814W filters. Two of the QSOs have face-on spiral host galaxies and the third is a QSO+galaxy pair. The velocity dispersion of the host galaxies, inferred from simple lens modeling, is between σ = 210 and 285 km s-1, making these host galaxies comparable in mass with the SLACS sample of early-type strong lenses. Based on data obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. Also based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program #GO12233.

  15. Young Stellar Object Candidates in the Aquila Rift Region

    NASA Astrophysics Data System (ADS)

    Zhang, Miao-miao; Wang, Hong-chi; Stecklum, B.

    2010-10-01

    Using the 2m telescope of the Turingia State Observatory at Tauten-berg (TLS), imaging observations in 3 wavebands (H α, R and I) are performed in the 16 fields in the Aquila Rift region. The observed fields cover about 7 square degrees. Excluding the 3 fields with unqualified data, the photometrical analysis is made for the remaining 13 fields, from which point sources are identified, and finally 7 H α emission-line star candidates are identified by color-color diagrams. The 7 candidates are located in five fields. Three of them are located near the Galactic plane, while the galactic latitudes of the rest are greater than 4°. The 2 M ASS counterparts of the point sources are identified, and the properties of the 7 H α emission-line star candidates are further analyzed by using the two-color diagrams. It is found that the near-infrared radiation from these H α emission-line star candidates has no obvious infrared excess, one of them even falls on the main-sequence branch. This indicates that the H α-emissive young stellar objects (YSOs) are not always accompanied with the infrared excess, and that the results of the H α emission line observation and the infrared excess observation are mutually supplemented. If the 7 H α emission-line star candidates are regarded as YSO candidates, then the number of YSOs in the Aquila Rift region is quite small. The further confirmation of these candidates needs subsequent spectral observations.

  16. THREE-DIMENSIONAL RADIATION TRANSFER IN YOUNG STELLAR OBJECTS

    SciTech Connect

    Whitney, B. A.; Honor, J.; Robitaille, T. P.; Bjorkman, J. E.; Dong, R.; Wolff, M. J.; Wood, K.

    2013-08-15

    We have updated our publicly available dust radiative transfer code (HOCHUNK3D) to include new emission processes and various three-dimensional (3D) geometries appropriate for forming stars. The 3D geometries include warps and spirals in disks, accretion hotspots on the central star, fractal clumping density enhancements, and misaligned inner disks. Additional axisymmetric (2D) features include gaps in disks and envelopes, ''puffed-up inner rims'' in disks, multiple bipolar cavity walls, and iteration of disk vertical structure assuming hydrostatic equilibrium (HSEQ). We include the option for simple power-law envelope geometry, which, combined with fractal clumping and bipolar cavities, can be used to model evolved stars as well as protostars. We include non-thermal emission from polycyclic aromatic hydrocarbons (PAHs) and very small grains, and external illumination from the interstellar radiation field. The grid structure was modified to allow multiple dust species in each cell; based on this, a simple prescription is implemented to model dust stratification. We describe these features in detail, and show example calculations of each. Some of the more interesting results include the following: (1) outflow cavities may be more clumpy than infalling envelopes. (2) PAH emission in high-mass stars may be a better indicator of evolutionary stage than the broadband spectral energy distribution slope; and related to this, (3) externally illuminated clumps and high-mass stars in optically thin clouds can masquerade as young stellar objects. (4) Our HSEQ models suggest that dust settling is likely ubiquitous in T Tauri disks, in agreement with previous observations.

  17. 76 FR 81004 - Culturally Significant Objects Imported for Exhibition Determinations: “Woman in Blue, Against...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-12-27

    ... From the Federal Register Online via the Government Publishing Office ] DEPARTMENT OF STATE Culturally Significant Objects Imported for Exhibition Determinations: ``Woman in Blue, Against Blue Water..., 2003), I hereby determine that the object ``Woman in Blue, Against Blue Water'' by Edvard...

  18. Testing the Formation Mechanism of Sub-Stellar Objects in Lupus (A SOLA Team Study)

    NASA Astrophysics Data System (ADS)

    De Gregorio-Monsalvo, Itziar; Lopez, C.; Takahashi, S.; Santamaria-Miranda

    2017-06-01

    The international SOLA team (Soul of Lupus with ALMA) has identified a set of pre- and proto-stellar candidates in Lupus 1 and 3 of substellar nature using 1.1mm ASTE/AzTEC maps and our optical to submillimeter database. We have observed with ALMA the most promising pre- and proto-brown dwarfs candidates. Our aims are to provide insights on how substellar objects form and evolve, from the equivalent to the pre-stellar cores to the Class II stage in the low mass regime of star formation. Our sample comprises 33 pre-stellar objects, 7 Class 0 and I objects, and 22 Class II objects.

  19. The Dynamics of Outflows from Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Ridge, Naomi A.

    2001-01-01

    The prevalence of CO outflows around young stellar objects (YSOs) suggests that mass-loss is a necessary ingredient of the star-formation process, and they are thought to provide a means to remove angular momentum from the accreting matter. Our understanding of molecular outflows from low-mass YSOs has come from a large number of studies performed during the last decade. However there have been relatively few similar detailed studies of high-mass YSO outflows, and it is still not clear whether outflows from high-mass YSOs are generated and entrained by the same mechanism as those from their low-mass counterparts. Studies of high-mass star-formation which attempt to extend the established correlations between outflow momentum-flux and source bolometric luminosity into the high-mass regime are further hindered by the problem of Malmquist bias, which we show to be prevalent in the existing studies of high-mass YSOs. We therefore selected a sample of known intermediate to high-mass YSOs with outflows with a range of luminosities but all located at a distance of 2 +/- 0.3 kpc. With this sample we are able to test the correlations between outflow dynamical properties and source properties free from biases due to source distance, and to investigate whether the other phenomena associated with low-mass YSO outflows are also common in high-mass flows. We present high-sensitivity 12CO maps of the 11 outflows from intermediate to high-mass YSOs, and discuss their morphology and dynamics. These data were also used to re-investigate the uncertainties involved in using spectral-line data to derive flow properties, particularly the importance of variations in optical depth and the problem of separating ambient cloud emssion from flow emission. We also present 13CO and C18O observations of the ``cores'' surrounding each YSO and discuss how the cloud core and outflow may be related. The primary conclusions of this work are: The correlation between outflow momentum flux (FrmCO ) and

  20. Accelerating a water maser face-on jet from a high mass young stellar object

    NASA Astrophysics Data System (ADS)

    Motogi, Kazuhito; Sorai, Kazuo; Honma, Mareki; Hirota, Tomoya; Hachisuka, Kazuya; Niinuma, Kotaro; Sugiyama, Koichiro; Yonekura, Yoshinori; Fujisawa, Kenta

    2016-10-01

    We report on long-term single-dish and VLBI monitoring for intermittent flare activities of a dominant blue-shifted H2O maser associated with a southern high mass young stellar object, G353.273+0.641. Bi-weekly single-dish monitoring using the Hokkaido University Tomakomai 11 m radio telescope has shown that a systematic acceleration continues over four years beyond the lifetime of individual maser features. This fact suggests that the H2O maser traces a region where molecular gas is steadily accelerated. There were five maser flares during the five years of monitoring, and maser distributions in four of them were densely monitored by VLBI Exploration of Radio Astrometry (VERA). The overall distribution of the maser features suggests the presence of a bipolar jet, with the 3D kinematics indicating that it is almost face-on (inclination angle of ˜ 8°-17° from the line of sight). Most maser features were recurrently excited within a region of 100×100 au2 around the radio continuum peak, while their spatial distributions significantly varied between each flare. This confirms that episodic propagations of outflow shocks recurrently invoke intermittent flare activities. We also measured annual parallax, deriving a source distance of 1.70^{+0.19}_{-0.16} kpc that is consistent with the commonly used photometric distance.

  1. 78 FR 8682 - Culturally Significant Object Imported for Exhibition Determinations: “Vermeer's Woman in Blue...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-02-06

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF STATE Culturally Significant Object Imported for Exhibition Determinations: ``Vermeer's Woman in Blue Reading a... ``Vermeer's Woman in Blue Reading a Letter,'' imported from abroad for temporary exhibition within...

  2. 75 FR 82128 - Culturally Significant Objects Imported for Exhibition Determinations: “Vishnu: Hinduism's Blue...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-12-29

    ... for Exhibition Determinations: ``Vishnu: Hinduism's Blue-Skinned Savior'' SUMMARY: Notice is hereby... hereby determine that the objects to be included in the exhibition ``Vishnu: Hinduism's Blue-Skinned...

  3. The Early History of Stellar Spin: the Theory of Accretion onto Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Pudritz, Ralph E.; Matt, Sean

    2014-01-01

    The interaction of the magnetospheres of forming stars with their surrounding protostellar disks results in magnetospheric accretion flow onto the star. How is the associated angular momentum of accreting material channelled? The resolution of this issue is crucial for understanding the origin of the spins of pre main sequence stars. A significant fraction of these rotate very slowly, which indicates that an efficient angular momentum transport mechanism is at work to counteract the strong accretion spin up torques. We review the observational, theoretical, and computational advances in the field and argue that an accretion powered stellar winds together with highly time variable mass ejections from the disk/magnetosphere interface is a likely solution.

  4. Polarization and Structure of Broad Absorption Line Quasi-Stellar Objects

    NASA Astrophysics Data System (ADS)

    Ogle, Patrick Michael

    This thesis is a spectropolarimetric survey of broad absorption line quasi-stellar objects (BAL QSO). We observed 36 BAL QSO at the Palomar and W. M. Keck Observatories. BAL QSO have higher polarization than other quasars, reinforcing the view that they are normal quasars viewed from an equatorial aspect. However, there is a wide distribution of polarization values, which may be due to intrinsic differences in the geometry or optical depth to scattering. No correlations are found among emission line or broad absorption line properties and continuum polarization, suggesting that these properties are regulated by internal differences unrelated to viewing angle. The continuum polarization of BAL QSO is weakly wavelength-dependent after correction for emission line dilution. In most objects, the polarisation rises to the blue, suggesting that dust scattering or absorption may be important. Broad emission line photons are polarized less than the continuum; and the position angle of the electric vector is rotated with respect to the continuum. The semi-forbidden C III) emission line is polarized differently than the C IV emission line, suggesting resonance scattering in the C III) emission line region. Resonantly scattered photons from the broad absorption line region are detected at high velocities red-ward and blue-ward of the C IV line center in the spectra of some objects. These photons are negatively polarized with respect to the continuum photons, showing that the broad absorption line region and the continuum scattering region are oriented perpendicular to each other. The polarization increases in the BAL troughs, due mainly to partial coverage of the central source by the broad absorption line region. The geometry of the intervening BAL clouds is skewed with respect to the continuum scattering region, which results in position angle rotations in the BAL. The variation of polarization with velocity in the BAL is consistent with a non-radial, accelerating outflow

  5. Near infrared photographic sky survey. 1: Catalog of red stellar objects

    NASA Technical Reports Server (NTRS)

    Craine, E. R.; Duerr, R. E.; Horner, V. M.; Imhoff, C. L.; Routsis, D. E.; Swihart, D. L.; Turnshek, D. A.

    1979-01-01

    Red stellar objects for which V-1 was greater than a value of about 2 (supm). 5 were extracted from photographs of 23 program fields. Tabular data for each field show the object name; the 1950 epoch right ascension, declination, galactic longitude, galactic latitude; radial distance from field venter in decimal degrees; color classes; and objects ordered by redness.

  6. Stellarators

    SciTech Connect

    Hartmann, D.A.

    2004-03-15

    Stellarators are toroidal devices where the required rotational transform of the magnetic field lines is generated by external field coils and not via an induced net toroidal plasma current. This confinement scheme has the advantages that, in principle, steady-state plasma operation is possible and that it does not have to brace itself against disruptions of a toroidal plasma current. At the cost of having to give up toroidal symmetry the properties of the stellarator field can be tailored to suit reactor needs. Research focuses on the plasma confinement properties of different stellarator fields and investigates the problems arising when one extrapolates to reactor parameters.

  7. Outflows from Young Stellar Objects: Bringing Numerical Simulations Closer to Observations of Herbig-Haro Objects

    NASA Astrophysics Data System (ADS)

    Hansen, Edward C.

    High resolution observations of Young Stellar Object (YSO) jets show them to be composed of many small-scale knots or clumps. 2-D and 3-D numerical simulations were conducted with the code AstroBEAR to study how such clumps interact and create morphologies and kinematic patterns seen in emission line observations. Two main classes of simulations were used in this study: outflows of spherical, over-dense clumps, and pulsed jets in which the pulsations create clumps within the jet. Such flows lead to the formation of bow shocks which then interact with each other as faster material overtakes slower material. We show that much of the spatial structure apparent in emission line images of jets arises from the dynamics and interactions of these bow shocks. The simulations show a variety of time-dependent features, including bright knots associated with Mach stems where the shocks intersect, a "frothy" emission structure that arises from the presence of the Non-linear Thin Shell Instability (NTSI) along the surfaces of the bow shocks, and the merging and fragmentation of clumps. Simulations with magnetic fields show how the field affects the dynamics of YSO jets and the emission they produce. This work contributes to the ultimate goal of one day being able to observationally estimate the strength of the magnetic field within these jets. The simulations use a new non-equilibrium cooling method to produce synthetic emission maps in H? and [S II]. These are directly compared with multi-epoch Hubble Space Telescope (HST) observations of Herbig-Haro (HH) jets. There is excellent agreement between features seen in the simulations and the observations in terms of both proper motion and morphologies. Thus, YSO jets may be dominated by heterogeneous structures, and interactions between these structures and the shocks they produce can account for many details of YSO jet evolution.

  8. Evolution of stellar collision products in open clusters. I. Blue stragglers in N-body models of M 67

    NASA Astrophysics Data System (ADS)

    Glebbeek, E.; Pols, O. R.; Hurley, J. R.

    2008-09-01

    Stellar collisions are an important formation channel for blue straggler stars in globular and old open clusters. Hydrodynamical simulations have shown that the remnants of such collisions are out of thermal equilibrium, are not strongly mixed and can rotate very rapidly. Detailed evolution models of collision products are needed to interpret observed blue straggler populations and to use them to probe the dynamical history of a star cluster. We expand on previous studies by presenting an efficient procedure to import the results of detailed collision simulations into a fully implicit stellar evolution code. Our code is able to evolve stellar collision products in a fairly robust manner and allows for a systematic study of their evolution. Using our code we have constructed detailed models of the collisional blue stragglers produced in the N-body simulation of M 67 performed by Hurley et al. in 2005. We assume the collisions are head-on and thus ignore the effects of rotation in this paper. Our detailed models are more luminous than normal stars of the same mass and in the same stage of evolution, but cooler than homogeneously mixed versions of the collision products. The increased luminosity and inefficient mixing decrease the remaining main-sequence lifetimes of the collision products, which are much shorter than predicted by the simple prescription commonly used in N-body simulations.

  9. Near-infrared spectroscopy of young stellar objects

    NASA Astrophysics Data System (ADS)

    Kelly, D. M.; Rieke, G. H.; Campbell, B.

    1994-04-01

    We present spectra between 0.9 and 1.35 micrometers for MWC 349, LkH-alpha 101, R Mon, V645 Cyg, GL 490, T Tau, and HH 1. The spectra are rich in emission lines. We find evidence for many different emission regions, including virtually all those previously deduced from shorter wavelength spectra. A number of objects have optically thick regions in which O I emission is excited by UV and Ly-Beta fluorescence. We discuss the physical implications of the observed lines and the role spectroscopy between 0.9 and 1.35 micrometers can play in future investigations of the evolution of young stars.

  10. SPARCO : a semi-parametric approach for image reconstruction of chromatic objects. Application to young stellar objects

    NASA Astrophysics Data System (ADS)

    Kluska, J.; Malbet, F.; Berger, J.-P.; Baron, F.; Lazareff, B.; Le Bouquin, J.-B.; Monnier, J. D.; Soulez, F.; Thiébaut, E.

    2014-04-01

    Context. The emergence of optical interferometers with three and more telescopes allows image reconstruction of astronomical objects at the milliarcsecond scale. However, some objects contain components with very different spectral energy distributions (SED; i.e. different temperatures), which produces strong chromatic effects on the interferograms that have to be managed with care by image reconstruction algorithms. For example, the gray approximation for the image reconstruction process results in a degraded image if the total (u,v)-coverage given by the spectral supersynthesis is used. Aims: The relative flux contribution of the central object and an extended structure changes with wavelength for different temperatures. For young stellar objects, the known characteristics of the central object (i.e., stellar SED), or even the fit of the spectral index and the relative flux ratio, can be used to model the central star while reconstructing the image of the extended structure separately. Methods: We present a new method, called SPARCO (semi-parametric algorithm for the image reconstruction of chromatic objects), which describes the spectral characteristics of both the central object and the extended structure to consider them properly when reconstructing the image of the surrounding environment. We adapted two image-reconstruction codes ( Macim , Squeeze , and MiRA ) to implement this new prescription. Results: SPARCO is applied using Macim , Squeeze , and MiRA on a young stellar object model and also on literature data on HR 5999 in the near-infrared with the VLTI. We obtain smoother images of the modeled circumstellar emission and improve the χ2 by a factor 9. Conclusions: This method paves the way to improved aperture-synthesis imaging of several young stellar objects with existing datasets. More generally, the approach can be used on astrophysical sources with similar features, such as active galactic nuclei, planetary nebulae, and asymptotic giant branch

  11. Exploring Cosmic Voids with GALEX: Stellar Populations and Primordial Jeans Mass Objects

    NASA Astrophysics Data System (ADS)

    Gregg, Michael

    This proposed research program will revolutionize the study of cosmic voids and their inhabitant galaxy populations. By combining archival GALEX photometry with SDSS data for thousands of galaxies in hundreds of voids, we will be able to characterize voids, void galaxies, and the formation and evolution of galaxies in the lowest density environments of the Universe. In addition, we propose to use the joint GALEX-SDSS database to search in several of the nearest cosmic voids for the original building blocks of galaxy formation: surviving Jeans mass primordial objects which formed right after recombination during the earliest stages of structure formation in the Universe. Our program will first characterize known void galaxies in the UV using the extensive GALEX NUV and FUV imaging archives. Adding GALEX UV photometry to SDSS optical enables estimating star formation rates and also separating stars from unresolved galaxies. Based on this effort, we will look for trends in galaxy properties with location within a void and with global void properties such as size and underdensity. We are particularly interested in identifying and characterizing the early type galaxy population in voids. While most void galaxies are blue, there do exist ellipticals in voids; comparison with ellipticals in denser regions will inform elliptical galaxy models in new ways, and teach us about the oldest and earliest stages of galaxy formation in voids. Early type galaxies are easy to miss in void redshift surveys, even with the comprehensive nature of SDSS, because most have relied on emission line searches or infrared excess. Our approach is fundamentally different, using an enhanced GALEX UV-optical selection technique which we have developed specifically for this work. A search for early type objects is necessary to fully understand void galaxy populations. In parallel, we will use our UV-optical selection technique to search for primordial Jeans mass sized objects in the nearest voids

  12. The host galaxies of quasi-stellar objects

    NASA Astrophysics Data System (ADS)

    Hamilton, Timothy Scott

    The results of an archival study of 71 medium-redshift QSOs observed with the Wide Field Planetary Camera 2 on board the Hubble Space Telescope are presented. The QSOs have magnitudes MV ≤ -23 mag (total nuclear + host light) and red shifts 0.06 ≤ z ≤ 0.46, with no additional criteria imposed. For each object, the nuclear light component is subtracted, using two-dimensional image fits, and the luminosity and size of the underlying host galaxy are determined by fitting both an r1/4 and an exponential light profile, which represent a bulge and disk component, respectively. The total number of objects considered is more than triple that of previous studies, and the general QSO population for redshifts z ≤ 0.46 is reasonably sampled. A luminosity function which is not grossly affected by selection criteria is derived for the QSO host galaxies. This luminosity function is compared with that of normal galaxies and a ratio of luminosity functions for QSO hosts and normal galaxies is derived. The logarithm of this ratio follows a nearly straight line when plotted against galaxy magnitude. Previous results which indicate that QSO hosts are more luminous than typical bright galaxies are confirmed. The relationship between host and nuclear luminosity is studied in the context of morphology and radio-loudness. The surface brightnesses of the host galaxies are compared to the known relationships between the effective surface magnitude and size of Brightest Cluster Galaxies. The surface brightness distribution is also examined in the context of radio-loudness and the merger history of the hosts. Black hole masses for a subset of the QSOs are taken from the literature and used to calculate the Eddington limit for those objects. The black hole mass, the nuclear luminosity, and the nuclear luminosity as a fraction of the Eddington limit are examined as functions of each other. Multi-parameter analyses are performed using Principal Components Analysis to search for

  13. The real-time stellar evolution of Sakurai's object.

    PubMed

    Hajduk, Marcin; Zijlstra, Albert A; Herwig, Falk; van Hoof, Peter A M; Kerber, Florian; Kimeswenger, Stefan; Pollacco, Don L; Evans, Aneurin; Lopéz, José A; Bryce, Myfanwy; Eyres, Stewart P S; Matsuura, Mikako

    2005-04-08

    After a hot white dwarf ceases its nuclear burning, its helium may briefly and explosively reignite. This causes the star to evolve back into a cool giant, whereupon it experiences renewed mass ejection before reheating. A reignition event of this kind was observed in 1996 in V4334 Sgr (Sakurai's object). Its temperature decrease was 100 times the predicted rate. To understand its unexpectedly fast evolution, we have developed a model in which convective mixing is strongly suppressed under the influence of flash burning. The model predicts equally rapid reheating of the star. Radio emission from freshly ionized matter now shows that this reheating has begun. Such events may be an important source of carbon and carbonaceous dust in the Galaxy.

  14. A stellar endgame - the born-again Sakurai's object.

    NASA Astrophysics Data System (ADS)

    Asplund, M.; Gustafsson, B.; Lambert, D. L.; Kameswara Rao, N.

    1997-05-01

    The surface chemical composition of this remarkable star shows that it is hydrogen-deficient, carbon-rich and enriched in the light s-process elements. Spectra taken in May and October 1996 indicate a decrease in the surface hydrogen abundance by 0.7dex in five months along with an increase in the abundances of Li, Sr, Y and Zr. The abundance changes are in agreement with the hypothesis of the star being a rapidly evolving "born-again" AGB star experiencing a final He-shell flash, similar to FGSge. The ^12^C/^13^C ratio in October is very low, also suggesting hydrogen ingestion. By chemical composition, Sakurai's object resembles the R Coronae Borealis (RCrB) stars.

  15. Hot and cold gas toward young stellar objects

    NASA Technical Reports Server (NTRS)

    Mitchell, George F.; Maillard, Jean-Pierre; Allen, Mark; Beer, Reinhard; Belcourt, Kenneth

    1990-01-01

    High-resolution M band spectra are presented for the seven embedded IR sources W3 IRS 5, S140 IRS1, NGC 7538 IRS 1, NGC 7538 IRS 9, GL 2136, LkH-alpha 101, and MWC 349A, and the data are combined with previously published work for W33A and GL 2591. Cold CO is seen toward all nine sources, with temperatures from 11 K to 66 K. Column densities of cold CO are presented. Hot gas is seen toward eight of the nine objects with temperatures from 120 K to 1010 K. New lower limits to the hot gas density are obtained. The hot gas toward GL 2591, GL 2136, W3 IRS 5, and S140 IRS 1 is probably very near the central source and heated via gas-grain collisions. The optical depth in the silicate feature is strongly correlated with the (C-13)O column density, confirming that silicate optical depth is a useful measure of gas column density. The ratio of solid-to-gaseous CO is obtained for seven sources.

  16. An Infrared Search for Young Stellar Objects in IC 1396

    NASA Astrophysics Data System (ADS)

    Johnson, Chelen H.; Linahan, Marcella; Gibbs, John; Rebull, Luisa M.; Archibald, Andrew R.; Dickmann, Samantha Rose; Hart, Erica A.; Hedlund, Audrey R.; Hilfer, Shannon L.; Lacher, Thomas; McKernan, John T.; Medeiros, Emma M.; Nelson, Samantha Brooks; O'Leary, Harrison; Peña, Nicholas D.; Peterson, Alexis; Reader, Livia K.; Ropinski, Brandi Lucia; Scarpa, Gabriella; Sundeen, Kiera A.; Takara, Amber L.; Thiel, Theresa

    2017-01-01

    About 700 parsecs away from Earth, IC1396 lies along the galactic plane, in the direction of the constellation Cepheus, and includes many dark nebulae, including the Elephant’s Trunk Nebula. IC 1396A has been examined with a variety of telescopes, including Spitzer, 2MASS, IPHAS, Chandra, and WISE. The YSOVAR project (Rebull et al. 2014) also has Spitzer monitoring data in this region at 3.6 and 4.5 microns. Our team has merged these catalogs and identified candidate YSOs using IR color selection, X-ray detection, and variability metrics. In order to interpret the YSOVAR light curves, it is critical to understand which of the 700+ YSO candidates in this region are likely YSOs, and which are foreground/background stars or are extragalactic objects. As a first attempt to confirm these candidate YSOs, we have created spectral energy distributions (SEDs) for wavelengths from IPHAS r band to 24 microns, which we use, coupled with image inspection, to confirm (or refute) YSO candidates from this list of identified YSO candidates. We will then compare our vetted list of YSO candidates to the lists of YSO candidates already identified in the literature in this region. The goal of this study is to identify candidate YSO sources, as well as support the greater understanding of the variety, evolution and variability of young stars. This project is a collaborative effort of high school students from three states. They analyzed data individually and later collaborated online to compare results. This project is the result of many years of work with the NASA/IPAC Teacher Archive Research Program (NITARP).

  17. TRANSITS AND LENSING BY COMPACT OBJECTS IN THE KEPLER FIELD: DISRUPTED STARS ORBITING BLUE STRAGGLERS

    SciTech Connect

    Di Stefano, R.

    2011-05-15

    Kepler's first major discoveries are two hot (T > 10,000 K) small-radius objects orbiting stars in its field. A viable hypothesis is that these are the cores of stars that have each been eroded or disrupted by a companion star. The companion, which is the star monitored today, is likely to have gained mass from its now-defunct partner and can be considered to be a blue straggler. KOI-81 is almost certainly the product of stable mass transfer; KOI-74 may be as well, or it may be the first clear example of a blue straggler created through three-body interactions. We show that mass-transfer binaries are common enough that Kepler should discover {approx}1000 white dwarfs orbiting main-sequence stars. Most of these, like KOI-74 and KOI-81, will be discovered through transits, but many will be discovered through a combination of gravitational lensing and transits, while lensing will dominate for a subset. In fact, some events caused by white dwarfs will have the appearance of 'anti-transits' - i.e., short-lived enhancements in the amount of light received from the monitored star. Lensing and other mass-measurement methods provide a way to distinguish white dwarf binaries from planetary systems. This is important for the success of Kepler's primary mission, in light of the fact that white dwarf radii are similar to the radii of terrestrial planets, and that some white dwarfs will have orbital periods that place them in the habitable zones of their stellar companions. By identifying transiting and/or lensing white dwarfs, Kepler will conduct pioneering studies of white dwarfs and of the end states of mass transfer. It may also identify orbiting neutron stars or black holes. The calculations inspired by the discovery of KOI-74 and KOI-81 have implications for ground-based wide-field surveys as well as for future space-based surveys.

  18. Transits and Lensing by Compact Objects in the Kepler Field: Disrupted Stars Orbiting Blue Stragglers

    NASA Astrophysics Data System (ADS)

    Di Stefano, R.

    2011-05-01

    Kepler's first major discoveries are two hot (T > 10,000 K) small-radius objects orbiting stars in its field. A viable hypothesis is that these are the cores of stars that have each been eroded or disrupted by a companion star. The companion, which is the star monitored today, is likely to have gained mass from its now-defunct partner and can be considered to be a blue straggler. KOI-81 is almost certainly the product of stable mass transfer; KOI-74 may be as well, or it may be the first clear example of a blue straggler created through three-body interactions. We show that mass-transfer binaries are common enough that Kepler should discover ~1000 white dwarfs orbiting main-sequence stars. Most of these, like KOI-74 and KOI-81, will be discovered through transits, but many will be discovered through a combination of gravitational lensing and transits, while lensing will dominate for a subset. In fact, some events caused by white dwarfs will have the appearance of "anti-transits"—i.e., short-lived enhancements in the amount of light received from the monitored star. Lensing and other mass-measurement methods provide a way to distinguish white dwarf binaries from planetary systems. This is important for the success of Kepler's primary mission, in light of the fact that white dwarf radii are similar to the radii of terrestrial planets, and that some white dwarfs will have orbital periods that place them in the habitable zones of their stellar companions. By identifying transiting and/or lensing white dwarfs, Kepler will conduct pioneering studies of white dwarfs and of the end states of mass transfer. It may also identify orbiting neutron stars or black holes. The calculations inspired by the discovery of KOI-74 and KOI-81 have implications for ground-based wide-field surveys as well as for future space-based surveys.

  19. The WISE Census of Young Stellar Objects and Clusters in Canis Major

    NASA Astrophysics Data System (ADS)

    Fischer, W. J.; Padgett, D. L.; Stapelfeldt, K. R.

    The photometric data returned by WISE, the Wide-field Infrared Survey Explorer, can be used to search the sky for young stellar objects (YSOs) away from the molecular clouds studied in detail by Spitzer and Herschel. We present updated results for a 100 deg2 region centered on Canis Major, including a look at the clustering properties of YSOs in the region.

  20. A FOURIER OPTICS METHOD FOR CALCULATING STELLAR OCCULTATION LIGHT CURVES BY OBJECTS WITH THIN ATMOSPHERES

    SciTech Connect

    Young, E. F.

    2012-08-15

    A stellar occultation occurs when a solar system object passes in front of a distant star. The light curves resulting from stellar occultations can reveal many aspects of the obscuring object. For airless bodies, the diffraction light curve specifies the object's size, distance and, if several chords are observed, shape. Occultation light curves are especially sensitive to the presence of atmospheres; the refraction light curve is a function of the atmosphere's density, pressure, and temperature profiles. The goal of this paper is to develop a practical algorithm to model the simultaneous effects of diffraction and refraction for objects in which both phenomena are observable. The algorithm we present is flexible: it can be used to calculate light curves by objects with arbitrary shapes and arbitrary atmospheres (including the presence of opacity sources such as hazes), provided that the atmosphere can be represented by a thin screen with a phase delay and an opacity defined at each location in the screen. Because the algorithm is limited at present to thin atmospheres (in which rays from a star are bent but undergo virtually no translation as they pass through an atmosphere), the gas giants, Earth, Mars, and Venus are not treated. Examples of stellar occultations are presented for round or irregularly shaped objects having thin atmospheres of various column densities.

  1. A discovery of young stellar objects in older clusters of the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    For, Bi-Qing; Bekki, Kenji

    2017-06-01

    Recent studies have shown that an extended main-sequence turn-off is a common feature among intermediate-age clusters (1-3 Gyr) in the Magellanic Clouds. Multiple-generation star formation and stellar rotation or interacting binaries have been proposed to explain the feature. However, it remains controversial in the field of stellar populations. Here we present the main results of an ongoing star formation among older star clusters in the Large Magellanic Cloud. Cross-matching the positions of star clusters and young stellar objects has yielded 15 matches, with 7 located in the cluster centre. We demonstrate that this is not by chance by estimating local number densities of young stellar objects for each star cluster. This method is not based on isochrone fitting, which leads to some uncertainties in age estimation and methods of background subtraction. We also find no direct correlation between atomic hydrogen and the clusters. This suggests that gas accretion for fueling the star formation must be happening in situ. These findings support for the multiple-generations scenario as a plausible explanation for the extended main-sequence turn-off.

  2. Population Synthesis in the Blue. IV. Accurate Model Predictions for Lick Indices and UBV Colors in Single Stellar Populations

    NASA Astrophysics Data System (ADS)

    Schiavon, Ricardo P.

    2007-07-01

    We present a new set of model predictions for 16 Lick absorption line indices from Hδ through Fe5335 and UBV colors for single stellar populations with ages ranging between 1 and 15 Gyr, [Fe/H] ranging from -1.3 to +0.3, and variable abundance ratios. The models are based on accurate stellar parameters for the Jones library stars and a new set of fitting functions describing the behavior of line indices as a function of effective temperature, surface gravity, and iron abundance. The abundances of several key elements in the library stars have been obtained from the literature in order to characterize the abundance pattern of the stellar library, thus allowing us to produce model predictions for any set of abundance ratios desired. We develop a method to estimate mean ages and abundances of iron, carbon, nitrogen, magnesium, and calcium that explores the sensitivity of the various indices modeled to those parameters. The models are compared to high-S/N data for Galactic clusters spanning the range of ages, metallicities, and abundance patterns of interest. Essentially all line indices are matched when the known cluster parameters are adopted as input. Comparing the models to high-quality data for galaxies in the nearby universe, we reproduce previous results regarding the enhancement of light elements and the spread in the mean luminosity-weighted ages of early-type galaxies. When the results from the analysis of blue and red indices are contrasted, we find good consistency in the [Fe/H] that is inferred from different Fe indices. Applying our method to estimate mean ages and abundances from stacked SDSS spectra of early-type galaxies brighter than L*, we find mean luminosity-weighed ages of the order of ~8 Gyr and iron abundances slightly below solar. Abundance ratios, [X/Fe], tend to be higher than solar and are positively correlated with galaxy luminosity. Of all elements, nitrogen is the more strongly correlated with galaxy luminosity, which seems to indicate

  3. The flux-weighted gravity-luminosity relationship of blue supergiant stars as a constraint for stellar evolution

    NASA Astrophysics Data System (ADS)

    Meynet, Georges; Kudritzki, Rolf-Peter; Georgy, Cyril

    2015-09-01

    Context. The flux-weighted gravity-luminosity relationship (FGLR) of blue supergiant stars (BSG) links their absolute magnitude to the spectroscopically determined flux-weighted gravity log g/T_text{eff ^4}. BSG are the brightest stars in the universe at visual light and the application of the FGLR has become a powerful tool for determining extragalactic distances. Aims: Observationally, the FGLR is a tight relationship with only small scatter. It is, therefore, ideal for using as a constraint for stellar evolution models. The goal of this work is to investigate whether stellar evolution can reproduce the observed FGLR and to develop an improved foundation for the FGLR as an extragalactic distance indicator. Methods: We used different grids of stellar models for initial masses between 9 and 40 M⊙ and for metallicities between Z = 0.002 and 0.014, with and without rotation, which were computed with various mass loss rates during the red supergiant phase. For each of these models, we discuss the details of post-main sequence evolution and construct theoretical FGLRs by means of population synthesis models that we then compare with the observed FGLR. Results: In general, the stellar evolution model FGLRs agree reasonably well with the observed one. There are, however, differences between the models, in particular with regard to the shape and width (scatter) in the flux-weighted gravity-luminosity plane. The best agreement is obtained with models that include the effects of rotation and assume that the large majority, if not all, of the observed BSG evolve toward the red supergiant phase and that only a few are evolving back from this stage. The effects of metallicity on the shape and scatter of the FGLR are small. Conclusions: The shape, scatter, and metallicity dependence of the observed FGLR are explained well by stellar evolution models. This provides a solid theoretical foundation for using this relationship as a robust extragalactic distance indicator.

  4. A Model for (Quasi-)Periodic Multiwavelength Photometric Variability in Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Kesseli, Aurora Y.; Petkova, Maya A.; Wood, Kenneth; Whitney, Barbara A.; Hillenbrand, L. A.; Gregory, Scott G.; Stauffer, J. R.; Morales-Calderon, M.; Rebull, L.; Alencar, S. H. P.

    2016-09-01

    We present radiation transfer models of rotating young stellar objects (YSOs) with hot spots in their atmospheres, inner disk warps, and other three-dimensional effects in the nearby circumstellar environment. Our models are based on the geometry expected from magneto-accretion theory, where material moving inward in the disk flows along magnetic field lines to the star and creates stellar hot spots upon impact. Due to rotation of the star and magnetosphere, the disk is variably illuminated. We compare our model light curves to data from the Spitzer YSOVAR project to determine if these processes can explain the variability observed at optical and mid-infrared wavelengths in young stars. We focus on those variables exhibiting “dipper” behavior that may be periodic, quasi-periodic, or aperiodic. We find that the stellar hot-spot size and temperature affects the optical and near-infrared light curves, while the shape and vertical extent of the inner disk warp affects the mid-IR light curve variations. Clumpy disk distributions with non-uniform fractal density structure produce more stochastic light curves. We conclude that magneto-accretion theory is consistent with certain aspects of the multiwavelength photometric variability exhibited by low-mass YSOs. More detailed modeling of individual sources can be used to better determine the stellar hot-spot and inner disk geometries of particular sources.

  5. The 8-13 micron spectrum of the young stellar object WL 16

    NASA Technical Reports Server (NTRS)

    Hanner, M. S.; Tokunaga, A. T.; Geballe, T. R.

    1992-01-01

    Spectroscopy of WL 16 in the 8-13-micron region reveals a spectrum dominated by the hydrocarbon emission features at 7.7, 8.6, 11.25, and 12.7 microns. The emission plateau between the latter two features is detected, the first such detection in a young stellar object. The expected silicate feature is badly masked by the strong emission bands. Combining our spectra with the infrared spectral energy distribution indicates that silicate absorption is probably present.

  6. Stellar Occultations by Transneptunian and Centaurs Objects: results from more than 10 observed events

    NASA Astrophysics Data System (ADS)

    Braga-Ribas, F.; Vieira-Martins, R.; Assafin, M.; Camargo, J. I. B.; Sicardy, B.; Ortiz, J. L.

    2014-10-01

    Transneptunian objects (TNOs) are small fossils of the Solar System orbiting beyond Neptune. We use stellar occultations to derive their size and shape. This work summarizes the main results derived, so far, from all detected TNO occultations (excluding Pluto system). We have developed a process, constructing astrometric star catalogues to make long-term reliable predictions (Camargo et al. 2014). Information about their physical properties are invaluable to the understanding of the dynamical evolution of the Solar System.

  7. A MEGACAM SURVEY OF OUTER HALO SATELLITES. II. BLUE STRAGGLERS IN THE LOWEST STELLAR DENSITY SYSTEMS

    SciTech Connect

    Santana, Felipe A.; Munoz, Ricardo R.; Geha, Marla; Cote, Patrick; Stetson, Peter; Simon, Joshua D.; Djorgovski, S. G. E-mail: rmunoz@das.uchile.cl

    2013-09-10

    We present a homogeneous study of blue straggler stars across 10 outer halo globular clusters, 3 classical dwarf spheroidal galaxies, and 9 ultra-faint galaxies based on deep and wide-field photometric data taken with MegaCam on the Canada-France-Hawaii Telescope. We find blue straggler stars to be ubiquitous among these Milky Way satellites. Based on these data, we can test the importance of primordial binaries or multiple systems on blue straggler star formation in low-density environments. For the outer halo globular clusters, we find an anti-correlation between the specific frequency of blue stragglers and absolute magnitude, similar to that previously observed for inner halo clusters. When plotted against density and encounter rate, the frequency of blue stragglers is well fit by a single trend with a smooth transition between dwarf galaxies and globular clusters; this result points to a common origin for these satellites' blue stragglers. The fraction of blue stragglers stays constant and high in the low encounter rate regime spanned by our dwarf galaxies, and decreases with density and encounter rate in the range spanned by our globular clusters. We find that young stars can mimic blue stragglers in dwarf galaxies only if their ages are 2.5 {+-} 0.5 Gyr and they represent {approx}1%-7% of the total number of stars, which we deem highly unlikely. These results point to mass-transfer or mergers of primordial binaries or multiple systems as the dominant blue straggler formation mechanism in low-density systems.

  8. Accretion-induced variability links young stellar objects, white dwarfs, and black holes

    PubMed Central

    Scaringi, Simone; Maccarone, Thomas J.; Körding, Elmar; Knigge, Christian; Vaughan, Simon; Marsh, Thomas R.; Aranzana, Ester; Dhillon, Vikram S.; Barros, Susana C. C.

    2015-01-01

    The central engines of disc-accreting stellar-mass black holes appear to be scaled down versions of the supermassive black holes that power active galactic nuclei. However, if the physics of accretion is universal, it should also be possible to extend this scaling to other types of accreting systems, irrespective of accretor mass, size, or type. We examine new observations, obtained with Kepler/K2 and ULTRACAM, regarding accreting white dwarfs and young stellar objects. Every object in the sample displays the same linear correlation between the brightness of the source and its amplitude of variability (rms-flux relation) and obeys the same quantitative scaling relation as stellar-mass black holes and active galactic nuclei. We also show that the most important parameter in this scaling relation is the physical size of the accreting object. This establishes the universality of accretion physics from proto-stars still in the star-forming process to the supermassive black holes at the centers of galaxies. PMID:26601307

  9. Accretion-induced variability links young stellar objects, white dwarfs, and black holes.

    PubMed

    Scaringi, Simone; Maccarone, Thomas J; Körding, Elmar; Knigge, Christian; Vaughan, Simon; Marsh, Thomas R; Aranzana, Ester; Dhillon, Vikram S; Barros, Susana C C

    2015-10-01

    The central engines of disc-accreting stellar-mass black holes appear to be scaled down versions of the supermassive black holes that power active galactic nuclei. However, if the physics of accretion is universal, it should also be possible to extend this scaling to other types of accreting systems, irrespective of accretor mass, size, or type. We examine new observations, obtained with Kepler/K2 and ULTRACAM, regarding accreting white dwarfs and young stellar objects. Every object in the sample displays the same linear correlation between the brightness of the source and its amplitude of variability (rms-flux relation) and obeys the same quantitative scaling relation as stellar-mass black holes and active galactic nuclei. We also show that the most important parameter in this scaling relation is the physical size of the accreting object. This establishes the universality of accretion physics from proto-stars still in the star-forming process to the supermassive black holes at the centers of galaxies.

  10. Assessing the Effect of Stellar Companions from High-resolution Imaging of Kepler Objects of Interest

    NASA Astrophysics Data System (ADS)

    Hirsch, Lea A.; Ciardi, David R.; Howard, Andrew W.; Everett, Mark E.; Furlan, Elise; Saylors, Mindy; Horch, Elliott P.; Howell, Steve B.; Teske, Johanna; Marcy, Geoffrey W.

    2017-03-01

    We report on 176 close (<2″) stellar companions detected with high-resolution imaging near 170 hosts of Kepler Objects of Interest (KOIs). These Kepler targets were prioritized for imaging follow-up based on the presence of small planets, so most of the KOIs in these systems (176 out of 204) have nominal radii <6 {R}\\oplus . Each KOI in our sample was observed in at least two filters with adaptive optics, speckle imaging, lucky imaging, or the Hubble Space Telescope. Multi-filter photometry provides color information on the companions, allowing us to constrain their stellar properties and assess the probability that the companions are physically bound. We find that 60%–80% of companions within 1″ are bound, and the bound fraction is >90% for companions within 0.″5 the bound fraction decreases with increasing angular separation. This picture is consistent with simulations of the binary and background stellar populations in the Kepler field. We also reassess the planet radii in these systems, converting the observed differential magnitudes to a contamination in the Kepler bandpass and calculating the planet radius correction factor, X R = R p (true)/R p (single). Under the assumption that planets in bound binaries are equally likely to orbit the primary or secondary, we find a mean radius correction factor for planets in stellar multiples of X R = 1.65. If stellar multiplicity in the Kepler field is similar to the solar neighborhood, then nearly half of all Kepler planets may have radii underestimated by an average of 65%, unless vetted using high-resolution imaging or spectroscopy.

  11. Probing the link between dynamics and stellar evolution: Blue Straggler Stars in Globular clusters

    NASA Astrophysics Data System (ADS)

    Ferraro, F. R.; Lanzoni, B.

    2009-11-01

    In this contribution we review the main observational properties of Blue Straggler Stars (BSS) in Galactic Globular Clusters. A flower of results on the BSS frequency, radial distribution, and chemical composition are presented and discussed.

  12. Disk-mediated accretion burst in a high-mass young stellar object

    NASA Astrophysics Data System (ADS)

    Caratti O Garatti, A.; Stecklum, B.; Garcia Lopez, R.; Eislöffel, J.; Ray, T. P.; Sanna, A.; Cesaroni, R.; Walmsley, C. M.; Oudmaijer, R. D.; de Wit, W. J.; Moscadelli, L.; Greiner, J.; Krabbe, A.; Fischer, C.; Klein, R.; Ibañez, J. M.

    2016-11-01

    Solar-mass stars form via disk-mediated accretion. Recent findings indicate that this process is probably episodic in the form of accretion bursts, possibly caused by disk fragmentation. Although it cannot be ruled out that high-mass young stellar objects arise from the coalescence of their low-mass brethren, the latest results suggest that they more likely form via disks. It follows that disk-mediated accretion bursts should occur. Here we report on the discovery of the first disk-mediated accretion burst from a roughly twenty-solar-mass high-mass young stellar object. Our near-infrared images show the brightening of the central source and its outflow cavities. Near-infrared spectroscopy reveals emission lines typical for accretion bursts in low-mass protostars, but orders of magnitude more luminous. Moreover, the released energy and the inferred mass-accretion rate are also orders of magnitude larger. Our results identify disk-accretion as the common mechanism of star formation across the entire stellar mass spectrum.

  13. Study of young stellar objects around SNR G18.8+0.3

    NASA Astrophysics Data System (ADS)

    Celis Peña, M.; Paron, S.

    2016-08-01

    In recent works, through observations of molecular lines, we found that the supernova remnant (SNR) G18.8+0.3 is interacting with a molecular cloud towards its southern edge. Also it has been proven the presence of several neighboring H ii regions very likely located at the same distance as the remnant. The presence of dense molecular gas and the existence of shock fronts generated by the SNR and H ii regions make this region an interesting scenario to study the population of young stellar objects. Thus, using the most modern colour criteria applied to the emission in the mid-infrared bands obtained from IRAC and MIPS on board Spitzer, we characterized all the point sources lying in this region. We analyzed the spectral energy distributions of sources that show signs of being young stellar objects in order to confirm their nature and derive stellar parameters. Additionally, we present a map of the CO J=32 emission obtained with the ASTE telescope towards one of the H ii regions embedded in the molecular cloud. The molecular gas was studied with the aim to analyze whether the cloud is a potential site of star formation.

  14. A hot compact dust disk around a massive young stellar object.

    PubMed

    Kraus, Stefan; Hofmann, Karl-Heinz; Menten, Karl M; Schertl, Dieter; Weigelt, Gerd; Wyrowski, Friedrich; Meilland, Anthony; Perraut, Karine; Petrov, Romain; Robbe-Dubois, Sylvie; Schilke, Peter; Testi, Leonardo

    2010-07-15

    Circumstellar disks are an essential ingredient of the formation of low-mass stars. It is unclear, however, whether the accretion-disk paradigm can also account for the formation of stars more massive than about 10 solar masses, in which strong radiation pressure might halt mass infall. Massive stars may form by stellar merging, although more recent theoretical investigations suggest that the radiative-pressure limit may be overcome by considering more complex, non-spherical infall geometries. Clear observational evidence, such as the detection of compact dusty disks around massive young stellar objects, is needed to identify unambiguously the formation mode of the most massive stars. Here we report near-infrared interferometric observations that spatially resolve the astronomical-unit-scale distribution of hot material around a high-mass ( approximately 20 solar masses) young stellar object. The image shows an elongated structure with a size of approximately 13 x 19 astronomical units, consistent with a disk seen at an inclination angle of approximately 45 degrees . Using geometric and detailed physical models, we found a radial temperature gradient in the disk, with a dust-free region less than 9.5 astronomical units from the star, qualitatively and quantitatively similar to the disks observed in low-mass star formation. Perpendicular to the disk plane we observed a molecular outflow and two bow shocks, indicating that a bipolar outflow emanates from the inner regions of the system.

  15. Spitzer Observations of Long-term Infrared Variability among Young Stellar Objects in Chamaeleon I

    NASA Astrophysics Data System (ADS)

    Flaherty, Kevin M.; DeMarchi, Lindsay; Muzerolle, James; Balog, Zoltan; Herbst, William; Megeath, S. Thomas; Furlan, Elise; Gutermuth, Robert

    2016-12-01

    Infrared variability is common among young stellar objects, with surveys finding daily to weekly fluctuations of a few tenths of a magnitude. Space-based observations can produce highly sampled infrared light curves, but are often limited to total baselines of about 1 month due to the orientation of the spacecraft. Here we present observations of the Chameleon I cluster, whose low declination makes it observable by the Spitzer Space Telescope over a 200-day period. We observe 30 young stellar objects with a daily cadence to better sample variability on timescales of months. We find that such variability is common, occurring in ˜80% of the detected cluster members. The change in [3.6]-[4.5] color over 200 days for many of the sources falls between that expected for extinction and fluctuations in disk emission. With our high cadence and long baseline we can derive power spectral density curves covering two orders of magnitude in frequency and find significant power at low frequencies, up to the boundaries of our 200-day survey. Such long timescales are difficult to explain with variations driven by the interaction between the disk and stellar magnetic field, which has a dynamical timescale of days to weeks. The most likely explanation is either structural or temperature fluctuations spread throughout the inner ˜0.5 au of the disk, suggesting that the intrinsic dust structure is highly dynamic.

  16. Variable stars around selected open clusters in the VVV area: Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Medina, Nicolas; Borissova, Jura; Bayo, Amelia; Kurtev, Radostin; Lucas, Philip

    2017-09-01

    Time-varying phenomena are one of the most substantial sources of astrophysical information, and led to many fundamental discoveries in modern astronomy. We have developed an automated tool to search and analyze variable sources in the near infrared Ks band, using the data from the Vista Variables in the Vía Láctea (VVV) ESO Public Survey ([5, 8]). One of our main goals is to investigate the Young Stellar Objects (YSOs) in the Galactic star forming regions, looking for: Variability. New pre-main sequence star clusters. Here we present the newly discovered YSOs within some selected stellar clusters in our Galaxy.

  17. Absorption in the spectra of quasi-stellar objects and BL Lacertae objects

    NASA Technical Reports Server (NTRS)

    Perry, J. J.; Burbidge, E. M.; Burbidge, G. R.

    1978-01-01

    Observations of absorption in the spectra of 64 QSOs and two BL Lac objects are reviewed. Criteria for selecting the absorption-line objects are discussed along with line identifications, properties of identified absorption systems, the observed absence of variability in the absorption lines, the redshift distribution, line locking, and absorption shortward of the Lyman limit. The possibility of noncosmological redshifts is noted, and two interpretations of the absorption-line data are considered: (1) the 'intrinsic' hypothesis that the absorptions arise in gas associated with the QSOs and (2) the 'intervening' hypothesis that they are produced by intervening galaxies, galactic halos, or intergalactic clouds intersected by the line of sight to a QSO. Direct observational tests for the location of the absorbing hydrogen in several individual objects are described. It is concluded that no conclusive observational evidence exists which is capable of establishing whether the absorption is intrinsic or intervening.

  18. A new young stellar object in the S 187 complex: Photometry and spectroscopy

    NASA Astrophysics Data System (ADS)

    Zavagno, A.; Deharveng, L.; Caplan, J.

    1994-01-01

    We report the discovery in the S 187 complex of a young stellar object with an optical counterpart. High resolution spectroscopy in the red and near infrared indicates that this object is a pre-main-sequence star. In the red, the spectrumis dominated by a very bright H-alpha line with a total width (wing to wing) greater than 1000 km/s. This line exhibits a special type of P Cygni profile (Beal's Type III). The object's near infrared spectrum is dominated by the Ca II triplet emission at 8498 A, 8542 A, and 8662 A; these lines are broad and optically thick. Numerous Fe I and Fe II emission lines are observed also, B, V, R, I, H, K, and L magnitudes of the object, as well as its H-alpha luminosity, indicate that it is probably a Herbig late Be or early Ae star. It presents many characteristics of the 'outflow group' of Herbig stars identified by Hamann & Persson (1992B); it is very similar, both in luminosity and geometry, to the well-known young stellar objects V645 Cyh and R Mon.

  19. X-shooter spectroscopy of young stellar objects in Lupus. Accretion properties of class II and transitional objects

    NASA Astrophysics Data System (ADS)

    Alcalá, J. M.; Manara, C. F.; Natta, A.; Frasca, A.; Testi, L.; Nisini, B.; Stelzer, B.; Williams, J. P.; Antoniucci, S.; Biazzo, K.; Covino, E.; Esposito, M.; Getman, F.; Rigliaco, E.

    2017-03-01

    The mass accretion rate, Ṁacc, is a key quantity for the understanding of the physical processes governing the evolution of accretion discs around young low-mass (M⋆ ≲ 2.0 M⊙) stars and substellar objects (YSOs). We present here the results of a study of the stellar and accretion properties of the (almost) complete sample of class II and transitional YSOs in the Lupus I, II, III and IV clouds, based on spectroscopic data acquired with the VLT/X-shooter spectrograph. Our study combines the dataset from our previous work with new observations of 55 additional objects. We have investigated 92 YSO candidates in total, 11 of which have been definitely identified with giant stars unrelated to Lupus. The stellar and accretion properties of the 81 bona fide YSOs, which represent more than 90% of the whole class II and transition disc YSO population in the aforementioned Lupus clouds, have been homogeneously and self-consistently derived, allowing for an unbiased study of accretion and its relationship with stellar parameters. The accretion luminosity, Lacc, increases with the stellar luminosity, L⋆, with an overall slope of 1.6, similar but with a smaller scatter than in previous studies. There is a significant lack of strong accretors below L⋆ ≈ 0.1 L⊙, where Lacc is always lower than 0.01 L⋆. We argue that the Lacc - L⋆ slope is not due to observational biases, but is a true property of the Lupus YSOs. The log Ṁacc - log M⋆ correlation shows a statistically significant evidence of a break, with a steeper relation for M⋆ ≲ 0.2 M⊙ and a flatter slope for higher masses. The bimodality of the Ṁacc - M⋆ relation is confirmed with four different evolutionary models used to derive the stellar mass. The bimodal behaviour of the observed relationship supports the importance of modelling self-gravity in the early evolution of the more massive discs, but other processes, such as photo-evaporation and planet formation during the YSO's lifetime, may

  20. QUASI-STELLAR OBJECT SELECTION ALGORITHM USING TIME VARIABILITY AND MACHINE LEARNING: SELECTION OF 1620 QUASI-STELLAR OBJECT CANDIDATES FROM MACHO LARGE MAGELLANIC CLOUD DATABASE

    SciTech Connect

    Kim, Dae-Won; Protopapas, Pavlos; Alcock, Charles; Trichas, Markos; Byun, Yong-Ik; Khardon, Roni

    2011-07-10

    We present a new quasi-stellar object (QSO) selection algorithm using a Support Vector Machine, a supervised classification method, on a set of extracted time series features including period, amplitude, color, and autocorrelation value. We train a model that separates QSOs from variable stars, non-variable stars, and microlensing events using 58 known QSOs, 1629 variable stars, and 4288 non-variables in the MAssive Compact Halo Object (MACHO) database as a training set. To estimate the efficiency and the accuracy of the model, we perform a cross-validation test using the training set. The test shows that the model correctly identifies {approx}80% of known QSOs with a 25% false-positive rate. The majority of the false positives are Be stars. We applied the trained model to the MACHO Large Magellanic Cloud (LMC) data set, which consists of 40 million light curves, and found 1620 QSO candidates. During the selection none of the 33,242 known MACHO variables were misclassified as QSO candidates. In order to estimate the true false-positive rate, we crossmatched the candidates with astronomical catalogs including the Spitzer Surveying the Agents of a Galaxy's Evolution LMC catalog and a few X-ray catalogs. The results further suggest that the majority of the candidates, more than 70%, are QSOs.

  1. Combining colour and temperature: A blue object is more likely to be judged as warm than a red object.

    PubMed

    Ho, Hsin-Ni; Iwai, Daisuke; Yoshikawa, Yuki; Watanabe, Junji; Nishida, Shin'ya

    2014-07-03

    It is commonly believed that reddish colour induces warm feelings while bluish colour induces cold feelings. We, however, demonstrate an opposite effect when the temperature information is acquired by direct touch. Experiment 1 found that a red object, relative to a blue object, raises the lowest temperature required for an object to feel warm, indicating that a blue object is more likely to be judged as warm than a red object of the same physical temperature. Experiment 2 showed that hand colour also affects temperature judgment, with the direction of the effect opposite to object colours. This study provides the first demonstration that colour can modulate temperature judgments when the temperature information is acquired by direct touch. The effects apparently oppose the common conception of red-hot/blue-cold association. We interpret this phenomenon in terms of "Anti-Bayesian" integration, which suggests that the brain integrates direct temperature input with prior expectations about temperature relationship between object and hand in a way that emphasizes the contrast between the two.

  2. NuSTAR Observations of Bright X-ray Flares from Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Vievering, Juliana; Glesener, Lindsay; Grefenstette, Brian; Smith, David

    2016-05-01

    Bright x-ray flares are observed to occur on young stellar objects (YSOs) and are presumed to be driven by similar processes as those seen on our sun. Observations of the flaring activity of YSOs can add to our understanding of the early lives of stars and the development of planetary systems. In particular, x-ray observations of these stellar flares are essential for probing the youngest stars, as these stars are most obscured by dense molecular clouds. One such cloud complex of YSOs, rho Ophiuchi, has been a past target for soft x-ray (SXR) missions, including Chandra and XMM-Newton. However, the energy ranges covered by these missions drop off prior to the hard x-ray (HXR) regime, where the crossover to a dominant nonthermal component could be observed. Whether or not this nonthermal emission is strong enough to be observed could then be an indicator of how large an influence these flares have on the surrounding protoplanetary disk. To begin investigating this HXR emission, two 50ks observations of rho Ophiuchi have been taken with the Nuclear Spectroscopic Telescope Array (NuSTAR), which is optimized over the energy range of 3-79 keV. Multiple stellar flares have been identified in the observations; here we present the preliminary analysis, including light curves and spectra, of the brightest of these flaring events. We explore the implications of the data for flaring activity of YSOs and compare the results to typical flaring activity of the sun.

  3. Identification of new young stellar objects associated with IRAS point sources. III. The northern Galactic plane

    SciTech Connect

    Campbell, B.; Persson, S.E.; Matthews, K.; New Mexico Univ., Albuquerque; Palomar Observatory, Pasadena, CA )

    1989-08-01

    A third list of new candidate young stellar objects found by searching the vicinities of IRAS positions along the galactic plane is presented. The list comprises 40 new objects in 39 fields with 2.2-micron magnitudes brighter than 10.5, and with near-infrared colors similar to those of fiducial objects such as GL 490. An additional 12 objects are identified as probable YSOs on the basis of incomplete data. Positions accurate to + or - 2 arcsec and deep red CCD pictures of 31 of the fields are given. Contemporaneous 10-micron observations allow an assessment of the reliability of the identifications; at least 80 percent of the near-infrared sources are directly related to the IRAS source, and the remainder are probably associated, but may not be the exciting sources of the regions. 11 refs.

  4. LBT/LUCIFER near-infrared spectroscopy of PV Cephei. An outbursting young stellar object with an asymmetric jet

    NASA Astrophysics Data System (ADS)

    Caratti o Garatti, A.; Garcia Lopez, R.; Weigelt, G.; Tambovtseva, L. V.; Grinin, V. P.; Wheelwright, H.; Ilee, J. D.

    2013-06-01

    Context. Young stellar objects (YSOs) occasionally experience enhanced accretion events, the nature of which is still poorly understood. The discovery of various embedded outbursting YSOs has recently questioned the classical definition of EXors and FUors. Aims: We present a detailed spectroscopic investigation of the young eruptive star PV Cep, to improve our understanding of its nature and characterise its circumstellar environment after its last outburst in 2004. Methods: The analysis of our medium-resolution spectroscopy in the near-infrared (NIR, 0.9-2.35 μm), collected in 2012 at the Large Binocular Telescope with the IR spectrograph LUCIFER, allows us to infer the main stellar parameters (visual extinction, accretion luminosity, mass accretion and ejection rates), and model the inner disc, jet, and wind. Results: The NIR spectrum displays several strong emission lines associated with accretion/ejection activity and circumstellar environment. Our analysis shows that the brightness of PV Cep is fading, as well as the mass accretion rate (2 × 10-7 M⊙ yr-1 in 2012 vs. ~5 × 10-6 M⊙ yr-1 in 2004), which is more than one order of magnitude lower than in the outburst phase. Among the several emission lines, only the [Fe ii] intensity increased after the outburst. The observed [Fe ii] emission delineates blue- and red-shifted lobes, both with high- and low-velocity components, which trace an asymmetric jet and wind, respectively. The observed emission in the jet has a dynamical age of 7-8 years, indicating that it was produced during the last outburst. The visual extinction decreases moving from the red-shifted (AV(red) = 10.1 ± 0.7 mag) to the blue-shifted lobe (AV(blue) = 6.5 ± 0.4 mag). We measure an average electron temperature of 17 500 K and electron densities of 30 000 cm-3 and 15 000 cm-3 for the blue and the red lobe, respectively. The mass ejection rate in both lobes is ~1.5 × 10-7 M⊙ yr-1, approximately matching the high accretion rate observed

  5. BlueJ Visual Debugger for Learning the Execution of Object-Oriented Programs?

    ERIC Educational Resources Information Center

    Bennedsen, Jens; Schulte, Carsten

    2010-01-01

    This article reports on an experiment undertaken in order to evaluate the effect of a program visualization tool for helping students to better understand the dynamics of object-oriented programs. The concrete tool used was BlueJ's debugger and object inspector. The study was done as a control-group experiment in an introductory programming…

  6. Bright-rimmed clouds and Young Stellar Objects in IC 1396

    NASA Astrophysics Data System (ADS)

    Choudhury, R.; Bhatt, H. C.

    Spectroscopic observations of Young Stellar Objects (YSOs) in IC 1396 are presented. It is found that there is a systematic variation, as a function of position, in W_{λ} (Hα) of the YSOs in/around SFO 38 e.g YSOs close to bright-rim have stronger Hα emission and show significant variations compared to the W_{λ} (Hα) obtained from literature. The nearly coplanar geometry of HD 206267 and the globules is also discussed using 1.4 GHz images from NRAO VLA Sky Survey.

  7. Stellar, Remnant, Planetary, and Dark-Object Masses from Astrometric Microlensing

    NASA Technical Reports Server (NTRS)

    Gould, Andrew P.; Bennett, David P.; Boden, Andrew; Depoy, Darren L.; Gaudi, Scott B.; Griest, Kim; Han, Cheongho; Paczynski, Bohdan; Reid, I. Neill

    2004-01-01

    The primary goal of our project is to make a complete census of the stellar population of the Galaxy. We are broadening the term stellar here to include both ordinary stars and dark stars. Ordinary stars, burning their nuclear fuel and shining, can perhaps best be studied with traditional astronomical techniques, but dark stars, by which we include old brown dwarfs, black holes, old white dwarfs, neutron stars, and perhaps exotic objects such as mirror matter stars or primordial black holes, can only be studied by their gravitational effects. Traditionally, these objects have been probed in binaries, and thus selected in a way that may or may not be representative of their respective field populations. The only way to examine the field population of these stars is through microlensing, the deflection of light from a visible star in the background by an object (dark or not) in the foreground. When lensed, there are two images of the background star. Although these images cannot be resolved when the lens has a stellar mass, the lensing effect can be detected in two ways: photometrically, i.e. by measuring the magnification of the source by the lens, and astrometrically, i.e. by measuring the shift in the centroid of the two images. Photometric microlensing experiments have detected hundreds of microlensing events over the past decade. Despite its successes, photometric microlensing has so far been somewhat frustrating because these events are difficult to interpret. Almost nothing is known about the masses of individual lenses and very little is known about the statistical properties of the lenses treated as a whole, such as their average mass. Although probably over 100 of the lenses are in fact dark objects, we can't determine which they are, let alone investigate finer details such as what their masses are, and where they are in the Galaxy. With SIM, we will break the microlensing degeneracy, and allow detailed interpretation of individual microlensing events. We

  8. Testing the Jet-Accretion Connection in Young Stellar Objects in the Time Domain

    NASA Astrophysics Data System (ADS)

    Galván-Madrid, R.; Rodríguez, L. F.; Liu, H. B.; Costigan, G.; Carrasco-González, C.; Manara, C. F.; Forbrich, J.; Ramsay, S.

    2017-07-01

    It is known that in the formation of a star, accretion of mass through a circumstellar disk is accompanied by the ejection of a fraction of this material through jets and outflows. It is usually assumed that this fraction is fixed in time, or that it slowly evolves on the star formation timescale of 105 to 106 yr. But, is this true? Do accretion and ejection follow each other within samples of objects, or in time for a given object? We present preliminary results of a project aimed at testing the relation between accretion and ejection of mass in star formation. The first component of the project looks for radio-jet ejections in young stellar objects (YSOs) known to have accretion-related infrared outbursts. The second component is a radio/IR time monitoring with facilities such as the JVLA and the VLT of a large number of YSOs in some of the nearest star forming clouds.

  9. Hubble Space Telescope WFPC2 Imaging of M16: Photoevaporation and Emerging Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Hester, J. J.; Scowen, P. A.; Sankrit, R.; Lauer, T. R.; Ajhar, E. A.; Baum, W. A.; Code, A.; Currie, D. G.; Danielson, G. E.; Ewald, S. P.; Faber, S. M.; Grillmair, C. J.; Groth, E. J.; Holtzman, J. A.; Hunter, D. A.; Kristian, J.; Light, R. M.; Lynds, C. R.; Monet, D. G.; O'Neil, E. J., Jr.; Shaya, E. J.; Seidelmann, P. K.; Westphal, J. A.

    1996-06-01

    We present Hubble Space Telescope WFPC2 images of elephant trunks in the H II region M16. There are three principle results of this study. First, the morphology and stratified ionization structure of the interface between the dense molecular material and the interior of the H II region is well understood in terms of photoionization of a photoevaporative flow. Photoionization models of an empirical density profile capture the essential features of the observations, including the extremely localized region of [S II] emission at the interface and the observed offset between emission peaks in lower and higher ionization lines. The details of this structure are found to be a sensitive function both of the density profile of the interface and of the shape of the ionizing continuum. Interpretation of the interaction of the photoevaporative flow with gas in the interior of the nebula supports the view that much of the emission from H II regions may arise in such flows. Photoionization of photoevaporative flows may provide a useful paradigm for interpreting a wide range of observations of H II regions. Second, we report the discovery of a population of small cometary globules that are being uncovered as the main bodies of the elephant trunks are dispersed. Several lines of evidence connect these globules to ongoing star formation, including the association of a number of globules with stellar objects seen in IR images of M16 or in the continuum HST images themselves. We refer to these structures as evaporating gaseous globules, or "EGGs." These appear to be the same type of object as the nebular condensations seen previously in M42. The primary difference between the two cases is that in M16 we are seeing the objects from the side, while in M42 the objects are seen more nearly face-on against the backdrop of the ionized face of the molecular cloud. We find that the "evaporating globule" interpretation naturally accounts for the properties of objects in both nebulae, while

  10. Intense accretion and mass loss of a very low mass young stellar object

    NASA Astrophysics Data System (ADS)

    Fernández, M.; Comerón, F.

    2001-12-01

    We present visible and near-infrared photometry and spectroscopy of LS-RCrA 1, a faint, very late-type object (M 6.5-M 7) seen in the direction of the R Coronae Australis star forming complex. While its emission spectrum shows prominent features of accretion and mass loss typical of young stellar objects, its underlying continuum and photometric properties are puzzling when trying to derive a mass and age based on pre-main sequence evolutionary tracks: the object appears to be far too faint for a young member of the R Coronae Australis complex of its spectral type. We speculate that this may be due to either its evolution along pre-main sequence tracks being substantially altered by the intense accretion, or to a combination of partial blocking and scattering of the light of the object by a nearly edge-on circumstellar disk. The rich emission line spectrum superimposed on the stellar continuum is well explained by an intense accretion process: the Halpha , CaII infrared triplet, and HeI 6678 lines show equivalent widths typical of very active classical T Tauri stars. The near-infrared observations show anomalously weak spectral features and no significant excess emission in the K band, which we tentatively interpret as indicating line filling due to emission in a magnetic accretion funnel flow. At the same time, numerous, strong forbidden optical lines ([OI], [NII] and [SII]) and H2 emission at 2.12 mu m suggest that the object is simultaneously undergoing mass loss, providing another example that shows that mass loss and accretion are closely related processes. Such an intense accretion and mass loss activity is observed for the first time in a young stellar object in the transition region between low mass stars and brown dwarfs, and provides a valuable observational test on the effects of accretion on the evolution of objects with such low masses. Based on observations collected at the European Southern Observatory in La Silla and Cerro Paranal (Chile), in

  11. The Use of Stellar Occultations to Study Trans-Neptunian Objects

    NASA Astrophysics Data System (ADS)

    ROSSI, GUSTAVO B.; Sicardy, Bruno; Braga-Ribas, Felipe; Vieira Martins, Roberto; Camargo, Julio; Assafin, Marcelo

    2014-11-01

    The physical parameters of the Trans-Neptunian Objects (TNO's) such as size, shape, density, presence of atmosphere, and rings, provide important information on their formation and evolution. At more than 30 Astronomical Units (AU) from the Sun, those objects receive low solar radiation and have low mutual collisions velocities so they can be considered as remnants of the primordial outer Solar System. Besides that, information on TNO's is of great relevance when trying to establish a general formation scenario for the recently discovered planetary systems.The problem is that such bodies have a diameter smaller than 2300 km (Eris, one of the largest TNO, has 2326 km) and, when viewed from Earth, they usually subtend angles smaller than 50 milli-arcseconds, preventing direct imaging. One method to obtain very accurate information on the TNO's is the stellar occultation technique. Sizes at kilometer accuracies and pressure at nanobar levels can be achieved with this method, as well as detection of ring systems. Shape, density, albedo and other physical parameters can also be derived from this technique.Since 2010, we observed stellar occultations of several TNO's (Eris, Makemake, 2003VS2, Quaoar, Ixion, Varuna, 2002KX14, and 2003AZ84) besides some other occultations by Pluto and Charon, and by the largest Centaur known to date, Chariklo. We also predicted future events in 2014 and 2015 for 40 TNO's and Centaurs. On this work, we present the process of our campains - predictions, follow ups, world wide cooperation, post-occutation data analysis -, the new results obtained from recent stellar occultations of TNO's, and the expectations of improvements after GAIA.

  12. The SEEDS High-Contrast Imaging Survey of Exoplanets Around Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Uyama, Taichi; Hashimoto, Jun; Kuzuhara, Masayuki; Mayama, Satoshi; Akiyama, Eiji; Currie, Thayne; Livingston, John; Kudo, Tomoyuki; Kusakabe, Nobuhiko; Abe, Lyu; Brandner, Wolfgang; Brandt, Timothy D.; Carson, Joseph C.; Egner, Sebastian; Feldt, Markus; Goto, Miwa; Grady, Carol A.; Guyon, Olivier; Hayano, Yutaka; Hayashi, Masahiko; Hayashi, Saeko S.; Henning, Thomas; Hodapp, Klaus W.; Ishii, Miki; Iye, Masanori; Janson, Markus; Kandori, Ryo; Knapp, Gillian R.; Kwon, Jungmi; Matsuo, Taro; Mcelwain, Michael W.; Miyama, Shoken; Morino, Jun-Ichi; Moro-Martin, Amaya; Nishimura, Tetsuo; Pyo, Tae-Soo; Serabyn, Eugene; Suenaga, Takuya; Suto, Hiroshi; Suzuki, Ryuji; Takahashi, Yasuhiro H.; Takami, Michihiro; Takato, Naruhisa; Terada, Hiroshi; Thalmann, Christian; Turner, Edwin L.; Watanabe, Makoto; Wisniewski, John; Yamada, Toru; Takami, Hideki; Usuda, Tomonori; Tamura, Motohide

    2017-03-01

    We present high-contrast observations of 68 young stellar objects (YSOs) that have been explored as part of the Strategic Exploration of Exoplanets and Disks with Subaru (SEEDS) survey on the Subaru telescope. Our targets are very young (<10 Myr) stars, which often harbor protoplanetary disks where planets may be forming. We achieve a typical contrast of ∼10‑4–10‑5.5 at an angular distance of 1″ from the central star, corresponding to typical mass sensitivities (assuming hot-start evolutionary models) of ∼10 M J at 70 au and ∼6 M J at 140 au. We detected a new stellar companion to HIP 79462 and confirmed the substellar objects GQ Lup b and ROXs 42B b. An additional six companion candidates await follow-up observations to check for common proper motion. Our SEEDS YSO observations probe the population of planets and brown dwarfs at the very youngest ages; these may be compared to the results of surveys targeting somewhat older stars. Our sample and the associated observational results will help enable detailed statistical analyses of giant planet formation.

  13. THE EXTENDED NARROW-LINE REGION OF TWO TYPE-I QUASI-STELLAR OBJECTS

    SciTech Connect

    Oh, Semyeong; Woo, Jong-Hak; Bennert, Vardha N.; Jungwiert, Bruno; Leipski, Christian; Albrecht, Marcus E-mail: woo@astro.snu.ac.kr E-mail: bruno@ig.cas.cz E-mail: leipski@mpia-hd.mpg.de

    2013-04-20

    We investigate the narrow-line region (NLR) of two radio-quiet QSOs, PG1012+008 and PG1307+085, using high signal-to-noise spatially resolved long-slit spectra obtained with FORS1 at the Very Large Telescope. Although the emission is dominated by the point-spread function of the nuclear source, we are able to detect extended NLR emission out to several kiloparsec scales in both QSOs by subtracting the scaled central spectrum from outer spectra. In contrast to the nuclear spectrum, which shows a prominent blue wing and a broad line profile of the [O III] line, the extended emission reveals no clear signs of large-scale outflows. Exploiting the wide wavelength range, we determine the radial change of the gas properties in the NLR, i.e., gas temperature, density, and ionization parameter, and compare them with those of Seyfert galaxies and type-II QSOs. The QSOs have higher nuclear temperature and lower electron density than Seyferts, but show no significant difference compared to type-II QSOs, while the ionization parameter decreases with radial distance, similar to the case of Seyfert galaxies, For PG1012+008, we determine the stellar-velocity dispersion of the host galaxy. Combined with the black hole mass, we find that the luminous radio-quiet QSO follows the local M{sub BH}-{sigma}{sub *} relation of active galactic nuclei.

  14. Studying the molecular ambient towards the young stellar object EGO G35.04-0.47

    NASA Astrophysics Data System (ADS)

    Paron, Sergio; Ortega, Martín; Astort, Ana; Rubio, Mónica; Fariña, Cecilia

    2014-02-01

    We are performing a systematic study of the interstellar medium around extended green objects (EGOs), likely massive young stellar objects driving outflows. EGO G35.04-0.47 is located towards a dark cloud at the north-western edge of an H II region. Recently, H2 jets were discovered towards this source, mainly towards its south-west, where the H2 1-0 S(1) emission peaks. Therefore, the source was catalogued as the molecular hydrogen emission-line object MHO 2429. In order to study the molecular ambient towards this star-forming site, we observed a region around the aforementioned EGO using the Atacama Submillimeter Telescope Experiment in the 12CO J = 3-2, 13CO J = 3-2, HCO+ J = 4-3, and CS J = 7-6 lines with an angular and spectral resolution of 22'' and 0.11 km s-1, respectively. The observations revealed a molecular clump where the EGO is embedded at vLSR ˜ 51 km s-1, in coincidence with the velocity of a Class I 95 GHz methanol maser previously detected. Analyzing the 12CO line we discovered high velocity molecular gas in the range from 34 to 47 km s-1, most likely a blueshifted outflow driven by the EGO. The alignment and shape of this molecular structure coincide with those of the south-west lobe of MHO 2429, mainly between 46 and 47 km s-1, confirming that we are mapping its CO counterpart. Performing a spectral energy distribution analysis of EGO G35.04-0.47, we found that its central object should be an intermediate-mass young stellar object accreting mass at a rate similar to those found in some massive YSOs. We suggest that this source can become a massive YSO.

  15. The peculiar dipping events in the disc-bearing young-stellar object EPIC 204278916

    NASA Astrophysics Data System (ADS)

    Scaringi, S.; Manara, C. F.; Barenfeld, S. A.; Groot, P. J.; Isella, A.; Kenworthy, M. A.; Knigge, C.; Maccarone, T. J.; Ricci, L.; Ansdell, M.

    2016-12-01

    EPIC 204278916 has been serendipitously discovered from its K2 light curve that displays irregular dimmings of up to 65 per cent for ≈25 consecutive days out of 78.8 d of observations. For the remaining duration of the observations, the variability is highly periodic and attributed to stellar rotation. The star is a young, low-mass (M-type) pre-main-sequence star with clear evidence of a resolved tilted disc from Atacama Large Millimeter/submillimeter Array (ALMA) observations. We examine the K2 light curve in detail and hypothesize that the irregular dimmings are caused by either a warped inner disc edge or transiting cometary-like objects in either circular or eccentric orbits. The explanations discussed here are particularly relevant for other recently discovered young objects with similar absorption dips.

  16. Faint quasi-stellar-object candidates in selected areas 28 and 68 identified from multicolor photometry

    SciTech Connect

    Shields, J.C.; Koo, D.C.; Kron, R.C.; California Univ., Berkeley; Lick Observatory, Santa Cruz, CA; Yerkes Observatory, Williams Bay, WI )

    1989-04-01

    Forty-five QSO candidates over a total area of 0.53 square degree in two fields at high Galactic latitudes have been identified. These candidates reached B of about 21.5 for field Lynx.3 in SA 28 and B of about 22 for field SA68.2, and were selected from a subset of objects in catalogs generated from multicolor photometry (UBV) of deep Kitt Peak 4-m plates with limits of B of about 24. This subset consists of all objects which appeared stellar-like in size but which did not have the UBV colors of common Galactic stars. Besides several probable high-redshift QSOs, this study yields faint QSO counts consistent with those from other surveys, and thus provides further support to models that include mainly the luminosity evolution of QSOs. 29 refs.

  17. Near-infrared observations of young stellar objects in the Rho Ophiuchi dark cloud

    NASA Technical Reports Server (NTRS)

    Greene, Thomas P.; Young, Erick T.

    1992-01-01

    We have conducted an imaging survey of 1.4 sq pc of the Rho Ophiuchi dark cloud in the J, H, and K near-infrared photometric bands. Approximately 337 of our 481 detected sources are associated with the cloud, and we estimate that 48 percent of these have near-infrared excesses, indicative of disks or circumstellar material surrounding these young stellar objects (YSOs). The K-band luminosity function is significantly different in different regions of our survey area, suggesting that YSOs in these regions have different ages or mass functions. We estimate that the entire survey area has a high star-formation efficiency, at roughly 23 percent. Finally, our many newly detected sources provide a relatively large, uniformly sensitive sample of objects for study at longer wavelengths to better determine true source luminosities and evolutionary lifetimes.

  18. First Spectroscopic Identification of Massive Young Stellar Objects in the Galactic Center

    NASA Technical Reports Server (NTRS)

    An, Deokkeun; Ramirez, V.; Sellgren, Kris; Arendt, Richard G.; Boogert, A. C.; Schultheis, Mathias; Stolovy, Susan R.; Cotera, Angela S.; Robitaille, Thomas P.; Smith, Howard A.

    2009-01-01

    We report the detection of several molecular gas-phase and ice absorption features in three photometrically-selected young stellar object (YSO) candidates in the central 280 pc of the Milky Way. Our spectra, obtained with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope, reveal gas-phase absorption from CO2 (15.0 microns), C2H2 (13.7 microns) and HCN (14.0 microns). We attribute this absorption to warm, dense gas in massive YSOs. We also detect strong and broad 15 microns CO2 ice absorption features, with a remarkable double-peaked structure. The prominent long-wavelength peak is due to CH3OH-rich ice grains, and is similar to those found in other known massive YSOs. Our IRS observa.tions demonstra.te the youth of these objects, and provide the first spectroscopic identification of massive YSOs in the Galactic Center.

  19. Further Mapping of the Radio Emission from Massive Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Hoare, Melvin G.; Garrington, Simon T.

    1995-08-01

    We present high-resolution radio maps at a frequency of 1.6 GHz made with the MERLIN array of the luminous young stellar objects Cep A2 and LkHα 101. The elongation seen previously in Cep A2 appears to extend even farther in our map, supporting a jet interpretation for the morphology of this source. We discuss this and alternative mechanisms in the context of the large-scale outflows in the Cep A region. The 1.6 GHz map of LkHα 101 is more symmetric, although it does show a bright bar of emission at P.A. ≍ 135° plus other extended structures. This map is compared with the previous ones, and overall the ionized wind from this object appears to be far from homogeneous.

  20. Spectroscopic Assessment of WISE-based Young Stellar Object Selection Near λ and σ Orionis

    NASA Astrophysics Data System (ADS)

    Koenig, Xavier; Hillenbrand, Lynne A.; Padgett, Deborah L.; DeFelippis, Daniel

    2015-10-01

    We have conducted a sensitive search down to the hydrogen burning limit for unextincted stars over ∼200 square degrees around Lambda Orionis and 20 square degrees around Sigma Orionis using the methodology of Koenig & Leisawitz. From WISE and 2MASS data we identify 544 and 418 candidate young stellar objects (YSOs) in the vicinity of λ and σ respectively. Based on our followup spectroscopy for some candidates and the existing literature for others, we found that ∼80% of the K14-selected candidates are probable or likely members of the Orion star-forming region. The yield from the photometric selection criteria shows that WISE sources with {K}S-w3\\gt 1.5 mag and KS between 10 and 12 mag are most likely to show spectroscopic signs of youth, while WISE sources with {K}S-w3 > 4 mag and {K}S\\gt 12 were often active galactic nuclei when followed up spectroscopically. The population of candidate YSOs traces known areas of active star formation, with a few new “hot spots” of activity near Lynds 1588 and 1589 and a more dispersed population of YSOs in the northern half of the H ii region bubble around σ and ɛ Ori. A minimal spanning tree analysis of the two regions to identify stellar groupings finds that roughly two-thirds of the YSO candidates in each region belong to groups of 5 or more members. The population of stars selected by WISE outside the MST groupings also contains spectroscopically verified YSOs, with a local stellar density as low as 0.5 stars per square degree.

  1. A Search for Water Maser Emission from Brown Dwarfs and Low-luminosity Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Gómez, José F.; Palau, Aina; Uscanga, Lucero; Manjarrez, Guillermo; Barrado, David

    2017-05-01

    We present a survey for water maser emission toward a sample of 44 low-luminosity young objects, comprising (proto-)brown dwarfs, first hydrostatic cores (FHCs), and other young stellar objects (YSOs) with bolometric luminosities lower than 0.4 L ⊙. Water maser emission is a good tracer of energetic processes, such as mass-loss and/or accretion, and is a useful tool to study these processes with very high angular resolution. This type of emission has been confirmed in objects with L bol ≳ 1 L ⊙. Objects with lower luminosities also undergo mass-loss and accretion, and thus, are prospective sites of maser emission. Our sensitive single-dish observations provided a single detection when pointing toward the FHC L1448 IRS 2E. However, follow-up interferometric observations showed water maser emission associated with the nearby YSO L1448 IRS 2 (a Class 0 protostar of L bol ≃ 3.6-5.3 L ⊙) and did not find any emission toward L1448 IRS 2E. The upper limits for water maser emission determined by our observations are one order of magnitude lower than expected from the correlation between water maser luminosities and bolometric luminosities found for YSOs. This suggests that this correlation does not hold at the lower end of the (sub)stellar mass spectrum. Possible reasons are that the slope of this correlation is steeper at L bol ≤ 1 L ⊙ or that there is an absolute luminosity threshold below which water maser emission cannot be produced. Alternatively, if the correlation still stands at low luminosity, the detection rates of masers would be significantly lower than the values obtained in higher-luminosity Class 0 protostars.

  2. Near-infrared (JHK) spectroscopy of young stellar and substellar objects in orion

    SciTech Connect

    Ingraham, P.; Albert, L.; Doyon, R.; Artigau, E.

    2014-02-10

    We performed low-resolution (R ∼ 40) near-infrared (0.9-2.4 μm) multi-object spectroscopy of 240 isolated point sources having apparent H-band magnitudes between 9 and 18 in the central 5' × 6' of the Orion Trapezium cluster. The observations were performed over four nights at the Canada-France-Hawaii Telescope using the visiting instrument SIMON, an infrared imager and multi-object spectrograph. We present the spectra of 104 objects with accurately derived spectral types including 7 new objects having masses below the hydrogen-burning limit, and 6 objects with masses below the deuterium-burning limit. The spectral classification is performed by fitting previously classified spectral templates of dwarf stars (K4-M3) and optically classified young stellar and substellar objects (M4-L0), to the entire 0.9-2.4 μm spectral energy distribution in order to assign a spectral type and visual extinction for each object. Of the 104 objects studied, 44 have been previously classified spectroscopically using various techniques. We perform a rigorous comparison between the previous classifications and our own and find them to be in good agreement. Using the dereddened H-band magnitudes, the classified objects are used to create an Hertzsprung-Russell diagram for the cluster. We find that the previous age estimates of ∼1 Myr to be consistent with our results. Consistent with previous studies, numerous objects are observed to have luminosities several magnitudes above the 1 Myr isochrone. Numerous objects exhibiting emission features in the J band are also reported.

  3. Radio Properties of Young Stellar Objects in the Core of the Serpens South Infrared Dark Cloud

    NASA Astrophysics Data System (ADS)

    Kern, Nicholas S.; Keown, Jared A.; Tobin, John J.; Mead, Adrian; Gutermuth, Robert A.

    2016-02-01

    We present deep radio continuum observations of the star-forming core of the Serpens South Infrared Dark Cloud with the Karl G. Jansky Very Large Array. Observations were conducted in two bands centered at 7.25 GHz (4.14 cm) and 4.75 GHz (6.31 cm) with a {σ }{rms} of 8.5 and 11.1 μJy/beam, respectively. We also use 2MASS, Spitzer and Herschel data to put our radio observations in the context of young stellar populations characterized by near and far-infrared observations. Within a 5‧ × 5‧ region of interest around the central cluster, we detect roughly eighteen radio sources, seven of which we determine are protostellar in nature due to their radio spectral indices and their association with infrared sources. We find evidence for a previously undetected embedded Class 0 protostar and reaffirm Class 0 protostellar classifications determined by previous millimeter wavelength continuum studies. We use our infrared data to derive mid-infrared luminosities for three of our protostellar sources and find relative agreement between the known young stellar object (YSO) radio luminosity versus bolometric luminosity correlation. Lastly, we marginally detect an additional six radio sources at the 2-3σ level that lie within two arcseconds of infrared YSO candidates, providing motivation for higher sensitivity studies to clarify the nature of these sources and further probe embedded and/or low luminosity YSOs in Serpens South.

  4. On the accretion properties of young stellar objects in the L1615/L1616 cometary cloud

    NASA Astrophysics Data System (ADS)

    Biazzo, K.; Alcalá, J. M.; Frasca, A.; Zusi, M.; Getman, F.; Covino, E.; Gandolfi, D.

    2014-12-01

    We present the results of FLAMES/UVES and FLAMES/GIRAFFE spectroscopic observations of 23 low-mass stars in the L1615/L1616 cometary cloud, complemented with FORS2 and VIMOS spectroscopy of 31 additional stars in the same cloud. L1615/L1616 is a cometary cloud in which the star formation was triggered by the impact of massive stars in the Orion OB association. From the measurements of the lithium abundance and radial velocity, we confirm the membership of our sample to the cloud. We use the equivalent widths of the Hα, Hβ, and the He i λ5876, λ6678, λ7065 Å emission lines to calculate the accretion luminosities, Lacc, and the mass accretion rates, Ṁacc. We find in L1615/L1616 a fraction of accreting objects (~30%), which is consistent with the typical fraction of accretors in T associations of similar age (~3 Myr). The mass accretion rate for these stars shows a trend with the mass of the central object similar to that found for other star-forming regions, with a spread at a given mass that depends on the evolutionary model used to derive the stellar mass. Moreover, the behavior of the 2MASS/WISE colors with Ṁacc indicates that strong accretors with log Ṁacc ≳ -8.5 dex show large excesses in the JHKs bands, as in previous studies. We also conclude that the accretion properties of the L1615/L1616 members are similar to those of young stellar objects in T associations, like Lupus. Based on FLAMES (UVES+GIRAFFE) observations collected at the Very Large Telescope (VLT; Paranal, Chile). Program 076.C-0385(A).Tables 3-6 and Appendices are available in electronic form at http://www.aanda.org

  5. Young Stellar Objects in Lynds 1641: Disks, Accretion, and Star Formation History

    NASA Astrophysics Data System (ADS)

    Fang, Min; Kim, Jinyoung Serena; van Boekel, Roy; Sicilia-Aguilar, Aurora; Henning, Thomas; Flaherty, Kevin

    2013-07-01

    We investigate the young stellar objects (YSOs) in the Lynds 1641 (L1641) cloud using multi-wavelength data including Spitzer, WISE, the Two Micron All Sky Survey, and XMM covering ~1390 YSOs across a range of evolutionary stages. In addition, we targeted a sub-sample of YSOs for optical spectroscopy with the MMT/Hectospec and the MMT/Hectochelle. We use these data, along with archival photometric data, to derive spectral types, extinction values, masses, ages, and accretion rates. We obtain a disk fraction of ~50% in L1641. The disk frequency is almost constant as a function of stellar mass with a slight peak at log (M */M ⊙) ≈ -0.25. The analysis of multi-epoch spectroscopic data indicates that the accretion variability of YSOs cannot explain the two orders of magnitude of scatter for YSOs with similar masses. Forty-six new transition disk (TD) objects are confirmed in this work, and we find that the fraction of accreting TDs is lower than for optically thick disks (40%-45% versus 77%-79%, respectively). We confirm our previous result that the accreting TDs have a median accretion rate similar to normal optically thick disks. We confirm that two star formation modes (isolated versus clustered) exist in L1641. We find that the diskless YSOs are statistically older than the YSOs with optically thick disks and the TD objects have a median age that is intermediate between those of the other two populations. We tentatively study the star formation history in L1641 based on the age distribution and find that star formation started to be active 2-3 Myr ago.

  6. Near-IR imaging toward a puzzling young stellar object precessing jet

    NASA Astrophysics Data System (ADS)

    Paron, S.; Fariña, C.; Ortega, M. E.

    2016-10-01

    Aims: The study of jets that are related to stellar objects in formation is important because it enables us to understand the history of how the stars have built up their mass. Many studies currently examine jets towards low-mass young stellar objects, while equivalent studies toward massive or intermediate-mass young stellar objects are rare. In a previous study, based on 12CO J = 3-2 and public near-IR data, we found highly misaligned molecular outflows toward the infrared point source UGPS J185808.46+010041.8 (IRS) and some infrared features suggesting the existence of a precessing jet. Methods: Using near-IR data acquired with Gemini-NIRI at the JHKs broad- and narrowbands centered on the emission lines of [FeII], H2 1-0 S(1), H2 2-1 S(1), Brγ, and CO 2-0 (bh), we studied the circumstellar environment of IRS with an angular resolution between 0.̋35 and 0.̋45. Results: The emission in the JHKs broadbands shows in great detail a cone-shaped nebula extending to the north-northeast of the point source, which appears to be attached to it by a jet-like structure. In the three bands the nebula is resolved in a twisted-shaped feature composed of two arc-like features and a bow-shock-like structure seen mainly in the Ks band, which strongly suggests the presence of a precessing jet. An analysis of proper motions based on our Gemini observations and UKIDSS data additionally supports the precession scenario. We present one of the best-resolved cone-like nebula that is most likely related to a precessing jet up to date. The analysis of the observed near-IR lines shows that the H2 is collisionally excited, and the spatially coincidence of the [FeII] and H2 emissions in the closer arc-like feature suggests that this region is affected by a J shock. The second arc-like feature presents H2 emission without [FeII], which suggests a nondissociated C shock or a less energetic J shock. The H2 1-0 S(1) continuum-subtracted image reveals several knots and filaments at a larger

  7. Kinematics of the Stellar Halo and the Mass Distribution of the Milky Way Using Blue Horizontal Branch Stars

    NASA Astrophysics Data System (ADS)

    Kafle, Prajwal R.; Sharma, Sanjib; Lewis, Geraint F.; Bland-Hawthorn, Joss

    2012-12-01

    Here, we present a kinematic study of the Galactic halo out to a radius of ~60 kpc, using 4664 blue horizontal branch stars selected from the SDSS/SEGUE survey to determine key dynamical properties. Using a maximum likelihood analysis, we determine the velocity dispersion profiles in spherical coordinates (σ r , σθ, σphi) and the anisotropy profile (β). The radial velocity dispersion profile (σ r ) is measured out to a galactocentric radius of r ~ 60 kpc, but due to the lack of proper-motion information, σθ, σphi, and β could only be derived directly out to r ~ 25 kpc. From a starting value of β ≈ 0.5 in the inner parts (9 < r/kpc < 12), the profile falls sharply in the range r ≈ 13-18 kpc, with a minimum value of β = -1.2 at r = 17 kpc, rising sharply at larger radius. In the outer parts, in the range 25 < r/kpc < 56, we predict the profile to be roughly constant with a value of β ≈ 0.5. The newly discovered kinematic anomalies are shown not to arise from halo substructures. We also studied the anisotropy profile of simulated stellar halos formed purely by accretion and found that they cannot reproduce the sharp dip seen in the data. From the Jeans equation, we compute the stellar rotation curve (v circ) of the Galaxy out to r ~ 25 kpc. The mass of the Galaxy within r <~ 25 kpc is determined to be 2.1 × 1011 M ⊙, and with a three-component fit to v circ(r), we determine the virial mass of the Milky Way dark matter halo to be M vir = 0.9+0.4 -0.3 × 1012 M ⊙ (R vir = 249+34 -31 kpc).

  8. Candidate stellar occultations by large trans-Neptunian objects up to 2015

    NASA Astrophysics Data System (ADS)

    Assafin, M.; Camargo, J. I. B.; Vieira Martins, R.; Braga-Ribas, F.; Sicardy, B.; Andrei, A. H.; da Silva Neto, D. N.

    2012-05-01

    Context. We study large trans-Neptunian objects (TNOs) using stellar occultations. Aims: We derive precise astrometric predictions for stellar occultations by Eris, Haumea, Ixion, Makemake, Orcus, Quaoar, Sedna, Varuna, 2002 TX300, and 2003 AZ84 for 2011-2015. We construct local astrometric catalogs of stars complete to magnitudes as faint as R = 18 - 19 in the UCAC2 (Second US Naval Observatory CCD Astrograph Catalog) frame covering the sky path of these objects. Methods: During 2007-2009, we carried out an observational program at the ESO2p2/WFI (2.2 m Max-Planck ESO telescope with the Wide Field Imager) instrument. The observations covered the sky path of the selected targets from 2008 to 2015. We performed the astrometry of 316 GB images using the Platform for Reduction of Astronomical Images Automatically (PRAIA). With the help of field distortion patterns derived for the WFI mosaic of CCDs, we reduced the overlapping mosaics of CCDs. Results: We derive positions in the UCAC2 frame with 40 mas precision for stars up to the catalog magnitude completeness limit (about R = 19). New stellar proper motions are also determined with 2MASS (Two Micron All Sky Survey) and the USNO B1.0 (United States Naval Observatory B 1.0) catalog positions as a first epoch. Astrometric catalogs with proper motions were produced for each TNO, containing more than 5.35 million stars covering the sky paths with 30' width in declination. The magnitude completeness is about R = 19 with a limit of about R = 21. We predicted 2717 stellar occultation candidates for all targets. Ephemeris offsets with about from 50 mas to 100 mas precision were applied to each TNO orbit to improve the predictions. They were obtained during 2007-2010 from a parallel observational campaign carried out with telescopes from 0.6 m to 2.2 m in size. Conclusions: This extends our previous work for the Pluto system to large TNOs, using the same observational and astrometric procedures. The obtained astrometric

  9. VizieR Online Data Catalog: Displaced red and blue components objects (Jayson, 2016)

    NASA Astrophysics Data System (ADS)

    Jayson, J. S.

    2017-07-01

    This feasibility study aimed at demonstrating the value of the USNO-B catalogue for selecting objects with displaced blue and red components. The specifics of the approach were developed with the aid of analysis of three sample test sets of known properties. Over 91000 USNO-B entries were then sifted and analysed and the results visually screened to obtain a candidate list of 144 objects. (3 data files).

  10. Detection of water masers toward young stellar objects in the Large Magellanic Cloud

    SciTech Connect

    Johanson, A. K.; Migenes, V.; Breen, S. L.

    2014-02-01

    We present results from a search for water maser emission toward N4A, N190, and N206, three regions of massive star formation in the Large Magellanic Cloud (LMC). Four water masers were detected; two toward N4A, and two toward N190. In the latter region, no previously known maser emission has been reported. Future studies of maser proper motion to determine the galactic dynamics of the LMC will benefit from the independent data points the new masers in N190 provide. Two of these masers are associated with previously identified massive young stellar objects (YSOs), which strongly supports the authenticity of the classification. We argue that the other two masers identify previously unknown YSOs. No masers were detected toward N206, but it does host a newly discovered 22 GHz continuum source, also associated with a massive YSO. We suggest that future surveys for water maser emission in the LMC be targeted toward the more luminous, massive YSOs.

  11. High spatial resolution IR observations of young stellar objects - A possible disk surrounding HL Tauri

    NASA Technical Reports Server (NTRS)

    Grasdalen, G. L.; Strom, S. E.; Strom, K. M.; Capps, R. W.; Thompson, D.; Castelaz, M.

    1984-01-01

    High spatial resolution images of the T Tauri star HL Tau were obtained at 1.6 microns and 2.2 microns. The original images as well as maximum entropy image reconstructions reveal a circumstellar envelope structure, similar at both wavelenghts, and extended along P.A. = 112 deg; the 10 percent width of the structure is 1.9 sec (300 AU at 160 pc). The extended structure is interpreted as light scattered toward earth by dust in a disk surrounding this young stellar object. Polarization measurements made at 2.2 microns support this hypothesis. The total solid particle mass is, at minimum, 5 x 10 to the -7th solar mass.

  12. Accretion discs around young stellar objects and the proto-sun

    NASA Technical Reports Server (NTRS)

    Lin, D. N. C.

    1989-01-01

    Observed IR and UV excesses have widely been interpreted as signatures for accretion disks around young stellar objects. Analyses of the observed properties of these disks are important for the investigation of star formation as well as the dynamics of the protoplanetary disk out of which the solar system was formed. Accretion-disk theories suggest that evolution of protoplanetary disks is determined by the efficiency of angular momentum transport. During the formation stages, the disk dynamics are regulated by mixing of infalling material and disk gas. In the outermost regions of the disk, self-gravity may promote the growth of nonaxisymmetric perturbations which can transfer angular momentum outwards. After infall has ceased, convectively driven turbulence can redistribute angular momentum with an evolutionary timescale of 0.1 - 1 Myr. Convection in protoplanetary disks may eventually be stabilized by surface heating as the disk material is depleted.

  13. A molecular Einstein ring: imaging a starburst disk surrounding a quasi-stellar object.

    PubMed

    Carilli, C L; Lewis, G F; Djorgovski, S G; Mahabal, A; Cox, P; Bertoldi, F; Omont, A

    2003-05-02

    Images of the molecular CO 2-1 line emission and the radio continuum emission from the redshift 4.12 gravitationally lensed quasi-stellar object (QSO) PSS J2322+1944 reveal an Einstein ring with a diameter of 1.5". These observations are modeled as a star-forming disk surrounding the QSO nucleus with a radius of 2 kiloparsecs. The implied massive star formation rate is 900 solar masses per year. At this rate, a substantial fraction of the stars in a large elliptical galaxy could form on a dynamical time scale of 108 years. The observation of active star formation in the host galaxy of a high-redshift QSO supports the hypothesis of coeval formation of supermassive black holes and stars in spheroidal galaxies.

  14. Optical evidence for the unification of active galactic nuclei and quasi-stellar objects.

    PubMed

    Miller, J S

    1995-12-05

    There is a variety of optical evidence for some unification of different types of active galactic nuclei and quasi-stellar objects (QSOs). The case is very strong for the unification of at least some Seyfert galaxies, where polarization data show that the type assigned to the Seyfert galaxy must depend on viewing direction. It has been proposed that Fanaroff-Riley type 2 (FR2) radio galaxies are quasars seen in a direction from which the quasar is obscured, and there is some limited direct evidence for this picture. The broad absorption line QSOs may be normal QSOs seen from a special direction. Some of the sources observed to have high luminosities in the far infrared could be obscured QSOs and active nuclei. Mergers and interactions are likely to play an important role in nuclear activity, and active galaxies and QSOs could change their apparent types through these encounters followed by subsequent evolution.

  15. High spatial resolution IR observations of young stellar objects - A possible disk surrounding HL Tauri

    NASA Technical Reports Server (NTRS)

    Grasdalen, G. L.; Strom, S. E.; Strom, K. M.; Capps, R. W.; Thompson, D.; Castelaz, M.

    1984-01-01

    High spatial resolution images of the T Tauri star HL Tau were obtained at 1.6 microns and 2.2 microns. The original images as well as maximum entropy image reconstructions reveal a circumstellar envelope structure, similar at both wavelenghts, and extended along P.A. = 112 deg; the 10 percent width of the structure is 1.9 sec (300 AU at 160 pc). The extended structure is interpreted as light scattered toward earth by dust in a disk surrounding this young stellar object. Polarization measurements made at 2.2 microns support this hypothesis. The total solid particle mass is, at minimum, 5 x 10 to the -7th solar mass.

  16. Hydrogen line and continuum emission in young stellar objects. III - Line ratios and physical conditions

    NASA Technical Reports Server (NTRS)

    Alonso-Costa, Jose L.; Kwan, John

    1990-01-01

    A detailed analysis of the dependence of Br-gamma/Br-alpha and other hydrogen line ratios on nucleon density (over the range 10 to the 10th - 10 to the 12th/cu cm), column density (about 10 to the 18th - 10 to the 24th/sq cm), young stellar object (YSO) luminosity (about 10-10,000 solar luminosities), and distance of the gas cloud from the YSO, r (about 10 to the 12th - 10 to the 14th cm). For a given continuum model, the value of Br-gamma/Br-alpha can provide a constraint on r. The ionization and thermal structures of the emission region are described. The electron fraction is fairly constant and is small (less than 10 percent) in the region where most of the hydrogen line fluxes are produced. The temperature in this region is also quite constant, with a value of 5000-7000 K.

  17. IRAS observations of young stellar objects in the Corona Australis dark cloud

    NASA Technical Reports Server (NTRS)

    Wilking, Bruce A.; Greene, Thomas P.; Lada, Charles J.; Meyer, Michael R.; Young, Erick T.

    1992-01-01

    The young stellar object (YSO) population associated with the dark cloud complex in Corona Australis is studied by synthesizing IRAS data with newly obtained near-IR and mid-IR photometry and previously published optical/IR data. Twenty-four YSOs in the Cr A complex are identified. The observed range of spectral energy distribution shapes and bolometric luminosities are consistent with those observed in other dark clouds. The duration and efficiency of star formation are found to be similar to the Rho Ophiuchi IR cluster. The low number of YSOs compared to other dark clouds is understood by a reevaluation of the molecular mass of the R Cr A cloud which shows it to be much less massive than previously assumed.

  18. Optical evidence for the unification of active galactic nuclei and quasi-stellar objects.

    PubMed Central

    Miller, J S

    1995-01-01

    There is a variety of optical evidence for some unification of different types of active galactic nuclei and quasi-stellar objects (QSOs). The case is very strong for the unification of at least some Seyfert galaxies, where polarization data show that the type assigned to the Seyfert galaxy must depend on viewing direction. It has been proposed that Fanaroff-Riley type 2 (FR2) radio galaxies are quasars seen in a direction from which the quasar is obscured, and there is some limited direct evidence for this picture. The broad absorption line QSOs may be normal QSOs seen from a special direction. Some of the sources observed to have high luminosities in the far infrared could be obscured QSOs and active nuclei. Mergers and interactions are likely to play an important role in nuclear activity, and active galaxies and QSOs could change their apparent types through these encounters followed by subsequent evolution. PMID:11607611

  19. YOUNG STELLAR OBJECTS IN THE MASSIVE STAR-FORMING REGION W49

    SciTech Connect

    Saral, G.; Hora, J. L.; Willis, S. E.; Koenig, X. P.; Gutermuth, R. A.; Saygac, A. T.

    2015-11-01

    We present the initial results of our investigation of the star-forming complex W49, one of the youngest and most luminous massive star-forming regions in our Galaxy. We used Spitzer/Infrared Array Camera (IRAC) data to investigate massive star formation with the primary objective of locating a representative set of protostars and the clusters of young stars that are forming around them. We present our source catalog with the mosaics from the IRAC data. In this study we used a combination of IRAC, MIPS, Two Micron All Sky Survey, and UKIRT Deep Infrared Sky Survey (UKIDSS) data to identify and classify the young stellar objects (YSOs). We identified 232 Class 0/I YSOs, 907 Class II YSOs, and 74 transition disk candidate objects using color–color and color–magnitude diagrams. In addition, to understand the evolution of star formation in W49, we analyzed the distribution of YSOs in the region to identify clusters using a minimal spanning tree method. The fraction of YSOs that belong to clusters with ≥7 members is found to be 52% for a cutoff distance of 96″, and the ratio of Class II/I objects is 2.1. We compared the W49 region to the G305 and G333 star-forming regions and concluded that W49 has the richest population, with seven subclusters of YSOs.

  20. Extended red objects and stellar-wind bow shocks in the Carina Nebula

    NASA Astrophysics Data System (ADS)

    Sexton, Remington O.; Povich, Matthew S.; Smith, Nathan; Babler, Brian L.; Meade, Marilyn R.; Rudolph, Alexander L.

    2015-01-01

    We report the results of infrared photometry on 39 extended red objects (EROs) in the Carina Nebula, observed with the Spitzer Space Telescope. Most EROs are identified by bright, extended 8.0 μm emission, which ranges from 10 arcsec to 40 arcsec in size, but our sample also includes four EROs identified by extended 24 μm emission. Of particular interest are nine EROs associated with late O- or early B-type stars and characterized by arc-shaped morphology, suggesting dusty, stellar-wind bow shocks. These objects are preferentially oriented towards the central regions of the Carina Nebula, suggesting that these bow shocks are generally produced by the interactions of OB winds with the bulk expansion of the H II region rather than high proper motion. We identify preferred regions of mid-infrared colour space occupied by our bow shock candidates, which also contain bow shock candidates in M17 and RCW 49 but are well separated from polycyclic aromatic hydrocarbon emission or circumstellar discs. Colour cuts identify an additional 12 marginally resolved bow shock candidates, 10 of which are also associated with known late O or early B stars. H II region expansion velocities derived from bow shock candidate standoff distances are ˜10 km s-1, assuming typical H II region gas densities, comparable to expansion velocities derived from bow shocks in M17 and RCW 49. One candidate bow shock provides direct evidence of physical interaction between the massive stellar winds originating in the Trumpler 15 and Trumpler 14 clusters, supporting the conclusion that both clusters are at similar heliocentric distances.

  1. THE YOUNG STELLAR OBJECT POPULATION IN THE VELA-D MOLECULAR CLOUD

    SciTech Connect

    Strafella, F.; Maruccia, Y.; Maiolo, B.; Lorenzetti, D.; Giannini, T.; Elia, D.; Molinari, S.; Pezzuto, S.; Massi, F.; Olmi, L.

    2015-01-10

    We investigate the young stellar population in the Vela Molecular Ridge, Cloud-D, a star-forming region observed by both the Spitzer/NASA and Herschel/ESA space telescopes. The point-source, band-merged, Spitzer-IRAC catalog complemented with MIPS photometry previously obtained is used to search for candidate young stellar objects (YSOs), also including sources detected in less than four IRAC bands. Bona fide YSOs are selected by using appropriate color-color and color-magnitude criteria aimed at excluding both Galactic and extragalactic contaminants. The derived star formation rate and efficiency are compared with the same quantities characterizing other star-forming clouds. Additional photometric data, spanning from the near-IR to the submillimeter, are used to evaluate both bolometric luminosity and temperature for 33 YSOs located in a region of the cloud observed by both Spitzer and Herschel. The luminosity-temperature diagram suggests that some of these sources are representative of Class 0 objects with bolometric temperatures below 70 K and luminosities of the order of the solar luminosity. Far-IR observations from the Herschel/Hi-GAL key project for a survey of the Galactic plane are also used to obtain a band-merged photometric catalog of Herschel sources intended to independently search for protostars. We find 122 Herschel cores located on the molecular cloud, 30 of which are protostellar and 92 of which are starless. The global protostellar luminosity function is obtained by merging the Spitzer and Herschel protostars. Considering that 10 protostars are found in both the Spitzer and Herschel lists, it follows that in the investigated region we find 53 protostars and that the Spitzer-selected protostars account for approximately two-thirds of the total.

  2. X-shooter spectroscopy of young stellar objects in Lupus. Atmospheric parameters, membership, and activity diagnostics

    NASA Astrophysics Data System (ADS)

    Frasca, A.; Biazzo, K.; Alcalá, J. M.; Manara, C. F.; Stelzer, B.; Covino, E.; Antoniucci, S.

    2017-06-01

    Aims: A homogeneous determination of basic stellar parameters of young stellar object (YSO) candidates is needed to confirm their pre-main sequence evolutionary stage and membership to star forming regions (SFRs), and to get reliable values of the quantities related to chromospheric activity and accretion. Methods: We used the code ROTFIT and synthetic BT-Settl spectra for the determination of the atmospheric parameters (Teff and log g), veiling (r), radial (RV), and projected rotational velocity (vsini) from X-shooter spectra of 102 YSO candidates (95 of infrared Class II and seven Class III) in the Lupus SFR. The spectral subtraction of inactive templates, rotationally broadened to match the vsini of the targets, enabled us to measure the line fluxes for several diagnostics of both chromospheric activity and accretion, such as Hα, Hβ, Ca ii, and Na i lines. Results: We have shown that 13 candidates can be rejected as Lupus members based on their discrepant RV with respect to Lupus and/or the very low log g values. At least 11 of them are background giants, two of which turned out to be lithium-rich giants. Regarding the members, we found that all Class III sources have Hα fluxes that are compatible with a pure chromospheric activity, while objects with disks lie mostly above the boundary between chromospheres and accretion. Young stellar objects with transitional disks display both high and low Hα fluxes. We found that the line fluxes per unit surface are tightly correlated with the accretion luminosity (Lacc) derived from the Balmer continuum excess. This rules out that the relationships between Lacc and line luminosities found in previous works are simply due to calibration effects. We also found that the Ca ii-IRT flux ratio, FCaII8542/FCaII8498, is always small, indicating an optically thick emission source. The latter can be identified with the accretion shock near the stellar photosphere. The Balmer decrement reaches instead, for several accretors, high

  3. X-shooter spectroscopy of young stellar objects. VI. H i line decrements

    NASA Astrophysics Data System (ADS)

    Antoniucci, S.; Nisini, B.; Giannini, T.; Rigliaco, E.; Alcalá, J. M.; Natta, A.; Stelzer, B.

    2017-03-01

    Context. Hydrogen recombination emission lines commonly observed in accreting young stellar objects represent a powerful tracer for the gas conditions in the circumstellar structures (accretion columns, and winds or jets). Aims: Here we perform a study of the H i decrements and line profiles, from the Balmer and Paschen H i lines detected in the X-shooter spectra of a homogeneous sample of 36 T Tauri objects in Lupus, the accretion and stellar properties of which were already derived in a previous work. We aim to obtain information on the H i gas physical conditions to delineate a consistent picture of the H i emission mechanisms in pre-main sequence low-mass stars (M∗< 2 M⊙). Methods: We have empirically classified the sources based on their H i line profiles and decrements. We identified four Balmer decrement types (which we classified as 1, 2, 3, and 4) and three Paschen decrement types (A, B, and C), characterised by different shapes. We first discussed the connection between the decrement types and the source properties and then compared the observed decrements with predictions from recently published local line excitation models. Results: We identify a few groups of sources that display similar H i properties. One third of the objects show lines with narrow symmetric profiles, and present similar Balmer and Paschen decrements (straight decrements, types 2 and A). Lines in these sources are consistent with optically thin emission from gas with hydrogen densities of order 109 cm-3 and 5000 < T < 15 000 K. These objects are associated with low mass accretion rates. Type 4 (L-shaped) Balmer and type B Paschen decrements are found in conjunction with very wide line profiles and are characteristic of strong accretors, with optically thick emission from high-density gas (log nH > 11 cm-3). Type 1 (curved) Balmer decrements are observed only in three sub-luminous sources viewed edge-on, so we speculate that these are actually type 2 decrements that are reddened

  4. A New Spectroscopic and Interferometric Study of the Young Stellar Object V645 Cyg

    NASA Technical Reports Server (NTRS)

    Miroshinichenko, A. S.; Hofmann, K.-H.; Schertl, D.; Weigelt, G.; Kraus, S.; Manset, N.; Balega, Y. Y.; Klochkova, V. G.; Rudy, R. J.; Lynch, D. K.; Mazuk, S.; Venturini, C. C.; Grankin, K. N.; Puetter, R. C.; Perry, R. B.

    2009-01-01

    Aims. We present the results of high-resolution optical spectroscopy, low-resolution near-IR spectroscopy and near-infrared speckle interferometry of the massive young stellar object candidate V645 Cyg that were taken in order to refine its fundamental parameters and properties of its circumstellar envelope. Methods. Speckle interferometry in the H- and K-bands and an optical spectrum in the range 5200-6680 A with a spectral resolving power of R = 60000 were obtained at the 6 m telescope of the Russian Academy of Sciences. Another optical spectrum in the range 4300-10500 A with R = 79000 was obtained at the 3.6m CFHT. A low-resolution spectrum in the ranges 0.46-1.4 and 1.4-2.5 microns with a R approx. 800 and approx. 700, respectively, were obtained at the 3m Shain telescope of the Lick Observatory. Results. Using a new kinematic method based on non-linear modeling of the neutral hydrogen density profile in the direction toward the object, we suggest a new a distance D = 4.2+/-0.2 kpc. We also suggest a new estimate for the star's effective temperature, T(sub eff) approx. 25000 K. We have resolved the object in both H- and K-bands. Using a two-component ring fit, we derived a compact component size of 18 mas and 15 mas in the H- and K-band, respectively, which correspond to 37 and 33 AU at the new distance. Analysis of our and previously published data shows a approx. 2 mag drop of the near-infrared brightness of V645 Cyg in the beginning of the 1980 s. At the same time, the cometary nebular condensation N1 seems to fade in this wavelength range with respect to the N0 object, which represent the star with a nearly pole-on optically-thick disk and an optically-thin envelope. Conclusions. We conclude that V645 Cyg is a young massive main-sequence star, which recently emerged from its cocoon. and already passed the protostellar accretion stage. The presence of accretion is not necessary to account for the high observed luminosity of (2.6) x 10(exp 4) Solar Mass

  5. A New Spectroscopic and Interferometric Study of the Young Stellar Object V645 Cyg

    NASA Technical Reports Server (NTRS)

    Miroshinichenko, A. S.; Hofmann, K.-H.; Schertl, D.; Weigelt, G.; Kraus, S.; Manset, N.; Balega, Y. Y.; Klochkova, V. G.; Rudy, R. J.; Lynch, D. K.; hide

    2009-01-01

    Aims. We present the results of high-resolution optical spectroscopy, low-resolution near-IR spectroscopy and near-infrared speckle interferometry of the massive young stellar object candidate V645 Cyg that were taken in order to refine its fundamental parameters and properties of its circumstellar envelope. Methods. Speckle interferometry in the H- and K-bands and an optical spectrum in the range 5200-6680 A with a spectral resolving power of R = 60000 were obtained at the 6 m telescope of the Russian Academy of Sciences. Another optical spectrum in the range 4300-10500 A with R = 79000 was obtained at the 3.6m CFHT. A low-resolution spectrum in the ranges 0.46-1.4 and 1.4-2.5 microns with a R approx. 800 and approx. 700, respectively, were obtained at the 3m Shain telescope of the Lick Observatory. Results. Using a new kinematic method based on non-linear modeling of the neutral hydrogen density profile in the direction toward the object, we suggest a new a distance D = 4.2+/-0.2 kpc. We also suggest a new estimate for the star's effective temperature, T(sub eff) approx. 25000 K. We have resolved the object in both H- and K-bands. Using a two-component ring fit, we derived a compact component size of 18 mas and 15 mas in the H- and K-band, respectively, which correspond to 37 and 33 AU at the new distance. Analysis of our and previously published data shows a approx. 2 mag drop of the near-infrared brightness of V645 Cyg in the beginning of the 1980 s. At the same time, the cometary nebular condensation N1 seems to fade in this wavelength range with respect to the N0 object, which represent the star with a nearly pole-on optically-thick disk and an optically-thin envelope. Conclusions. We conclude that V645 Cyg is a young massive main-sequence star, which recently emerged from its cocoon. and already passed the protostellar accretion stage. The presence of accretion is not necessary to account for the high observed luminosity of (2.6) x 10(exp 4) Solar Mass

  6. Blue compact dwarf galaxies. II - Near-infrared studies and stellar populations

    NASA Technical Reports Server (NTRS)

    Thuan, T. X.

    1983-01-01

    An IR photometric survey was performed of 36 blue compact dwarf galaxies (BCDG) where intense bursts of star formation have been observed. The survey covered the J, H, and K lines, with all readings taken at the level of a few mJy. Although the near-IR fluxes observed in the galaxies are due to K and M giants, the bursts have calculated ages of less than 50 million yr. However, the BCDG galaxies surveyed are not young, with the least chemically evolved galaxy observed, I Zw 18, featuring 50 pct of its stars formed prior to its last burst, but with a missing mass that is not accounted for by H I interferometric observations. It is concluded that the old stars must be more spatially extended than the young stars, and a mixture of OB stars with the K and M giants is projected as capable of displaying the colors observed. The star formation processes in the BCDG galaxies is defined as dependent on the total mass of the galaxies, with low mass galaxies having a high ratio of star formation, compared to their previous rates.

  7. Infrared Search for Young Brown Dwarf Companions around Young Stellar Objects in the ρ Ophiuchi and the Serpens Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Shirono, Chiaki; Itho, Yoichi; Oasa, Yumiko

    2011-10-01

    We conducted an infrared search for faint companions around 351 young stellar objects in the ρ Ophiuchi molecular cloud and the Serpens molecular cloud. Nine objects in the Spitzer/IRAC archival images were identified as being young stellar companion candidates. They showed an intrinsic infrared excess; one object was extremely red both in the [3.6] - [4.5] color and in the [4.5] - [5.8] color, and two objects were red in the [4.5] - [5.8] color. They were as faint as 15 mag in the [3.6] band. Follow-up K-band spectroscopy revealed that the three objects had deep water absorption bands, indicative of low effective temperatures. By comparing their spectra and infrared spectral energy distributions with synthesized spectra of low-temperature objects, we derived the effective temperatures and continuum excesses for these objects. It is very likely that one is a low-mass stellar companion, and two others are young brown dwarf companions associated with young stellar objects.

  8. Some Results of Scanning Fabry-Perot Observations of the Jets from Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Movsessian, T. A.; Magakian, T. Yu.

    2017-07-01

    In this paper we summarise main results of our investigations of Herbig-Haro objects and jets from young stellar objects using scanning Fabry-Perot etalon. This method allows to separate structures of various kinematical characteristics in theses objects. Our investigations focus on the separation and study of a different type inner structures in Herbig-Haro jets as bow-shocks, Mach disks and deflection shocks. To collate radial velocity and proper motion data, the new method of measuring the proper motions of spectrally separated structures using two epoch observations with Fabry-Perot was developed. This method allows to confirm presence of internal working surfaces in the collimated jets. We suppose that characteristic knotty structures in the jets result of episodic velocity variations in the flows, which form internal working surfaces in the flow. Observations were started at 2.6 m telescope of Byurakan Observatory and after were continued at 6 m telescope of SAO RAS. On the other hand, the compact emission structure near the source of FS Tau B flow system was recognised as the jet base with wider opening angle by comparison with the jet itself. This scenario was confirmed by spectra-polarimetric observations performed at 6m telescope.

  9. MAIN-SEQUENCE STARS MASQUERADING AS YOUNG STELLAR OBJECTS IN THE CENTRAL MOLECULAR ZONE

    SciTech Connect

    Koepferl, Christine M.; Robitaille, Thomas P.; Morales, Esteban F. E.; Johnston, Katharine G.

    2015-01-20

    In contrast to most other galaxies, star formation rates in the Milky Way can be estimated directly from young stellar objects (YSOs). In the central molecular zone the star formation rate calculated from the number of YSOs with 24 μm emission is up to an order of magnitude higher than the value estimated from methods based on diffuse emission (such as free-free emission). Whether this effect is real or whether it indicates problems with either or both star formation rate measures is not currently known. In this paper, we investigate whether estimates based on YSOs could be heavily contaminated by more evolved objects such as main-sequence stars. We present radiative transfer models of YSOs and of main-sequence stars in a constant ambient medium which show that the main-sequence objects can indeed mimic YSOs at 24 μm. However, we show that in some cases the main-sequence models can be marginally resolved at 24 μm, whereas the YSO models are always unresolved. Based on the fraction of resolved MIPS 24 μm sources in the sample of YSOs previously used to compute the star formation rate, we estimate the fraction of misclassified ''YSOs'' to be at least 63%, which suggests that the star formation rate previously determined from YSOs is likely to be at least a factor of three too high.

  10. The detection of a discrete outflow from the young stellar object GL 490

    NASA Technical Reports Server (NTRS)

    Mitchell, G. F.; Allen, M.; Beer, R.; Dekany, R.; Huntress, W.

    1988-01-01

    A high-resolution (0.059/cm) M-band spectrum has been obtained of the embedded young stellar object GL490. The spectrum shows interstellar absorption in the fundamental vibrational band, v = 1-0, of (C-12)O. Two strong and narrow (10 km/s) velocity components are present. One, at the velocity of GL490 (vLSR = -16 km/s), is likely gas in the molecular cloud within which GL490 is embedded. The other component is blueshifted by 13 km/s relative to GL490. An observation of emission from the J = 3-2 transition of HCO(+) using a 20-arcsec beam supports the view that the blueshifted gas is near the central object. The -29-km/s feature is interpreted as a recently ejected shell. It is conjectured that the extended outflows of cold molecular gas seen by millimeter CO emission observations are driven by sporadic outbursts rather than by continuous flows from the central object.

  11. Characterizing stellar halo populations II: the age gradient in blue horizontal-branch stars

    NASA Astrophysics Data System (ADS)

    Das, Payel; Williams, Angus; Binney, James

    2016-12-01

    The distribution of Milky Way halo blue horizontal-branch (BHB) stars is examined using action-based extended distribution functions (EDFs) that describe the locations of stars in phase space, metallicity, and age. The parameters of the EDFs are fitted using stars observed in the Sloan Extension for Galactic Understanding and Exploration-II (SEGUE-II) survey that traces the phase-space kinematics and chemistry out to ˜70 kpc. A maximum a posteriori probability (MAP) estimate method and a Markov Chain Monte Carlo method are applied, taking into account the selection function in positions, distance, and metallicity for the survey. The best-fitting EDF declines with actions less steeply at actions characteristic of the inner halo than at the larger actions characteristic of the outer halo, and older ages are found at smaller actions than at larger actions. In real space, the radial density profile steepens smoothly from -2 at ˜2 kpc to -4 in the outer halo, with an axis ratio ˜0.7 throughout. There is no indication for rotation in the BHBs, although this is highly uncertain. A moderate level of radial anisotropy is detected, with βs varying from isotropic to between ˜0.1 and ˜0.3 in the outer halo depending on latitude. The BHB data are consistent with an age gradient of -0.03 Gyr kpc-1, with some uncertainty in the distribution of the larger ages. These results are consistent with a scenario in which older, larger systems contribute to the inner halo, whilst the outer halo primarily comprises younger, smaller systems.

  12. Accretion, jets and winds: High-energy emission from young stellar objects

    NASA Astrophysics Data System (ADS)

    Günther, H. M.

    2011-06-01

    This article summarizes the processes of high-energy emission in young stellar objects. Stars of spectral type A and B are called Herbig Ae/Be (HAeBe) stars in this stage, all later spectral types are termed classical T Tauri stars (CTTS). Both types are studied by high-resolution X-ray and UV spectroscopy and modeling. Three mechanisms contribute to the high-energy emission from CTTS: 1) CTTS have active coronae similar to main-sequence stars, 2) the accreted material passes through an accretion shock at the stellar surface, which heats it to a few MK, and 3) some CTTS drive powerful outflows. Shocks within these jets can heat the plasma to X-ray emitting temperatures. Coronae are already well characterized in the literature; for the latter two scenarios models are shown. The magnetic field suppresses motion perpendicular to the field lines in the accretion shock, thus justifying a 1D geometry. The radiative loss is calculated as optically thin emission. A mixture of shocked and coronal gas is fitted to X-ray observations of accreting CTTS. Specifically, the model explains the peculiar line-ratios in the He-like triplets of Ne IX and O VII. All stars require only small mass accretion rates to power the X-ray emission. In contrast, the HAeBe HD 163296 has line ratios similar to coronal sources, indicating that neither a high density nor a strong UV-field is present in the region of the X-ray emission. This could be caused by a shock in its jet. Similar emission is found in the deeply absorbed CTTS DG Tau. Shock velocities between 400 and 500 km s-1 are required to explain the observed spectrum. Doctoral Thesis Award Lecture 2010

  13. Migratory and resident blue tits Cyanistes caeruleus differ in their reaction to a novel object.

    PubMed

    Nilsson, Anna L K; Nilsson, Jan-Åke; Alerstam, Thomas; Bäckman, Johan

    2010-11-01

    Individuals differ consistently in their behavioural reactions towards novel objects and new situations. Reaction to novelty is one part of a suit of individually consistent behaviours called coping strategies or personalities and is often summarised as bold or shy behaviour. Coping strategies could be particularly important for migrating birds exposed to novel environments on their journeys. We compared the average approach latencies to a novel object among migrants and residents in partially migratory blue tits Cyanistes caeruleus. In this test, we found migrating blue tits to have shorter approach latencies than had resident ones. Behavioural reactions to novelty can affect the readiness to migrate and short approach latency may have an adaptive value during migration. Individual behaviour towards novelty might be incorporated among the factors associated with migratory or resident behaviour in a partially migratory population.

  14. Migratory and resident blue tits Cyanistes caeruleus differ in their reaction to a novel object

    NASA Astrophysics Data System (ADS)

    Nilsson, Anna L. K.; Nilsson, Jan-Åke; Alerstam, Thomas; Bäckman, Johan

    2010-11-01

    Individuals differ consistently in their behavioural reactions towards novel objects and new situations. Reaction to novelty is one part of a suit of individually consistent behaviours called coping strategies or personalities and is often summarised as bold or shy behaviour. Coping strategies could be particularly important for migrating birds exposed to novel environments on their journeys. We compared the average approach latencies to a novel object among migrants and residents in partially migratory blue tits Cyanistes caeruleus. In this test, we found migrating blue tits to have shorter approach latencies than had resident ones. Behavioural reactions to novelty can affect the readiness to migrate and short approach latency may have an adaptive value during migration. Individual behaviour towards novelty might be incorporated among the factors associated with migratory or resident behaviour in a partially migratory population.

  15. FIRST SPECTROSCOPIC IDENTIFICATION OF MASSIVE YOUNG STELLAR OBJECTS IN THE GALACTIC CENTER

    SciTech Connect

    An, Deokkeun; Boogert, A. C. Adwin; RamIrez, Solange V.; Sellgren, Kris; Arendt, Richard G.; Stolovy, Susan R.; Cotera, Angela S.; Robitaille, Thomas P.; Smith, Howard A. E-mail: sellgren@astronomy.ohio-state.edu

    2009-09-10

    We report the detection of several molecular gas-phase and ice absorption features in three photometrically selected young stellar object (YSO) candidates in the central 280 pc of the Milky Way. Our spectra, obtained with the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope, reveal gas-phase absorption from CO{sub 2} (15.0 {mu}m), C{sub 2}H{sub 2} (13.7 {mu}m), and HCN (14.0 {mu}m). We attribute this absorption to warm, dense gas in massive YSOs. We also detect strong and broad 15 {mu}m CO{sub 2} ice absorption features, with a remarkable double-peaked structure. The prominent long-wavelength peak is due to CH{sub 3}OH-rich ice grains, and is similar to those found in other known massive YSOs. Our IRS observations demonstrate the youth of these objects, and provide the first spectroscopic identification of massive YSOs in the Galactic Center.

  16. Nothing to Hide: An X-ray Survey for Young Stellar Objects in the Pipe Nebula

    NASA Astrophysics Data System (ADS)

    Forbrich, Jan; Posselt, Bettina; Covey, Kevin R.; Lada, Charles J.

    2010-08-01

    We have previously analyzed sensitive mid-infrared observations to establish that the Pipe Nebula (PiN) has a very low star formation efficiency. That study focused on young stellar objects (YSOs) with excess infrared emission (i.e., protostars and pre-main-sequence stars with disks), however, and could have missed a population of more evolved pre-main-sequence stars or Class III objects (i.e., young stars with dissipated disks that no longer show excess infrared emission). Evolved pre-main-sequence stars are X-ray bright, so we have used ROSAT All-Sky Survey data to search for diskless pre-main-sequence stars throughout the PiN. We have also analyzed archival XMM-Newton observations of three prominent areas within the Pipe: Barnard 59 (B 59), containing a known cluster of YSOs; Barnard 68, a dense core that has yet to form stars; and the Pipe molecular ring, a high-extinction region in the bowl of the Pipe. We also characterize the X-ray properties of YSOs in B 59. The ROSAT and XMM-Newton data provide no indication of a significant population of more evolved pre-main-sequence stars within the Pipe, reinforcing our previous measurement of the Pipe's very low star formation efficiency.

  17. Size and albedo of Kuiper belt object 55636 from a stellar occultation.

    PubMed

    Elliot, J L; Person, M J; Zuluaga, C A; Bosh, A S; Adams, E R; Brothers, T C; Gulbis, A A S; Levine, S E; Lockhart, M; Zangari, A M; Babcock, B A; Dupré, K; Pasachoff, J M; Souza, S P; Rosing, W; Secrest, N; Bright, L; Dunham, E W; Sheppard, S S; Kakkala, M; Tilleman, T; Berger, B; Briggs, J W; Jacobson, G; Valleli, P; Volz, B; Rapoport, S; Hart, R; Brucker, M; Michel, R; Mattingly, A; Zambrano-Marin, L; Meyer, A W; Wolf, J; Ryan, E V; Ryan, W H; Morzinski, K; Grigsby, B; Brimacombe, J; Ragozzine, D; Montano, H G; Gilmore, A

    2010-06-17

    The Kuiper belt is a collection of small bodies (Kuiper belt objects, KBOs) that lie beyond the orbit of Neptune and which are believed to have formed contemporaneously with the planets. Their small size and great distance make them difficult to study. KBO 55636 (2002 TX(300)) is a member of the water-ice-rich Haumea KBO collisional family. The Haumea family are among the most highly reflective objects in the Solar System. Dynamical calculations indicate that the collision that created KBO 55636 occurred at least 1 Gyr ago. Here we report observations of a multi-chord stellar occultation by KBO 55636, which occurred on 9 October 2009 ut. We find that it has a mean radius of 143 +/- 5 km (assuming a circular solution). Allowing for possible elliptical shapes, we find a geometric albedo of in the V photometric band, which establishes that KBO 55636 is smaller than previously thought and that, like its parent body, it is highly reflective. The dynamical age implies either that KBO 55636 has an active resurfacing mechanism, or that fresh water-ice in the outer Solar System can persist for gigayear timescales.

  18. X-ray-selected broad absorption line quasi-stellar objects

    NASA Astrophysics Data System (ADS)

    Page, M. J.; Carrera, F. J.; Ceballos, M.; Corral, A.; Ebrero, J.; Esquej, P.; Krumpe, M.; Mateos, S.; Rosen, S.; Schwope, A.; Streblyanska, A.; Symeonidis, M.; Tedds, J. A.; Watson, M. G.

    2017-02-01

    We study a sample of six X-ray-selected broad absorption line (BAL) quasi-stellar objects (QSOs) from the XMM-Newton Wide Angle Survey. All six objects are classified as BALQSOs using the classic balnicity index, and together they form the largest sample of X-ray-selected BALQSOs. We find evidence for absorption in the X-ray spectra of all six objects. An ionized absorption model applied to an X-ray spectral shape that would be typical for non-BAL QSOs (a power law with energy index α = 0.98) provides acceptable fits to the X-ray spectra of all six objects. The optical to X-ray spectral indices, αOX, of the X-ray-selected BALQSOs, have a mean value of <αOX> = 1.69 ± 0.05, which is similar to that found for X-ray-selected and optically selected non-BAL QSOs of a similar ultraviolet luminosity. In contrast, optically selected BALQSOs typically have much larger αOX and so are characterized as being X-ray weak. The results imply that X-ray selection yields intrinsically X-ray bright BALQSOs, but their X-ray spectra are absorbed by a similar degree to that seen in optically selected BALQSO samples; X-ray absorption appears to be ubiquitous in BALQSOs, but X-ray weakness is not. We argue that BALQSOs sit at one end of a spectrum of X-ray absorption properties in QSOs related to the degree of ultraviolet absorption in C IV 1550 Å.

  19. Assessing the Effect of Stellar Companions to Kepler Objects of Interest

    NASA Astrophysics Data System (ADS)

    Hirsch, Lea; Ciardi, David R.; Howard, Andrew

    2017-01-01

    Unknown stellar companions to Kepler planet host stars dilute the transit signal, causing the planetary radii to be underestimated. We report on the analysis of 165 stellar companions detected with high-resolution imaging to be within 2" of 159 KOI host stars. The majority of the planets and planet candidates in these systems have nominal radii smaller than 6 REarth. Using multi-filter photometry on each companion, we assess the likelihood that the companion is bound and estimate its stellar properties, including stellar radius and flux. We then recalculate the planet radii in these systems, determining how much each planet's size is underestimated if it is assumed to 1) orbit the primary star, 2) orbit the companion star, or 3) be equally likely to orbit either star in the system. We demonstrate the overall effect of unknown stellar companions on our understanding of Kepler planet sizes.

  20. Velocity asymmetries in young stellar object jets. Intrinsic and extrinsic mechanisms

    NASA Astrophysics Data System (ADS)

    Matsakos, T.; Vlahakis, N.; Tsinganos, K.; Karampelas, K.; Sauty, C.; Cayatte, V.; Matt, S. P.; Massaglia, S.; Trussoni, E.; Mignone, A.

    2012-09-01

    Context. It is well established that some YSO jets (e.g. RW Aur) display different propagation speeds between their blue and red shifted parts, a feature possibly associated with the central engine or the environment in which the jet propagates. Aims: To understand the origin of asymmetric YSO jet velocities, we investigate the efficiency of two candidate mechanisms, one based on the intrinsic properties of the system and the other on the role of the external medium. In particular, a parallel or anti-parallel configuration between the protostellar magnetosphere and the disk magnetic field is considered, and the resulting dynamics examined both in an ideal and in a resistive magneto-hydrodynamical (MHD) regime. Moreover, we explore the effects of a potential difference in the pressure of the environment, as a consequence of the nonuniform density distribution of molecular clouds. Methods: Ideal and resistive axisymmetric numerical simulations were carried out for a variety of models, all of which are based on a combination of two analytical solutions, a disk wind and a stellar outflow. The initial two-component jet is modified by either inverting the orientation of its inner magnetic field or imposing a constant surrounding pressure. The velocity profiles are studied by assuming steady flows as well as after strong time variable ejection is incorporated. Results: Discrepancies between the speeds of the two outflows in opposite directions can indeed occur both due to unaligned magnetic fields and different outer pressures. In the former case, the asymmetry appears only on the dependence of the velocity on the cylindrical distance, but the implied observed value is significantly altered when the density distribution is also taken into account. On the other hand, a nonuniform medium collimates the two jets unevenly, directly affecting their propagation speed. A further interesting feature of the pressure-confined outflow simulations is the formation of static knots

  1. The evolution of the spectral energy distribution in massive young stellar objects

    NASA Astrophysics Data System (ADS)

    Molinari, S.; Pezzuto, S.; Cesaroni, R.; Brand, J.; Faustini, F.; Testi, L.

    2008-04-01

    core prescriptions show that the three classes of sources possibly mark different periods in the formation of a massive YSO. The IR-P objects are consistent with being at the end of the main accretion phase, while MM-P sources are probably in an earlier evolutionary stage. The timescales for the formation decrease from ~ 4×105 to ~ 1×105 years with stellar mass increasing from ~6 to ~40 M⊙; these timescales, and the association with young clusters with median stellar age of a few 106 years suggest that the most massive objects are among the last ones to form. Conclusions: Our results are consistent with the high-mass star formation being a scaled-up analogue of the traditional accretion-dominated paradigm valid for the low-mass regime. Appendix A is only available in electronic form at http://www.aanda.org

  2. X-shooter spectroscopy of young stellar objects. IV. Accretion in low-mass stars and substellar objects in Lupus

    NASA Astrophysics Data System (ADS)

    Alcalá, J. M.; Natta, A.; Manara, C. F.; Spezzi, L.; Stelzer, B.; Frasca, A.; Biazzo, K.; Covino, E.; Randich, S.; Rigliaco, E.; Testi, L.; Comerón, F.; Cupani, G.; D'Elia, V.

    2014-01-01

    We present VLT/X-shooter observations of a sample of 36 accreting low-mass stellar and substellar objects (YSOs) in the Lupus star-forming region, spanning a range in mass from ~0.03 to ~1.2 M⊙, but mostly with 0.1 M⊙object. The accretion luminosity (Lacc), and in turn the accretion rate (Ṁacc), was derived by modelling the excess emission from the UV to the near-infrared as the continuum emission of a slab of hydrogen. We computed the flux and luminosity (Lline) of many emission lines of H , He , and Ca ii, observed simultaneously in the range from ~330 nm to 2500 nm. The luminosity of all the lines is well correlated with Lacc. We provide empirical relationships between Lacc and the luminosity of 39 emission lines, which have a lower dispersion than relationships previously reported in the literature. Our measurements extend the Paβ and Brγ relationships to Lacc values about two orders of magnitude lower than those reported in previous studies. We confirm that different methodologies of measuring Lacc and Ṁacc yield significantly different results: Hα line profile modelling may underestimate Ṁacc by 0.6 to 0.8 dex with respect to Ṁacc derived from continuum-excess measures. These differences may explain the probably spurious bi-modal relationships between Ṁacc and other YSOs properties reported in the literature. We derived Ṁacc in the range 2 × 10-12-4 × 10-8 M⊙ yr-1 and conclude that Ṁacc ∝ M⋆1.8(±0.2), with a dispersion lower by a factor of about 2 than in previous studies. A number of properties indicate that the physical conditions of the accreting gas are similar over more than 5 orders of magnitude in Ṁacc, confirming previous suggestions that the geometry of the accretion flow

  3. A New Approach to Identifying Massive Young Stellar Objects: Extended Green Objects (EGOs) from the GLIMPSE Survey

    NASA Astrophysics Data System (ADS)

    Cyganowski, Claudia Jane Klimick

    2010-07-01

    A promising new diagnostic for identifying actively accreting massive young stellar objects (MYSOs) has emerged from large-scale Spitzer Space Telescope surveys of the Galactic plane: extended emission in the IRAC 4.5 micron band, believed to trace shocked molecular gas in active protostellar outflows. I present the GLIMPSE I catalog of extended 4.5 micron sources (called EGOs, Extended Green Objects, for the common coding of the [4.5] band as green in 3-color composite IRAC images) and the evidence that EGOs, as a population, are massive YSOs. I also present the results of high-resolution EVLA surveys of 20 EGOs in the 6.7 GHz Class II and 44 GHz Class I methanol maser transitions, which respectively trace high-mass protostars and molecular outflows, and a JCMT survey in the molecular outflow tracers HCO+ and SiO. High detection rates of all outflow tracers and the spatial distribution of the masers with respect to the midinfrared emission provide convincing evidence that the surveyed EGOs are much-sought MYSOs which are actively accreting and driving outflows. I complement the survey results with detailed case studies of two EGOs using SMA and CARMA data. The high-resolution mm observations reveal bipolar molecular outflows coincident with the 4.5 micron lobes in both sources. A single dominant outflow is identified in each of the studied EGOs, with tentative evidence for multiple flows in one source (G11.92-0.61). Strong SiO(2-1) emission is also detected, confirming that the extended 4.5 micron emission traces recently shocked gas in active outflows. The outflow driving sources are compact mm continuum cores that exhibit hot-core spectral line emission, and are associated with 6.7 GHz methanol masers. The mm data also reveal considerable chemical and evolutionary diversity even within a small EGO subsample. The EGO G11.92-0.61 is associated with at least three compact cores, and is forming a protocluster of intermediate to high-mass stars. Other than the

  4. Ices around massive young stellar objects : the RAFGL 7009S test case

    NASA Astrophysics Data System (ADS)

    Dartois, E.; D'Hendecourt, L.

    2000-11-01

    With its large spectral coverage and resolution, well adapted to the study of solid state features arising from icy interstellar grain mantles present in dense molecular clouds, the SWS instrument on board ISO can be used to probe the molecular material in the lines of sight to bright infrared protostellar sources. An example is presented here with the observations of the protostellar object RAFGL 7009S. However, the results presented are applicable to numerous extinct massive young stellar objects which behave similarly. Deep solid state features are detected in such extinguished sources. These features can be compared with laboratory data which allow the identification of ice mixtures composed of H2O, CH4, CO, CO2 and CH3OH condensed on top of refractory grains. Quantitative estimates of the abundances of these molecules can therefore be derived. Superimposed on these solid state features, one generally observe the ro-vibrational lines of gas phase species such as H2O, CO, CO2 and CH4. Analysis of these lines helps to derive some physical parameters such as the gas temperature and the gas-to-solid ratios for these molecules. In the RAFGL 7009S source, an upper limit on the deuterium/hydrogen ratio can also be placed and the consequences for the high fractionation observed in the gas can be discussed. The analysis of the profile of the solid carbon dioxide ν2 bending mode reveals particular interactions in the ice mantles. Indeed, through the peculiar substructure observed in the CO2 band we can monitor in such sources the formation of a complex involving the CO2 and CH3OH and the temperature evolution of the ices. These results may shed light on the relationship between the gas and the grains with possible implication for interstellar chemistry around these objects. Careful laboratory experiments involving matrix isolation techniques allow us to describe the physical nature of the observed ices as well as their photochemical evolution.

  5. Near-infrared imaging polarimetry of young stellar objects in ρ Ophiuchi

    NASA Astrophysics Data System (ADS)

    Beckford, A. F.; Lucas, P. W.; Chrysostomou, A. C.; Gledhill, T. M.

    2008-03-01

    The results of a near-infrared (J H K LP) imaging linear polarimetry survey of 20 young stellar objects (YSOs) in ρ Ophiuchi are presented. The majority of the sources are unresolved, with K-band polarizations, PK < 6 per cent. Several objects are associated with extended reflection nebulae. These objects have centrosymmetric vector patterns with polarization discs over their cores; maximum polarizations of PK > 20 per cent are seen over their envelopes. Correlations are observed between the degree of core polarization and the evolutionary status inferred from the spectral energy distribution. K-band core polarizations >6 per cent are only observed in Class I YSOs. A 3D Monte Carlo model with oblate grains aligned with a magnetic field is used to investigate the flux distributions and polarization structures of three of the ρ Oph YSOs with extended nebulae. A ρ ~ r-1.5 power law for the density is applied throughout the envelopes. The large-scale centrosymmetric polarization structures are due to scattering. However, the polarization structure in the bright core of the nebula appears to require dichroic extinction by aligned non-spherical dust grains. The position angle indicates a toroidal magnetic field in the inner part of the envelope. Since the measured polarizations attributed to dichroic extinction are usually <=10 per cent, the grains must either be nearly spherical or very weakly aligned. The higher polarizations observed in the outer parts of the reflection nebulae require that the dust grains responsible for scattering have maximum grain sizes <=1.05 μm.

  6. Abundant Methanol Ice toward a Massive Young Stellar Object in the Central Molecular Zone

    NASA Astrophysics Data System (ADS)

    An, Deokkeun; Sellgren, Kris; Boogert, A. C. Adwin; Ramírez, Solange V.; Pyo, Tae-Soo

    2017-07-01

    Previous radio observations revealed widespread gas-phase methanol (CH3OH) in the Central Molecular Zone (CMZ) at the Galactic center (GC), but its origin remains unclear. Here, we report the discovery of CH3OH ice toward a star in the CMZ, based on a Subaru 3.4-4.0 μm spectrum, aided by NASA/IRTF L\\prime imaging and 2-4 μm spectra. The star lies ˜8000 au away in projection from a massive young stellar object (MYSO). Its observed high CH3OH ice abundance (17 % +/- 3 % relative to H2O ice) suggests that the 3.535 μm CH3OH ice absorption likely arises in the MYSO’s extended envelope. However, it is also possible that CH3OH ice forms with a higher abundance in dense clouds within the CMZ, compared to within the disk. Either way, our result implies that gas-phase CH3OH in the CMZ can be largely produced by desorption from icy grains. The high solid CH3OH abundance confirms the prominent 15.4 μm shoulder absorption observed toward GC MYSOs arises from CO2 ice mixed with CH3OH. Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

  7. An intermediate luminosity optical transient (ILOTs) model for the young stellar object ASASSN-15qi

    NASA Astrophysics Data System (ADS)

    Kashi, Amit; Soker, Noam

    2017-07-01

    We construct a scenario where the outburst of the young stellar object ASASSN-15qi is an intermediate luminosity optical transient (ILOT). In this scenario, a sub-Jupiter young planet was tidally destructed on to a young main-sequence (MS) star. The system is young, and therefore the radius of the planet is larger than its final value; consequently, its density is smaller. The lower density allows the tidal destruction of the young Saturn-like planet on to the MS star of mass ≈2.4 M⊙, resulting in the formation of a disc and a gravitationally powered ILOT. Unlike the case of the more energetic ILOT V838 Mon, the mass of the destructed planet is too low to inflate a giant envelope, and hence the merger remnant remains hot. If our suggested model holds, this ILOT possesses two interesting properties: (i) its luminosity and total energy are below those of novae; (ii) it is not as red as other ILOTs. The unusual outburst of ASASSN-15qi - if indeed is an ILOT - further increases the diversity of the already heterogeneous group of ILOTs. We mark the region on the energy-time diagram occupied by such young ILOTs.

  8. ABSENCE OF SIGNIFICANT COOL DISKS IN YOUNG STELLAR OBJECTS EXHIBITING REPETITIVE OPTICAL OUTBURSTS

    SciTech Connect

    Liu, Hauyu Baobab; Hirano, Naomi; Takami, Michihiro; Dong, Ruobing; Galván-Madrid, Roberto; Rodríguez, Luis F.; Carrasco-González, Carlos; Vorobyov, Eduard I.; Kóspál, Ágnes; Dunham, Michael M.; Henning, Thomas; Hashimoto, Jun; Hasegawa, Yasuhiro

    2016-01-10

    We report Submillimeter Array 1.3 mm high angular resolution observations toward the four EXor-type outbursting young stellar objects VY Tau, V1118 Ori, V1143 Ori, and NY Ori. The data mostly show low dust masses M{sub dust} in the associated circumstellar disks. Among the sources, NY Ori possesses a relatively massive disk with M{sub dust} ∼ 9 × 10{sup −4}M{sub ⊙}. V1118 Ori has a marginal detection equivalent to M{sub dust} ∼ 6 × 10{sup −5}M{sub ⊙}. V1143 Ori has a non-detection also equivalent to M{sub dust} < 6 × 10{sup −5}M{sub ⊙}. For the nearest source, VY Tau, we get a surprising non-detection that provides a stringent upper limit M{sub dust} < 6 × 10{sup −6}M{sub ⊙}. We interpret our findings as suggesting that the gas and dust reservoirs that feed the short-duration, repetitive optical outbursts seen in some EXors may be limited to the small-scale, innermost region of their circumstellar disks. This hot dust may have escaped our detection limits. Follow-up, more sensitive millimeter observations are needed to improve our understanding of the triggering mechanisms of EXor-type outbursts.

  9. Narrow-band imaging and velocity maps of young stellar objects - Initial results

    NASA Technical Reports Server (NTRS)

    Morgan, J. S.; Wolff, S. C.; Strom, S. E.; Strom, K. M.

    1984-01-01

    The first trials of a new technique, designed to map low-excitation ionized gas surrounding young stellar objects, are reported. The region surrounding the T Tau stars HL Tau and XZ Tau, that near HH 101, and that near IRS 5 in L1551 have been imaged through a narrow-band (4.7 A FWHM) forbidden S II filter; three-phase CCD chip was used as the detector. By tilting the narrow-band filter, it is possible to vary the wavelength of peak transmission and thus to detect high-velocity radial flows as well as map the morphology of the excited gas near these young stars. Evidence of an apparently helical outflow is found for HH 101. Redshifted gas appears to extend southward from HL Tau toward HH 30; a blueshifted jet extends northeastward of HL Tau. A series of forbidden S II knots is seen to extend along a jet directed southwestward from the infrared source IRS 5; the knot chain appears to delineate a blueshifted outflow that decelerates as it recedes from IRS 5.

  10. The compact far infrared emission from the young stellar object IRAS 16293-2422

    NASA Technical Reports Server (NTRS)

    Butner, Harold M.; Evans, N. J., III; Lester, D. F.; Mundy, L. G.; Harvey, P. M.; Campbell, M. F.

    1989-01-01

    High resolution far IR observations at 50 and 100 microns were made of the young stellar object (YSO), IRAS 16293-2422. The observations are part of a systematic high resolution study of nearby YSO's. The purpose is to obtain resolution in the far IR comparable to that at other wavelengths. Until recently, the high resolution that has been available in the far IR has been from either IRAS (angular resolution of approx 4 min) or the KAO using standard FIR photometry (approx 35 sec). With scanning techniques, it is possible to obtain 10 sec resolution on bright sources. Such a resolution is necessary to better determine the physical conditions of the YSO, and to compare with model of star formation. In order to better constrain the models for the source, the YSO was observed at both 50 and 100 microns on several flights in 1988 April from the KAO. Estimates are presented of the size both along the major and minor axis of the disk, as well as estimates of the dust temperature and 100 micron opacity for the YSO.

  11. Star formation in the vicinity of nuclear black holes: young stellar objects close to Sgr A*

    NASA Astrophysics Data System (ADS)

    Jalali, B.; Pelupessy, F. I.; Eckart, A.; Portegies Zwart, S.; Sabha, N.; Borkar, A.; Moultaka, J.; Mužić, K.; Moser, L.

    2014-10-01

    It is often assumed that the strong gravitational field of a super-massive black hole disrupts an adjacent molecular cloud preventing classical star formation in the deep potential well of the black hole. Yet, young stars have been observed across the entire nuclear star cluster of the Milky Way including the region close (<0.5 pc) to the central black hole, Sgr A*. Here, we focus particularly on small groups of young stars, such as IRS 13N located 0.1 pc away from Sgr A*, which is suggested to contain about five embedded massive young stellar objects (<1 Myr). We perform three-dimensional hydrodynamical simulations to follow the evolution of molecular clumps orbiting about a 4 × 106 M⊙ black hole, to constrain the formation and the physical conditions of such groups. The molecular clumps in our models are assumed to be isothermal containing 100 M⊙ in <0.2 pc radius. Such molecular clumps exist in the circumnuclear disc of the Galaxy. In our highly eccentrically orbiting clump, the strong orbital compression of the clump along the orbital radius vector and perpendicular to the orbital plane causes the gas densities to increase to values higher than the tidal density of Sgr A*, which are required for star formation. Additionally, we speculate that the infrared excess source G2/DSO approaching Sgr A* on a highly eccentric orbit could be associated with a dust-enshrouded star that may have been formed recently through the mechanism supported by our models.

  12. Mass Accretion Processes in Young Stellar Objects: Role of Intense Flaring Activity

    NASA Astrophysics Data System (ADS)

    Orlando, Salvatore; Reale, Fabio; Peres, Giovanni; Mignone, Andrea

    2014-11-01

    According to the magnetospheric accretion scenario, young low-mass stars are surrounded by circumstellar disks which they interact with through accretion of mass. The accretion builds up the star to its final mass and is also believed to power the mass outflows, which may in turn have a signicant role in removing the excess angular momentum from the star-disk system. Although the process of mass accretion is a critical aspect of star formation, some of its mechanisms are still to be fully understood. On the other hand, strong flaring activity is a common feature of young stellar objects (YSOs). In the Sun, such events give rise to perturbations of the interplanetary medium. Similar but more energetic phenomena occur in YSOs and may influence the circumstellar environment. In fact, a recent study has shown that an intense flaring activity close to the disk may strongly perturb the stability of circumstellar disks, thus inducing mass accretion episodes (Orlando et al. 2011). Here we review the main results obtained in the field and the future perspectives.

  13. YOUNG STELLAR OBJECTS IN THE LARGE MAGELLANIC CLOUD STAR-FORMING REGION N206

    SciTech Connect

    Romita, Krista Alexandra; Meixner, M.; Sewilo, M.; Shiao, B.; Carlson, Lynn Redding; Whitney, B.; Babler, B.; Meade, M.; Indebetouw, R.; Hora, J. L. E-mail: carlson@stsci.ed E-mail: brian@sal.wisc.ed E-mail: jhora@cfa.harvard.ed

    2010-09-20

    We present analysis of the energetic star-forming region Henize 206 (N206) located near the southern edge of the Large Magellanic Cloud (LMC) based on photometric data from the Spitzer Surveying the Agents of Galaxy Evolution (SAGE-LMC; IRAC 3.6, 4.5, 5.8, 8.0 {mu}m and MIPS 24 {mu}m), Infrared Survey Facility near-infrared survey (J, H, K{sub s}), and the Magellanic Clouds Photometric Survey (MCPS UBVI) covering a wavelength range of 0.36-24 {mu}m. Young stellar object (YSO) candidates are identified based upon their location in infrared color-magnitude space and classified by the shapes of their spectral energy distributions in comparison with a pre-computed grid of YSO models. We identify 116 YSO candidates: 102 are well characterized by the YSO models, predominately Stage I, and 14 may be multiple sources or young sources with transition disks. Careful examination of the individual sources and their surrounding environment allows us to identify a factor of {approx}14.5 more YSO candidates than have already been identified. The total mass of these well-fit YSO candidates is {approx}520 M{sub sun}. We calculate a current star formation rate of 0.27 x 10{sup -1} M{sub sun} yr{sup -1} kpc{sup -2}. The distribution of YSO candidates appears to follow shells of neutral material in the interstellar medium.

  14. Effects of Grain Growth on Molecular Abundances in Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Harada, Nanase; Hasegawa, Yasuhiro; Aikawa, Yuri; Hirashita, Hiroyuki; Liu, Haoyu Baobab; Hirano, Naomi

    2017-03-01

    Recent observations suggested that the growth of dust grains may have already occurred in class 0/I young stellar objects (YSOs). Since chemical reactions on dust grain surfaces are important in determining molecular abundances, the dust size growth may affect chemical compositions in YSOs significantly. In this work, we aim to determine how grain growth affects chemical abundances. We use a time-dependent gas-grain chemical model for a star-forming core to calculate the gas-phase and grain-surface chemical abundances with variation of surface areas of grains to imitate grain growth. We also perform parameter studies in which the initial molecular abundances vary. Our results show that a smaller extent of the surface areas caused by grain growth changes the dominant form of sulfur-bearing molecules by decreasing H2S abundances and increasing SO and/or SO2 abundances. We also find that complex organic molecules such as CH3CN decrease in abundances with larger grain sizes, while the abundance of other species such as CH3OCH3 is dependent on other parameters such as the initial conditions. Comparisons with observations of a class 0 protostar, IRAS 16293-2422, indicate that the observed abundance ratios between sulfur-bearing molecules H2S, SO, and SO2 can be reproduced very well when dust grains grow to a maximum grain size of a max = 10–100 μm.

  15. A modular set of synthetic spectral energy distributions for young stellar objects

    NASA Astrophysics Data System (ADS)

    Robitaille, T. P.

    2017-04-01

    In this paper, I present a new set of synthetic spectral energy distributions (SEDs) for young stellar objects (YSOs) spanning a wide range of evolutionary stages, from the youngest deeply embedded protostars to pre-main-sequence stars with few or no disks. These models include significant improvements on the previous generation of published models: in particular, the new models cover a much wider and more uniform region of parameter space, do not include highly model-dependent parameters, and include a number of improvements that make them more suited to modeling far-infrared and sub-mm observations of forming stars. Rather than all being part of a single monolithic set of models, the new models are split up into sets of varying complexity. The aim of the new set of models is not to provide the most physically realistic models for young stars, but rather to provide deliberately simplified models for initial modeling, which allows a wide range of parameter space to be explored. I present the design of the model set, and show examples of fitting these models to real observations to show how the new grid design can help us better understand what can be determined from limited unresolved observations. The models, as well as a Python-based fitting tool are publicly available to the community.

  16. Evolutionary stages and disk properties of young stellar objects in the Perseus cloud

    NASA Astrophysics Data System (ADS)

    Zhang, Hong-Xin; Gao, Yu; Fang, Min; Yuan, Hai-Bo; Zhao, Ying-He; Chang, Rui-Xiang; Jiang, Xue-Jian; Liu, Xiao-Wei; Luo, A.-Li; Ma, Hong-Jun; Shao, Zheng-Yi; Wang, Xiao-Long

    2015-08-01

    We investigated the evolutionary stages and disk properties of 211 young stellar objects (YSOs) across the Perseus cloud by modeling their broadband optical to mid-infrared (IR) spectral energy distribution (SED). Our optical gri photometry data were obtained from the recently finished Purple Mountain Observatory Xuyi Schmidt Telescope Photometric Survey of the Galactic Anti-center (XSTPS-GAC). About 81% of our sample fall into the Stage II phase which is characterized by having optically thick disks, while 14% into the Stage I phase characterized by having significant infalling envelopes, and the remaining 5% into the Stage III phase characterized by having optically thin disks. The median stellar age and mass of the Perseus YSOs are 3.1 Myr and 0.3 M⊙ respectively. By exploring the relationships among the turnoff wave bands λturnoff (longward of which significant IR excesses above the stellar photosphere are observed), the excess spectral index αexcess as determined for λ > λturnoff, and the disk inner radius Rin (determined from SED modeling) for YSOs at different evolutionary stages, we found that the median and standard deviation of αexcess for YSOs with optically thick disks tend to increase with λturnoff, especially at λturnoff ≥5.8 μm, whereas the median fractional dust luminosities Ldust/L★ tend to decrease with increasing λturnoff. This points to an inside-out process of disk clearing for small dust grains. Moreover, a positive correlation between αexcess and Rin was found at αexcess ≳ 0 and Rin ≳ 10 × the dust sublimation radius Rsub, irrespective of λturnoff, Ldust/L★ and disk flaring. This suggests that the outer disk flaring either does not evolve synchronously with the inside-out disk clearing of small dust grains or has little appreciable influence on the spectral slopes at λ ≲ 24 μm. About 23% of our YSO disks are classified as transitional disks, which have λturnoff ≥ 5.8 μm and Ldust/L★ > 10-3. The transitional

  17. Young stellar object variability (YSOVAR): Long timescale variations in the mid-infrared

    SciTech Connect

    Rebull, L. M.; Cody, A. M.; Stauffer, J. R.; Morales-Calderón, M.; Carey, S. J.; Covey, K. R.; Günther, H. M.; Poppenhaeger, K.; Wolk, S. J.; Hora, J. L.; Hillenbrand, L. A.; Plavchan, P.; Gutermuth, R.; Song, I.; Barrado, D.; Bayo, A.; James, D.; Vrba, F. J.; Alves de Oliveira, C.; Bouvier, J.; and others

    2014-11-01

    The YSOVAR (Young Stellar Object VARiability) Spitzer Space Telescope observing program obtained the first extensive mid-infrared (3.6 and 4.5 μm) time series photometry of the Orion Nebula Cluster plus smaller footprints in 11 other star-forming cores (AFGL 490, NGC 1333, Mon R2, GGD 12-15, NGC 2264, L1688, Serpens Main, Serpens South, IRAS 20050+2720, IC 1396A, and Ceph C). There are ∼29,000 unique objects with light curves in either or both IRAC channels in the YSOVAR data set. We present the data collection and reduction for the Spitzer and ancillary data, and define the 'standard sample' on which we calculate statistics, consisting of fast cadence data, with epochs roughly twice per day for ∼40 days. We also define a 'standard sample of members' consisting of all the IR-selected members and X-ray-selected members. We characterize the standard sample in terms of other properties, such as spectral energy distribution shape. We use three mechanisms to identify variables in the fast cadence data—the Stetson index, a χ{sup 2} fit to a flat light curve, and significant periodicity. We also identified variables on the longest timescales possible of six to seven years by comparing measurements taken early in the Spitzer mission with the mean from our YSOVAR campaign. The fraction of members in each cluster that are variable on these longest timescales is a function of the ratio of Class I/total members in each cluster, such that clusters with a higher fraction of Class I objects also have a higher fraction of long-term variables. For objects with a YSOVAR-determined period and a [3.6]-[8] color, we find that a star with a longer period is more likely than those with shorter periods to have an IR excess. We do not find any evidence for variability that causes [3.6]-[4.5] excesses to appear or vanish within our data set; out of members and field objects combined, at most 0.02% may have transient IR excesses.

  18. Do individual Spitzer young stellar object candidates enclose multiple UKIDSS sources?

    NASA Astrophysics Data System (ADS)

    Morales, Esteban F. E.; Robitaille, Thomas P.

    2017-02-01

    Aims: We analyze United Kingdom Infrared Deep Sky Survey (UKIDSS) observations of a sample of 8325 objects taken from a catalog of intrinsically red sources selected in the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE). Given the differences in angular resolution (factor >2 better in UKIDSS), our aim is to investigate whether there are multiple UKIDSS sources that might all contribute to the GLIMPSE flux, or whether there is only one dominant UKIDSS counterpart. We then study possible corrections to estimates of the star formation rate (SFR) based on counts of GLIMPSE young stellar objects (YSOs). This represents an exploratory work toward the construction of a hierarchical YSO catalog. Methods: After performing PSF fitting photometry in the UKIDSS data, we implemented a technique to recognize the dominant UKIDSS sources automatically by evaluating their match with the spectral energy distribution (SED) of the associated GLIMPSE red sources. This is a generic method that could be robustly applied for matching SEDs across gaps at other wavelengths. Results: We found that most (87.0 ± 1.6%) of the candidate YSOs from the GLIMPSE red source catalog have only one dominant UKIDSS counterpart that matches the mid-infrared SED (fainter associated UKIDSS sources might still be present). Although at first sight this could seem surprising, given that YSOs are typically in clustered environments, we argue that within the mass range covered by the GLIMPSE YSO candidates (intermediate to high masses), clustering with objects with comparable mass is unlikely at the GLIMPSE resolution. Indeed, by performing simple clustering experiments based on a population synthesis model of Galactic YSOs, we found that although 60% of the GLIMPSE YSO enclose at least two UKIDSS sources, in general only one dominates the flux. Conclusions: No significant corrections are needed for estimates of the SFR of the Milky Way based on the assumption that the GLIMPSE YSOs

  19. Young Stellar Object VARiability (YSOVAR): Long Timescale Variations in the Mid-infrared

    NASA Astrophysics Data System (ADS)

    Rebull, L. M.; Cody, A. M.; Covey, K. R.; Günther, H. M.; Hillenbrand, L. A.; Plavchan, P.; Poppenhaeger, K.; Stauffer, J. R.; Wolk, S. J.; Gutermuth, R.; Morales-Calderón, M.; Song, I.; Barrado, D.; Bayo, A.; James, D.; Hora, J. L.; Vrba, F. J.; Alves de Oliveira, C.; Bouvier, J.; Carey, S. J.; Carpenter, J. M.; Favata, F.; Flaherty, K.; Forbrich, J.; Hernandez, J.; McCaughrean, M. J.; Megeath, S. T.; Micela, G.; Smith, H. A.; Terebey, S.; Turner, N.; Allen, L.; Ardila, D.; Bouy, H.; Guieu, S.

    2014-11-01

    The YSOVAR (Young Stellar Object VARiability) Spitzer Space Telescope observing program obtained the first extensive mid-infrared (3.6 and 4.5 μm) time series photometry of the Orion Nebula Cluster plus smaller footprints in 11 other star-forming cores (AFGL 490, NGC 1333, Mon R2, GGD 12-15, NGC 2264, L1688, Serpens Main, Serpens South, IRAS 20050+2720, IC 1396A, and Ceph C). There are ~29,000 unique objects with light curves in either or both IRAC channels in the YSOVAR data set. We present the data collection and reduction for the Spitzer and ancillary data, and define the "standard sample" on which we calculate statistics, consisting of fast cadence data, with epochs roughly twice per day for ~40 days. We also define a "standard sample of members" consisting of all the IR-selected members and X-ray-selected members. We characterize the standard sample in terms of other properties, such as spectral energy distribution shape. We use three mechanisms to identify variables in the fast cadence data—the Stetson index, a χ2 fit to a flat light curve, and significant periodicity. We also identified variables on the longest timescales possible of six to seven years by comparing measurements taken early in the Spitzer mission with the mean from our YSOVAR campaign. The fraction of members in each cluster that are variable on these longest timescales is a function of the ratio of Class I/total members in each cluster, such that clusters with a higher fraction of Class I objects also have a higher fraction of long-term variables. For objects with a YSOVAR-determined period and a [3.6]-[8] color, we find that a star with a longer period is more likely than those with shorter periods to have an IR excess. We do not find any evidence for variability that causes [3.6]-[4.5] excesses to appear or vanish within our data set; out of members and field objects combined, at most 0.02% may have transient IR excesses.

  20. A Large, Massive, Rotating Disk Around an Isolated Young Stellar Object

    NASA Astrophysics Data System (ADS)

    Quanz, Sascha P.; Beuther, Henrik; Steinacker, Jürgen; Linz, Hendrik; Birkmann, Stephan M.; Krause, Oliver; Henning, Thomas; Zhang, Qizhou

    2010-07-01

    the molecules' abundances are similar to those found in other circumstellar disks. We furthermore detected C2H toward the objects and discuss this finding in the context of star formation. Finally, we have performed radiative transfer modeling of the K-band scattered light image varying a disk plus outflow two-dimensional density profile and the stellar properties. The model approximately reproduces extent and location of the dark lane, and the basic appearance of the outflow. We discuss our findings in the context of circumstellar disks across all mass regimes and conclude that our discovery is an ideal laboratory to study the early phases in the evolution of massive circumstellar disks surrounding young stellar objects. Based on observations made at the Calar Alto Observatory. This work is based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan, and on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA.

  1. A LARGE, MASSIVE, ROTATING DISK AROUND AN ISOLATED YOUNG STELLAR OBJECT

    SciTech Connect

    Quanz, Sascha P.; Beuther, Henrik; Steinacker, Juergen; Linz, Hendrik; Krause, Oliver; Henning, Thomas; Birkmann, Stephan M.

    2010-07-10

    dense gas in the disk and the molecules' abundances are similar to those found in other circumstellar disks. We furthermore detected C{sub 2}H toward the objects and discuss this finding in the context of star formation. Finally, we have performed radiative transfer modeling of the K-band scattered light image varying a disk plus outflow two-dimensional density profile and the stellar properties. The model approximately reproduces extent and location of the dark lane, and the basic appearance of the outflow. We discuss our findings in the context of circumstellar disks across all mass regimes and conclude that our discovery is an ideal laboratory to study the early phases in the evolution of massive circumstellar disks surrounding young stellar objects.

  2. 76 FR 39974 - Culturally Significant Object Imported for Exhibition Determinations: “Titian's Woman in a Blue...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-07-07

    ... Culturally Significant Object Imported for Exhibition Determinations: ``Titian's Woman in a Blue Dress `La... ``Titian's Woman in a Blue Dress `La Bella','' imported from abroad for temporary exhibition within the..., Assistant Secretary, Bureau of Educational and Cultural Affairs, Department of State. BILLING CODE 4710-05-P...

  3. Orbit determination of trans-Neptunian objects and Centaurs for the prediction of stellar occultations

    NASA Astrophysics Data System (ADS)

    Desmars, J.; Camargo, J. I. B.; Braga-Ribas, F.; Vieira-Martins, R.; Assafin, M.; Vachier, F.; Colas, F.; Ortiz, J. L.; Duffard, R.; Morales, N.; Sicardy, B.; Gomes-Júnior, A. R.; Benedetti-Rossi, G.

    2015-12-01

    Context. The prediction of stellar occultations by trans-Neptunian objects (TNOs) and Centaurs is a difficult challenge that requires accuracy both in the occulted star position and in the object ephemeris. Until now, the most used method of prediction, involving dozens of TNOs/Centaurs, has been to consider a constant offset for the right ascension and for the declination with respect to a reference ephemeris, usually the latest public version. This offset is determined as the difference between the most recent observations of the TNO/Centaur and the reference ephemeris. This method can be successfully applied when the offset remains constant with time, i.e. when the orbit is stable enough. In this case, the prediction even holds for occultations that occur several days after the last observations. Aims: This paper presents an alternative method of prediction, based on a new accurate orbit determination procedure, which uses all the available positions of the TNO from the Minor Planet Center database, as well as sets of new astrometric positions from unpublished observations. Methods: Orbits were determined through a numerical integration procedure called NIMA, in which we developed a specific weighting scheme that considers the individual precision of the observation, the number of observations performed during one night by the same observatory, and the presence of systematic errors in the positions. Results: The NIMA method was applied to 51 selected TNOs and Centaurs. For this purpose, we performed about 2900 new observations in several observatories (European South Observatory, Observatório Pico dos Dias, Pic du Midi, etc.) during the 2007-2014 period. Using NIMA, we succeed in predicting the stellar occultations of 10 TNOs and 3 Centaurs between July 2013 and February 2015. By comparing the NIMA and Jet Propulsion Laboratory (JPL) ephemerides, we highlight the variation in the offset between them with time, by showing that, generally, the constant offset

  4. Characterizing the nature of embedded young stellar objects through silicate, ice and millimeter observations

    NASA Astrophysics Data System (ADS)

    Crapsi, A.; van Dishoeck, E. F.; Hogerheijde, M. R.; Pontoppidan, K. M.; Dullemond, C. P.

    2008-07-01

    Context: Determining the evolutionary stage of a Young Stellar Object (YSO) is of fundamental importance to test star formation theories. Classification schemes for YSOs are based on evaluating the degree of dissipation of the surrounding envelope, whose main effects are the extinction of the optical radiation from the central YSO and re-emission in the far-infrared to millimeter part of the electromagnetic spectrum. Since extinction is a property of column density along the line of sight, the presence of a protoplanetary disk may lead to a misclassification of pre-main sequence stars with disks when viewed edge-on. Aims: We performed radiative transfer calculations to show the effects of different geometries on the main indicators of YSO evolutionary stage. In particular we tested not only the effects on the infrared colors, like the slope α of the flux between 2.2 and 24 μm, but also on other popular indicators of YSO evolutionary stage, such as the bolometric temperature and the optical depth of silicates and ices. Methods: We used the axisymmetric 3D radiative transfer codes RADMC and RADICAL to calculate the spectral energy distribution including silicates and ice features in a grid of models covering the range of physical properties typical of embedded and pre-main sequence sources. Results: Our set of models compares well with existing observations, supporting the assumed density parametrization and the adopted dust opacities. We show that for systems viewed at intermediate angles (25°-70°) the “classical” indicators of evolution are able to classify the degree of evolution of young stellar objects since they accurately trace the envelope column density, and they all agree with each other. On the other hand, edge-on system are misclassified for inclinations larger than 65° ± 5°, where the spread is mostly due to the range of mass and the flaring degree of the disk. In particular, silicate emission, typical of pre-main sequence stars with disks

  5. MASSIVE YOUNG STELLAR OBJECTS IN THE GALACTIC CENTER. I. SPECTROSCOPIC IDENTIFICATION FROM SPITZER INFRARED SPECTROGRAPH OBSERVATIONS

    SciTech Connect

    An, Deokkeun; RamIrez, Solange V.; Boogert, A. C. Adwin; Sellgren, Kris; Arendt, Richard G.; Schultheis, Mathias; Cotera, Angela S.; Stolovy, Susan R.

    2011-08-01

    We present results from our spectroscopic study, using the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope, designed to identify massive young stellar objects (YSOs) in the Galactic center (GC). Our sample of 107 YSO candidates was selected based on Infrared Array Camera (IRAC) colors from the high spatial resolution, high sensitivity Spitzer/IRAC images in the Central Molecular Zone, which spans the central {approx}300 pc region of the Milky Way. We obtained IRS spectra over 5-35 {mu}m using both high- and low-resolution IRS modules. We spectroscopically identify massive YSOs by the presence of a 15.4 {mu}m shoulder on the absorption profile of 15 {mu}m CO{sub 2} ice, suggestive of CO{sub 2} ice mixed with CH{sub 3}OH ice on grains. This 15.4 {mu}m shoulder is clearly observed in 16 sources and possibly observed in an additional 19 sources. We show that nine massive YSOs also reveal molecular gas-phase absorption from CO{sub 2}, C{sub 2}H{sub 2}, and/or HCN, which traces warm and dense gas in YSOs. Our results provide the first spectroscopic census of the massive YSO population in the GC. We fit YSO models to the observed spectral energy distributions and find YSO masses of 8-23 M{sub sun}, which generally agree with the masses derived from observed radio continuum emission. We find that about 50% of photometrically identified YSOs are confirmed with our spectroscopic study. This implies a preliminary star formation rate of {approx}0.07 M{sub sun} yr{sup -1} at the GC.

  6. Survey of Infrared Variability of Young Stellar Objects in Nearby Molecular Clouds

    NASA Astrophysics Data System (ADS)

    Huard, Tracy L.; Storm, S.; Mundy, L. G.

    2012-01-01

    The Spitzer Space Telescope archive provides a means for studying mid-infrared variability in large numbers of young stellar objects (YSOs) in different star-forming regions. We are conducting such a study, as part of NASA's Astrophysics Data Analysis Program (ADAP), to identify those YSOs exhibiting variability and to characterize the frequency, magnitude, and color of this variability. Our results for isolated core regions, for example, demonstrate that (70 +/- 20)% of Class I and Flat-spectrum YSOs exhibit variability over timescales of 1-2 years, while only (24 +/- 8)% of Class II and III YSOs appear to be variable over these times, suggestive of a dependence on evolutionary class. In contrast, we find no such dependence in the IC 5146 cluster forming region or the Perseus or Serpens regions, where 35-45% of the YSOs exhibit variability. In general, the variable YSOs brighten or dim consistently across the IRAC 3.6-8.0 micron bands; the mid-infrared color changes are typically inconsistent with variable line-of-sight extinction. The magnitude of maximum IRAC variability for many YSOs is inconsistent with starspots as the dominant cause. Instead, intermittent heating and cooling by episodic accretion is the favored mechanism. In some cases, YSO observations were repeated over shorter timescales, from 0.2 to 2 days. We analyzed these observations to determine whether YSOs exhibited variability over these timescales and, if so, whether it was consistent with the longterm variations that we observed. Results from this study and implications for accretion will be presented.

  7. Massive Young Stellar Objects in the Galactic Center. 1; Spectroscopic Identification from Spitzer/IRS Observations

    NASA Technical Reports Server (NTRS)

    An, Deokkeun; Ramirez, Solange V.; Sellgren, Kris; Arendt, Richard G.; Boogert, A. C. Adwin; Robitaille, Thomas P.; Schultheis, Mathias; Cotera, Angela S.; Smith, Howard A.; Stolovy, Susan R.

    2011-01-01

    We present results from our spectroscopic study, using the Infrared Spectrograph (IRS) onboard the Spitzer Space Telescope, designed to identify massive young stellar objects (YSOs) in the Galactic Center (GC). Our sample of 107 YSO candidates was selected based on IRAC colors from the high spatial resolution, high sensitivity Spitzer/IRAC images in the Central Molecular Zone (CMZ), which spans the central approximately 300 pc region of the Milky Way Galaxy. We obtained IRS spectra over 5 micron to 35 micron using both high- and low-resolution IRS modules. We spectroscopically identify massive YSOs by the presence of a 15.4 micron shoulder on the absorption profile of 15 micron CO2 ice, suggestive of CO2 ice mixed with CH30H ice on grains. This 15.4 micron shoulder is clearly observed in 16 sources and possibly observed in an additional 19 sources. We show that 9 massive YSOs also reveal molecular gas-phase absorption from C02, C2H2, and/or HCN, which traces warm and dense gas in YSOs. Our results provide the first spectroscopic census of the massive YSO population in the GC. We fit YSO models to the observed spectral energy distributions and find YSO masses of 8 - 23 solar Mass, which generally agree with the masses derived from observed radio continuum emission. We find that about 50% of photometrically identified YSOs are confirmed with our spectroscopic study. This implies a preliminary star formation rate of approximately 0.07 solar mass/yr at the GC.

  8. Evolution of the Bolometric Temperature and Luminosity of Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Myers, P. C.; Adams, F. C.; Chen, H.; Schaff, E.

    1998-01-01

    We model the broadband emission from a star-disk-envelope system to obtain expressions for the bolometric temperature Tbol and luminosity Lbol as functions of time, from the youngest class 0 protostars to stars on the zero-age main sequence. The model predicts evolution, driven by infall and contraction luminosity, in terms of position on the log Tbol-log Lbol diagram, a close analog of the H-R diagram. The evolutionary tracks depend on the envelope initial conditions, the main-sequence mass of the star, and the envelope dissipation timescale. The model Lbol rises due to infall and then falls due to contraction, while Tbol increases steadily toward the main sequence due to central heating and envelope dissipation. In order to smoothly join the protostellar and pre-main-sequence phases it is necessary to model the termination of infall as gradual rather than sudden. This change reduces the peak infall luminosity for the collapse of a singular isothermal sphere by a factor 4, bringing predicted infall luminosities into better agreement with observations. For stars of main-sequence mass 0.5 M⊙, the model decrease in Lbol from its peak value of ~3 L⊙ at Tbol ~ 250 K (class I) to ~0.4 L⊙ at Tbol ~ 3000 K (class II/III) closely matches the observed decrease in median Lbol for young stellar objects in Chamaeleon, Corona Australis, Lupus, Ophiuchus, and Taurus. The model should be useful for estimating the distributions of mass and age, and for describing the birth history, of stars younger than 1 Myr in well-studied complexes.

  9. ICE CHEMISTRY IN EMBEDDED YOUNG STELLAR OBJECTS IN THE LARGE MAGELLANIC CLOUD

    SciTech Connect

    Oliveira, J. M.; Van Loon, J. Th.; Chen, C.-H. R.; Indebetouw, R.; Tielens, A. G. G. M.; Sloan, G. C.; Woods, P. M.; Kemper, F.; Gordon, K. D.; Boyer, M. L.; Shiao, B.; Meixner, M.; Madden, S.; Speck, A. K.; Marengo, M.

    2009-12-20

    We present spectroscopic observations of a sample of 15 embedded young stellar objects (YSOs) in the Large Magellanic Cloud (LMC). These observations were obtained with the Spitzer Infrared Spectrograph (IRS) as part of the SAGE-Spec Legacy program. We analyze the two prominent ice bands in the IRS spectral range: the bending mode of CO{sub 2} ice at 15.2 mum and the ice band between 5 and 7 mum that includes contributions from the bending mode of water ice at 6 mum among other ice species. The 5-7 mum band is difficult to identify in our LMC sample due to the conspicuous presence of polycyclic aromatic hydrocarbon emission superimposed onto the ice spectra. We identify water ice in the spectra of two sources; the spectrum of one of those sources also exhibits the 6.8 mum ice feature attributed in the literature to ammonium and methanol. We model the CO{sub 2} band in detail, using the combination of laboratory ice profiles available in the literature. We find that a significant fraction (approx>50%) of CO{sub 2} ice is locked in a water-rich component, consistent with what is observed for Galactic sources. The majority of the sources in the LMC also require a pure-CO{sub 2} contribution to the ice profile, evidence of thermal processing. There is a suggestion that CO{sub 2} production might be enhanced in the LMC, but the size of the available sample precludes firmer conclusions. We place our results in the context of the star formation environment in the LMC.

  10. A Theoretical Model of X-Ray Jets from Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Takasao, Shinsuke; Suzuki, Takeru K.; Shibata, Kazunari

    2017-09-01

    There is a subclass of X-ray jets from young stellar objects that are heated very close to the footpoint of the jets, particularly DG Tau jets. Previous models have attributed the strong heating to shocks in the jets. However, the mechanism that localizes the heating at the footpoint remains puzzling. We presented a different model of such X-ray jets, in which the disk atmosphere is magnetically heated. Our disk corona model is based on the so-called nanoflare model for the solar corona. We show that the magnetic heating near the disks can result in the formation of a hot corona with a temperature of ≳106 K, even if the average field strength in the disk is moderately weak, ≳1 G. We determine the density and the temperature at the jet base by considering the energy balance between the heating and cooling. We derive the scaling relations of the mass-loss rate and terminal velocity of jets. Our model is applied to the DG Tau jets. The observed temperature and estimated mass-loss rate are consistent with the prediction of our model in the case of a disk magnetic field strength of ∼20 G and a heating region of <0.1 au. The derived scaling relation of the temperature of X-ray jets could be a useful tool for estimating the magnetic field strength. We also find that the jet X-ray can have a significant impact on the ionization degree near the disk surface and the dead zone size.

  11. Multi-Sensory Approach to Search for Young Stellar Objects in CG4

    NASA Astrophysics Data System (ADS)

    Hoette, Vivian L.; Rebull, L. M.; McCarron, K.; Johnson, C. H.; Gartner, C.; VanDerMolen, J.; Gamble, L.; Matche, L.; McCartney, A.; Doering, M.; Crump, R.; Laorr, A.; Mork, K.; Steinbergs, E.; Wigley, E.; Caruso, S.; Killingstad, N.; McCanna, T.

    2011-01-01

    Individuals with disabilities - specifically individuals who are deaf or hard of hearing (DHH) and/or blind and visually-impaired (BVI) - have traditionally been underrepresented in the fields of Science, Technology, Engineering, and Math (STEM). The low incidence rate of these populations, coupled with geographic isolation, creates limited opportunities for students to work with and receive mentoring by professionals who not only have specialty knowledge in disability areas but also work in STEM fields. Yerkes Observatory scientists, along with educators from the Wisconsin School for the Deaf, the Wisconsin Center for the Blind and Visually Impaired, Breck School, and Oak Park and River Forest High School, are engaged in active research with a Spitzer Science Center (SSC) scientist. Our ultimate goals are threefold; to engage DHH and BVI students with equal success as their sighted and hearing peers, to share our techniques to make astronomy more accessible to DHH and BVI youth, and to generate a life-long interest which will lead our students to STEM careers. This poster tracks our work with an SSC scientist during the spring, summer, and fall of 2010. The group coauthored another AAS poster on finding Young Stellar Objects (YSO) in the CG4 Nebula in Puppis. During the project, the students, scientists and teachers developed a number of techniques for learning the necessary science as well as doing the required data acquisition and analysis. Collaborations were formed between students with disabilities and their non-disabled peers to create multi-media projects. Ultimately, the projects created for our work with NITARP will be disseminated through our professional connections in order to ignite a passion for astronomy in all students - with and without disabilities. This research was made possible through the NASA/IPAC Teacher Archive Research Project (NITARP) and was funded by NASA Astrophysics Data Program and Archive Outreach funds.

  12. Measuring the 3D shape of high temperature objects using blue sinusoidal structured light

    NASA Astrophysics Data System (ADS)

    Zhao, Xianling; Liu, Jiansheng; Zhang, Huayu; Wu, Yingchun

    2015-12-01

    The visible light radiated by some high temperature objects (less than 1200 °C) almost lies in the red and infrared waves. It will interfere with structured light projected on a forging surface if phase measurement profilometry (PMP) is used to measure the shapes of objects. In order to obtain a clear deformed pattern image, a 3D measurement method based on blue sinusoidal structured light is proposed in this present work. Moreover, a method for filtering deformed pattern images is presented for correction of the unwrapping phase. Blue sinusoidal phase-shifting fringe pattern images are projected on the surface by a digital light processing (DLP) projector, and then the deformed patterns are captured by a 3-CCD camera. The deformed pattern images are separated into R, G and B color components by the software. The B color images filtered by a low-pass filter are used to calculate the fringe order. Consequently, the 3D shape of a high temperature object is obtained by the unwrapping phase and the calibration parameter matrixes of the DLP projector and 3-CCD camera. The experimental results show that the unwrapping phase is completely corrected with the filtering method by removing the high frequency noise from the first harmonic of the B color images. The measurement system can complete the measurement in a few seconds with a relative error of less than 1 : 1000.

  13. Optically visible post-AGB stars, post-RGB stars and young stellar objects in the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Kamath, D.; Wood, P. R.; Van Winckel, H.

    2015-12-01

    We have carried out a search for optically visible post-asymptotic giant branch (post-AGB) stars in the Large Magellanic Cloud (LMC). First, we selected candidates with a mid-IR excess and then obtained their optical spectra. We disentangled contaminants with unique spectra such as M stars, C stars, planetary nebulae, quasi-stellar objects and background galaxies. Subsequently, we performed a detailed spectroscopic analysis of the remaining candidates to estimate their stellar parameters such as effective temperature, surface gravity (log g), metallicity ([Fe/H]), reddening and their luminosities. This resulted in a sample of 35 likely post-AGB candidates with late-G to late-A spectral types, low log g, and [Fe/H] < -0.5. Furthermore, our study confirmed the existence of the dusty post-red giant branch (post-RGB) stars, discovered previously in our Small Magellanic Cloud survey, by revealing 119 such objects in the LMC. These objects have mid-IR excesses and stellar parameters (Teff, log g, [Fe/H]) similar to those of post-AGB stars except that their luminosities (< 2500 L⊙), and hence masses and radii, are lower. These post-RGB stars are likely to be products of binary interaction on the RGB. The post-AGB and post-RGB objects show spectral energy distribution properties similar to the Galactic post-AGB stars, where some have a surrounding circumstellar shell, while some others have a surrounding stable disc similar to the Galactic post-AGB binaries. This study also resulted in a new sample of 162 young stellar objects, identified based on a robust log g criterion. Other interesting outcomes include objects with an UV continuum and an emission line spectrum; luminous supergiants; hot main-sequence stars; and 15 B[e] star candidates, 12 of which are newly discovered in this study.

  14. Blue stragglers and X -ray binaries in open clusters: An observational study of alternative pathways in stellar evolution

    NASA Astrophysics Data System (ADS)

    Gosnell, Natalie Marie

    Membership studies of evolved open clusters reveal many alternative pathway stellar products whose evolution cannot be explained using single-star evolutionary models. These stars are neither rare nor anomalous, and in fact are a common occurrence in cluster populations. The goal of this thesis is to investigate the origin and evolutionary pathways of such stars through the careful study of X-ray binaries in NGC 6819 and white dwarf (WD) companions of mass transfer-formed blue straggler stars (BSSs) in NGC 188. I present the first X-ray study of the intermediate-age open cluster NGC 6819, using observations from XMM-Newton. This study of NGC 6819 is part of a systematic survey to investigate the relationship between the number of X-ray sources and cluster dynamics in the regime of massive open clusters. Of the 12 X-ray sources within the half-light radius of NGC 6819, four sources challenge single-star evolutionary models, including a candidate quiescent low-mass X-ray binary. Next, I present the first results from a Hubble Space Telescope (HST) far-ultraviolet (FUV) campaign to search for WD companions of BSSs as indicators of mass transfer formation. I find direct observational detections of young (< 250 Myr), hot WD companions in three BSS binaries. Their presence in a well-studied cluster environment allows for unparalleled constraints on the pre-mass transfer system. I outline potential formation timelines for these three BSSs, which all formed through recent mass transfer. Finally, I use HST photometry of the complete NGC 188 BSS population to place limits on the mass transfer BSS formation frequency. Comparison of the observations with models for BSS FUV emission reveals seven WD companions with temperatures greater than 11,000 K. The location of the young BSSs on an optical color-magnitude diagram suggests that using single-star evolutionary models to age luminous BSSs may be problematic. Considering other formation scenarios, the total mass transfer

  15. The Palomar Transient Factory Orion Project: Eclipsing Binaries and Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    van Eyken, Julian C.; Ciardi, David R.; Rebull, Luisa M.; Stauffer, John R.; Akeson, Rachel L.; Beichman, Charles A.; Boden, Andrew F.; von Braun, Kaspar; Gelino, Dawn M.; Hoard, D. W.; Howell, Steve B.; Kane, Stephen R.; Plavchan, Peter; Ramírez, Solange V.; Bloom, Joshua S.; Cenko, S. Bradley; Kasliwal, Mansi M.; Kulkarni, Shrinivas R.; Law, Nicholas M.; Nugent, Peter E.; Ofek, Eran O.; Poznanski, Dovi; Quimby, Robert M.; Grillmair, Carl J.; Laher, Russ; Levitan, David; Mattingly, Sean; Surace, Jason A.

    2011-08-01

    The Palomar Transient Factory (PTF) Orion project is one of the experiments within the broader PTF survey, a systematic automated exploration of the sky for optical transients. Taking advantage of the wide (3fdg5 × 2fdg3) field of view available using the PTF camera installed at the Palomar 48 inch telescope, 40 nights were dedicated in 2009 December to 2010 January to perform continuous high-cadence differential photometry on a single field containing the young (7-10 Myr) 25 Ori association. Little is known empirically about the formation of planets at these young ages, and the primary motivation for the project is to search for planets around young stars in this region. The unique data set also provides for much ancillary science. In this first paper, we describe the survey and the data reduction pipeline, and present some initial results from an inspection of the most clearly varying stars relating to two of the ancillary science objectives: detection of eclipsing binaries and young stellar objects. We find 82 new eclipsing binary systems, 9 of which are good candidate 25 Ori or Orion OB1a association members. Of these, two are potential young W UMa type systems. We report on the possible low-mass (M-dwarf primary) eclipsing systems in the sample, which include six of the candidate young systems. Forty-five of the binary systems are close (mainly contact) systems, and one of these shows an orbital period among the shortest known for W UMa binaries, at 0.2156509 ± 0.0000071 days, with flat-bottomed primary eclipses, and a derived distance that appears consistent with membership in the general Orion association. One of the candidate young systems presents an unusual light curve, perhaps representing a semi-detached binary system with an inflated low-mass primary or a star with a warped disk, and may represent an additional young Orion member. Finally, we identify 14 probable new classical T-Tauri stars in our data, along with one previously known (CVSO 35) and

  16. THE PALOMAR TRANSIENT FACTORY ORION PROJECT: ECLIPSING BINARIES AND YOUNG STELLAR OBJECTS

    SciTech Connect

    Van Eyken, Julian C.; Ciardi, David R.; Akeson, Rachel L.; Beichman, Charles A.; Von Braun, Kaspar; Gelino, Dawn M.; Kane, Stephen R.; Plavchan, Peter; RamIrez, Solange V.; Rebull, Luisa M.; Stauffer, John R.; Hoard, D. W.; Howell, Steve B.; Bloom, Joshua S.; Cenko, S. Bradley; Kasliwal, Mansi M.; Kulkarni, Shrinivas R.; Law, Nicholas M.; Nugent, Peter E.

    2011-08-15

    The Palomar Transient Factory (PTF) Orion project is one of the experiments within the broader PTF survey, a systematic automated exploration of the sky for optical transients. Taking advantage of the wide (3.{sup 0}5 x 2.{sup 0}3) field of view available using the PTF camera installed at the Palomar 48 inch telescope, 40 nights were dedicated in 2009 December to 2010 January to perform continuous high-cadence differential photometry on a single field containing the young (7-10 Myr) 25 Ori association. Little is known empirically about the formation of planets at these young ages, and the primary motivation for the project is to search for planets around young stars in this region. The unique data set also provides for much ancillary science. In this first paper, we describe the survey and the data reduction pipeline, and present some initial results from an inspection of the most clearly varying stars relating to two of the ancillary science objectives: detection of eclipsing binaries and young stellar objects. We find 82 new eclipsing binary systems, 9 of which are good candidate 25 Ori or Orion OB1a association members. Of these, two are potential young W UMa type systems. We report on the possible low-mass (M-dwarf primary) eclipsing systems in the sample, which include six of the candidate young systems. Forty-five of the binary systems are close (mainly contact) systems, and one of these shows an orbital period among the shortest known for W UMa binaries, at 0.2156509 {+-} 0.0000071 days, with flat-bottomed primary eclipses, and a derived distance that appears consistent with membership in the general Orion association. One of the candidate young systems presents an unusual light curve, perhaps representing a semi-detached binary system with an inflated low-mass primary or a star with a warped disk, and may represent an additional young Orion member. Finally, we identify 14 probable new classical T-Tauri stars in our data, along with one previously known

  17. Early-stage young stellar objects in the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Oliveira, J. M.; van Loon, J. Th.; Sloan, G. C.; Sewiło, M.; Kraemer, K. E.; Wood, P. R.; Indebetouw, R.; Filipović, M. D.; Crawford, E. J.; Wong, G. F.; Hora, J. L.; Meixner, M.; Robitaille, T. P.; Shiao, B.; Simon, J. D.

    2013-02-01

    We present new observations of 34 young stellar object (YSO) candidates in the Small Magellanic Cloud (SMC). The photometric selection required sources to be bright at 24 and 70 μm (to exclude evolved stars and galaxies). The anchor of the analysis is a set of Spitzer Infrared Spectrograph (IRS) spectra, supplemented by ground-based 3-5 μm spectra, Spitzer Infrared Array Camera and Multiband Imaging Photometer for Spitzer photometry, near-infrared (IR) imaging and photometry, optical spectroscopy and radio data. The sources' spectral energy distributions and spectral indices are consistent with embedded YSOs; prominent silicate absorption is observed in the spectra of at least 10 sources, silicate emission is observed towards four sources. Polycyclic aromatic hydrocarbon (PAH) emission is detected towards all but two sources. Based on band ratios (in particular the strength of the 11.3-μm and the weakness of the 8.6-μm bands) PAH emission towards SMC YSOs is dominated by predominantly small neutral grains. Ice absorption is observed towards 14 sources in the SMC. The comparison of H2O and CO2 ice column densities for SMC, Large Magellanic Cloud and Galactic samples suggests that there is a significant H2O column density threshold for the detection of CO2 ice. This supports the scenario proposed by Oliveira et al., where the reduced shielding in metal-poor environments depletes the H2O column density in the outer regions of the YSO envelopes. No CO ice is detected towards the SMC sources. Emission due to pure rotational 0-0 transitions of molecular hydrogen is detected towards the majority of SMC sources, allowing us to estimate rotational temperatures and H2 column densities. All but one source are spectroscopically confirmed as SMC YSOs. Based on the presence of ice absorption, silicate emission or absorption and PAH emission, the sources are classified and placed in an evolutionary sequence. Of the 33 YSOs identified in the SMC, 30 sources populate different

  18. HIGH- AND INTERMEDIATE-MASS YOUNG STELLAR OBJECTS IN THE LARGE MAGELLANIC CLOUD

    SciTech Connect

    Gruendl, Robert A.; Chu, Y.-H. E-mail: chu@astro.illinois.edu

    2009-09-01

    Archival Spitzer Infrared Array Camera (IRAC) and MIPS observations of the Large Magellanic Cloud (LMC) have been used to search for young stellar objects (YSOs). We have carried out independent aperture photometry of these data and merged the results from different passbands to produce a photometric catalog. To verify our methodology we have also analyzed the data from the SAGE and SWIRE Legacy programs; our photometric measurements are in general agreement with the photometry released by these programs. A detailed completeness analysis for our photometric catalog of the LMC shows that the 90% completeness limits are, on average, 16.0, 15.0, 14.3, 13.1, and 9.2 mag at 3.6, 4.5, 5.8, 8.0, and 24 {mu}m, respectively. Using our mid-infrared photometric catalogs and two simple selection criteria, [4.5]-[8.0]>2.0 to exclude normal and evolved stars and [8.0]>14-([4.5]-[8.0]) to exclude background galaxies, we have identified a sample of 2910 sources in the LMC that could potentially be YSOs. We then used the Spitzer observations complemented by optical and near-infrared data to carefully assess the nature of each source. To do so we simultaneously considered multiwavelength images and photometry to assess the source morphology, spectral energy distribution (SED) from the optical through the mid-infrared wavelengths, and the surrounding interstellar environment to determine the most likely nature of each source. From this examination of the initial sample, we suggest that 1172 sources are most likely YSOs. We have also identified 1075 probable background galaxies, consistent with the expected number estimated from the SWIRE survey. Spitzer IRS observations of 269 of the brightest YSOs from our sample have confirmed that {approx}>95% are indeed YSOs. An examination of color-color and color-magnitude diagrams shows no simple criteria in color-magnitude space that can unambiguously separate the LMC YSOs from all asymptotic giant branch (AGB)/post-AGB stars, planetary

  19. Stellar Vampires Unmasked

    NASA Astrophysics Data System (ADS)

    2006-10-01

    Astronomers have found possible proofs of stellar vampirism in the globular cluster 47 Tucanae. Using ESO's Very Large Telescope, they found that some hot, bright, and apparently young stars in the cluster present less carbon and oxygen than the majority of their sisters. This indicates that these few stars likely formed by taking their material from another star. "This is the first detection of a chemical signature clearly pointing to a specific scenario to form so-called 'Blue straggler stars' in a globular cluster", said Francesco Ferraro, from the Astronomy Department of Bologna University (Italy) and lead-author of the paper presenting the results. Blue stragglers are unexpectedly young-looking stars found in stellar aggregates, such as globular clusters, which are known to be made up of old stars. These enigmatic objects are thought to be created in either direct stellar collisions or through the evolution and coalescence of a binary star system in which one star 'sucks' material off the other, rejuvenating itself. As such, they provide interesting constraints on both binary stellar evolution and star cluster dynamics. To date, the unambiguous signatures of either stellar traffic accidents or stellar vampirism have not been observed, and the formation mechanisms of Blue stragglers are still a mystery. The astronomers used ESO's Very Large Telescope to measure the abundance of chemical elements at the surface of 43 Blue straggler stars in the globular cluster 47 Tucanae [1]. They discovered that six of these Blue straggler stars contain less carbon and oxygen than the majority of these peculiar objects. Such an anomaly indicates that the material at the surface of the blue stragglers comes from the deep interiors of a parent star [2]. Such deep material can reach the surface of the blue straggler only during the mass transfer process occurring between two stars in a binary system. Numerical simulations indeed show that the coalescence of stars should not

  20. Solid CO2 in low-mass young stellar objects. Comparison between Spitzer and laboratory spectra

    NASA Astrophysics Data System (ADS)

    Ioppolo, S.; Sangiorgio, I.; Baratta, G. A.; Palumbo, M. E.

    2013-06-01

    Context. Solid interstellar CO2 is an abundant component of ice dust mantles. Its ubiquity towards quiescent molecular clouds, as well as protostellar envelopes, has recently been confirmed by the IRS (InfraRed Spectrograph) aboard the Spitzer Space Telescope. Although it has been shown that CO2 cannot be efficiently formed in the gas phase, the CO2 surface formation pathway is still unclear. To date several CO2 surface formation mechanisms induced by energetic (e.g., UV photolysis and cosmic ray irradiation) and non-energetic (e.g., cold atom addition) input have been proposed. Aims: Our aim is to investigate the contribution of cosmic ray irradiation to the formation of CO2 in different regions of the interstellar medium (ISM). To achieve this goal we compared quantitatively laboratory data with the CO2 bending mode band profile observed towards several young stellar objects (YSOs) and a field star by the Spitzer Space Telescope. Methods: All the experiments presented here were performed at the Laboratory for Experimental Astrophysics in Catania (Italy). The interstellar relevant samples were all irradiated with fast ions (30-200 keV) and subsequently annealed in a stainless steel high vacuum chamber (P < 10-7 mbar). Chemical and structural modifications of the ice samples were monitored by means of infrared spectroscopy. Laboratory spectra were then used to fit some thirty observational spectra. Results: A qualitative analysis shows that a good fit can be obtained with a minimum of two components. The choice of the laboratory components is based on the chemical-physical condition of each source. A quantitative analysis of the sources with known visual extinction (AV) and methanol abundances highlights that the solid carbon dioxide can be efficiently and abundantly formed after ion irradiation of interstellar ices in all the selected YSOs in a time compatible with cloud lifetimes (3 × 107 years). Only in the case of field stars can the expected CO2 column

  1. The extreme ultraviolet continuum of quasi-stellar objects and the ionization of the intergalactic medium

    NASA Astrophysics Data System (ADS)

    Telfer, Randal Crawford

    2002-09-01

    We use a sample of 332 Hubble Space Telescope spectra of 184 quasi-stellar objects (QSOs) with redshifts of z > 0.33 to study their typical extreme ultraviolet (EUV) spectral properties. We find that the continuum emission of QSOs between 500 and 1200 Å can be described by a power law with a typical index of αEUV ≈ -1.57 (Fν ∝ να ) for radio-quiet QSOs and αEUV ≈ -1.96 for radio-loud QSOs. Using the spectra from four of our sample QSOs, we create stacked composite absorption spectra to search for weak EUV absorption lines associated with intervening absorbers in the intergalactic medium (IGM) in the redshift range 1.6 < z < 2.9. We successfully detect O V λ630 in subsamples of Lyα absorbers throughout the 1013 to 1016.2 cm-2 range of H I column densities with at least 99% confidence. We only detect O IV λ788, O IV λ554, O III λ833, and He I λ584 in absorbers with Lyα equivalent widths ≳ 0.6 Å. Using photoionization models, we conclude that the lack of detectable O IV absorption except in the strongest absorption systems suggests a hard ultraviolet background, in agreement with measurements of the ratio of He II to H I in the IGM. The required background source spectrum is consistent with the EUV continuum shape of QSOs that we have derived, suggesting that photoionization by QSOs is the dominant ionization mechanism for the IGM at z ˜ 2 to 3. We estimate that the oxygen abundance relative to hydrogen in the IGM is around 10-1.5 to 10-1.9 times the standard solar abundance ratio. Comparing to studies of carbon, this implies that oxygen is a factor of 4 to 10 times more abundant than carbon with respect to the solar abundances. This relative overabundance of oxygen is consistent with other estimates of chemical abundances in the early universe and implies enrichment of the IGM by the products of high-mass stars.

  2. Chemistry of massive young stellar objects with a disk-like structure

    NASA Astrophysics Data System (ADS)

    Isokoski, K.; Bottinelli, S.; van Dishoeck, E. F.

    2013-06-01

    Aims: Our goal is to take an inventory of complex molecules in three well-known high-mass protostars for which disks or toroids have been claimed and to study the similarities and differences with a sample of massive young stellar objects (YSOs) without evidence of such flattened disk-like structures. With a disk-like geometry, UV radiation can escape more readily and potentially affect the ice and gas chemistry on hot-core scales. Methods: A partial submillimeter line survey, targeting CH3OH, H2CO, C2H5OH, HCOOCH3, CH3OCH3, CH3CN, HNCO, NH2CHO, C2H5CN, CH2CO, HCOOH, CH3CHO, and CH3CCH, was made toward three massive YSOs with disk-like structures, IRAS 20126+4104, IRAS 18089-1732, and G31.41+0.31. Rotation temperatures and column densities were determined by the rotation diagram method, as well as by independent spectral modeling. The molecular abundances were compared with previous observations of massive YSOs without evidence of any disk structure, targeting the same molecules with the same settings and using the same analysis method. Results: Consistent with previous studies, different complex organic species have different characteristic rotation temperatures and can be classified either as warm (>100 K) or cold (<100 K). The excitation temperatures and abundance ratios are similar from source to source and no significant difference can be established between the two source types. Acetone, CH3COCH3, is detected for the first time in G31.41+0.31 and IRAS 18089-1732. Temperatures and abundances derived from the two analysis methods generally agree within factors of a few. Conclusions: The lack of chemical differentiation between massive YSOs with and without observed disks suggest either that the chemical complexity is already fully established in the ices in the cold prestellar phase or that the material experiences similar physical conditions and UV exposure through outflow cavities during the short embedded lifetime. Appendices are available in electronic form

  3. Resolved 24.5 micron emission from massive young stellar objects

    NASA Astrophysics Data System (ADS)

    de Wit, W. J.; Hoare, M. G.; Fujiyoshi, T.; Oudmaijer, R. D.; Honda, M.; Kataza, H.; Miyata, T.; Okamoto, Y. K.; Onaka, T.; Sako, S.; Yamashita, T.

    2009-01-01

    Context: Massive young stellar objects (MYSO) are surrounded by massive dusty envelopes, whose physical structure and geometry are determined by the star formation process. Aims: Our principal aim is to establish the density structure of MYSO envelopes on scales of ~1000 AU. This constitutes an increase of a factor ~10 in angular resolution compared to similar studies performed in the (sub)mm. Methods: We have obtained diffraction-limited (0.6´´) 24.5 μm images (field of view of 40 arcsec×30 arcsec) of 14 well-known massive star formation regions with the COMICS instrument mounted on the 8.2 m Subaru telescope. We construct azimuthally averaged intensity profiles of the resolved MYSO envelopes and build spectral energy distributions (SEDs) from archival data and the COMICS 24.5 μm flux density. The SEDs range from near-infrared to millimeter wavelengths. Self-consistent 1-D radiative transfer models described by a density dependence of the form n(r) ∝ r-p are used to simultaneously compare the intensity profiles and SEDs to model predictions. Results: The images reveal the presence of discrete MYSO sources which are resolved on arcsecond scales, and, to first-order, the observed emission is circular on the sky. For many sources, the spherical models are capable of satisfactorily reproducing the 24.5 μm intensity profile, the 24.5 μm flux density, the 9.7 μm silicate absorption feature, and the submm emission. They are described by density distributions with p =1.0±0.25. Such distributions are shallower than those found on larger scales probed with single-dish (sub)mm studies. Other sources have density laws that are shallower/steeper than p=1.0 and there is evidence that these are viewed near edge-on or near face-on respectively. In these cases spherical models fail to provide good fits to the data. The images also reveal a diffuse component tracing somewhat larger scale structures, particularly visible in the regions S 140, AFGL 2136, IRAS 20126

  4. Young Stellar Objects in the Magellanic Clouds: Herschel spectroscopy first results

    NASA Astrophysics Data System (ADS)

    Oliveira, Joana M.; Theodorus van Loon, Jacco; Sewilo, Marta

    2015-08-01

    As the nearest gas-rich galaxies, the Large and Small Magellanic Clouds (LMC and SMC) offer the opportunity to bridge the gap between star formation processes on large galactic-wide scales and on the small scales of individual Young Stellar Objects (YSOs). These metal-deficient galaxies (Z ~ 0.2-0.4 Z⊙) also provide an invaluable window into a region of parameter space hitherto observationally unexplored. Metallicity reveals itself in at least two ways: abundances of gas-phase carbon and oxygen (and their molecular products), and abundance and properties of dust grains. The most efficient cooling mechanisms during the early collapse stages are via radiation through fine structure lines of C and O, as well as rotational transitions in abundant molecules such as CO and H2O. Furthermore, dust grains are crucial in driving molecular cloud chemistry, as dust opacity shields cores from radiation, and icy mantles on grain surfaces enable chemical reactions to occur that would not happen in the gas phase.We present the first results of a programme using spectroscopy obtained with PACS and SPIRE onboard the Herschel Space Observatory. The sample of massive SMC and LMC YSOs is well characterised at mid-IR wavelengths, and includes both deeply embedded sources and compact HII regions. We measure the strengths of key gas-phase cooling species ([OI], [CII], H2O, CO, OH), in order to estimate temperature, density, ionisation state and abundances. This analysis directly probes the potential metallicity effect, since it quantifies the relative luminosities of the species that promote envelope cooling and thus constrain the cooling budget of the YSO envelopes. Preliminary results indicate that while [OI], [CII] and CO emission is widely detected, H2O and OH is weak or absent in most YSOs. Does this re-enforce the scarcity of H2O hypothesized by Oliveira et al. (2011,2013), now in the gas-phase? We also use the extension and morphology of the [OI], [CII] and [OIII] emission to

  5. Envelope structure of deeply embedded young stellar objects in the Serpens Molecular Cloud

    NASA Technical Reports Server (NTRS)

    Hogerheijde, M. R.; van Dishoeck, E. F.; Salverda, J. M.; Blake, G. A.

    1999-01-01

    Aperture-synthesis and single-dish (sub-) millimeter molecular-line and continuum observations reveal in great detail the envelope structure of deeply embedded young stellar objects (SMM 1 = FIRS 1, SMM 2, SMM 3, SMM 4) in the densely star-forming Serpens Molecular Cloud. SMM 1, 3, and 4 show partially resolved (>2" = 800 AU) continuum emission in the beam of the Owens Valley Millimeter Array at lambda = 3.4-1.4 mm. The continuum visibilities accurately constrain the density structure in the envelopes, which can be described by a radial power law with slope -2.0 +/- 0.5 on scales of 300 to 8000 AU. Inferred envelope masses within a radius of 8000 AU are 8.7, 3.0, and 5.3 Msolar for SMM 1, 3, and 4, respectively. A point source with 20%-30% of the total flux at 1.1 mm is required to fit the observations on long baselines, corresponding to warm envelope material within approximately 100 AU or a circumstellar disk. No continuum emission is detected interferometrically toward SMM 2, corresponding to an upper limit of 0.2 Msolar assuming Td = 24 K. The lack of any compact dust emission suggests that the SMM 2 core does not contain a central protostar. Aperture-synthesis observations of the 13CO, C18O, HCO+, H13CO+, HCN, H13CN, N2H+ 1-0, SiO 2-1, and SO 2(2)-1(1) transitions reveal compact emission toward SMM 1, 3, and 4. SMM 2 shows only a number of clumps scattered throughout the primary field of view, supporting the conclusion that this core does not contain a central star. The compact molecular emission around SMM 1, 3, and 4 traces 5"-10" (2000-4000 AU) diameter cores that correspond to the densest regions of the envelopes, as well as material directly associated with the molecular outflow. Especially prominent are the optically thick HCN and HCO+ lines that show up brightly along the walls of the outflow cavities. SO and SiO trace shocked material, where their abundances may be enhanced by 1-2 orders of magnitude over dark-cloud values. A total of 31 molecular

  6. Envelope structure of deeply embedded young stellar objects in the Serpens Molecular Cloud.

    PubMed

    Hogerheijde, M R; van Dishoeck, E F; Salverda, J M; Blake, G A

    1999-03-01

    Aperture-synthesis and single-dish (sub-) millimeter molecular-line and continuum observations reveal in great detail the envelope structure of deeply embedded young stellar objects (SMM 1 = FIRS 1, SMM 2, SMM 3, SMM 4) in the densely star-forming Serpens Molecular Cloud. SMM 1, 3, and 4 show partially resolved (>2" = 800 AU) continuum emission in the beam of the Owens Valley Millimeter Array at lambda = 3.4-1.4 mm. The continuum visibilities accurately constrain the density structure in the envelopes, which can be described by a radial power law with slope -2.0 +/- 0.5 on scales of 300 to 8000 AU. Inferred envelope masses within a radius of 8000 AU are 8.7, 3.0, and 5.3 Msolar for SMM 1, 3, and 4, respectively. A point source with 20%-30% of the total flux at 1.1 mm is required to fit the observations on long baselines, corresponding to warm envelope material within approximately 100 AU or a circumstellar disk. No continuum emission is detected interferometrically toward SMM 2, corresponding to an upper limit of 0.2 Msolar assuming Td = 24 K. The lack of any compact dust emission suggests that the SMM 2 core does not contain a central protostar. Aperture-synthesis observations of the 13CO, C18O, HCO+, H13CO+, HCN, H13CN, N2H+ 1-0, SiO 2-1, and SO 2(2)-1(1) transitions reveal compact emission toward SMM 1, 3, and 4. SMM 2 shows only a number of clumps scattered throughout the primary field of view, supporting the conclusion that this core does not contain a central star. The compact molecular emission around SMM 1, 3, and 4 traces 5"-10" (2000-4000 AU) diameter cores that correspond to the densest regions of the envelopes, as well as material directly associated with the molecular outflow. Especially prominent are the optically thick HCN and HCO+ lines that show up brightly along the walls of the outflow cavities. SO and SiO trace shocked material, where their abundances may be enhanced by 1-2 orders of magnitude over dark-cloud values. A total of 31 molecular

  7. A Possible Origin of the H-H Objects in Young Stellar Outflows

    NASA Astrophysics Data System (ADS)

    de Gouveia dal Pino, E.; Opher, R.

    1990-11-01

    RESUMEN. La presencIa de flujos coljmados asocjados con objetos estelares j6venes es un fen6meno comun en reglones de formacI6n estelar. Estos chorros frecuentemente muestran una cadena de reglones de lineas de emjsI6n, a varIas de las cuales se les conoce desde bace mucho tlempo objetos HerbIg-Haro (HAl). En el presente trabajo examjnamos la poslbIlI dad de que estos nudos sean condensaciones producIdas por inestabilidad termica en un plasma que se se expande sujeto a `bremsstrahlung' reco - binaci6n y perdida por radjacj5n en lineas de emjsj6n. Nostramos que el valor minimo de = P0/PN0 bajo condjcjones Isobaricas para el crecimien to de la inestabilidad termica es = (6/5) [9/(STc\\)e) - 3/2]; en donde P0 es la presi6n de particulas, PM0 la presi6n magnetica, `)e la tasa de expansI5n y Tc el tiempo de enfriatniento radiativo en el flujo (3eI plasma ambiente. Haciendo calculos no lineales, encontratnos que l9s flujos colitnados de temperatura K, tasas de perdida de masa `4 = 10-6 - lO 8 Ne y velocidades de flujo VJ = 100-400 km/s, resultan favorables para la formacl6n de condensaciones por inestabilidad termica con contrastes de densidad Pp/ .3 -2.0 creados en intervalos de tiempo mas cortos que el tiempo estirnado de expansl6n en los chorros, en donde Pp(Po) es la densidad en la regi5n (ambiente) perturbada. ABSTRACT. The presence of collimated outflows associated with young stellar objects is a common phenomenon in star-fortning regions. These jets frequently show a chain of emission-line regions several of which have long been known as Herbig-Haro (H-H) objects. In this paper we examine the possibility that these knots are condensations produced by thermal instability in an expanding plasma , recombination and emission-line radiation losses. We show that the minimum value of = P /PNo under isobaric conditions for the growth of a thermal instability 0is = (6/5)1 [9/(STcN)e) - 3/2]; where P0 is the particle pressure, NQ tWe magnetic pressure, N) the expansion rate

  8. Linking low- to high-mass young stellar objects with Herschel-HIFI observations of water

    NASA Astrophysics Data System (ADS)

    San José-García, I.; Mottram, J. C.; van Dishoeck, E. F.; Kristensen, L. E.; van der Tak, F. F. S.; Braine, J.; Herpin, F.; Johnstone, D.; van Kempen, T. A.; Wyrowski, F.

    2016-01-01

    Context. Water probes the dynamics in young stellar objects (YSOs) effectively, especially shocks in molecular outflows. It is therefore a key molecule for exploring whether the physical properties of low-mass protostars can be extrapolated to massive YSOs, an important step in understanding the fundamental mechanisms regulating star formation. Aims: As part of the WISH key programme, we investigate excited water line properties as a function of source luminosity, in particular the dynamics and the excitation conditions of shocks along the outflow cavity wall. Methods: Velocity-resolved Herschel-HIFI spectra of the H2O 202-111 (988 GHz), 211-202 (752 GHz) and 312-303 (1097 GHz) lines were analysed, together with 12CO J = 10-9 and 16-15, for 52 YSOs with bolometric luminosities ranging from <1 to >105 L⊙. The H2O and 12CO line profiles were decomposed into multiple Gaussian components which are related to the different physical structures of the protostellar system. The non-LTE radiative transfer code radex was used to constrain the excitation conditions of the shocks along the outflow cavity. Results: The profiles of the three excited water lines are similar, indicating that they probe the same gas. Two main emission components are seen in all YSOs: a broad component associated with non-dissociative shocks in the outflow cavity wall ("cavity shocks") and a narrow component associated with the quiescent envelope material. More than 60% of the total integrated intensity in the excited water lines comes from the broad cavity shock component, while the remaining emission comes mostly from the envelope for low-mass Class I, intermediate- and high-mass objects, and dissociative "spot shocks" for low-mass Class 0 protostars. The widths of the water lines are surprisingly similar from low- to high-mass YSOs, whereas 12CO J = 10-9 line widths increase slightly with Lbol. The excitation analysis of the cavity shock component shows stronger 752 GHz emission for high

  9. YOUNG STELLAR OBJECT SEARCH TOWARD THE BOUNDARY OF THE CENTRAL MOLECULAR ZONE WITH NEAR-INFRARED POLARIMETRY

    SciTech Connect

    Yoshikawa, Tatsuhito; Nagata, Tetsuya; Nishiyama, Shogo; Kwon, Jungmi; Tamura, Motohide E-mail: nagata@kusastro.kyoto-u.ac.jp

    2014-08-01

    We have carried out near-infrared polarimetry toward the boundary of the Central Molecular Zone, in the field of (–1.°4 ≲ l ≲ –0.°3 and 1.°0 ≲ l ≲ 2.°9, |b| ≲ 0.°1), using the near-infrared polarimetric camera SIRPOL on the 1.4 m Infrared Survey Facility telescope. We have selected 112 intrinsically polarized sources on the basis of the estimate of interstellar polarization on Stokes Q/I – U/I planes. The selected sources are brighter than K{sub S} = 14.5 mag and have polarimetric uncertainty δP < 1%. Ten of these distinctive polarized sources are fit well with spectral energy distributions of young stellar objects when using the photometry in the archive of the Spitzer Space Telescope mid-infrared data. However, many sources have spectral energy distributions of normal stars suffering from heavy interstellar extinction; these might be stars behind dark clouds. Due to the small number of distinctive polarized sources and candidates of young stellar objects, we cannot judge if they are declining in number outside the Central Molecular Zone. Many massive candidates for young stellar objects in the literature have only small intrinsic polarization. This might suggest that their masses are 4-15 M {sub ☉}, whose intrinsic polarization has been expected to be small.

  10. MEASURING THE ABUNDANCE OF SUB-KILOMETER-SIZED KUIPER BELT OBJECTS USING STELLAR OCCULTATIONS

    SciTech Connect

    Schlichting, Hilke E.; Ofek, Eran O.; Gal-Yam, Avishay; Sari, Re'em; Nelan, Edmund P.; Livio, Mario; Wenz, Michael; Muirhead, Philip; Javanfar, Nikta

    2012-12-20

    We present here the analysis of about 19,500 new star hours of low ecliptic latitude observations (|b| {<=} 20 Degree-Sign ) obtained by the Hubble Space Telescope's Fine Guidance Sensors over a time span of more than nine years, which is in addition to the {approx}12, 000 star hours previously analyzed by Schlichting et al. Our search for stellar occultations by small Kuiper Belt Objects (KBOs) yielded one new candidate event corresponding to a body with a 530 {+-} 70 m radius at a distance of about 40 AU. Using bootstrap simulations, we estimate a probability of Almost-Equal-To 5% that this event is due to random statistical fluctuations within the new data set. Combining this new event with the single KBO occultation reported by Schlichting et al. we arrive at the following results: (1) the ecliptic latitudes of 6. Degree-Sign 6 and 14. Degree-Sign 4 of the two events are consistent with the observed inclination distribution of larger, 100-km-sized KBOs. (2) Assuming that small, sub-kilometer-sized KBOs have the same ecliptic latitude distribution as their larger counterparts, we find an ecliptic surface density of KBOs with radii larger than 250 m of N(r > 250 m) = 1.1{sup +1.5}{sub -0.7} Multiplication-Sign 10{sup 7} deg{sup -2}; if sub-kilometer-sized KBOs have instead a uniform ecliptic latitude distribution for -20 Degree-Sign < b < 20 Degree-Sign then N(r > 250 m) = 4.4{sup +5.8}{sub -2.8} Multiplication-Sign 10{sup 6} deg{sup -2}. This is the best measurement of the surface density of sub-kilometer-sized KBOs to date. (3) Assuming the KBO size distribution can be well described by a single power law given by N(> r){proportional_to}r{sup 1-q}, where N(> r) is the number of KBOs with radii greater than r, and q is the power-law index, we find q = 3.8 {+-} 0.2 and q = 3.6 {+-} 0.2 for a KBO ecliptic latitude distribution that follows the observed distribution for larger, 100-km-sized KBOs and a uniform KBO ecliptic latitude distribution for -20 Degree

  11. Circumstellar Structure Properties of Young Stellar Objects: Envelopes, Bipolar Outflows, and Disks

    NASA Astrophysics Data System (ADS)

    Kwon, Woojin

    2009-12-01

    Physical properties of the three main structures in young stellar objects (YSOs), envelopes, bipolar outflows, and circumstellar disks, have been studied using radio interferometers: the Berkeley-Illinois-Maryland Association (BIMA) array and the Combined Array for Research in Millimeter-wave Astronomy (CARMA). (1) Envelopes. Three Class 0 YSOs (L1448 IRS 2, L1448 IRS 3, and L1157) have been observed by CARMA at λ = 1.3 mm and 2.7 mm continuum. Through visibility modeling to fit the two wavelength continuum data simultaneously, we found that the dust opacity spectral index (β) of Class 0 YSOs is around unity, which implies that dust grains have significantly grown already at the earliest stage. In addition, we discussed the radial dependence of β detected in L1448 IRS 3B and also estimated the density distribution of the three targets. (2) Bipolar outflows. Polarimetric observations in the λ = 1.3 mm continuum and CO, as well as spectral line observations in 13CO and C18O have been carried out toward L1448 IRS 3, which has three Class 0 YSOs, using BIMA. We clearly identified two interacting bipolar outflows from the "binary system" of IRS 3A and 3B and estimated the velocity, inclination, and opening angle of the 3B bipolar outflow, using Bayesian inference. Also, we showed that the "binary system" can be bound gravitationally and we estimated the specific angular momentum, which is between those of binary stars and molecular cloud cores. In addition, we marginally detected linear polarizations at the center of IRS 3B (implying a toroidal magnetic field) in continuum and at the bipolar outflow region in CO. (3) Circumstellar disks. We present the results of 6 objects (CI Tau, DL Tau, DO Tau, FT Tau, Haro 6-13, and HL Tau) in our T Tauri disk survey using CARMA. The data consist of λ = 1.3 mm and 2.7 mm continuum with an angular resolution up to 0.13". Through visibility modeling of two disk models (power-law disk with a Gaussian edge and viscous accretion

  12. VARIATIONS IN THE MASS FUNCTIONS OF CLUSTERED AND ISOLATED YOUNG STELLAR OBJECTS

    SciTech Connect

    Kirk, Helen; Myers, Philip C.

    2012-02-01

    We analyze high-quality, complete stellar catalogs for four young (roughly 1 Myr) and nearby (within {approx}300 pc) star-forming regions: Taurus, Lupus3, ChaI, and IC348, which have been previously shown to have stellar groups whose properties are similar to those of larger clusters such as the Orion Nebula Cluster (ONC). We find that stars at higher stellar surface densities within a region or belonging to groups tend to have a relative excess of more massive stars, over a wide range of masses. We find statistically significant evidence for this result in Taurus and IC348 as well as in the ONC. These differences correspond to having typically a {approx}10%-20% higher mean mass in the more clustered environment. Stars in ChaI show no evidence for a trend with either surface density or grouped status, and there are too few stars in Lupus3 to make any definitive interpretation. Models of clustered star formation do not typically extend to sufficiently low masses or small group sizes in order for their predictions to be tested, but our results suggest that this regime is important to consider.

  13. STELLAR ROTATION PERIODS OF THE KEPLER OBJECTS OF INTEREST: A DEARTH OF CLOSE-IN PLANETS AROUND FAST ROTATORS

    SciTech Connect

    McQuillan, A.; Mazeh, T.; Aigrain, S.

    2013-09-20

    We present a large sample of stellar rotation periods for Kepler Objects of Interest, based on three years of public Kepler data. These were measured by detecting periodic photometric modulation caused by star spots, using an algorithm based on the autocorrelation function of the light curve, developed recently by McQuillan, Aigrain and Mazeh (2013). Of the 1919 main-sequence exoplanet hosts analyzed, robust rotation periods were detected for 737. Comparing the detected stellar periods to the orbital periods of the innermost planet in each system reveals a notable lack of close-in planets around rapid rotators. It appears that only slowly spinning stars with rotation periods longer than 5-10 days host planets on orbits shorter than 2 or 3 days, although the mechanism(s) that lead(s) to this is not clear.

  14. The role of stellar mass and environment for cluster blue fraction, AGN fraction and star formation indicators from a targeted analysis of Abell 1691

    NASA Astrophysics Data System (ADS)

    Pimbblet, Kevin A.; Jensen, Peter C.

    2012-10-01

    We present an analysis of the galaxy population of the intermediate X-ray luminosity galaxy cluster, Abell 1691, from Sloan Digital Sky Survey (SDSS) and Galaxy Zoo data to elucidate the relationships between environment and galaxy stellar mass for a variety of observationally important cluster populations that include the Butcher-Oemler blue fraction, the active galactic nucleus (AGN) fraction and other spectroscopic classifications of galaxies. From 342 cluster members, we determine a cluster recession velocity of 21257 ± 54 km s-1 and velocity dispersion of 1009-36+40 km s-1 and show that although the cluster is fed by multiple filaments of galaxies it does not possess significant sub-structure in its core. We identify the AGN population of the cluster from a Baldwin, Phillips & Terlevich diagram and show that there is a mild increase in the AGN fraction with radius from the cluster centre that appears mainly driven by high-mass galaxies [log(stellar mass) > 10.8]. Although the cluster blue fraction follows the same radial trend, it is caused primarily by lower mass galaxies [log(stellar mass) < 10.8]. Significantly, the galaxies that have undergone recent starbursts or are presently starbursting but dust-shrouded [spectroscopic e(a) class galaxies] are also nearly exclusively driven by low-mass galaxies. We therefore suggest that the Butcher-Oemler effect may be a mass-dependent effect. We also examine red and passive spiral galaxies and show that the majority are massive galaxies, much like the rest of the red and spectroscopically passive cluster population. We further demonstrate that the velocity dispersion profiles of low- and high-mass cluster galaxies are different. Taken together, we infer that the duty cycle of high- and low-mass cluster galaxies is markedly different, with a significant departure in star formation and specific star formation rates observed beyond r200 and we discuss these findings.

  15. Wide-Field Infrared Survey Explorer Observations of Young Stellar Objects in the Lynds 1509 Dark Cloud in Auriga

    NASA Technical Reports Server (NTRS)

    Liu, Wilson M.; Padgett, Deborah L.; Terebey, Susan; Angione, John; Rebull, Luisa M.; McCollum, Bruce; Fajardo-Acosta, Sergio; Leisawitz, David

    2015-01-01

    The Wide-Field Infrared Survey Explorer (WISE) has uncovered a striking cluster of young stellar object (YSO) candidates associated with the L1509 dark cloud in Auriga. The WISE observations, at 3.4, 4.6, 12, and 22 microns, show a number of objects with colors consistent with YSOs, and their spectral energy distributions suggest the presence of circumstellar dust emission, including numerous Class I, flat spectrum, and Class II objects. In general, the YSOs in L1509 are much more tightly clustered than YSOs in other dark clouds in the Taurus-Auriga star forming region, with Class I and flat spectrum objects confined to the densest aggregates, and Class II objects more sparsely distributed. We estimate a most probable distance of 485-700 pc, and possibly as far as the previously estimated distance of 2 kpc.

  16. Wide-field infrared survey explorer observations of young stellar objects in the Lynds 1509 dark cloud in Auriga

    SciTech Connect

    Liu, Wilson M.; McCollum, Bruce; Fajardo-Acosta, Sergio; Padgett, Deborah L.; Terebey, Susan; Angione, John; Rebull, Luisa M.; Leisawitz, David

    2014-06-01

    The Wide-Field Infrared Survey Explorer (WISE) has uncovered a striking cluster of young stellar object (YSO) candidates associated with the L1509 dark cloud in Auriga. The WISE observations, at 3.4 μm, 4.6 μm, 12 μm, and 22 μm, show a number of objects with colors consistent with YSOs, and their spectral energy distributions suggest the presence of circumstellar dust emission, including numerous Class I, flat spectrum, and Class II objects. In general, the YSOs in L1509 are much more tightly clustered than YSOs in other dark clouds in the Taurus-Auriga star forming region, with Class I and flat spectrum objects confined to the densest aggregates, and Class II objects more sparsely distributed. We estimate a most probable distance of 485-700 pc, and possibly as far as the previously estimated distance of 2 kpc.

  17. Compact object mergers: observations of supermassive binary black holes and stellar tidal disruption events

    NASA Astrophysics Data System (ADS)

    Komossa, S.; Zensus, J. A.

    2016-02-01

    The capture and disruption of stars by supermassive black holes (SMBHs), and the formation and coalescence of binaries, are inevitable consequences of the presence of SMBHs at the cores of galaxies. Pairs of active galactic nuclei (AGN) and binary SMBHs are important stages in the evolution of galaxy mergers, and an intense search for these systems is currently ongoing. In the early and advanced stages of galaxy merging, observations of the triggering of accretion onto one or both BHs inform us about feedback processes and BH growth. Identification of the compact binary SMBHs at parsec and sub-parsec scales provides us with important constraints on the interaction processes that govern the shrinkage of the binary beyond the ``final parsec''. Coalescing binary SMBHs are among the most powerful sources of gravitational waves (GWs) in the universe. Stellar tidal disruption events (TDEs) appear as luminous, transient, accretion flares when part of the stellar material is accreted by the SMBH. About 30 events have been identified by multi-wavelength observations by now, and they will be detected in the thousands in future ground-based or space-based transient surveys. The study of TDEs provides us with a variety of new astrophysical tools and applications, related to fundamental physics or astrophysics. Here, we provide a review of the current status of observations of SMBH pairs and binaries, and TDEs, and discuss astrophysical implications.

  18. Bipolar Flows and X-ray Emission from Young Stellar Object

    NASA Technical Reports Server (NTRS)

    Uchida, Y.; Shibata, K.

    1985-01-01

    Production of both the large scale CO bipolar flows and the small scale optical bipolar jets from the star-forming regions is given interpretation in terms of a magnetic mechanism related to accretion model. It is shown by an axisymmetric 2.5-dimensional simulation that the large scale cold bipolar flow may be produced in the relaxation of the magnetic twist which is created by the rotational winding-up of the magnetic field in the contracting disk. In contrast, the small scale warm bipolar jets may be driven by the recoiling shocks which are produced in the crash at the stellar surface of the infalling material released from the inner edge of the disk through magnetic reconnections.

  19. EC 19314 - 5915 - A bright, eclipsing cataclysmic variable from the Edinburgh-Cape Blue Object Survey

    NASA Technical Reports Server (NTRS)

    Buckley, D. A. H.; O'Donoghue, D.; Kilkenny, D.; Stobie, R. S.; Remillard, R. A.

    1992-01-01

    A deeply eclipsing cataclysmic variable, with an orbital period of 4.75 hr, has been discovered in the southern Edinburgh-Cape Blue Object Survey. The star, EC 19314 - 5915, lies close to the positional constraints of a previously unidentified HEAO-1 hard X-ray source, 1H1930 - 5989. Its optical spectrum is unusual in that it shows, apart from the emission lines characteristic of a novalike, or dwarf nova cataclysmic variable (Balmer, He I and He II), metallic absorption lines typical of a late-G star. The individual time-resolved spectra, with the tertiary absorption lines removed, show absorption reversals in the Balmer emission lines, increasing in strength for the higher series. The Balmer emission radial velocities are therefore severely distorted in comparison to the He II 4686-A emission and He I 4471-A absorption radial velocity curves. An independent distance estimate of about 600 pc is derived for EC19314 - 5915, from the spectroscopic parallax of the third star.

  20. YSOVAR: MID-INFRARED VARIABILITY OF YOUNG STELLAR OBJECTS AND THEIR DISKS IN THE CLUSTER IRAS 20050+2720

    SciTech Connect

    Poppenhaeger, K.; Wolk, S. J.; Hora, J. L.; Cody, A. M.; Covey, K. R.; Günther, H. M.; Hillenbrand, L. A.; Plavchan, P.; Rebull, L. M.; Stauffer, J. R.; Forbrich, J.; Gutermuth, R. A.; Morales-Calderón, M.; Song, Inseok

    2015-10-15

    We present a time-variability study of young stellar objects (YSOs) in the cluster IRAS 20050+2720, performed at 3.6 and 4.5 μm with the Spitzer Space Telescope; this study is part of the Young Stellar Object VARiability (YSOVAR) project. We have collected light curves for 181 cluster members over 60 days. We find a high variability fraction among embedded cluster members of ca. 70%, whereas young stars without a detectable disk display variability less often (in ca. 50% of the cases) and with lower amplitudes. We detect periodic variability for 33 sources with periods primarily in the range of 2–6 days. Practically all embedded periodic sources display additional variability on top of their periodicity. Furthermore, we analyze the slopes of the tracks that our sources span in the color–magnitude diagram (CMD). We find that sources with long variability time scales tend to display CMD slopes that are at least partially influenced by accretion processes, while sources with short variability timescales tend to display extinction-dominated slopes. We find a tentative trend of X-ray detected cluster members to vary on longer timescales than the X-ray undetected members.

  1. YSOVAR: Mid-infrared Variability of Young Stellar Objects and Their Disks in the Cluster IRAS 20050+2720

    NASA Astrophysics Data System (ADS)

    Poppenhaeger, K.; Cody, A. M.; Covey, K. R.; Günther, H. M.; Hillenbrand, L. A.; Plavchan, P.; Rebull, L. M.; Stauffer, J. R.; Wolk, S. J.; Espaillat, C.; Forbrich, J.; Gutermuth, R. A.; Hora, J. L.; Morales-Calderón, M.; Song, Inseok

    2015-10-01

    We present a time-variability study of young stellar objects (YSOs) in the cluster IRAS 20050+2720, performed at 3.6 and 4.5 μm with the Spitzer Space Telescope; this study is part of the Young Stellar Object VARiability (YSOVAR) project. We have collected light curves for 181 cluster members over 60 days. We find a high variability fraction among embedded cluster members of ca. 70%, whereas young stars without a detectable disk display variability less often (in ca. 50% of the cases) and with lower amplitudes. We detect periodic variability for 33 sources with periods primarily in the range of 2-6 days. Practically all embedded periodic sources display additional variability on top of their periodicity. Furthermore, we analyze the slopes of the tracks that our sources span in the color-magnitude diagram (CMD). We find that sources with long variability time scales tend to display CMD slopes that are at least partially influenced by accretion processes, while sources with short variability timescales tend to display extinction-dominated slopes. We find a tentative trend of X-ray detected cluster members to vary on longer timescales than the X-ray undetected members.

  2. Periodic Disk Eclipsing Stars: A New Class of Variable Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Plavchan, Peter; Laohakunakorn, N.; Seifahrt, A.; Staplefeldt, K.; Gee, A. H.

    2010-01-01

    We present the discovery of 92.6 day periodic near-infrared flu variability for the Class I T Tauri star YLW 16A. Our data are from the 2MASS Calibration Point Source Working Database and constitute 1582 observations in J, H and Ks of a field in Rho Ophiuchus used to calibrate the 2MASS All-Sky Survey. We identify a light curve that brightens from a quiescent faint state by 0.4 mag for only 20% of the period. The long period cannot be explained by stellar rotation. We propose that YLW 16A is a triple YSO system, with an inner binary orbital period of 92.6 days. We postulate that we are observing a component of the binary being eclipsed by a circumbinary disk with respect to our line of site. YLW 16A joins WL 4 and KH-15D as a third member of a new class of disk-eclipsing young stars. Both YLW 16A and WL 4 have been identified to have tertiary companions with projected separations of 20--50 AU. We propose that the tertiary companion can warp the inner circumbinary disk to produce the disk eclipses. We present NIRSPEC observations of WL 4 that suggest three distinct radial velocity components, and present a model SED for YLW 16A. These systems will be useful in investigating terrestrial-zone YSO disk properties and dynamics at 1 Myr.

  3. The nature of stationary components in jets from young stellar objects

    NASA Astrophysics Data System (ADS)

    Schneider, Peter

    2014-10-01

    There is increasing evidence that jets are essential for the star formation process. Our understanding of the jet launching process is, however, still fragmentary. In particular, new observations revealed (a) that jets from young stellar sources possess hot, stationary components close to the driving source that contrast the well-known moving parts of the jets further out and (b) possible evidence for plasma acceleration within a few 10 AU from the source.We propose to follow-up these new results by providing the required diagnostics to uncover the controversial origin of the stationary component and to constrain the location where the outflowing plasma is accelerated. Specifically, we propose to observe the classical T Tauri star DG Tau with STIS and the slit oriented along the jet axis to measure the plasma density of the warm (1e4 K) and hot (1e5 K) parts of the jet to distinguish between proposed models for the stationary component, as well as to follow the plasma traveling through the jet collimation region to test current jet launching models.

  4. Cataloged infrared sources in NIPSS data. I - The RSO 1 catalog. [Near Infrared Photographic Sky Survey Red Stellar Objects

    NASA Technical Reports Server (NTRS)

    Horner, V. M.; Craine, E. R.

    1980-01-01

    A small number of selected near-infrared and visual photographic pairs from the Steward Observatory Near Infrared Photographic Sky Survey have been examined for content of stars more red than (V-I) of about 2.5 magnitudes. A simple manual extraction of these objects was carried out as a part of a preliminary evaluation of survey data and techniques for reducing it; the resulting list has been compiled as the first installment of a Catalog of Red Stellar Objects (Craine et al. 1979). Results of a cross correlation of this catalog with the IRC, AFGL, and EIC infrared catalogs are here presented. The results indicate that these photographs may be particularly useful for purposes of optical identification of short-wavelength infrared sources to limits much fainter than represented by presently existing infrared catalogs.

  5. On the use of Video Camera Systems in the Detection of Kuiper Belt Objects by Stellar Occultations

    NASA Astrophysics Data System (ADS)

    Subasinghe, Dilini

    2012-10-01

    Due to the distance between us and the Kuiper Belt, direct detection of Kuiper Belt Objects (KBOs) is not currently possible for objects less than 10 km in diameter. Indirect methods such as stellar occultations must be employed to remotely probe these bodies. The size, shape, as well as atmospheric properties and ring system information of a body (if any), can be collected through observations of stellar occultations. This method has been previously used with some success - Roques et al. (2006) detected 3 Trans-Neptunian objects; Schlichting et al. (2009) detected a single object in archival data. However, previous assessments of KBO occultation detection rates have been calculated only for telescopes - we extend this method to video camera systems. Building on Roques & Moncuquet (2000), we present a derivation that can be applied to any video camera system, taking into account camera specifications and diffraction effects. This allows for a determination of the number of observable KBO occultations per night. Example calculations are presented for some of the automated meteor camera systems currently in use at the University of Western Ontario. The results of this project will allow us to refine and improve our own camera system, as well as allow others to enhance their systems for KBO detection. Roques, F., Doressoundiram, A., Dhillon, V., Marsh, T., Bickerton, S., Kavelaars, J. J., Moncuquet, M., Auvergne, M., Belskaya, I., Chevreton, M., Colas, F., Fernandez, A., Fitzsimmons, A., Lecacheux, J., Mousis, O., Pau, S., Peixinho, N., & Tozzi, G. P. (2006). The Astronomical Journal, 132(2), 819-822. Roques, F., & Moncuquet, M. (2000). Icarus, 147(2), 530-544. Schlichting, H. E., Ofek, E. O., Wenz, M., Sari, R., Gal-Yam, A., Livio, M., Nelan, E., & Zucker, S. (2009). Nature, 462(7275), 895-897.

  6. Outflow-Induced Dynamical and Radiative Instability in Stellar Envelopes with an Application to Luminous Blue Variables and Wolf-Rayet Stars

    NASA Technical Reports Server (NTRS)

    Stothers, Richard B.; Hansen, James E. (Technical Monitor)

    2002-01-01

    Theoretical models of the remnants of massive stars in a very hot, post-red-supergiant phase display no obvious instability if standard assumptions are made. However, the brightest observed classical luminous blue variables (LBVs) may well belong to such a phase. A simple time-dependent theory of moving stellar envelopes is developed in order to treat deep hydrodynamical disturbances caused by surface mass loss and to test the moving envelopes for dynamical instability. In the case of steady-state outflow, the theory reduces to the equivalent of the Castor, Abbott, and Klein formulation for optically thick winds at distances well above the sonic point. The time-dependent version indicates that the brightest and hottest LBVs are both dynamically and radiatively unstable, as a result of the substantial lowering of the generalized Eddington luminosity limit by the mass-loss acceleration. It is suggested that dynamical instability, by triggering secular cycles of mass loss, is primarily what differentiates LBVs from the purely radiatively unstable Wolf-Rayet stars. Furthermore, when accurate main-sequence mass-loss rates are used to calculate the evolutionary tracks, the predicted surface hydrogen and nitrogen abundances of the blue remnants agree much better with observations of the brightest LBVs than before.

  7. X-shooter spectroscopy of young stellar objects in Lupus. Lithium, iron, and barium elemental abundances

    NASA Astrophysics Data System (ADS)

    Biazzo, K.; Frasca, A.; Alcalá, J. M.; Zusi, M.; Covino, E.; Randich, S.; Esposito, M.; Manara, C. F.; Antoniucci, S.; Nisini, B.; Rigliaco, E.; Getman, F.

    2017-09-01

    Aims: With the purpose of performing a homogeneous determination of elemental abundances for members of the Lupus T association, we analyzed three chemical elements: lithium, iron, and barium. The aims were: 1) to derive the lithium abundance for the almost complete sample ( 90%) of known class II stars in the Lupus I, II, III, and IV clouds; 2) to perform chemical tagging of a region where few iron abundance measurements have been obtained in the past, and no determination of the barium content has been done up to now. We also investigated possible barium enhancement at the very young age of the region, as this element has become increasingly interesting in the last few years following the evidence of barium over-abundance in young clusters, the origin of which is still unknown. Methods: Using the X-shooter spectrograph mounted on the Unit 2 (UT2) at the Very Large Telescope (VLT), we analyzed the spectra of 89 cluster members, both class II (82) and class III (7) stars. We measured the strength of the lithium line at λ6707.8 Å and derived the abundance of this element through equivalent width measurements and curves of growth. For six class II stars we also derived the iron and barium abundances using the spectral synthesis method and the code MOOG. The veiling contribution was taken into account in the abundance analysis for all three elements. Results: We find a dispersion in the strength of the lithium line at low effective temperatures and identify three targets with severe Li depletion. The nuclear age inferred for these highly lithium-depleted stars is around 15 Myr, which exceeds by an order of magnitude the isochronal one. We derive a nearly solar metallicity for the members whose spectra could be analyzed. We find that Ba is over-abundant by 0.7 dex with respect to the Sun. Since current theoretical models cannot reproduce this abundance pattern, we investigated whether this unusually large Ba content might be related to effects due to stellar

  8. Observation and Analysis of a Single-Chord Stellar Occultation by Kuiper Belt Object (50000) Quaoar

    NASA Astrophysics Data System (ADS)

    Davis, Allen B.; Pasachoff, J. M.; Babcock, B. A.; Person, M. J.; Zuluaga, C. A.; Bosh, A. S.; Levine, S.; Naranjo, O. A.; Navas, G. R.; Gulbis, A.; Winters, J. G.; Bianco, F.

    2014-01-01

    The Williams-MIT collaboration (www.stellaroccultations.info) predicted and observed a stellar occultation of 2UCAC 26260847 (mag 14.35) by KBO 50000 Quaoar (mag 18.9) on 8/9 July 2013. Observations were attempted from a total of five sites in Chile, Venezuela, and Massachusetts. Only one site, Llano del Hato National Astronomical Observatory in Venezuela, had a positive detection of the occultation, giving us a single chord on Quaoar. All other sites were cloudy. The light curve from the 8/9 July 2013 event has been analyzed with the assumption that Quaoar is ellipsoidal or spherical, placing bounds on some of Quaoar’s properties: diameter (> 1138 ± 25 km), density (< 1.82 ± 0.28 g cm-3), and albedo (< 0.14 ± 0.10). An independent prediction of the occultation’s shadow path by Fraser, Gwyn, et al. (2013) suggests that the chord is near-equatorial, which means that our bounds on Quaoar’s properties are closer to estimates. We will compare our result with that of the 11 February 2011 single-chord occultation detected by Sallum et al. (2011) and Person et al. (2011). A subsequent attempt to observe a second Quaoar occultation, that of 12/13 July 2013 in South Africa, failed because of cloudy weather. This work was supported in part by NASA Planetary Astronomy grants NNX08AO50G and NNH11ZDA001N to Williams College, NNX10AB27G to MIT, and USRA grant #8500-98-003 to Lowell Observatory. We thank Steven P. Souza at Williams, and other collaborators in planning and carrying out the various observations: including Libardo Zerpa, Joresly Villarreal, Richard Rojas, and Jorge Moreno at Llano del Hato, and Patricio Rojo and Matias Jones at Cerro Calan/U. Chile.

  9. A catalog of extended green objects in the Glimpse survey: A new sample of massive young stellar object outflow candidates

    SciTech Connect

    Cyganowski, C. J.; Holden, E.; Braden, E.; Churchwell, E.; Babler, B. L.; Meade, M. R.; Povich, M. S.; Whitney, B. A.; Brogan, C. L.; Indebetouw, R.; Watson, D. F.; Benjamin, R.; Gomez, M.; Robitaille, T. P.; Watson, C. E-mail: bwhitney@spacescience.org

    2008-12-01

    Using images from the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), we have identified more than 300 extended 4.5 μm sources (Extended Green Objects (EGOs), for the common coding of the [4.5] band as green in three-color composite InfraRed Array Camera images). We present a catalog of these EGOs, including integrated flux density measurements at 3.6, 4.5, 5.8, 8.0, and 24 μm from GLIMPSE and the Multiband Imaging Photometer for Spitzer Galactic Plane Survey. The average angular separation between a source in our sample and the nearest IRAS point source is greater than 1'. The majority of EGOs are associated with infrared dark clouds (IRDCs), and where high-resolution 6.7 GHz CH{sub 3}OH maser surveys overlap the GLIMPSE coverage, EGOs and 6.7 GHz CH{sub 3}OH masers are strongly correlated. Extended 4.5 μm emission is thought to trace shocked molecular gas in protostellar outflows; the association of EGOs with IRDCs and 6.7 GHz CH{sub 3}OH masers suggests that the extended 4.5 μm emission may pinpoint outflows specifically from massive protostars. The mid-IR colors of EGOs lie in regions of color-color space occupied by young protostars still embedded in infalling envelopes.

  10. HUBBLE SPACE TELESCOPE/NEAR-INFRARED CAMERA AND MULTI-OBJECT SPECTROMETER OBSERVATIONS OF THE GLIMPSE9 STELLAR CLUSTER

    SciTech Connect

    Messineo, Maria; Figer, Donald F.; Davies, Ben; Trombley, Christine; Kudritzki, R. P.; Rich, R. Michael; MacKenty, John

    2010-01-10

    We present Hubble Space Telescope/Near-Infrared Camera and Multi-Object Spectrometer photometry, and low-resolution K-band spectra of the GLIMPSE9 stellar cluster. The newly obtained color-magnitude diagram shows a cluster sequence with H - K{sub S} = approx1 mag, indicating an interstellar extinction A{sub K{sub s}} = 1.6 +- 0.2 mag. The spectra of the three brightest stars show deep CO band heads, which indicate red supergiants with spectral type M1-M2. Two 09-B2 supergiants are also identified, which yield a spectrophotometric distance of 4.2 +- 0.4 kpc. Presuming that the population is coeval, we derive an age between 15 and 27 Myr, and a total cluster mass of 1600 +- 400 M{sub sun}, integrated down to 1 M{sub sun}. In the vicinity of GLIMPSE9 are several H II regions and supernova remnants, all of which (including GLIMPSE9) are probably associated with a giant molecular cloud (GMC) in the inner galaxy. GLIMPSE9 probably represents one episode of massive star formation in this GMC. We have identified several other candidate stellar clusters of the same complex.

  11. Investigation of Energy Release from X-ray Flares on Young Stellar Objects with NuSTAR

    NASA Astrophysics Data System (ADS)

    Vievering, Juliana; Glesener, Lindsay; Grefenstette, Brian; Smith, David M.

    2017-08-01

    Young stellar objects (YSOs), which tend to flare more frequently and at higher temperatures than what is typically observed on Sun-like stars, are excellent targets for studying the nature of energy release and transport in large flaring events. Multiple star-forming regions have been observed in the past by soft x-ray missions such as Chandra and XMM-Newton, but the energy ranges of these missions fall off prior to the hard x-ray regime, where it would be possible to search for a crossover from thermal to nonthermal emission. To investigate this hard x-ray emission, three 50ks observations of the star-forming region rho Ophiuchi have been taken with the Nuclear Spectroscopic Telescope Array (NuSTAR), which is optimized over the energy range of 3-79 keV. Multiple stellar flares have been identified in the observations; here we present the current spectral and timing analyses of the brightest of the these events, exploring the way energy is released as well as the effects of these large flares on the surrounding environment. We compare these results to what is typically observed for solar flares.

  12. 77 FR 23318 - Culturally Significant Object Imported for Exhibition Determinations: “African Cosmos: Stellar Arts”

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-04-18

    ... custodian. I also determine that the exhibition or display of the exhibit object at the Smithsonian Institution's National Museum of African Arts, Washington, DC, from on or about June 20, 2012, until on or...

  13. A single sub-kilometre Kuiper belt object from a stellar occultation in archival data.

    PubMed

    Schlichting, H E; Ofek, E O; Wenz, M; Sari, R; Gal-Yam, A; Livio, M; Nelan, E; Zucker, S

    2009-12-17

    The Kuiper belt is a remnant of the primordial Solar System. Measurements of its size distribution constrain its accretion and collisional history, and the importance of material strength of Kuiper belt objects. Small, sub-kilometre-sized, Kuiper belt objects elude direct detection, but the signature of their occultations of background stars should be detectable. Observations at both optical and X-ray wavelengths claim to have detected such occultations, but their implied abundances are inconsistent with each other and far exceed theoretical expectations. Here we report an analysis of archival data that reveals an occultation by a body with an approximately 500-metre radius at a distance of 45 astronomical units. The probability of this event arising from random statistical fluctuations within our data set is about two per cent. Our survey yields a surface density of Kuiper belt objects with radii exceeding 250 metres of 2.1(-1.7)(+4.8) x 10(7) deg(-2), ruling out inferred surface densities from previous claimed detections by more than 5sigma. The detection of only one event reveals a deficit of sub-kilometre-sized Kuiper belt objects compared to a population extrapolated from objects with radii exceeding 50 kilometres. This implies that sub-kilometre-sized objects are undergoing collisional erosion, just like debris disks observed around other stars.

  14. The Evolution of Accretion in Young Stellar Objects: Strong Accretors at 3-10 Myr

    NASA Astrophysics Data System (ADS)

    Ingleby, Laura; Calvet, Nuria; Hernández, Jesus; Hartmann, Lee; Briceno, Cesar; Miller, Jon; Espaillat, Catherine; McClure, Melissa

    2014-07-01

    While the rate of accretion onto T Tauri stars is predicted to decline with age, objects with strong accretion have been detected at ages of up to 10 Myr. We analyze a sample of these old accretors, identified by having a significant U band excess and infrared emission from a circumstellar disk. Objects were selected from the ~3 Myr σ Ori, 4-6 Myr Orion OB1b, and 7-10 Myr Orion OB1a star forming associations. We use high-resolution spectra from the Magellan Inamori Kyocera Echelle to estimate the veiling of absorption lines and calculate extinction for our T Tauri sample. We also use observations obtained with the Magellan Echellette and, in a few cases, the SWIFT Ultraviolet and Optical Telescope to estimate the excess produced in the accretion shock, which is then fit with accretion shock models to estimate the accretion rate. We find that even objects as old as 10 Myr may have high accretion rates, up to ~10-8 M ⊙ yr-1. These objects cannot be explained by viscous evolution models, which would deplete the disk in shorter timescales unless the initial disk mass is very high, a situation that is unstable. We show that the infrared spectral energy distribution of one object, CVSO 206, does not reveal evidence of significant dust evolution, which would be expected during the 10 Myr lifetime. We compare this object to predictions from photoevaporation and planet formation models and suggest that neither of these processes have had a strong impact on the disk of CVSO 206. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.

  15. The evolution of accretion in young stellar objects: Strong accretors at 3-10 Myr

    SciTech Connect

    Ingleby, Laura; Calvet, Nuria; Hartmann, Lee; Miller, Jon; McClure, Melissa; Hernández, Jesus; Briceno, Cesar; Espaillat, Catherine E-mail: ncalvet@umich.edu

    2014-07-20

    While the rate of accretion onto T Tauri stars is predicted to decline with age, objects with strong accretion have been detected at ages of up to 10 Myr. We analyze a sample of these old accretors, identified by having a significant U band excess and infrared emission from a circumstellar disk. Objects were selected from the ∼3 Myr σ Ori, 4-6 Myr Orion OB1b, and 7-10 Myr Orion OB1a star forming associations. We use high-resolution spectra from the Magellan Inamori Kyocera Echelle to estimate the veiling of absorption lines and calculate extinction for our T Tauri sample. We also use observations obtained with the Magellan Echellette and, in a few cases, the SWIFT Ultraviolet and Optical Telescope to estimate the excess produced in the accretion shock, which is then fit with accretion shock models to estimate the accretion rate. We find that even objects as old as 10 Myr may have high accretion rates, up to ∼10{sup –8} M{sub ☉} yr{sup –1}. These objects cannot be explained by viscous evolution models, which would deplete the disk in shorter timescales unless the initial disk mass is very high, a situation that is unstable. We show that the infrared spectral energy distribution of one object, CVSO 206, does not reveal evidence of significant dust evolution, which would be expected during the 10 Myr lifetime. We compare this object to predictions from photoevaporation and planet formation models and suggest that neither of these processes have had a strong impact on the disk of CVSO 206.

  16. [Searching for Rare Celestial Objects Automatically from Stellar Spectra of the Sloan Digital Sky Survey Data Release Eight].

    PubMed

    Si, Jian-min; Luo, A-li; Wu, Fu-zhao; Wu, Yi-hong

    2015-03-01

    There are many valuable rare and unusual objects in spectra dataset of Sloan Digital Sky Survey (SDSS) Data Release eight (DR8), such as special white dwarfs (DZ, DQ, DC), carbon stars, white dwarf main-sequence binaries (WDMS), cataclysmic variable (CV) stars and so on, so it is extremely significant to search for rare and unusual celestial objects from massive spectra dataset. A novel algorithm based on Kernel dense estimation and K-nearest neighborhoods (KNN) has been presented, and applied to search for rare and unusual celestial objects from 546 383 stellar spectra of SDSS DR8. Their densities are estimated using Gaussian kernel density estimation, the top 5 000 spectra in descend order by their densities are selected as rare objects, and the top 300 000 spectra in ascend order by their densities are selected as normal objects. Then, KNN were used to classify the rest objects, and simultaneously K nearest neighbors of the 5 000 rare spectra are also selected as rare objects. As a result, there are totally 21 193 spectra selected as initial rare spectra, which include error spectra caused by deletion, redden, bad calibration, spectra consisting of different physically irrelevant components, planetary nebulas, QSOs, special white dwarfs (DZ, DQ, DC), carbon stars, white dwarf main-sequence binaries (WDMS), cataclysmic variable (CV) stars and so on. By cross identification with SIMBAD, NED, ADS and major literature, it is found that three DZ white dwarfs, one WDMS, two CVs with company of G-type star, three CVs candidates, six DC white dwarfs, one DC white dwarf candidate and one BL Lacertae (BL lac) candidate are our new findings. We also have found one special DA white dwarf with emission lines of Ca II triple and Mg I, and one unknown object whose spectrum looks like a late M star with emission lines and its image looks like a galaxy or nebula.

  17. Maximum-magnitude estimation of the object's power spectrum in stellar speckle interferometry.

    PubMed

    Granrath, D J

    1984-11-01

    The maximum Fourier magnitude taken over a set of speckle images is proposed as a replacement for the standard power-spectrum average. This new statistic estimates the diffraction-limited object-times-telescope magnitude values in a statistically unbiased and sufficient fashion and has a variance that decreases with sample size faster than the average magnitude's variance. Simultaneous imaging of a nearby point source is unnecessary with this technique, and any object that lies within a single isoplanatic patch of the atmosphere can be estimated. Magnitude-estimation results of the double star Capella are shown to corroborate these claims.

  18. H2O masers in a jet-driven bow shock: episodic ejection from a massive young stellar object

    NASA Astrophysics Data System (ADS)

    Burns, R. A.; Handa, T.; Nagayama, T.; Sunada, K.; Omodaka, T.

    2016-07-01

    We report the results of VERA (VLBI Exploration of Radio Astrometry) multi-epoch VLBI (very long baseline interferometry) 22 GHz water maser observations of S255IR-SMA1, a massive young stellar object located in the S255 star-forming region. By annual parallax the source distance was measured as D = 1.78^{+0.12}_{-0.11} kpc and the source systemic motion was (μαcos δ, μδ) = (-0.13 ± 0.20, -0.06 ± 0.27) mas yr-1. Masers appear to trace a U-shaped bow shock whose morphology and proper motions are well reproduced by a jet-driven outflow model with a jet radius of about 6 au. The maser data, in the context of other works in the literature, reveal ejections from S255IR-SMA1 to be episodic, operating on time-scales of ˜1000 yr.

  19. Stellar encounters as the origin of distant Solar System objects in highly eccentric orbits.

    PubMed

    Kenyon, Scott J; Bromley, Benjamin C

    2004-12-02

    The Kuiper belt extends from the orbit of Neptune at 30 au to an abrupt outer edge about 50 au from the Sun. Beyond the edge is a sparse population of objects with large orbital eccentricities. Neptune shapes the dynamics of most Kuiper belt objects, but the recently discovered planet 2003 VB12 (Sedna) has an eccentric orbit with a perihelion distance of 70 au, far beyond Neptune's gravitational influence. Although influences from passing stars could have created the Kuiper belt's outer edge and could have scattered objects into large, eccentric orbits, no model currently explains the properties of Sedna. Here we show that a passing star probably scattered Sedna from the Kuiper belt into its observed orbit. The likelihood that a planet at 60-80 au can be scattered into Sedna's orbit is about 50 per cent; this estimate depends critically on the geometry of the fly-by. Even more interesting is the approximately 10 per cent chance that Sedna was captured from the outer disk of the passing star. Most captures have very high inclination orbits; detection of such objects would confirm the presence of extrasolar planets in our own Solar System.

  20. MID-INFRARED SIZE SURVEY OF YOUNG STELLAR OBJECTS: DESCRIPTION OF KECK SEGMENT-TILTING EXPERIMENT AND BASIC RESULTS

    SciTech Connect

    Monnier, J. D.; Tannirkulam, A.; Tuthill, P. G.; Ireland, M.; Cohen, R.; Perrin, M. D.

    2009-07-20

    The mid-infrared properties of pre-planetary disks are sensitive to the temperature and flaring profiles of disks for the regions where planet formation is expected to occur. In order to constrain theories of planet formation, we have carried out a mid-infrared ({lambda} = 10.7 {mu}m) size survey of young stellar objects using the segmented Keck telescope in a novel configuration. We introduced a customized pattern of tilts to individual mirror segments to allow efficient sparse-aperture interferometry, allowing full aperture synthesis imaging with higher calibration precision than traditional imaging. In contrast to previous surveys on smaller telescopes and with poorer calibration precision, we find that most objects in our sample are partially resolved. Here, we present the main observational results of our survey of five embedded massive protostars, 25 Herbig Ae/Be stars, 3 T Tauri stars, 1 FU Ori system, and five emission-line objects of uncertain classification. The observed mid-infrared sizes do not obey the size-luminosity relation found at near-infrared wavelengths and a companion paper will provide further modeling analysis of this sample. In addition, we report imaging results for a few of the most resolved objects, including complex emission around embedded massive protostars, the photoevaporating circumbinary disk around MWC 361A, and the subarcsecond binaries T Tau, FU Ori, and MWC 1080.

  1. FIRST KECK NULLING OBSERVATIONS OF A YOUNG STELLAR OBJECT: PROBING THE CIRCUMSTELLAR ENVIRONMENT OF THE HERBIG Ae STAR MWC 325

    SciTech Connect

    Ragland, S.; Hrynevich, M.; Ohnaka, K.; Hillenbrand, L.; Ridgway, S. T.; Colavita, M. M.; Traub, W. A.; Akeson, R. L.; Millan-Gabet, R.; Cotton, W.; Danchi, W. C.

    2012-02-20

    We present the first N-band nulling plus K- and L-band V{sup 2} observations of a young stellar object, MWC 325, taken with the 85 m baseline Keck Interferometer. The Keck nuller was designed for the study of faint dust signatures associated with debris disks, but it also has a unique capability for studying the temperature and density distribution of denser disks found around young stellar objects. Interferometric observations of MWC 325 at K, L, and N encompass a factor of five in spectral range and thus, especially when spectrally dispersed within each band, enable characterization of the structure of the inner disk regions where planets form. Fitting our observations with geometric models such as a uniform disk or a Gaussian disk show that the apparent size increases monotonically with wavelength in the 2-12 {mu}m wavelength region, confirming the widely held assumption based on radiative transfer models, now with spatially resolved measurements over a broad wavelength range, that disks are extended with a temperature gradient. The effective size is a factor of about 1.4 and 2.2 larger in the L band and N band, respectively, compared to that in the K band. The existing interferometric measurements and the spectral energy distribution can be reproduced by a flat disk or a weakly shadowed nearly flat disk model, with only slight flaring in the outer regions of the disk, consisting of representative 'sub-micron' (0.1 {mu}m) and 'micron' (2 {mu}m) grains of a 50:50 ratio of silicate and graphite. This is in marked contrast to the disks previously found in other Herbig Ae/Be stars, suggesting a wide variety in the disk properties among Herbig Ae/Be stars.

  2. First Keck Nulling Observations of a Young Stellar Object: Probing the Circumstellar Environment of the Herbig Ae star MWC 325

    NASA Technical Reports Server (NTRS)

    Ragland, S.; Ohnaka, K.; Hillenbrand, L.; Ridgway, S. T.; Colavita, M. M.; Akeson, R. L.; Cotton, W.; Danichi, W. C.; Hrynevych, M.; Milan-Gabet, R.; hide

    2012-01-01

    We present the first N-band nulling plus K- and L-band V(sup 2) observations of a young stellar object, MWC325, taken with the 85 m baseline Keck Interferometer. The Keck nuller was designed for the study of faint dust signatures associated with debris disks, but it also has a unique capability for studying the temperature and density distribution of denser disks found around young stellar objects. Interferometric observations of MWC 325 at K, L and N encompass a factor of five in spectral range and thus, especially when spectrally dispersed within each band, enable characterization of the structure of the inner disk regions where planets form. Fitting our observations with geometric models such as a uniform disk or a Gaussian disk show that the apparent size increases monotonically with wavelength in the 2-12 micrometer wavelength region, confirming the widely held assumption based on radiative transfer models, now with spatially resolved measurements over broad wavelength range, that disks are extended with a temperature gradient. The effective size is a factor of about 1.3 and 2 larger in the Lband and N-band, respectively, compared to that in the K-band. The existing interferometric measurements and the spectral energy distribution can be reproduced by a flat disk or a weakly shadowed nearly flat-disk model, with only slight flaring in the outer regions of the disk, consisting of representative "sub-micron" (0.1 micron) and "micron" (2 micron) grains of a 50:50 ratio of silicate and graphite. This is marked contrast with the disks previously found in other Herbig Ae/Be stars suggesting a wide variety in the disk properties among Herbig Ae/Be stars.

  3. First Keck Nulling Observations of a Young Stellar Object: Probing the Circumstellar Environment of the Herbig Ae Star MWC325

    NASA Technical Reports Server (NTRS)

    Ragland, S.; Ohnaka, K.; Hillenbrand, L.; Ridgway, S. T.; Colavita, M. M.; Akeson, R. L.; Cotton, W.; Danchi, W. C.; Hrynevich, M.; Millan-Gabet, R.; hide

    2012-01-01

    We present the first N-band nulling plus K- and L-band V(sup 2) observations of a young stellar object, MWC 325, taken with the 85 m baseline Keck Interferometer. The Keck nuller was designed for the study of faint dust signatures associated with debris disks, but it also has a unique capability for studying the temperature and density distribution of denser disks found around young stellar objects. Interferometric observations of MWC 325 at K, L, and N encompass a factor of five in spectral range and thus, especially when spectrally dispersed within each band, enable characterization of the structure of the inner disk regions where planets form. Fitting our observations with . geometric models such as a uniform disk or a Gaussian disk show that the apparent size increases 'monotonically with wavelength in the 2-12/Lm wavelength region, confirming the widely held assumption based on radiative transfer models, now with spatially resolved measurements over a broad wavelength range, that disks are extended with a temperature gradient. The effective size is a factor of about 1.4 and 2.2 larger in the L band and N band, respectively, compared to that in the K band. The existing interferometric measurements and the spectral energy distribution can be reproduced by a flat disk or a weakly shadowed nearly flat disk model, with only slight flaring in the outer regions of the disk, consisting of representative "sub-micron" (0.1 micron) and "micron" (2 micron) grains of a 50:50 ratio of silicate and graphite. This is in marked contrast io the disks previously found in other Herbig Ae/Be stars, suggesting a wide variety in the disk properties among Herbig Ae/Be stars.

  4. First Keck Nulling Observations of a Young Stellar Object: Probing the Circumstellar Environment of the Herbig Ae Star MWC325

    NASA Technical Reports Server (NTRS)

    Ragland, S.; Ohnaka, K.; Hillenbrand, L.; Ridgway, S. T.; Colavita, M. M.; Akeson, R. L.; Cotton, W.; Danchi, W. C.; Hrynevich, M.; Millan-Gabet, R.; Traub, W. A.

    2012-01-01

    We present the first N-band nulling plus K- and L-band V(sup 2) observations of a young stellar object, MWC 325, taken with the 85 m baseline Keck Interferometer. The Keck nuller was designed for the study of faint dust signatures associated with debris disks, but it also has a unique capability for studying the temperature and density distribution of denser disks found around young stellar objects. Interferometric observations of MWC 325 at K, L, and N encompass a factor of five in spectral range and thus, especially when spectrally dispersed within each band, enable characterization of the structure of the inner disk regions where planets form. Fitting our observations with . geometric models such as a uniform disk or a Gaussian disk show that the apparent size increases 'monotonically with wavelength in the 2-12/Lm wavelength region, confirming the widely held assumption based on radiative transfer models, now with spatially resolved measurements over a broad wavelength range, that disks are extended with a temperature gradient. The effective size is a factor of about 1.4 and 2.2 larger in the L band and N band, respectively, compared to that in the K band. The existing interferometric measurements and the spectral energy distribution can be reproduced by a flat disk or a weakly shadowed nearly flat disk model, with only slight flaring in the outer regions of the disk, consisting of representative "sub-micron" (0.1 micron) and "micron" (2 micron) grains of a 50:50 ratio of silicate and graphite. This is in marked contrast io the disks previously found in other Herbig Ae/Be stars, suggesting a wide variety in the disk properties among Herbig Ae/Be stars.

  5. A Mid-Infrared Imaging Survey of Embedded Young Stellar Objects in the (rho) Ophiuchi Cloud Core

    NASA Technical Reports Server (NTRS)

    Barsony, Mary; Ressler, Michael E.; Marsh, Kenneth A.

    2005-01-01

    Results of a comprehensive, new, ground-based mid-infrared imaging survey of the young stellar population of the (rho) Ophiuchi cloud are presented. Data were acquired at the Palomar 5m and at the Keck 10m telescopes with the MIRLIN and LWS instruments, at 0'.5 and 0'.25 resolutions, respectively. Of 172 survey objects, 85 were detected. Among the 22 multiple systems observed, 15 were resolved and their individual component fluxes determined. A plot of the frequency distribution of the detected objects with SED spectral slope shows that YSOs spend approx.4 x 10(exp 5) yr in the flat-spectrum phase, clearing out their remnant infall envelopes. Mid-infrared variability is found among a significant fraction of the surveyed objects and is found to occur for all SED classes with optically thick disks. Large-amplitude near-infrared variability, also found for all SED classes with optically thick disks, seems to occur with somewhat higher frequency at the earlier evolutionary stages. Although a general trend of mid-infrared excess and near-infrared veiling exists progressing through SED classes, with Class I objects generally exhibiting r(sub K) >= 1, flat-spectrum objects with r(sub K) >= 0.58, and Class III objects with r(sub K) =0, Class II objects exhibit the widest range of r(sub K) values, ranging from 0 <= r(sub K) <= 4.5. However, the highly variable value of veiling that a single source can exhibit in any of the SED classes in which active disk accretion can take place is striking and is direct observational evidence for highly time-variable accretion activity in disks. Finally, by comparing mid-infrared versus near-infrared excesses in a subsample with well-determined effective temperatures and extinction values, disk-clearing mechanisms are explored. The results are consistent with disk clearing proceeding from the inside out.

  6. Red-Green Versus Blue Tactical Light: A Direct, Objective Comparison.

    PubMed

    Pedler, Michelle; Ruiz, Frank; Lamari, Micaela; Hutchinson, Charles; Noyes, Brandon; Petrash, Mark; Calvano, Christopher J; La Porta, Anthony; Enzenauer, Robert W

    Success in Special Operations Forces medicine (SOFMED) depends on maximizing visual capability without compromising the provider or casualty when under fire. There is no single light that has been deemed "ideal" for all SOFMED environments. We used the Farnsworth-Munsell (FM) hue test to determine color vision of normal subjects under white, red-green, and blue flashlights to determine color discrimination. Then we used a timed color-determination visual test to determine how quickly normal subjects can identify color correctly. We had subjects perform a simulated surgery illuminated by a normal white-light source, then by red-green or blue light-emitting diode (LED) tactical light. The total error score for white light was 49.714, 272.923 for red/green light, and 531.4 for blue light. The subjective perception of simulated trauma wounds was not substantially different with red-green LED tactical light when compared with white LED light. However, simulated surgery under the blue LED was more difficult compared with simulated surgery under the red-green LED light. Red-green was a superior light source for SOFMED and military first responders in this study, especially, where light was required to allow accurate and efficient application of Tactical Combat Casualty Care to injured personnel. 2016.

  7. X-Ray Spectrum of a Narrow Line Quasi-Stellar Object

    NASA Technical Reports Server (NTRS)

    Halpern, Jules P.

    1996-01-01

    This AO-3 observation of a new narrow-line QSO was motivated by our extensive study of the unclassified X-ray sources from the ROSAT/IRAS survey of Boller et al. IRAS 2018.1-2244 was observed to have Balmer lines and forbidden lines of roughly equal width. There are possibly weak broad wings on the H-alpha line. One of the questions to be addressed by hard X-ray spectroscopy is whether or not these wings are to be interpreted as scattered or weakly transmitted flux from a hidden broad-line region. The optical spectrum of this QSO also has very weak permitted Fe II lines, possibly indicative of a hidden broad line region. A new wrinkle on the concept of the narrow-line QSO is the gradual realization that luminous objects with very strong but narrow Fe II lines are showing up preferentially in soft X-ray surveys. The AO-1 objective was to detect the Geminga Pulsar and to interpret its 2-10 keV spectrum and pulse profile in terms of its X-ray emission spectra. Also, the AO-1 observed the Seyfert galaxy NGC 3516 to obtain a high signal-to-noise ratio spectrum. We expected NGC 3516 to be one of the best candidates for a successful demonstration of the details of the warm-absorber model.

  8. Insights into stellar and binary evolution from gravitational-wave observations of merging compact objects

    NASA Astrophysics Data System (ADS)

    Stevenson, Simon

    2016-07-01

    Advanced LIGO finished its first observing run (O1) at the begining of 2016, at a sensitivity ~3 times that of the initial LIGO detectors. This increased sensitivity makes the possibility of detecting gravitational-waves a realistic prospect over the next few years. One of the most promising sources for advanced gravitational-wave detectors is the merger of two compact objects; neutron stars or black holes. These objects are formed as the end point of the evolution of massive stars in close binaries. There remain many poorly understood processes in the lives of massive stars and the evolution of close binary systems. These processes include the distribution of kicks received by black holes at birth, the amount of angular momentum lost from a system during a mass transfer episode, and the common envelope event. One way of attempting to understand these processes is to attempt to constrain them observationally using eventual gravitational-wave observations of compact binary mergers. Here we present recent work on this front.

  9. What is the difference between radio-loud and radio-quiet quasi-stellar objects?

    NASA Technical Reports Server (NTRS)

    Hutchings, J. B.; Janson, T.; Neff, S. G.

    1989-01-01

    Measures of the nuclear and host galaxy luminosities and colors and a morphological discussion of the host galaxies are presented for a sample of low-redshift, high-luminosity, radio-quiet QSOs whose redshift and luminosity distribution matches that of a radio-loud sample previously discussed. Radio-quiet QSOs are found to reside in galaxies which are smaller, fainter, and redder than the host galaxies of radio-loud QSOs. These properties are generally consistent with the suggestion that radio-quiet QSOs are located in spiral-type galaxies and radio-loud QSOs are located in more elliptical-type galaxies. Significantly less evidence is found for tidal interactions among the radio-quiet objects, although they appear to reside in somewhat richer environments in terms of nearby companions.

  10. A full 1---40 micron spectral energy distribution for the Becklin-Neugebauer object: Placing constraints on disk size for a runaway massive young stellar object

    NASA Astrophysics Data System (ADS)

    Shuping, Ralph; Keller, Luke D.; Adams, Joseph D.; Petkova, Maya; Wood, Kenneth; Herter, Terry; Sloan, Greg; Jaffe, Daniel Thomas; Greene, Thomas P.; Ennico, Kimberly

    2017-01-01

    The Becklin-Neugebauer (BN) Object—one of the brightest infrared obejcts in the sky—is a highly luminous young stellar object (YSO) deeply embedded in Orion Molecular Cloud 1 (OMC-1), which sits behind the Orion Nebula (M42). The BN object is likely a 8—15 M⊙ star and has no obvious optical counterpart due to high visual extinction on the line of sight. Furthermore, recent radio studies show that BN is moving towards the northwest at approximately 26 km/s with respect to the Orion Nebula Cluster (ONC), which may indicate that BN was dynamically ejected from either the Trapezium or from within OMC-1 itself. Near-IR polarimetry suggests that BN is surrounded by a large (R=800 AU) disk, which is surprising since a close encounter leading to an ejection would likely disrupt and/or truncate a disk of this size. In this poster presentation, we present new SOFIA-FORCAST grism spectroscopy of BN from 10—40 μm. In conjunction with previous SOFIA-FORCAST photometry and data form the literature, we present the full 1—40 μm SED of BN which we compare to theoretical models using the HOCHUNK-3D radiative equilibrium code. We report constraints on disk parameters and discuss implications for dynamical ejection scenarios.

  11. Fundamental Parameters and Spectral Energy Distributions of Young and Field Age Objects with Masses Spanning the Stellar to Planetary Regime

    NASA Astrophysics Data System (ADS)

    Filippazzo, Joe; Rice, Emily L.; Faherty, Jacqueline K.; Cruz, Kelle L.; Godfrey, Paige A.; BDNYC

    2016-01-01

    The physical and atmospheric properties of ultracool dwarfs are deeply entangled due to the degenerate effects of mass, age, metallicity, clouds and dust, activity, rotation, and possibly even formation mechanism on observed spectra. Accurate determination of fundamental parameters for a wide diversity of objects at the low end of the IMF is thus crucial to testing stellar and planetary formation theories. To determine these quantities, we constructed and flux calibrated nearly-complete spectral energy distributions (SEDs) for 221 M, L, T, and Y dwarfs using published parallaxes and 0.3-40 μm spectra and photometry. From these homogeneous SEDs, we calculated bolometric luminosity (Lbol), effective temperature (Teff), mass, surface gravity, radius, spectral indexes, synthetic photometry, and bolometric corrections (BCs) for each object. We used these results to derive Lbol, Teff, and BC polynomial relations across the entire very-low-mass star/brown dwarf/planetary mass regime. We use a subsample of objects with age constraints based on nearby young moving group membership, companionship with a young star, or spectral signatures of low surface gravity to define new age-sensitive diagnostics and characterize the reddening of young substellar atmospheres as a redistribution of flux from the near-infrared into the mid-infrared. Consequently we find the SED flux pivots at Ks band, making BCKs as a function of spectral type a tight and age independent relationship. We find that young L dwarfs are systematically 300 K cooler than field age objects of the same spectral type and up to 600 K cooler than field age objects of the same absolute H magnitude. Finally, we present preliminary comparisons of these empirical results to best fit parameters from four different model atmosphere grids via Markov-Chain Monte Carlo analysis in order to create prescriptions for the reliable and efficient characterization of new ultracool dwarfs.

  12. ASSOCIATIONS OF HIGH-REDSHIFT QUASI-STELLAR OBJECTS WITH ACTIVE, LOW-REDSHIFT SPIRAL GALAXIES

    SciTech Connect

    Burbidge, G.; Napier, W. M. E-mail: smawmn@cardiff.ac.u

    2009-11-20

    Following the discovery in the 1960s of radio and optical QSOs it was found that some of them lie very close to low-redshift (z <= 0.01) spiral galaxies with separations of approx<2 arcmin. These were discovered both serendipitously by many observers, and systematically by Arp. They are some of the brightest QSOs in radio and optical wavelengths and are very rare. We have carried out a new statistical analysis of most of those galaxy-QSO pairs and find that the configurations have high statistical significance. We show that gravitational microlensing due to stars or other dark objects in the halos of the galaxies apparently cannot account for the excess. Sampling or identification bias likewise seems unable to explain it. Following this up we selected all approx4000 QSOs with g <= 18 from a catalog of confirmed QSOs in the Sloan Digital Sky Survey, and compared them with various subsets of galaxies from the RC 3 galaxy catalog. In contrast to the earlier results, no significant excess of such QSOs was found around these galaxies. Possible reasons for the discrepancy are discussed.

  13. A HIGHLY COLLIMATED WATER MASER BIPOLAR OUTFLOW IN THE CEPHEUS A HW3d MASSIVE YOUNG STELLAR OBJECT

    SciTech Connect

    Chibueze, James O.; Imai, Hiroshi; Tafoya, Daniel; Omodaka, Toshihiro; Chong, Sze-Ning; Kameya, Osamu; Hirota, Tomoya; Torrelles, Jose M.

    2012-04-01

    We present the results of multi-epoch very long baseline interferometry (VLBI) water (H{sub 2}O) maser observations carried out with the VLBI Exploration of Radio Astrometry toward the Cepheus A HW3d object. We measured for the first time relative proper motions of the H{sub 2}O maser features, whose spatio-kinematics traces a compact bipolar outflow. This outflow looks highly collimated and expanding through {approx}280 AU (400 mas) at a mean velocity of {approx}21 km s{sup -1} ({approx}6 mas yr{sup -1}) without taking into account the turbulent central maser cluster. The opening angle of the outflow is estimated to be {approx}30 Degree-Sign . The dynamical timescale of the outflow is estimated to be {approx}100 years. Our results provide strong support that HW3d harbors an internal massive young star, and the observed outflow could be tracing a very early phase of star formation. We also have analyzed Very Large Array archive data of 1.3 cm continuum emission obtained in 1995 and 2006 toward Cepheus A. The comparative result of the HW3d continuum emission suggests the possibility of the existence of distinct young stellar objects in HW3d and/or strong variability in one of their radio continuum emission components.

  14. Growth of a Massive Young Stellar Object Fed by a Gas Flow from a Companion Gas Clump

    NASA Astrophysics Data System (ADS)

    Chen, Xi; Ren, Zhiyuan; Zhang, Qizhou; Shen, Zhiqiang; Qiu, Keping

    2017-02-01

    We present a Submillimeter Array (SMA) observation toward the young massive double-core system G350.69-0.49. This system consists of a northeast (NE) diffuse gas bubble and a southwest (SW) massive young stellar object (MYSO), both clearly seen in the Spitzer images. The SMA observations reveal a gas flow between the NE bubble and the SW MYSO in a broad velocity range from 5 to 30 km s-1 with respect to the system velocity. The gas flow is well confined within the interval between the two objects and traces a significant mass transfer from the NE gas bubble to the SW massive core. The transfer flow can supply the material accreted onto the SW MYSO at a rate of 4.2 × 10-4 M⊙ yr-1. The whole system therefore suggests a mode for the mass growth in the MYSO from a gas transfer flow launched from its companion gas clump, despite the driving mechanism of the transfer flow not being fully determined from the current data.

  15. THE SPITZER EXTRAGALACTIC REPRESENTATIVE VOLUME SURVEY: THE ENVIRONMENTS OF HIGH-z SDSS QUASI-STELLAR OBJECTS

    SciTech Connect

    Falder, J. T.; Stevens, J. A.; Jarvis, Matt J.; Bonfield, D. G.; Lacy, M.; Farrah, D.; Oliver, S.; Surace, J.; Mauduit, J.-C.; Gonzalez-Solares, E.; Afonso, J.; Cava, A.; Seymour, N.

    2011-07-10

    This paper presents a study of the environments of SDSS quasi-stellar objects (QSOs) in the Spitzer Extragalactic Representative Volume Survey (SERVS). We concentrate on the high-redshift QSOs as these have not been studied in large numbers with data of this depth before. We use the IRAC 3.6-4.5 {mu}m color of objects and ancillary r-band data to filter out as much foreground contamination as possible. This technique allows us to find a significant (>4{sigma}) overdensity of galaxies around QSOs in a redshift bin centered on z {approx} 2.0 and an (>2{sigma}) overdensity of galaxies around QSOs in a redshift bin centered on z {approx} 3.3. We compare our findings to the predictions of a semi-analytic galaxy formation model, based on the {Lambda}CDM MILLENNIUM simulation, and find for both redshift bins that the model predictions match well the source density we have measured from the SERVS data.

  16. Exoplanet Meteorology: Characterizing The Atmospheres Of Directly Imaged Sub-Stellar Objects

    NASA Astrophysics Data System (ADS)

    Rajan, Abhijith

    2017-05-01

    The field of exoplanet science has matured over the past two decades with over 3500 confirmed exoplanets. However, many fundamental questions regarding the composition, and formation mechanism remain unanswered. Atmospheres are a window into the properties of a planet, and spectroscopic studies can help resolve many of these questions. For the first part of my dissertation, I participated in two studies of the atmospheres of brown dwarfs to search for weather variations. To understand the evolution of weather on brown dwarfs we conducted a multi- epoch study monitoring four cool brown dwarfs to search for photometric variability. These cool brown dwarfs are predicted to have salt and sulfide clouds condensing in their upper atmosphere and we detected one high amplitude variable. Combining observations for all T5 and later brown dwarfs we note a possible correlation between variability and cloud opacity.For the second half of my thesis, I focused on characterizing the atmospheres of directly imaged exoplanets. In the first study Hubble Space Telescope data on HR8799, in wavelengths unobservable from the ground, provide constraints on the presence of clouds in the outer planets. Next, I present research done in collaboration with the Gemini Planet Imager Exoplanet Survey (GPIES) team including an exploration of the instrument contrast against environmental parameters, and an examination of the environment of the planet in the HD 106906 system. By analyzing archival HST data and examining the near-infrared colors of HD 106906b, we conclude that the companion shows weak evidence of a circumplanetary dust disk or cloud. Finally, I measure the properties of the low mass directly imaged planet 51 Eridani b. We combined published J, H spectra with updated LP photometry, new K1, K2 spectra, and MS photometry. The new data confirms that the planet has redder than similar pectral type objects, which might be due to the planet still transitioning from to L-to-T. Model

  17. A Ground-Based Mid-Infrared Imaging Survey of Embedded Young Stellar Objects in the Rho Ophiuchi Cloud Core

    NASA Astrophysics Data System (ADS)

    Barsony, M.; Ressler, M. E.; Marsh, K. A.

    2004-12-01

    Results of a comprehensive, new, ground-based mid-infrared imaging survey of the young stellar population of the ρ Ophiuchi cloud are presented. Data were acquired at the Palomar 5-m and at the Keck 10-m telescopes with the MIRLIN and LWS instruments, at 0.5'' and 0.25'' resolutions, respectively. Of 172 survey objects, 85 were detected. A plot of the frequency distribution of the detected objects with SED spectral slope shows that YSOs spend ˜ 3 × 105 yr in the Flat Spectrum phase, clearing out their remnant infall envelopes. Mid-infrared variability is found among a significant fraction of the surveyed objects and is found to occur for all SED classes with optically thick disks. Large amplitude near-infrared variability, also found for all SED classes with optically thick disks, seems to occur with somewhat higher frequency at the earlier evolutionary stages. The highly variable value of K-band veiling that a single source can exhibit in any of the SED classes in which active disk accretion can take place is striking, and is direct observational evidence for highly time-variable accretion activity in disks. Finallly, by comparing mid-infrared vs. near-infrared excesses in a subsample with well-determined effective temperatures and extinction values, disk clearing mechanisms are explored. Financial support for this project through NSF grants AST 00-96087 (CAREER), AST 97-53229 (POWRE), and AST 02-06146 is gratefully acknowledged. MB further thanks the NASA/ASEE Summer Faculty Fellowship program at JPL, that made this work possible.

  18. On the Nature of the FBS Blue Stellar Objects and the Completeness of the Bright Quasar Survey. Ii

    NASA Astrophysics Data System (ADS)

    Mickaelian, A.; Goncalves, A.; Veron-Cetty, M.; Veron, P.

    In Paper I (Mickaelian et al. 1999), we compared the surface density of QSOs in the Bright Quasar Survey (BQS) and in the First Byurakan Survey (FBS) and concluded that the completeness of the BQS is of the order of 70% rather than 30-50% as suggested by several authors. A number of new observations recently became available, allowing a re-evaluation of this completeness. We now obtain a surface density of QSOs brighter than B = 16.16 in a subarea of the FBS covering ~2250 deg^2, equal to 0.012 deg^-2 (26 QSOs), implying a completeness of 53+/-10%.

  19. On the Nature of the FBS Blue Stellar Objects and the Completeness of the Bright Quasar Survey. II

    NASA Astrophysics Data System (ADS)

    Mickaelian, A. M.; Gonçalves, A. C.; Véron-Cetty, M. P.; Véron, P.

    2001-01-01

    In Paper I we compared the surface density of QSOs in the Bright Quasar Survey (BQS) and in the First Byurakan Survey (FBS) and concluded that the completeness of the BQS is of the order of 70% rather than 30-50% as suggested by several authors. A number of new observations recently became available, allowing a reevaluation of this completeness. We now obtain a surface density of QSOs brighter than B = 16.16 in a subarea of the FBS covering 2250 deg2, equal to 0.012 deg-2 (26 QSOs), implying a completeness of 53 ± 10%.

  20. Application of USNO-B1.0 towards selecting objects with displaced blue and red components

    NASA Astrophysics Data System (ADS)

    Jayson, Joel S.

    2016-03-01

    We have conducted a feasibility study to determine the effectiveness of using USNO-B1.0 data to preferentially detect objects with displaced red and blue components. A procedure was developed to search catalogue entries for such objects, which include M dwarfs paired with white dwarfs or with earlier main-sequence stars, and galaxies with asymmetric colour distributions. Residual differences between red and blue and infrared and blue scanned emulsion images define vectors, which, when appropriately aligned and of sufficient length, signal potential candidates. Test sample sets were analysed to evaluate the effective discrimination of the technique. Over 91 000 USNO-B1.0 catalogue entries at points throughout the celestial sphere were then filtered for acceptable combinations of entry observations and magnitudes and the resulting total of about 17 000 entries was winnowed down to a little more than 200 objects of interest. These were screened by visual examination of photo images to a final total of 146 candidates. About one quarter of these candidates coincide with SDSS (Sloan Digital Sky Survey) data. Those constituents fall into two groups, single and paired objects. SDSS identified several galaxies in the first group. Regarding the second group, at least half of its members were tentatively identified as main-sequence pairs, the greater portion being of widely separated spectral types. Two white dwarf-main-sequence pairs were also identified. Most importantly, the vectors formed from USNO-B1.0 residuals were in alignment with corresponding SDSS pair position angles, thereby supporting this work's central thesis.

  1. Differential binding of colors to objects in memory: red and yellow stick better than blue and green.

    PubMed

    Kuhbandner, Christof; Spitzer, Bernhard; Lichtenfeld, Stephanie; Pekrun, Reinhard

    2015-01-01

    Both evolutionary considerations and recent research suggest that the color red serves as a signal indicating an object's importance. However, until now, there is no evidence that this signaling function of red is also reflected in human memory. To examine the effect of red on memory, we conducted four experiments in which we presented objects colored in four different colors (red, green, blue, and yellow) and measured later memory for the presence of an object and for the color of an object. Across experiments, we varied the type of objects (words vs. pictures), task complexity (single objects vs. multiple objects in visual scenes), and intentionality of encoding (intentional vs. incidental learning). Memory for the presence of an object was not influenced by color. However, in all four experiments, memory for the color of an object depended on color type and was particularly high for red and yellow-colored objects and particularly low for green-colored objects, indicating that the binding of colors into object memory representations varies as a function of color type. Analyzing the observers' confidence in their color memories revealed that color not only influenced objective memory performance but also subjective confidence. Subjective confidence judgments differentiated well between correct and incorrect color memories for red-colored objects, but poorly for green-colored objects. Our findings reveal a previously unknown color effect which may be of considerable interest for both basic color research and applied settings like eyewitness testimony in which memory for color features is relevant. Furthermore, our results indicate that feature binding in memory is not a uniform process by which any attended feature is automatically bound into unitary memory representations. Rather, memory binding seems to vary across different subtypes of features, a finding that supports recent research showing that object features are stored in memory rather independently from

  2. Extreme Radio Flares and Associated X-Ray Variability from Young Stellar Objects in the Orion Nebula Cluster

    NASA Astrophysics Data System (ADS)

    Forbrich, Jan; Reid, Mark J.; Menten, Karl M.; Rivilla, Victor M.; Wolk, Scott J.; Rau, Urvashi; Chandler, Claire J.

    2017-08-01

    Young stellar objects are known to exhibit strong radio variability on timescales of weeks to months, and a few reports have documented extreme radio flares with at least an order of magnitude change in flux density on timescales of hours to days. However, there have been few constraints on the occurrence rate of such radio flares or on the correlation with pre-main sequence X-ray flares, although such correlations are known for the Sun and nearby active stars. Here we report simultaneous deep VLA radio and Chandra X-ray observations of the Orion Nebula Cluster, targeting hundreds of sources to look for the occurrence rate of extreme radio variability and potential correlation with the most extreme X-ray variability. We identify 13 radio sources with extreme radio variability, with some showing an order of magnitude change in flux density in less than 30 minutes. All of these sources show X-ray emission and variability, but we find clear correlations with extreme radio flaring only on timescales <1 hr. Strong X-ray variability does not predict the extreme radio sources and vice versa. Radio flares thus provide us with a new perspective on high-energy processes in YSOs and the irradiation of their protoplanetary disks. Finally, our results highlight implications for interferometric imaging of sources violating the constant-sky assumption.

  3. Multi-Object Spectroscopy with the James Webb Space Telescope’s Near Infrared Spectrograph: Observing Resolved Stellar Populations

    NASA Astrophysics Data System (ADS)

    Gilbert, Karoline; Karakla, Diane M.; Beck, Tracy

    2015-08-01

    The James Webb Space Telescope’s (JWST) Near Infrared Spectrograph (NIRSpec) will provide a multi-object spectroscopy mode through the four Micro-Shutter Arrays (MSAs). Each MSA is a grid of contiguous shutters that can be configured to form slits on more than 100 astronomical targets simultaneously. The combination of JWST’s sensitivity and superb resolution in the infrared and NIRSpec’s full wavelength coverage from 0.6 to 5 μm will open new parameter space for studies of galaxies and resolved stellar populations alike. We describe a NIRSpec MSA observing scenario for obtaining spectroscopy of individual stars in an external galaxy, and investigate the technical challenges posed by this scenario. We examine the multiplexing capability of the MSA as a function of the possible MSA configuration design choices, and investigate the primary sources of error in velocity measurements and the prospects for minimizing them. We give examples of how this and other use cases are guiding development of the NIRSpec user interfaces, including proposal planning and pipeline calibrations.

  4. Study of the Plutino Object (208996) 2003 AZ84 from Stellar Occultations: Size, Shape, and Topographic Features

    NASA Astrophysics Data System (ADS)

    Dias-Oliveira, A.; Sicardy, B.; Ortiz, J. L.; Braga-Ribas, F.; Leiva, R.; Vieira-Martins, R.; Benedetti-Rossi, G.; Camargo, J. I. B.; Assafin, M.; Gomes-Júnior, A. R.; Baug, T.; Chandrasekhar, T.; Desmars, J.; Duffard, R.; Santos-Sanz, P.; Ergang, Z.; Ganesh, S.; Ikari, Y.; Irawati, P.; Jain, J.; Liying, Z.; Richichi, A.; Shengbang, Q.; Behrend, R.; Benkhaldoun, Z.; Brosch, N.; Daassou, A.; Frappa, E.; Gal-Yam, A.; Garcia-Lozano, R.; Gillon, M.; Jehin, E.; Kaspi, S.; Klotz, A.; Lecacheux, J.; Mahasena, P.; Manfroid, J.; Manulis, I.; Maury, A.; Mohan, V.; Morales, N.; Ofek, E.; Rinner, C.; Sharma, A.; Sposetti, S.; Tanga, P.; Thirouin, A.; Vachier, F.; Widemann, T.; Asai, A.; Hayato, Watanabe; Hiroyuki, Watanabe; Owada, M.; Yamamura, H.; Hayamizu, T.; Bradshaw, J.; Kerr, S.; Tomioka, H.; Andersson, S.; Dangl, G.; Haymes, T.; Naves, R.; Wortmann, G.

    2017-07-01

    We present results derived from four stellar occultations by the plutino object (208996) 2003 AZ84, detected on 2011 January 8 (single-chord event), 2012 February 3 (multi-chord), 2013 December 2 (single-chord), and 2014 November 15 (multi-chord). Our observations rule out an oblate spheroid solution for 2003 AZ84's shape. Instead, assuming hydrostatic equilibrium, we find that a Jacobi triaxial solution with semiaxes (470+/- 20)× (383+/- 10)× (245+/- 8) km can better account for all our occultation observations. Combining these dimensions with the rotation period of the body (6.75 hr) and the amplitude of its rotation light curve, we derive a density ρ =0.87+/- 0.01 g cm-3, a geometric albedo {p}V=0.097+/- 0.009. A grazing chord observed during the 2014 occultation reveals a topographic feature along 2003 AZ84's limb, which can be interpreted as an abrupt chasm of width ˜23 km and depth > 8 km, or a smooth depression of width ˜80 km and depth ˜13 km (or an intermediate feature between those two extremes).

  5. THE SIZE, SHAPE, ALBEDO, DENSITY, AND ATMOSPHERIC LIMIT OF TRANSNEPTUNIAN OBJECT (50000) QUAOAR FROM MULTI-CHORD STELLAR OCCULTATIONS

    SciTech Connect

    Braga-Ribas, F.; Vieira-Martins, R.; Camargo, J. I. B.; Sicardy, B.; Lellouch, E.; Lecacheux, J.; Ortiz, J. L.; Morales, N.; Tancredi, G.; Roland, S.; Bruzzone, S.; Assafin, M.; Vachier, F.; Colas, F.; Maury, A.; Emilio, M.; Amorim, A.; Unda-Sanzana, E.; Almeida, L. A.; and others

    2013-08-10

    We present results derived from the first multi-chord stellar occultations by the transneptunian object (50000) Quaoar, observed on 2011 May 4 and 2012 February 17, and from a single-chord occultation observed on 2012 October 15. If the timing of the five chords obtained in 2011 were correct, then Quaoar would possess topographic features (crater or mountain) that would be too large for a body of this mass. An alternative model consists in applying time shifts to some chords to account for possible timing errors. Satisfactory elliptical fits to the chords are then possible, yielding an equivalent radius R{sub equiv} = 555 {+-} 2.5 km and geometric visual albedo p{sub V} = 0.109 {+-} 0.007. Assuming that Quaoar is a Maclaurin spheroid with an indeterminate polar aspect angle, we derive a true oblateness of {epsilon}= 0.087{sup +0.0268}{sub -0.0175}, an equatorial radius of 569{sup +24}{sub -17} km, and a density of 1.99 {+-} 0.46 g cm{sup -3}. The orientation of our preferred solution in the plane of the sky implies that Quaoar's satellite Weywot cannot have an equatorial orbit. Finally, we detect no global atmosphere around Quaoar, considering a pressure upper limit of about 20 nbar for a pure methane atmosphere.

  6. THE MYSTERIOUS SICKLE OBJECT IN THE CARINA NEBULA: A STELLAR WIND INDUCED BOW SHOCK GRAZING A CLUMP?

    SciTech Connect

    Ngoumou, Judith; Preibisch, Thomas; Ratzka, Thorsten; Burkert, Andreas

    2013-06-01

    Optical and near-infrared images of the Carina Nebula show a peculiar arc-shaped feature, which we call the ''Sickle'', next to the B-type star Trumpler 14 MJ 218. We use multi-wavelength observations to explore and constrain the nature and origin of the nebulosity. Using submillimeter data from APEX/LABOCA as well as Herschel far-infrared maps, we discovered a dense, compact clump with a mass of {approx}40 M{sub Sun} located close to the apex of the Sickle. We investigate how the B star MJ 218, the Sickle, and the clump are related. Our numerical simulations show that, in principle, a B-type star located near the edge of a clump can produce a crescent-shaped wind shock front, similar to the observed morphology. However, the observed proper motion of MJ 218 suggests that the star moves with high velocity ({approx}100 km s{sup -1}) through the ambient interstellar gas. We argue that the star is just about to graze along the surface of the clump, and the Sickle is a bow shock induced by the stellar wind, as the object moves supersonically through the density gradient in the envelope of the clump.

  7. An EXES Search for Formaldehyde Gas in the Class I/II Young Stellar Object IRAS 04278+2253

    NASA Astrophysics Data System (ADS)

    Sargent, Benjamin

    2013-10-01

    We propose to obtain high-resolution mid-infrared spectroscopy at 5.65915 microns wavelength of the Class I/II Young Stellar Object (YSO) IRAS 04278+2253 using EXES on SOFIA to search for absorption from formaldehyde (H2CO) gas. Low spectral resolution (R~90) Spitzer-IRS spectra of this YSO and a number of T Tauri stars (TTSs) show an unresolved band of absorption of full width half maximum (FWHM) of ~0.6 microns centered around 5.7 microns wavelength. Modeling of the Spitzer-IRS spectrum of IRAS 04278+2253 and the other TTSs indicates this band may be due to formaldehyde. Detection of individual absorption lines in high spectral resolution mid-infrared spectra of YSOs would be a significant finding, as the relatively recent mid-infrared spectral studies of TTSs that have found evidence for circumstellar gas in protoplanetary disks have found emission lines from gases such as H2O, OH, CO, CO2, HCN, and C2H2 (e.g., Carr & Najita 2008; Salyk et al 2008; Salyk et al 2009; Carr & Najita 2011; Pontoppidan et al 2011), but they do not find absorption lines, and they do not find H2CO.

  8. Probing the Evolution of Massive Young Stellar Objects using Weak Class II 6.7GHz Methanol Maser Emission

    NASA Astrophysics Data System (ADS)

    Ludwig, Bethany Ann; Cunningham, Nichol

    2017-01-01

    We present results from an investigation of class II 6.7GHz methanol masers towards four Massive Young Stellar Objects (MYSOs). The sources, selected from the Red MSX Source (RMS) Survey (Lumsden et al. 2013), were previously understood to be non-detections for class II methanol maser emission in the methanol multi-beam (MMB) Survey (Caswell et al. 2010.) Class II methanol masers are a well-known sign post of massive star forming regions and may be utilized to probe their relatively poorly understood formation. It is possible that these non-detections are simply weak masers that are potentially associated with a younger evolutionary phase of MYSOs as hypothesized by Olmi et al. (2014). The sources were chosen to sample various stages of evolution, having similar 21 to 8 micron flux ratios and bolometric luminosities as other MYSOs with previous class II methanol maser detections. We observed all 4 MYSOs with ATCA (~2" resolution) at 10 times deeper sensitivity than previously obtained with the MMB survey and have a spectral resolution of 0.087kms^-1 . The raw data is reduced using the program Miriad (Sault, R. J., et al., 1995) and deconvolutioned using the program CASA (McMullin, J. P., et al. 2007.) We determine one of the four observed MYSOs is harboring a weak class II methanol maser. We discuss the possibility of sensitivity limitations on the remaining sources as well as environmental and evolutionary differences between the sources.

  9. Near-infrared multiwavelength imaging polarimetry of the low-mass proto-stellar object HL Tauri

    NASA Astrophysics Data System (ADS)

    Murakawa, K.; Oya, S.; Pyo, T.-S.; Ishii, M.

    2008-12-01

    We present the {JHK}-band high-resolution polarimetric images of the low-mass proto-stellar object HL Tau using the adaptive optics-equipped CIAO instrument on the Subaru telescope. Our polarization images show a butterfly-shaped polarization disk with an ˜0.9 arcsec × 3.0 arcsec extension. In the nebula, where polarization vectors are centro-symmetrically aligned, the polarization is as high as PJ ˜30%, P_H˜42%, and PK ˜55%. On the other hand, low polarizations of P<3% in the J, H, and K bands and a low color excess ratio of EJ-H/EH-K=1.1 compared to the standard cloud value of 1.75 are detected towards the central star. We estimated the upper limit of the grain sizes a_max to be 0.4 μm in the nebula and ⪆0.7 μm in the line of sight towards the central star. Our high-resolution polarimetric data, which spatially resolves the polarization disk, provides us with important information about grain growth in the region close to the central star.

  10. Differential binding of colors to objects in memory: red and yellow stick better than blue and green

    PubMed Central

    Kuhbandner, Christof; Spitzer, Bernhard; Lichtenfeld, Stephanie; Pekrun, Reinhard

    2015-01-01

    Both evolutionary considerations and recent research suggest that the color red serves as a signal indicating an object’s importance. However, until now, there is no evidence that this signaling function of red is also reflected in human memory. To examine the effect of red on memory, we conducted four experiments in which we presented objects colored in four different colors (red, green, blue, and yellow) and measured later memory for the presence of an object and for the color of an object. Across experiments, we varied the type of objects (words vs. pictures), task complexity (single objects vs. multiple objects in visual scenes), and intentionality of encoding (intentional vs. incidental learning). Memory for the presence of an object was not influenced by color. However, in all four experiments, memory for the color of an object depended on color type and was particularly high for red and yellow-colored objects and particularly low for green-colored objects, indicating that the binding of colors into object memory representations varies as a function of color type. Analyzing the observers’ confidence in their color memories revealed that color not only influenced objective memory performance but also subjective confidence. Subjective confidence judgments differentiated well between correct and incorrect color memories for red-colored objects, but poorly for green-colored objects. Our findings reveal a previously unknown color effect which may be of considerable interest for both basic color research and applied settings like eyewitness testimony in which memory for color features is relevant. Furthermore, our results indicate that feature binding in memory is not a uniform process by which any attended feature is automatically bound into unitary memory representations. Rather, memory binding seems to vary across different subtypes of features, a finding that supports recent research showing that object features are stored in memory rather independently

  11. Nature versus Nurture: Luminous Blue Variable Nebulae in and near Massive Stellar Clusters at the Galactic Center

    NASA Astrophysics Data System (ADS)

    Lau, R. M.; Herter, T. L.; Morris, M. R.; Adams, J. D.

    2014-04-01

    Three luminous blue variables (LBVs) are located in and near the Quintuplet Cluster at the Galactic center: the Pistol Star, G0.120-0.048, and qF362. We present imaging at 19, 25, 31, and 37 μm of the region containing these three LBVs, obtained with SOFIA using FORCAST. We argue that Pistol and G0.120-0.048 are identical "twins" that exhibit contrasting nebulae due to the external influence of their different environments. Our images reveal the asymmetric, compressed shell of hot dust surrounding the Pistol Star and provide the first detection of the thermal emission from the symmetric, hot dust envelope surrounding G0.120-0.048. However, no detection of hot dust associated with qF362 is made. Dust and gas composing the Pistol nebula are primarily heated and ionized by the nearby Quintuplet Cluster stars. The northern region of the Pistol nebula is decelerated due to the interaction with the high-velocity (2000 km s-1) winds from adjacent Wolf-Rayet Carbon (WC) stars. From fits to the spectral energy distribution (SED) of the Pistol nebula with the DustEM code we determine that the Pistol nebula is composed of a distribution of very small, transiently heated grains (10 to ~ 35 Å) having a total dust mass of 0.03 M ⊙, and that it exhibits a gradient of decreasing grain size from south to north due to differential sputtering by the winds from the WC stars. The total IR luminosity of the Pistol nebula is 5.2 × 105 L ⊙. Dust in the G0.120-0.048 nebula is primarily heated by the central star; however, the nebular gas is ionized externally by the Arches Cluster. Unlike the Pistol nebula, the G0.120-0.048 nebula is freely expanding into the surrounding medium. A grain size distribution identical to that of the non-sputtered region of the Pistol nebula satisfies the constraints placed on the G0.120-0.048 nebula from DustEM model fits to its SED and implies a total dust mass of 0.021 M ⊙. The total IR luminosity of the G0.120-0.048 nebula is ~105 L ⊙. From

  12. Nature versus nurture: Luminous blue variable nebulae in and near massive stellar clusters at the galactic center

    SciTech Connect

    Lau, R. M.; Herter, T. L.; Adams, J. D.; Morris, M. R.

    2014-04-20

    Three luminous blue variables (LBVs) are located in and near the Quintuplet Cluster at the Galactic center: the Pistol Star, G0.120-0.048, and qF362. We present imaging at 19, 25, 31, and 37 μm of the region containing these three LBVs, obtained with SOFIA using FORCAST. We argue that Pistol and G0.120-0.048 are identical 'twins' that exhibit contrasting nebulae due to the external influence of their different environments. Our images reveal the asymmetric, compressed shell of hot dust surrounding the Pistol Star and provide the first detection of the thermal emission from the symmetric, hot dust envelope surrounding G0.120-0.048. However, no detection of hot dust associated with qF362 is made. Dust and gas composing the Pistol nebula are primarily heated and ionized by the nearby Quintuplet Cluster stars. The northern region of the Pistol nebula is decelerated due to the interaction with the high-velocity (2000 km s{sup –1}) winds from adjacent Wolf-Rayet Carbon (WC) stars. From fits to the spectral energy distribution (SED) of the Pistol nebula with the DustEM code we determine that the Pistol nebula is composed of a distribution of very small, transiently heated grains (10 to ∼ 35 Å) having a total dust mass of 0.03 M {sub ☉}, and that it exhibits a gradient of decreasing grain size from south to north due to differential sputtering by the winds from the WC stars. The total IR luminosity of the Pistol nebula is 5.2 × 10{sup 5} L {sub ☉}. Dust in the G0.120-0.048 nebula is primarily heated by the central star; however, the nebular gas is ionized externally by the Arches Cluster. Unlike the Pistol nebula, the G0.120-0.048 nebula is freely expanding into the surrounding medium. A grain size distribution identical to that of the non-sputtered region of the Pistol nebula satisfies the constraints placed on the G0.120-0.048 nebula from DustEM model fits to its SED and implies a total dust mass of 0.021 M {sub ☉}. The total IR luminosity of the G0

  13. A characterization of young stellar objects in BOK globules: Infrared imaging, spectral energy distributions, and molecular outflows

    NASA Astrophysics Data System (ADS)

    Yun, Joao Lin

    1993-09-01

    A large-scale observational study of star formation in Bok globules is presented. A sample of 248 optically selected, small molecular clouds (mostly Bok globules) was probed using IRAS co-added images to search for associated young stellar objects (YSO's). Fifty-seven of the globules show evidence for a total of 72 point sources near locations of local dust heating. A sub-sample of 41 globules was observed, in the CO J = 1-0 line, to search for molecular outflows associated with the YSO's. Outflows were found in about one-third of the sample (14 of 41). The presence of an outflow was found to be correlated with the value of the IRAS-based spectral index (between 12 and 25 microns) of the YSO's. A near-infrared imaging survey of 34 globules containing YSO-candidates was conducted in the J, H, and K bands using infrared arrays. Eleven YSO-candidates displayed near-infrared nebulosities. This group of objects, when ordered by their values of the 12/25 microns spectral index, seems to form an evolutionary sequence, from younger objects with negative (red) indices and whose nebulosities are brighter in the K-band, to objects in later stages of pre-main-sequence evolution with positive (bluer) indices and whose nebular emission is brighter in the J-band. Comparison of the morphology of the infrared nebulae with the corresponding CO outflow morphology supports the idea that infrared reflection nebulae, seen at 2.2 microns, are good morphological tracers of CO mass outflow, and that CO outflows occur during the earliest YSO phases. Photometry of the near-infrared counterparts of the YSO-candidates was combined with their IRAS fluxes to yield broad-band spectral energy distributions (SED's). The broadness and steepness of the SED's indicated clear evidence of the evolutionary stage of the objects confirming their youth. Given all of the new information obtained, a firm conclusion emerged, namely that Bok globules are active sites of low-mass star formation.

  14. European VLBI Network observations of 6.7 GHz methanol masers in clusters of massive young stellar objects

    NASA Astrophysics Data System (ADS)

    Bartkiewicz, A.; Szymczak, M.; van Langevelde, H. J.

    2014-04-01

    Context. Methanol masers at 6.7 GHz are associated with high-mass star-forming regions (HMSFRs) and often have mid-infrared (MIR) counterparts characterized by extended emission at 4.5 μm, which likely traces outflows from massive young stellar objects (MYSOs). Aims: Our objectives are to determine the milliarcsecond (mas) morphology of the maser emission and to examine if it comes from one or several candidate MIR counterparts in the clusters of MYSOs. Methods: The European VLBI Network (EVN) was used to image the 6.7 GHz maser line with ~2.´1 field of view toward 14 maser sites from the Torun catalog. Quasi-simultaneous observations were carried out with the Torun 32 m telescope. Results: We obtained maps with mas angular resolution that showed diversity of methanol emission morphology: a linear distribution (e.g., G37.753-00.189), a ring-like (G40.425+00.700), and a complex one (e.g., G45.467+00.053). The maser emission is usually associated with the strongest MIR counterpart in the clusters; no maser emission was detected from other MIR sources in the fields of view of 2.´1 in diameter. The maser source luminosity seems to correlate with the total luminosity of the central MYSO. Although the Very Long Baseline Interferometry (VLBI) technique resolves a significant part of the maser emission, the morphology is still well determined. This indicates that the majority of maser components have compact cores. Appendices are available in electronic form at http://www.aanda.org

  15. Stellar Winds

    NASA Astrophysics Data System (ADS)

    Owocki, Stan

    A "stellar wind" is the continuous, supersonic outflow of matter from the surface layers of a star. Our sun has a solar wind, driven by the gas-pressure expansion of the hot (T > 106 K) solar corona. It can be studied through direct in situ measurement by interplanetary spacecraft; but analogous coronal winds in more distant solar-type stars are so tenuous and transparent that that they are difficult to detect directly. Many more luminous stars have winds that are dense enough to be opaque at certain wavelengths of the star's radiation, making it possible to study their wind outflows remotely through careful interpretation of the observed stellar spectra. Red giant stars show slow, dense winds that may be driven by the pressure from magnetohydrodyanmic waves. As stars with initial mass up to 8 M ⊙ evolve toward the Asymptotic Giant Branch (AGB), a combination of stellar pulsations and radiative scattering off dust can culminate in "superwinds" that strip away the entire stellar envelope, leaving behind a hot white dwarf stellar core with less than the Chandrasekhar mass of ˜ ​​ 1. 4M ⊙. The winds of hot, luminous, massive stars are driven by line-scattering of stellar radiation, but such massive stars can also exhibit superwind episodes, either as Red Supergiants or Luminous Blue Variable stars. The combined wind and superwind mass loss can strip the star's hydrogen envelope, leaving behind a Wolf-Rayet star composed of the products of earlier nuclear burning via the CNO cycle. In addition to such direct effects on a star's own evolution, stellar winds can be a substantial source of mass, momentum, and energy to the interstellar medium, blowing open large cavities or "bubbles" in this ISM, seeding it with nuclear processed material, and even helping trigger the formation of new stars, and influencing their eventual fate as white dwarves or core-collapse supernovae. This chapter reviews the properties of such stellar winds, with an emphasis on the various

  16. A MULTI-EPOCH, SIMULTANEOUS WATER AND METHANOL MASER SURVEY TOWARD INTERMEDIATE-MASS YOUNG STELLAR OBJECTS

    SciTech Connect

    Bae, Jae-Han; Kim, Kee-Tae; Youn, So-Young; Kim, Won-Ju; Byun, Do-Young; Kang, Hyunwoo; Oh, Chung Sik E-mail: whorujh@kasi.re.kr

    2011-10-01

    We report a multi-epoch, simultaneous 22 GHz H{sub 2}O and 44 GHz Class I CH{sub 3}OH maser line survey toward 180 intermediate-mass young stellar objects, including 14 Class 0 and 19 Class I objects, and 147 Herbig Ae/Be stars. We detected H{sub 2}O and CH{sub 3}OH maser emission toward 16 (9%) and 10 (6%) sources with one new H{sub 2}O and six new CH{sub 3}OH maser sources. The detection rates of both masers rapidly decrease as the central (proto)stars evolve, which is contrary to the trends in high-mass star-forming regions. This suggests that the excitations of the two masers are closely related to the evolutionary stage of the central (proto)stars and the circumstellar environments. H{sub 2}O maser velocities deviate on average 9 km s{sup -1} from the ambient gas velocities whereas CH{sub 3}OH maser velocities match quite well with the ambient gas velocities. For both maser emissions, large velocity differences (|v{sub H{sub 2}O} - v{sub sys}| > 10kms{sup -1} and |v{sub CH3OH} - v{sub sys}| > 1kms{sup -1}) are mostly confined to Class 0 objects. The formation and disappearance of H{sub 2}O masers is frequent and their integrated intensities change by up to two orders of magnitude. In contrast, CH{sub 3}OH maser lines usually show no significant change in intensity, shape, or velocity. This is consistent with the previous suggestion that H{sub 2}O maser emission originates from the base of an outflow while 44 GHz Class I CH{sub 3}OH maser emission arises from the interaction region of the outflow with the ambient gas. The isotropic maser luminosities are well correlated with the bolometric luminosities of the central objects. The fitted relations are L{sub H2O}= 1.71x10{sup -9}(L{sub bol}){sup 0.97} and L{sub CH3OH}= 1.71x10{sup -10}(L{sub bol}){sup 1.22}.

  17. Optical/Near-infrared Selection of Red Quasi-stellar Objects: Evidence for Steep Extinction Curves toward Galactic Centers?

    NASA Astrophysics Data System (ADS)

    Fynbo, J. P. U.; Krogager, J.-K.; Venemans, B.; Noterdaeme, P.; Vestergaard, M.; Møller, P.; Ledoux, C.; Geier, S.

    2013-01-01

    We present the results of a search for red QSOs using a selection based on optical imaging from the Sloan Digital Sky Survey (SDSS) and near-infrared imaging from UKIDSS. Our main goal with the selection is to search for QSOs reddened by foreground dusty absorber galaxies. For a sample of 58 candidates (including 20 objects fulfilling our selection criteria that already have spectra in the SDSS), 46 (79%) are confirmed to be QSOs. The QSOs are predominantly dust-reddened except for a handful at redshifts z >~ 3.5. However, the dust is most likely located in the QSO host galaxies (and for two, the reddening is primarily caused by Galactic dust) rather than in the intervening absorbers. More than half of the QSOs show evidence of associated absorption (BAL absorption). Four (7%) of the candidates turned out to be late-type stars, and another four (7%) are compact galaxies. We could not identify the remaining four objects. In terms of their optical spectra, these QSOs are similar to the QSOs selected in the FIRST-2MASS Red Quasar Survey except they are on average fainter, more distant, and only two are detected in the FIRST survey. As per the usual procedure, we estimate the amount of extinction using the SDSS QSO template reddened by Small-Magellanic-Cloud-(SMC) like dust. It is possible to get a good match to the observed (rest-frame ultraviolet) spectra, but it is not possible to match the observed near-IR photometry from UKIDSS for nearly all the reddened QSOs. The most likely reasons are that the SDSS QSO template is too red at optical wavelengths due to contaminating host galaxy light and because the assumed SMC extinction curve is too shallow. Three of the compact galaxies display old stellar populations with ages of several Gyr and masses of about 1010 M ⊙ (based on spectral energy distribution modeling). The inferred stellar densities in these galaxies exceed 1010 M ⊙ kpc-2, which is among the highest measured for early-type galaxies. Our survey has

  18. Systematic Analysis of Spectral Energy Distributions and the Dust Opacity Indices for Class 0 Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Li, Jennifer I-Hsiu; Liu, Hauyu Baobab; Hasegawa, Yasuhiro; Hirano, Naomi

    2017-05-01

    We are motivated by the recent measurements of dust opacity indices (β) around young stellar objects (YSOs), which suggest that efficient grain growth may have occurred earlier than the Class I stage. The present work makes use of abundant archival interferometric observations at submillimeter, millimeter, and centimeter wavelength bands to examine grain growth signatures in the dense inner regions (<1000 au) of nine Class 0 YSOs. A systematic data analysis is performed to derive dust temperatures, optical depths, and dust opacity indices based on single-component modified blackbody fittings to the spectral energy distributions (SEDs). The fitted dust opacity indices (β) are in a wide range of 0.3-2.0 when single-component SED fitting is adopted. Four out of the nine observed sources show β lower than 1.7, the typical value of the interstellar dust. Low dust opacity index (or spectral index) values may be explained by the effect of dust grain growth, which makes β < 1.7. Alternatively, the very small observed values of β may be interpreted by the presence of deeply embedded and hot inner disks, which only significantly contribute to the observed fluxes at long wavelength bands. This possibility can be tested by the higher angular resolution imaging observations of ALMA or more detailed sampling of SEDs in the millimeter and centimeter bands. The β values of the remaining five sources are close to or consistent with 1.7, indicating that grain growth would start to significantly reduce the values of β no earlier than the late Class 0 stage for these YSOs.

  19. ADAPTIVE OPTICS IMAGING OF QUASI-STELLAR OBJECTS WITH DOUBLE-PEAKED NARROW LINES: ARE THEY DUAL ACTIVE GALACTIC NUCLEI?

    SciTech Connect

    Rosario, D. J.; McGurk, R. C.; Max, C. E.; Shields, G. A.; Smith, K. L.; Ammons, S. M. E-mail: mcgurk@ucsc.edu E-mail: shieldsga@mail.utexas.edu E-mail: ammons@as.arizona.edu

    2011-09-20

    Active galaxies hosting two accreting and merging supermassive black holes (SMBHs)-dual active galactic nuclei (AGNs)-are predicted by many current and popular models of black-hole-galaxy co-evolution. We present here the results of a program that has identified a set of probable dual AGN candidates based on near-infrared laser guide star adaptive optics imaging with the Keck II telescope. These candidates are selected from a complete sample of radio-quiet quasi-stellar objects (QSOs) drawn from the Sloan Digital Sky Survey (SDSS), which show double-peaked narrow AGN emission lines. Of the 12 AGNs imaged, we find 6 with double galaxy structure, of which four are in galaxy mergers. We measure the ionization of the two velocity components in the narrow AGN lines to test the hypothesis that both velocity components come from an active nucleus. The combination of a well-defined parent sample and high-quality imaging allows us to place constraints on the fraction of SDSS QSOs that host dual accreting black holes separated on kiloparsec scales: {approx}0.3%-0.65%. We derive from this fraction the time spent in a QSO phase during a typical merger and find a value that is much lower than estimates that arise from QSO space densities and galaxy merger statistics. We discuss possible reasons for this difference. Finally, we compare the SMBH mass distributions of single and dual AGNs and find little difference between the two within the limited statistics of our program, hinting that most SMBH growth happens in the later stages of a merger process.

  20. Integral field spectroscopy of nearby quasi-stellar objects - II. Molecular gas content and conditions for star formation

    NASA Astrophysics Data System (ADS)

    Husemann, B.; Davis, T. A.; Jahnke, K.; Dannerbauer, H.; Urrutia, T.; Hodge, J.

    2017-09-01

    We present single-dish 12CO(1-0) and 12CO(2-1) observations for 14 low-redshift quasi-stellar objects (QSOs). In combination with optical integral field spectroscopy, we study how the cold gas content relates to the star formation rate (SFR) and black hole accretion rate. 12CO(1-0) is detected in 8 of 14 targets and 12CO(2-1) is detected in 7 out of 11 cases. The majority of disc-dominated QSOs reveal gas fractions and depletion times matching normal star-forming systems. Two gas-rich major mergers show clear starburst signatures with higher than average gas fractions and shorter depletion times. Bulge-dominated QSO hosts are mainly undetected in 12CO(1-0), which corresponds, on average, to lower gas fractions than in disc-dominated counterparts. Their SFRs, however, imply shorter than average depletion times and higher star formation efficiencies. Negative QSO feedback through removal of cold gas seems to play a negligible role in our sample. We find a trend between black hole accretion rate and total molecular gas content for disc-dominated QSOs when combined with literature samples. We interpret this as an upper envelope for the nuclear activity and it is well represented by a scaling relation between the total and circumnuclear gas reservoir accessible for accretion. Bulge-dominated QSOs significantly differ from that scaling relation and appear uncorrelated with the total molecular gas content. This could be explained either by a more compact gas reservoir, blown out of the gas envelope through outflows, or a different interstellar medium phase composition.

  1. Apparent Disk-mass Reduction and Planetisimal Formation in Gravitationally Unstable Disks in Class 0/I Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Tsukamoto, Y.; Okuzumi, S.; Kataoka, A.

    2017-04-01

    We investigate the dust structure of gravitationally unstable disks undergoing mass accretion from the envelope, envisioning its application to Class 0/I young stellar objects (YSOs). We find that the dust disk quickly settles into a steady state and that, compared to a disk with interstellar medium (ISM) dust-to-gas mass ratio and micron-sized dust, the dust mass in the steady state decreases by a factor of 1/2 to 1/3, and the dust thermal emission decreases by a factor of 1/3 to 1/5. The latter decrease is caused by dust depletion and opacity decrease owing to dust growth. Our results suggest that the masses of gravitationally unstable disks in Class 0/I YSOs are underestimated by a factor of 1/3 to 1/5 when calculated from the dust thermal emission assuming an ISM dust-to-gas mass ratio and micron-sized dust opacity, and that a larger fraction of disks in Class 0/I YSOs is gravitationally unstable than was previously believed. We also investigate the orbital radius {r}{{P}} within which planetesimals form via coagulation of porous dust aggregates and show that {r}{{P}} becomes ∼20 au for a gravitationally unstable disk around a solar mass star. Because {r}{{P}} increases as the gas surface density increases and a gravitationally unstable disk has maximum gas surface density, {r}{{P}}∼ 20 {au} is the theoretical maximum radius for planetesimal formation. We suggest that planetesimal formation in the Class 0/I phase is preferable to that in the Class II phase because a large amount of dust is supplied by envelope-to-disk accretion.

  2. High Resolution SOFIA/EXES Spectroscopy of CH4 and SO2 toward Massive Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Boogert, Abraham C. A.; Richter, Matt; DeWitt, Curtis; Indriolo, Nick; Neufeld, David A.; Karska, Agata; Bergin, Edwin A.; Smith, Rachel L.; Montiel, Edward

    2017-01-01

    The ro-vibrational transitions of molecules in the near to mid-infrared are excellent tracers of the composition, dynamics, and excitation of the inner regions of Young Stellar Objects (YSOs). They sample a wide range of excitations in a short wavelength range, they can be seen in absorption against strong hot dust continuum sources, and they trace molecules without permanent dipole moment not observable at radio wavelengths. In particular, at high infrared spectral resolution, spatial scales smaller than those imaged by millimeter wave interferometers can be studied dynamically.We present high resolution (R=λ/Δλ˜50,000-100,000 6-12 km/s) infrared (7-8 μm) spectra of massive YSOs observed with the Echelon-Cross-Echelle Spectrograph (EXES) on the Stratospheric Observatory For Infrared Astronomy (SOFIA). Absorption lines of gas phase methane (CH4) are detected in our Cycle 2 observations. CH4 is thought to be a starting point of the formation of carbon chain molecules. Abundances are derived in the different dynamical regions along the sight-line towards the central star by comparing the line profiles to those of CO and other species observed at ground based facilities such as EXES' sister instrument TEXES at IRTF and Gemini. A search is also conducted for sulfur-dioxide, using data from our ongoing Cycle 4 program. SO2 was previously detected towards these massive YSOs with the space-based ISO/SWS instrument (Keane et al. 2001, A&A 376, L5) at much lower spectral resolution (R˜2,000). At high spectral resolution we should be able to pin-point the dynamical location of this SO2 gas. Up to 98% of the sulfur in dense clouds and protostellar envelopes is presently missing, and we are searching for that with the EXES/SOFIA observations.

  3. K- band integral field spectroscopy and optical spectroscopy of massive young stellar objects in the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Ward, J. L.; Oliveira, J. M.; van Loon, J. Th.; Sewiło, M.

    2017-01-01

    We present K-band integral field spectroscopic observations towards 17 massive young stellar objects (YSOs) in the low-metallicity Small Magellanic Cloud (SMC) and two YSO candidates in the compact H II regions N81 and N88 A (also in the SMC). These sources, originally identified using Spitzer photometry and/or spectroscopy, have been resolved into 29 K-band continuum sources. By comparing Brγ emission luminosities with those presented for a Galactic sample of massive YSOs, we find tentative evidence for increased accretion rates in the SMC. Around half of our targets exhibit emission-line (Brγ, He I and H2) morphologies that extend significantly beyond the continuum source and we have mapped both the emission morphologies and the radial velocity fields. This analysis also reveals evidence for the existence of ionized low-density regions in the centre outflows from massive YSOs. Additionally, we present an analysis of optical spectra towards a similar sample of massive YSOs in the SMC, revealing that the optical emission is photoexcited and originates near the outer edges of molecular clouds, and is therefore consistent with a high mean-free path of UV photons in the interstellar medium (ISM) of the SMC. Finally, we discuss the sample of YSOs in an evolutionary context incorporating the results of previous infrared and radio observations, as well as the near-infrared and optical observations presented in this work. Our spectroscopic analysis in both the K band and the optical regimes, combined with previously obtained infrared and radio data, exposes differences between properties of massive YSOs in our own Galaxy and the SMC, including tracers of accretion, discs and YSO-ISM interactions.

  4. VizieR Online Data Catalog: South Galactic cap MCT blue objects (Lamontagne+, 2000)

    NASA Astrophysics Data System (ADS)

    Lamontagne, R.; Demers, S.; Wesemael, F.; Fontaine, G.; Irwin, M. J.

    2016-07-01

    A detailed description of the first part of our survey, namely, the photographic observations (including plate scanning, photometric calibrations, and candidate selection), has been presented by Demers et al. (1986AJ.....92..878D). Briefly summarized, the MCT survey consists of 430 doubly exposed U and B plates, taken with the Curtis Schmidt telescope at the Cerro Tololo Inter-American Observatory (CTIO) and covering 6750 deg2 (~15% of the whole sky) in a region defined by 19h<~RA<~7h and -90°<=DE<=0°. Our survey blankets most of the south Galactic cap of our Galaxy accessible from CTIO, up to b=-30°. The bulk of our spectroscopic material was gathered at CTIO with the 1.5m and 4m telescopes in the course of several observing runs since 1985. We have identified all 228 selected blue candidates [(U-B)pg<=-0.6] brighter than Bpg=16.5 in this region of the sky. (1 data file).

  5. A FEATURE MOVIE OF SiO EMISSION 20-100 AU FROM THE MASSIVE YOUNG STELLAR OBJECT ORION SOURCE I

    SciTech Connect

    Matthews, L. D.; Greenhill, L. J.; Goddi, C.; Humphreys, E. M. L.; Chandler, C. J.; Kunz, M. W.

    2010-01-01

    We present multi-epoch Very Long Baseline Array imaging of the {sup 28}SiO v = 1 and v = 2, J = 1-0 maser emission toward the massive young stellar object (YSO) Orion Source I. Both SiO transitions were observed simultaneously with an angular resolution of approx0.5 mas (approx0.2 AU for d = 414 pc) and a spectral resolution of approx0.2 km s{sup -1}. Here we explore the global properties and kinematics of the emission through two 19-epoch animated movies spanning 21 months (from 2001 March 19 to 2002 December 10). These movies provide the most detailed view to date of the dynamics and temporal evolution of molecular material within approx20-100 AU of a massive (approx>8 M{sub sun}) YSO. As in previous studies, we find that the bulk of the SiO masers surrounding Source I lie in an X-shaped locus; the emission in the south and east arms is predominantly blueshifted, and emission in the north and west is predominantly redshifted. In addition, bridges of intermediate-velocity emission are observed connecting the red and blue sides of the emission distribution. We have measured proper motions of over 1000 individual maser features and found that these motions are characterized by a combination of radially outward migrations along the four main maser-emitting arms and motions tangent to the intermediate-velocity bridges. We interpret the SiO masers as arising from a wide-angle bipolar wind emanating from a rotating, edge-on disk. The detection of maser features along extended, curved filaments suggests that magnetic fields may play a role in launching and/or shaping the wind. Our observations appear to support a picture in which stars with masses as high as at least 8 M{sub sun} form via disk-mediated accretion. However, we cannot yet rule out that the Source I disk may have been formed or altered following a recent close encounter.

  6. Looking for high-mass young stellar objects: H2O and OH masers in ammonia cores

    NASA Astrophysics Data System (ADS)

    Codella, C.; Cesaroni, R.; López-Sepulcre, A.; Beltrán, M. T.; Furuya, R.; Testi, L.

    2010-02-01

    Context. The earliest stages of high-mass star formation have yet to be characterised well, because high-angular resolution observations are required to infer the properties of the molecular gas hosting the newly formed stars. Aims: We search for high-mass molecular cores in a large sample of 15 high-mass star-forming regions that are observed at high-angular resolution, extending a pilot survey based on a smaller number of objects. Methods: The sample was chosen from surveys of H2O and OH masers to favour the earliest phases of high-mass star formation. Each source was first observed with the 32-m single-dish Medicina antenna in the (1, 1) and (2, 2) inversion transitions at 1.3 cm of ammonia, which is an excellent tracer of dense gas. High-resolution maps in the NH3(2, 2) and (3, 3) lines and the 1.3 cm continuum were obtained successively with the VLA interferometer. Results: We detect continuum emission in almost all the observed star-forming regions, which corresponds to extended and UCHii regions created by young stellar objects with typical luminosities of ˜10^4~L⊙. However, only in three cases do we find a projected overlap between Hii regions and H2O and OH maser spots. On the other hand, the VLA images detect eight ammonia cores closely associated with the maser sources. The ammonia cores have sizes of ˜10^4 AU, and high masses (up to 104M⊙), and are very dense (from ˜10^6 to a few ×10^9 cm-3). The typical relative NH3 abundance is ≤10-7, in agreement with previous measurements in high-mass star-forming regions. Conclusions: The statistical analysis of the distribution between H2O and OH masers, NH3 cores, and Hii regions confirms that the earliest stages of high-mass star formation are characterised by high-density molecular cores with temperatures of on average ≥30 K, either without a detectable ionised region or associated with a hypercompact Hii region.

  7. Linking pre- and proto-stellar objects in the intermediate-/high-mass star forming region IRAS 05345+3157

    NASA Astrophysics Data System (ADS)

    Fontani, F.; Zhang, Q.; Caselli, P.; Bourke, T. L.

    2009-05-01

    Context: To better understand the initial conditions of the high-mass star formation process, it is crucial to study at high angular resolution the morphology, the kinematics, and the interactions of the coldest condensations associated with intermediate-/high-mass star forming regions. Aims: This paper studies the cold condensations in the intermediate-/high-mass proto-cluster IRAS 05345+3157, focusing on the interaction with the other objects in the cluster. Methods: We performed millimeter high-angular resolution observations, both in the continuum and several molecular lines, with the PdBI and the SMA. In a recent paper, we published part of these data. The main finding of that work was the detection of two cold and dense gaseous condensations, called N and S (masses ˜ 2 and ˜ 9 M_⊙), characterised by high values of deuterium fractionation (˜ 0.1 in both cores) obtained from the column density ratio N(N{2}D+)/N(N{2}H+). In this paper, we present a full report of the observations, and a complete analysis of the data obtained. Results: The millimeter maps reveal the presence of 3 cores inside the interferometer primary beam, called C1-a, C1-b and C2. None of them are associated with cores N and S. C1-b is very likely associated with a newly formed early-B ZAMS star embedded inside a hot core, while C1-a is more likely associated with a class 0 intermediate-mass protostar. The nature of C2 is unclear. Both C1-a and C1-b are good candidates as driving sources of a powerful 12CO outflow, which strongly interacts with N, as demonstrated by the velocity gradient of the gas along this condensation. The N{2}H+ linewidths are between ˜ 1 and 2 km s-1 in the region where the continuum cores are located, and smaller (˜ 0.5-1.5 km s-1) towards N and S, indicating that the gas in the deuterated condensations is more quiescent than that associated with the continuum sources. This is consistent with the fact that they are still in the pre-stellar phase and hence the

  8. An objective determination of blue star groupings in the Andromeda galaxy.

    NASA Astrophysics Data System (ADS)

    Battinelli, P.; Efremov, Y.; Magnier, E. A.

    1996-10-01

    We have used an objective method, the Path Linkage Criterion (PLC), to identify large groupings of young stars in the Andromeda Galaxy. Previously, work has been done to objectively identify the structures which correspond in size to the OB associations observed in the Galaxy and Magellanic Clouds (Magnier et al. 1993). In this work, we attempt to identify structures which correspond to the 500 pc-sized complexes described by Efremov et al. (1987) and to test for a hierarchical arrangement of the observed structures. We find that complex-sized structures can naturally be identified using the PLC, and that there is indeed a hierarchical arrangement of the complexes and associations identified.

  9. Time dependent emission line profiles in the radially streaming particle model of Seyfert galaxy nuclei and quasi-stellar objects

    NASA Technical Reports Server (NTRS)

    Hubbard, R.

    1974-01-01

    The radially-streaming particle model for broad quasar and Seyfert galaxy emission features is modified to include sources of time dependence. The results are suggestive of reported observations of multiple components, variability, and transient features in the wings of Seyfert and quasi-stellar emission lines.

  10. HETEROGENEITY IN {sup 12}CO/{sup 13}CO ABUNDANCE RATIOS TOWARD SOLAR-TYPE YOUNG STELLAR OBJECTS

    SciTech Connect

    Smith, Rachel L.; Pontoppidan, Klaus M.; Young, Edward D.; Morris, Mark R. E-mail: smithrl2@appstate.edu

    2015-11-10

    This study reports an unusual heterogeneity in [{sup 12}C{sup 16}O]/[{sup 13}C{sup 16}O] abundance ratios of carbon monoxide observed in the gas phase toward seven ∼solar-mass young stellar objects (YSOs) and three dense foreground clouds in the nearby star-forming regions, Ophiuchus, Corona Australis, Orion, and Vela, and an isolated core, L43. Robust isotope ratios were derived using infrared absorption spectroscopy of the 4.7 μm fundamental and 2.3 μm overtone rovibrational bands of CO at very high spectral resolution (λ/Δλ ≈ 95,000), observed with the Cryogenic Infrared Echelle Spectrograph (CRIRES) on the Very Large Telescope. We find [{sup 12}C{sup 16}O]/[{sup 13}C{sup 16}O] values ranging from ∼85 to 165, significantly higher than those of the local interstellar medium (ISM) (∼65–69). These observations are evidence for isotopic heterogeneity in carbon reservoirs in solar-type YSO environments, and encourage the need for refined galactic chemical evolution models to explain the {sup 12}C/{sup 13}C discrepancy between the solar system and local ISM. The oxygen isotope ratios are consistent with isotopologue-specific photodissociation by CO self-shielding toward the disks, VV CrA N and HL Tau, further substantiating models predicting CO self-shielding on disk surfaces. However, we find that CO self-shielding is an unlikely general explanation for the high [{sup 12}C{sup 16}O]/[{sup 13}C{sup 16}O] ratios observed in this study. Comparison of the solid CO against gas-phase [{sup 12}C{sup 16}O]/[{sup 13}C{sup 16}O] suggests that interactions between CO ice and gas reservoirs need to be further investigated as at least a partial explanation for the unusually high [{sup 12}C{sup 16}O]/[{sup 13}C{sup 16}O] observed.

  11. MULTIDIMENSIONAL CHEMICAL MODELING OF YOUNG STELLAR OBJECTS. III. THE INFLUENCE OF GEOMETRY ON THE ABUNDANCE AND EXCITATION OF DIATOMIC HYDRIDES

    SciTech Connect

    Bruderer, S.; Benz, A. O.; Staeuber, P.; Doty, S. D.

    2010-09-10

    The Herschel Space Observatory enables observations in the far-infrared at high spectral and spatial resolution. A particular class of molecules will be directly observable: light diatomic hydrides and their ions (CH, OH, SH, NH, CH{sup +}, OH{sup +}, SH{sup +}, NH{sup +}). These simple constituents are important both for the chemical evolution of the region and as tracers of high-energy radiation. If outflows of a forming star erode cavities in the envelope, protostellar far-UV (FUV; 6 < E{sub {gamma}} < 13.6 eV) radiation may escape through such low-density regions. Depending on the shape of the cavity, the FUV radiation then irradiates the quiescent envelope in the walls along the outflow. The chemical composition in these outflow walls is altered by photoreactions and heating via FUV photons in a manner similar to photo-dominated regions. In this work, we study the effect of cavity shapes, outflow density, and of a disk with the two-dimensional chemical model of a high-mass young stellar object introduced in the second paper in this series. The model has been extended with a self-consistent calculation of the dust temperature and a multi-zone escape probability method for the calculation of the molecular excitation and the prediction of line fluxes. We find that the shape of the cavity is particularly important in the innermost part of the envelope, where the dust temperatures are high enough ({approx}>100 K) for water ice to evaporate. If the cavity shape allows FUV radiation to penetrate this hot-core region, the abundance of FUV-destroyed species (e.g., water) is decreased. On larger scales, the shape of the cavity is less important for the chemistry in the outflow wall. In particular, diatomic hydrides and their ions CH{sup +}, OH{sup +}, and NH{sup +} are enhanced by many orders of magnitude in the outflow walls due to the combination of high gas temperatures and rapid photodissociation of more saturated species. The enhancement of these diatomic hydrides

  12. Stellarator hybrids

    SciTech Connect

    Furth, H.P.; Ludescher, C.

    1984-08-01

    The present paper briefly reviews the subject of tokamak-stellarator and pinch-stellarator hybrids, and points to two interesting new possibilities: compact-torus-stellarators and mirror-stellarators.

  13. Stellar Metamorphosis:

    NASA Technical Reports Server (NTRS)

    2002-01-01

    edge-on, where the direct starlight is blocked by the dusty cocoon. Otherwise, the starlight would overwhelm the nebular light, making it very difficult to see the butterfly-shaped nebula. In a few hundred years, intense ultraviolet radiation from the central star will energize the surrounding gas, causing it to glow brightly, and a planetary nebula is born. These observations were made with the Wide Field and Planetary Camera 2 using three filters: yellow-green, blue, and near-infrared. The images were taken in 1997 by Sun Kwok and in 1996 by Matt Bobrowsky. Credits: Sun Kwok and Kate Su (University of Calgary), Bruce Hrivnak (Valparaiso University), and NASA ----------------- The Hubble Space Telescope Sees Remarkable Structure in the Heart of a Planetary Nebula [BOTTOM LEFT AND RIGHT] This Wide Field and Planetary Camera 2 image of NGC 6818 shows two distinct layers of gas (with dust): a spherical outer region and a brighter, vase-shaped interior 'bubble.' Astronomers believe that a fast wind - material propelled by radiation from the hot central star - is creating the inner elongated shape. The central star of the planetary nebula appears as a tiny blue dot. The material in the wind is traveling so fast that it smashes through older, slower-moving stellar debris, causing a 'blowout' at both ends of the bubble (lower right and upper left). This nebula looks like a twin of NGC 3918, another planetary nebula that has been observed by the Hubble telescope. The structure of NGC 3918 is remarkably similar to that of NGC 6818. It has an outer spherical envelope and an inner, brighter, elongated bubble. A fast-moving wind also appears to have created an orifice at one end (bottom right-hand corner) of the inner bubble. There are even faint wisps of material that were probably blown out of this hole. In the opposite direction (top left-hand corner), there is a protrusion that seems on the verge of breaking through to form a hole. By finding and studying such similar objects

  14. Nested object watermarking: comparison of block-luminance and blue channel LSB wet paper code image watermarking

    NASA Astrophysics Data System (ADS)

    Vielhauer, Claus; Dittmann, Jana

    2007-02-01

    Annotation watermarking (sometimes also called caption or illustration watermarking) denotes a specific application of watermarks, which embeds supplementary information directly in the media, so that additional information is intrinsically linked to media content and does not get separated from the media by non-malicious processing steps such as image cropping or compression. Recently, nested object annotation watermarking (NOAWM) has been introduced as a specialized annotation watermarking domain, whereby hierarchical object information is embedded in photographic images. In earlier work, the Hierarchical Graph Concept (HGC) has been suggested as a first approach to model object relations, which are defined by users during editing processes, into a hierarchical tree structure. The original HGC method uses a code-book decomposition of the annotation tree and a block-luminance algorithm for embedding. In this article, two new approaches for embedding nested object annotations are presented and experimentally compared to the original HGC approach. The first one adopts the code-book scheme of HGC using an alternative embedding based on Wet Paper Codes in blue-channel LSB domain, whereas the second suggests a new method based on the concept of intrinsic signal inheritance by sub-band energy and phase modulation of image luminance blocks. A comparative experimental evaluation based on more than 100 test images is presented in the paper, whereby aspects of transparency and robustness with respect to the most relevant image modifications to annotations, cropping and JPEG compression, are discussed comparatively for the two code-book schemes and the novel inheritance approach.

  15. The Effects of Stellar Dynamics on the Evolution of Young, Dense Stellar Systems

    NASA Astrophysics Data System (ADS)

    Belkus, H.; van Bever, J.; Vanbeveren, D.

    In this paper, we report on first results of a project in Brussels in which we study the effects of stellar dynamics on the evolution of young dense stellar systems using 3 decades of expertise in massive-star evolution and our population (number and spectral) synthesis code. We highlight an unconventionally formed object scenario (UFO-scenario) for Wolf Rayet binaries and study the effects of a luminous blue variable-type instability wind mass-loss formalism on the formation of intermediate-mass black holes.

  16. Physical and Chemical Properties of Protocluster Clumps and Massive Young Stellar Objects Associated to Infrared Dark Clouds

    NASA Astrophysics Data System (ADS)

    Gomez Gonzalez, Laura

    2012-01-01

    The study of high-mass stars is important not only because of the effects they produce in their environment through outflows, expanding HII regions, stellar winds, and eventually supernova shock waves, but also because they play a crucial role in estimating star formation rates in other galaxies. Although we have an accepted evolutionary scenario that explains (isolated) low-mass star formation, the processes that produce massive stars (M_star > 8 M_sol) and star clusters, especially their earliest stages, are not well understood. The newly discovered class of interstellar clouds now termed infrared dark clouds (IRDCs) represent excellent laboratories to study the earliest stages of high-mass star formation given that some of the clumps within them are known to have high masses (~100's M_sol), high densities (n > 10^5 cm^-3), and low temperatures (10-20K) as expected for the birthplaces of high-mass stars. Some questions remain unanswered: Do IRDCs harbor the very early stages of high-mass star formation, i.e., the pre-protocluster phase? If so, how do they compare with low-mass star formation sites? Is there chemical differentiation in IRDC clumps? What is the mass distribution of IRDCs? In this dissertation and for the first time, a catalog of 12529 IRDC candidates at 24 um has been created using archival data from the MIPSGAL/Spitzer survey, as a first step in searching for the massive pre-protocluster clumps. From this catalog, a sample of ~60 clumps has been selected in order to perform single-pointing observations with the IRAM 30m, Effelsberg 100m, and APEX 12m telescopes. One IRDC clump seems to be a promising candidate for being in the pre-protocluster phase. In addition, molecular line mapping observations have been performed on three clumps within IRDCs and a detailed chemical study of 10 molecular lines has been carried out. A larger difference in column densities and abundances has been found between these clumps and high-m! ass protostellar objects

  17. Suzaku Observation of Strong Fluorescent Iron Line Emission from the Young Stellar Object V1647 Ori during Its New X-ray Outburst

    NASA Technical Reports Server (NTRS)

    Hamaguchi, Kenji; Grosso, Nicolas; Kastner, Joel H.; Weintraub, David A.; Richmond, Michael

    2009-01-01

    The Suzaku X-ray satellite observed the young stellar object V1647 Ori on 2008 October 8 during the new mass accretion outburst reported in August 2008. During the 87 ksec observation with a net exposure of 40 ks, V1647 Ori showed a. high level of X-ray emission with a gradual decrease in flux by a factor of 5 and then displayed an abrupt flux increase by an order of magnitude. Such enhanced X-ray variability was also seen in XMM-Newton observations in 2004 and 2005 during the 2003-2005 outburst, but has rarely been observed for other young stellar objects. The spectrum clearly displays emission from Helium-like iron, which is a signature of hot plasma (kT approx.5 keV). It also shows a fluorescent iron Ka line with a remarkably large equivalent width of approx. 600 eV. Such a, large equivalent width indicates that a part of the incident X-ray emission that irradiates the circumstellar material and/or the stellar surface is hidden from our line of sight. XMM-Newton spectra during the 2003-2005 outburst did not show a strong fluorescent iron Ka line ; so that the structure of the circumstellar gas very close to the stellar core that absorbs and re-emits X-ray emission from the central object may have changed in between 2005 and 2008. This phenomenon may be related to changes in the infrared morphology of McNeil's nebula between 2004 and 2008.

  18. Envelope structure on 700 AU scales and the molecular outflows of low-mass young stellar objects

    NASA Technical Reports Server (NTRS)

    Hogerheijde, M. R.; van Dishoeck, E. F.; Blake, G. A.; van Langevelde, H. J.

    1998-01-01

    Aperture synthesis observations of HCO+ J = 1-0, 13CO 1-0, and C18O 1-0 obtained with the Owens Valley Millimeter Array are used to probe the small-scale (5" approximately 700 AU) structure of the molecular envelopes of a well-defined sample of nine embedded low-mass young stellar objects in Taurus. The interferometer results can be understood in terms of: (1) a core of radius approximately or less than 1000 AU surrounding the central star, possibly flattened and rotating; (2) condensations scattered throughout the envelope that may be left over from the inhomogeneous structure of the original cloud core or that may have grown during collapse; and (3) material within the outflow or along the walls of the outflow cavity. Masses of the central cores are 0.001-0.1 M (solar), and agree well with dust continuum measurements. Averaged over the central 20" (3000 AU) region, an HCO+ abundance of 4 x 10(-8) is inferred, with a spread of a factor of 3 between the different sources. Reanalysis of previously presented single-dish data yields an HCO+ abundance of (5.0 +/- 1.7) x 10(-9), which may indicate an average increase by a factor of a few on the smaller scales sampled by the interferometer. Part of this apparent abundance variation could be explained by contributions from extended cloud emission to the single-dish C18O lines, and uncertainties in the assumed excitation temperatures and opacities. The properties of the molecular envelopes and outflows are further investigated through single-dish observations of 12CO J = 6-5, 4-3, and 3-2, 13CO 6-5 and 3-2, and C18O 3-2 and 2-1, obtained with the James Clerk Maxwell and IRAM 30 m telescopes, along with the Caltech Submillimeter Observatory. Ratios of the mid-J CO lines are used to estimate the excitation temperature, with values of 25-80 K derived for the gas near line centre. The outflow wings show a similar range, although Tex is enhanced by a factor of 2-3 in at least two sources. In contrast to the well-studied L1551

  19. NEAR-INFRARED PROPERTIES OF THE X-RAY-EMITTING YOUNG STELLAR OBJECTS IN THE CARINA NEBULA

    SciTech Connect

    Preibisch, Thomas; Hodgkin, Simon; Irwin, Mike; Lewis, James R.; King, Robert R.; McCaughrean, Mark J.; Zinnecker, Hans; Townsley, Leisa; Broos, Patrick

    2011-05-01

    The Great Nebula in Carina (NGC 3372) is the best target to study in detail the process of violent massive star formation and the resulting feedback effects of cloud dispersal and triggered star formation. While the population of massive stars is rather well studied, the associated low-mass stellar population was largely unknown up to now. The near-infrared study in this paper builds on the results of the Chandra Carina Complex Project, that detected 14,368 X-ray sources in the 1.4 deg{sup 2} survey region, an automatic source classification study that classified 10,714 of these X-ray sources as very likely young stars in Carina, and an analysis of the clustering properties of the X-ray-selected Carina members. In order to determine physical properties of the X-ray-selected stars, most of which were previously unstudied, we used HAWK-I at the ESO Very Large Telescope to conduct a very deep near-IR survey with subarcsecond angular resolution, covering an area of about 1280 arcmin{sup 2}. The HAWK-I images reveal more than 600,000 individual infrared sources, whereby objects as faint as J {approx} 23, H {approx} 22, and K{sub s} {approx} 21 are detected at signal-to-noise ratio (S/N) {>=}3. While less than half of the Chandra X-ray sources have counterparts in the Two Micron All Sky Survey catalog, the {approx}5 mag deeper HAWK-I data reveal infrared counterparts to 6636 (=88.8%) of the 7472 Chandra X-ray sources in the HAWK-I field. We analyze near-infrared color-color and color-magnitude diagrams to derive information about the extinctions, infrared excesses (as tracers for circumstellar disks), ages, and masses of the X-ray-selected objects. The near-infrared properties agree well with the results of the automatic X-ray source classification, showing that the remaining contamination in the X-ray-selected sample of Carina members is very low ({approx}<7%). The shape of the K-band luminosity function of the X-ray-selected Carina members agrees well with that derived

  20. Envelope structure on 700 AU scales and the molecular outflows of low-mass young stellar objects.

    PubMed

    Hogerheijde, M R; van Dishoeck, E F; Blake, G A; van Langevelde, H J

    1998-07-20

    Aperture synthesis observations of HCO+ J = 1-0, 13CO 1-0, and C18O 1-0 obtained with the Owens Valley Millimeter Array are used to probe the small-scale (5" approximately 700 AU) structure of the molecular envelopes of a well-defined sample of nine embedded low-mass young stellar objects in Taurus. The interferometer results can be understood in terms of: (1) a core of radius approximately or less than 1000 AU surrounding the central star, possibly flattened and rotating; (2) condensations scattered throughout the envelope that may be left over from the inhomogeneous structure of the original cloud core or that may have grown during collapse; and (3) material within the outflow or along the walls of the outflow cavity. Masses of the central cores are 0.001-0.1 M (solar), and agree well with dust continuum measurements. Averaged over the central 20" (3000 AU) region, an HCO+ abundance of 4 x 10(-8) is inferred, with a spread of a factor of 3 between the different sources. Reanalysis of previously presented single-dish data yields an HCO+ abundance of (5.0 +/- 1.7) x 10(-9), which may indicate an average increase by a factor of a few on the smaller scales sampled by the interferometer. Part of this apparent abundance variation could be explained by contributions from extended cloud emission to the single-dish C18O lines, and uncertainties in the assumed excitation temperatures and opacities. The properties of the molecular envelopes and outflows are further investigated through single-dish observations of 12CO J = 6-5, 4-3, and 3-2, 13CO 6-5 and 3-2, and C18O 3-2 and 2-1, obtained with the James Clerk Maxwell and IRAM 30 m telescopes, along with the Caltech Submillimeter Observatory. Ratios of the mid-J CO lines are used to estimate the excitation temperature, with values of 25-80 K derived for the gas near line centre. The outflow wings show a similar range, although Tex is enhanced by a factor of 2-3 in at least two sources. In contrast to the well-studied L1551

  1. Revisiting NGC 3109: A Systematic Blue Massive Stars Analysis

    NASA Astrophysics Data System (ADS)

    Castro, Norberto; Urbaneja, Miguel A.; Evans, Chris; Garcia, Miriam; Herrero, Artemio; Bresolin, Fabio

    2013-06-01

    In the last years thoughtful quantitative analyses of extragalactic blue massive stars have shown not only that these studies are doable even at large distances (e.g. ˜2 Mpc away), but also essential for a better understanding of host galaxies and stellar evolution, in environments with different metallicities. Carrying out a systematic analysis is mandatory. We present in this work the tools and the FASTWIND stellar grids designed for overcoming this issue, measuring stellar parameters and chemical abundances. We have applied these techniques to the complete sample of blue massive stars observed in NGC 3109, a low metallicity irregular galaxy at 1.3 Mpc, by the ARAUCARIA project and presented by Evans et al. (2007). We report the first systematic quantitative analysis in this galaxy, together with the stellar parameters and the evolution stages of these objects. The chemical composition obtained will shed new light about the chemical composition and distribution along NGC 3109.

  2. Quasi-stellar objects in the ALHAMBRA survey. I. Photometric redshift accuracy based on 23 optical-NIR filter photometry

    NASA Astrophysics Data System (ADS)

    Matute, I.; Márquez, I.; Masegosa, J.; Husillos, C.; del Olmo, A.; Perea, J.; Alfaro, E. J.; Fernández-Soto, A.; Moles, M.; Aguerri, J. A. L.; Aparicio-Villegas, T.; Benítez, N.; Broadhurst, T.; Cabrera-Cano, J.; Castander, F. J.; Cepa, J.; Cerviño, M.; Cristóbal-Hornillos, D.; Infante, L.; González Delgado, R. M.; Martínez, V. J.; Molino, A.; Prada, F.; Quintana, J. M.

    2012-06-01

    Context. Even the spectroscopic capabilities of today's ground and space-based observatories can not keep up with the enormous flow of detections (>105 deg-2) unveiled in modern cosmological surveys as: i) would be required enormous telescope time to perform the spectroscopic follow-ups and ii) spectra remain unattainable for the fainter detected population. In the past decade, the typical accuracy of photometric redshift (photo-z) determination has drastically improved. Nowdays, it has become a perfect complement to spectroscopy, closing the gap between photometric surveys and their spectroscopic follow-ups. The photo-z precision for active galactic nuclei (AGN) has always lagged behind that for the galaxy population owing to the lack of proper templates and their intrinsic variability. Aims: Our goal is to characterize the ability of the Advanced Large, Homogeneous Area Medium-Band Redshift Astronomical (ALHAMBRA) survey in assigning accurate photo-z's to broad-line AGN (BLAGN) and quasi-stellar objects (QSOs) based on their ALHAMBRA very-low-resolution optical-near-infrared (NIR) spectroscopy. This will serve as a benchmark for any future compilation of ALHAMBRA selected QSOs and the basis for the statistical analysis required to derive luminosity functions up to z ~ 5. Methods: We selected a sample of spectroscopically identified BLAGN and QSOs and used a library of templates (including the SEDs of AGN and both normal and starburst galaxies, as well as stars) to fit the 23 photometric data points provided by ALHAMBRA in the optical and NIR (20 medium-band optical filters plus the standard JHKs). Results: We find that the ALHAMBRA photometry is able to provide an accurate photo-z and spectral classification for ~88% of the 170 spectroscopically identified BLAGN/QSOs over 2.5 deg2 in different areas of the survey and brighter than m678 = 23.5 (equivalent to rSLOAN ~ 24.0). The derived photo-z accuracy is below 1% and is comparable to the most recent results in

  3. APEX-CHAMP+ high-J CO observations of low-mass young stellar objects. IV. Mechanical and radiative feedback

    NASA Astrophysics Data System (ADS)

    Yıldız, U. A.; Kristensen, L. E.; van Dishoeck, E. F.; Hogerheijde, M. R.; Karska, A.; Belloche, A.; Endo, A.; Frieswijk, W.; Güsten, R.; van Kempen, T. A.; Leurini, S.; Nagy, Z.; Pérez-Beaupuits, J. P.; Risacher, C.; van der Marel, N.; van Weeren, R. J.; Wyrowski, F.

    2015-04-01

    Context. During the embedded stage of star formation, bipolar molecular outflows and UV radiation from the protostar are important feedback processes. Both processes reflect the accretion onto the forming star and affect subsequent collapse or fragmentation of the cloud. Aims: Our aim is to quantify the feedback, mechanical and radiative, for a large sample of low-mass sources in a consistent manner. The outflow activity is compared to radiative feedback in the form of UV heating by the accreting protostar to search for correlations and evolutionary trends. Methods: Large-scale maps of 26 young stellar objects, which are part of the Herschel WISH key program are obtained using the CHAMP+ instrument on the Atacama Pathfinder EXperiment (12CO and 13CO 6-5; Eup ~ 100 K), and the HARP-B instrument on the James Clerk Maxwell Telescope (12CO and 13CO 3-2; Eup ~ 30 K). The maps have high spatial resolution, particularly the CO 6-5 maps taken with a 9″ beam, resolving the morphology of the outflows. The maps are used to determine outflow parameters and the results are compared with higher-J CO lines obtained with Herschel. Envelope models are used to quantify the amount of UV-heated gas and its temperature from 13CO 6-5 observations. Results: All sources in our sample show outflow activity, with the spatial extent decreasing from the Class 0 to the Class I stage. Consistent with previous studies, the outflow force, FCO, is larger for Class 0 sources than for Class I sources, even if their luminosities are comparable. The outflowing gas typically extends to much greater distances than the power-law envelope and therefore influences the surrounding cloud material directly. Comparison of the CO 6-5 results with HIFI H2O and PACS high-J CO lines, both tracing currently shocked gas, shows that the two components are linked, even though the transitions do not probe the same gas. The link does not extend down to CO 3-2. The conclusion is that CO 6-5 depends on the shock

  4. Impact of photometric variability on age and mass determination in young stellar objects: the case of the Orion Nebula Cluster

    NASA Astrophysics Data System (ADS)

    Messina, Sergio; Parihar, Padmakar; Distefano, Elisa

    2017-06-01

    Very young stars, like the Orion Nebula Cluster (ONC) members analysed in the present study, exhibit photometric variability with a wide range of amplitudes. Such a prominent variability reflects in the inferred values of stellar colours and luminosities and, in turn, in the inferred stellar ages and masses. In this study, we measure the amplitudes of the photometric variability in V, R and I optical bands of a sample of 346 ONC members. We use these measurements to investigate how this variability affects the inferred masses and ages and whether it alone can account for the age spread among ONC members reported by earlier studies. We make use of colour-magnitude and Hertzprung-Russell (HR) diagrams. We find that members that show periodic and smooth photometric rotational modulation have masses and ages that are unaffected by variability when theoretical isochrones and evolutionary mass tracks are used in either colour-magnitude or HR diagrams. On the other hand, members with periodic but very scattered photometric rotational modulation and non-periodic members have masses and ages that are significantly affected. Moreover, using HR diagrams, we find that the observed I-band photometric variability can take account of only a fraction (˜50 per cent) of the inferred age spread, whereas the V-band photometric variability is large enough to mask any age spread.

  5. Stellar Metamorphosis:

    NASA Technical Reports Server (NTRS)

    2002-01-01

    edge-on, where the direct starlight is blocked by the dusty cocoon. Otherwise, the starlight would overwhelm the nebular light, making it very difficult to see the butterfly-shaped nebula. In a few hundred years, intense ultraviolet radiation from the central star will energize the surrounding gas, causing it to glow brightly, and a planetary nebula is born. These observations were made with the Wide Field and Planetary Camera 2 using three filters: yellow-green, blue, and near-infrared. The images were taken in 1997 by Sun Kwok and in 1996 by Matt Bobrowsky. Credits: Sun Kwok and Kate Su (University of Calgary), Bruce Hrivnak (Valparaiso University), and NASA ----------------- The Hubble Space Telescope Sees Remarkable Structure in the Heart of a Planetary Nebula [BOTTOM LEFT AND RIGHT] This Wide Field and Planetary Camera 2 image of NGC 6818 shows two distinct layers of gas (with dust): a spherical outer region and a brighter, vase-shaped interior 'bubble.' Astronomers believe that a fast wind - material propelled by radiation from the hot central star - is creating the inner elongated shape. The central star of the planetary nebula appears as a tiny blue dot. The material in the wind is traveling so fast that it smashes through older, slower-moving stellar debris, causing a 'blowout' at both ends of the bubble (lower right and upper left). This nebula looks like a twin of NGC 3918, another planetary nebula that has been observed by the Hubble telescope. The structure of NGC 3918 is remarkably similar to that of NGC 6818. It has an outer spherical envelope and an inner, brighter, elongated bubble. A fast-moving wind also appears to have created an orifice at one end (bottom right-hand corner) of the inner bubble. There are even faint wisps of material that were probably blown out of this hole. In the opposite direction (top left-hand corner), there is a protrusion that seems on the verge of breaking through to form a hole. By finding and studying such similar objects

  6. Optically visible post-AGB/RGB stars and young stellar objects in the Small Magellanic Cloud: candidate selection, spectral energy distributions and spectroscopic examination

    NASA Astrophysics Data System (ADS)

    Kamath, D.; Wood, P. R.; Van Winckel, H.

    2014-04-01

    We have carried out a search for optically visible post-asymptotic giant branch (post-AGB) candidates in the Small Magellanic Cloud (SMC). First, we used mid-IR observations from the Spitzer Space Telescope to select optically visible candidates with excess mid-IR flux and then we obtained low-resolution optical spectra for 801 of the candidates. After removing poor-quality spectra and contaminants, such as M-stars, C-stars, planetary nebulae, quasi-stellar objects and background galaxies, we ended up with a final sample of 63 high-probability post-AGB/RGB candidates of A-F spectral type. From the spectral observations, we estimated the stellar parameters: effective temperature (Teff), surface gravity (log g) and metallicity ([Fe/H]). We also estimated the reddening and deduced the luminosity using the stellar parameters combined with photometry. For the post-AGB/RGB candidates, we found that the metallicity distribution peaks at [Fe/H] ≈ -1.00 dex. Based on a luminosity criterion, 42 of these 63 sources were classified as post-red giant branch (post-RGB) candidates and the remaining 21 as post-AGB candidates. From the spectral energy distributions, we were able to infer that 6 of the 63 post-AGB/RGB candidates have a surrounding circumstellar shell suggesting that they are single stars, while 27 of the post-AGB/RGB candidates have a surrounding disc, suggesting that they lie in binary systems. For the remaining 30 post-AGB/RGB candidates the nature of the circumstellar environment was unclear. Variability is displayed by 38 of the 63 post-AGB/RGB candidates with the most common variability types being the Population II Cepheids (including RV-Tauri stars) and semiregular variables. This study has also revealed a new RV Tauri star in the SMC, J005107.19-734133.3, which shows signs of s-process enrichment. From the numbers of post-AGB/RGB stars in the SMC, we were able to estimate evolutionary rates. We find that the number of post-AGB and post-RGB candidates that

  7. NEAR-INFRARED SPECTROSCOPY OF INFRARED-EXCESS STELLAR OBJECTS IN THE YOUNG SUPERNOVA REMNANT G54.1+0.3

    SciTech Connect

    Kim, Hyun-Jeong; Koo, Bon-Chul; Moon, Dae-Sik E-mail: koo@astro.snu.ac.kr

    2013-09-01

    We present the results of broadband near-infrared spectroscopic observations of the recently discovered mysterious stellar objects in the young supernova remnant G54.1+0.3. These objects, which show significant mid-infrared-excess emission, are embedded in a diffuse loop structure of {approx}1' in radius. Their near-infrared spectra reveal characteristics of late O- or early B-type stars with numerous H and He I absorption lines, and we classify their spectral types to be between O9 and B2 based on an empirical relation derived here between the equivalent widths of the H lines and stellar photospheric temperatures. The spectral types, combined with the results of spectral energy distribution fits, constrain the distance to the objects to be 6.0 {+-} 0.4 kpc. The photometric spectral types of the objects are consistent with those from the spectroscopic analyses, and the extinction distributions indicate a local enhancement of matter in the western part of the loop. If these objects originate via triggered formation by the progenitor star of G54.1+0.3, then their formations likely began during the later evolutionary stages of the progenitor, although a rather earlier formation may still be possible. If the objects and the progenitor belong to the same cluster of stars, then our results constrain the progenitor mass of G54.1+0.3 to be between 18 and {approx}35 M{sub Sun} and suggest that G54.1+0.3 was either a Type IIP supernova or, with a relatively lower possibility, Type Ib/c from a binary system.

  8. Long-Term Multicolour Photometry of the Young Stellar Objects FHO 26, FHO 27, FHO 28, FHO 29, and V1929 Cygni

    NASA Astrophysics Data System (ADS)

    Ibryamov, S. I.; Semkov, E. H.; Peneva, S. P.

    2015-05-01

    Results from long-term multicolour optical photometric observations of the pre-main-sequence stars FHO 26, FHO 27, FHO 28, FHO 29, and V1929 Cyg collected during the period from 1997 June to 2014 December are presented. The objects are located in the dense molecular cloud L935, named `Gulf of Mexico', in the field between the North America and Pelican nebulae. All stars from our study exhibit strong photometric variability in all optical passbands. Using our BVRI observations and data published by other authors, we tried to define the reasons for the observed brightness variations. The presented paper is a part of our long-term photometric study of the young stellar objects in the region of `Gulf of Mexico'.

  9. Blue stragglers as remnants of stellar mergers - The discovery of short-period eclipsing binaries in the globular cluster NGC 5466

    SciTech Connect

    Mateo, M.; Harris, H.C.; Nemec, J.; Olszewski, E.W. Naval Observatory, Flagstaff, AZ British Columbia Univ., Vancouver Steward Observatory, Tucson, AZ )

    1990-08-01

    Results are reported from a search for short-period variables among blue stragglers in the central region of NGC 5466, based on analysis of 248 B and V CCD images obtained with the U.S. Naval Observatory 1-m, Palomar Observatory 1.5-m, and Steward Observatory 2.3-m telescopes during 1987-1989. The data are presented in extensive tables and graphs and characterized in detail. Nine variable blue stragglers are identified, of which three are eclipsing binaries with periods 0.298-0.511 d (two contact binaries of W UMa type and one detached or semidetached binary) and six are pulsating SX Phe stars. Theoretical models indicate that all of the noneclipsing blue stragglers could be merged close binaries, although other formation mechanisms cannot be completely ruled out. 111 refs.

  10. An HST Survey for 100-1000 au Companions around Young Stellar Objects in the Orion Molecular Clouds: Evidence for Environmentally Dependent Multiplicity

    NASA Astrophysics Data System (ADS)

    Kounkel, M.; Megeath, S. T.; Poteet, C. A.; Fischer, W. J.; Hartmann, L.

    2016-04-01

    We present a near-infrared survey for the visual multiples in the Orion molecular clouds region at separations between 100 and 1000 au. These data were acquired at 1.6 μm with the NICMOS and WFC3 cameras on the Hubble Space Telescope. Additional photometry was obtained for some of the sources at 2.05 μm with NICMOS and in the L‧ band with NSFCAM2 on NASA’s InfraRed Telescope Facility. Toward 129 protostars and 197 pre-main-sequence stars with disks observed with WFC3, we detect 21 and 28 candidate companions between the projected separations of 100-1000 au, of which less than 5 and 8, respectively, are chance line-of-sight coincidences. The resulting companion fraction (CF) after the correction for the line-of-sight contamination is {14.4}-1.3+1.1% for protostars and {12.5}-0.8+1.2% for the pre-main-sequence stars. These values are similar to those found for main-sequence stars, suggesting that there is little variation in the CF with evolution, although several observational biases may mask a decrease in the CF from protostars to the main-sequence stars. After segregating the sample into two populations based on the surrounding surface density of young stellar objects, we find that the CF in the high stellar density regions (ΣYSO > 45 pc-2) is approximately 50% higher than that found in the low stellar density regions (ΣYSO < 45 pc-2). We interpret this as evidence for the elevated formation of companions at 100-1000 au in the denser environments of Orion. We discuss possible reasons for this elevated formation.

  11. Common Envelope Wind Tunnel: Coefficients of Drag and Accretion in a Simplified Context for Studying Flows around Objects Embedded within Stellar Envelopes

    NASA Astrophysics Data System (ADS)

    MacLeod, Morgan; Antoni, Andrea; Murguia-Berthier, Ariadna; Macias, Phillip; Ramirez-Ruiz, Enrico

    2017-03-01

    This paper examines the properties of flows around objects embedded within common envelopes in the simplified context of a “wind tunnel.” We establish characteristic relationships between key common envelope flow parameters like the Mach number and density scale height. Our wind tunnel is a three-dimensional, Cartesian geometry hydrodynamic simulation setup that includes the gravity of the primary and secondary stars and allows us to study the coefficients of drag and accretion experienced by the embedded object. Accretion and drag lead to a transformation of an embedded object and its orbit during a common envelope phase. We present two suites of simulations spanning a range of density gradients and Mach numbers—relevant for flow near the limb of a stellar envelope to the deep interior. In one suite, we adopt an ideal gas adiabatic exponent of γ =5/3, in the other, γ =4/3. We find that coefficients of drag rise in flows with steeper density gradients and that coefficients of drag and accretion are consistently higher in the more compressible, γ =4/3 flow. We illustrate the impact of these newly derived coefficients by integrating the inspiral of a secondary object through the envelopes of 3{M}⊙ (γ ≈ 5/3) and 80{M}⊙ (γ ≈ 4/3) giants. In these examples, we find a relatively rapid initial inspiral because, near the stellar limb, dynamical friction drag is generated mainly from dense gas focused from deeper within the primary-star’s envelope. This rapid initial inspiral timescale carries potential implications for the timescale of transients from early common envelope interaction.

  12. The Edinburgh-Cape Blue Object Survey - V. The end: Partial Zones 4-6; Galactic latitudes -50° > b > -90°

    NASA Astrophysics Data System (ADS)

    Kilkenny, D.; Worters, H. L.; O'Donoghue, D.; Koen, C.; Koen, T.; Hambly, N.; MacGillivray, H.; Stobie, R. S.

    2016-07-01

    Results for the remaining zones of the Edinburgh-Cape (EC) Blue Object survey are presented. These are incomplete, but lie in that part of the South Galactic Cap between 50° and 90° from the Galactic plane and south of about -12.3° of declination. This part of the survey comprises 79 UK Schmidt Telescope fields covering about 2150 deg2, in which we find 536 blue objects - including hot subdwarfs (˜33 per cent), white dwarfs (˜30 per cent), binaries (˜12 per cent), cataclysmic variables (˜1.5 per cent) and some `star-like' galaxies (˜12 per cent). A further 254 stars observed in the survey, mainly low-metallicity F- and G-type stars, are also listed. Low-dispersion spectroscopic classification is given for all the hot objects and UBV photometry for most of them. Either spectroscopy or photometry is listed for the cooler types.

  13. VY Monocerotis and the IC 446 region - Far-infrared and submillimeter images of a massive young stellar object and its environment

    SciTech Connect

    Casey, S.C.; Harper, D.A. Yerkes Observatory, Williams Bay, WI )

    1990-10-01

    The reflection nebulae IC 446 has been mapped in an 8 x 8-arcmin area at 100, 160, and 370 microns using 32-channel bolometer-array detectors on the 0.9-m telescope of the NASA Kuiper Airborne Observatory and the 3-m telescope of the NASA Infrared Telescope Facility. These data have been combined with IRAS profiles at 12, 25, 60, and 100 microns to investigate the morphology and energetics of the region. The FIR through submm emission in the neighborhood of IC 446 is composed of three components: a compact point source associated with the young stellar object VY Mon, warm extended emission associated with dust in the reflection nebula IC 446, and cold extended emission associated with a dark absorption nebula or globule. 69 refs.

  14. X-shooter reveals powerful outflows in z ˜ 1.5 X-ray selected obscured quasi-stellar objects

    NASA Astrophysics Data System (ADS)

    Brusa, M.; Bongiorno, A.; Cresci, G.; Perna, M.; Marconi, A.; Mainieri, V.; Maiolino, R.; Salvato, M.; Lusso, E.; Santini, P.; Comastri, A.; Fiore, F.; Gilli, R.; La Franca, F.; Lanzuisi, G.; Lutz, D.; Merloni, A.; Mignoli, M.; Onori, F.; Piconcelli, E.; Rosario, D.; Vignali, C.; Zamorani, G.

    2015-01-01

    We present X-shooter at Very Large Telescope observations of a sample of 10 luminous, X-ray obscured quasi-stellar objects (QSOs) at z ˜ 1.5 from the XMM-COSMOS survey, expected to be caught in the transitioning phase from starburst to active galactic nucleus (AGN)-dominated systems. The main selection criterion is X-ray detection at bright fluxes (LX ≳ 1044 erg s-1) coupled to red optical-to-near-infrared-to-mid-infrared colours. Thanks to its large wavelength coverage, X-shooter allowed us to determine accurate redshifts from the presence of multiple emission lines for five out of six targets for which we had only a photometric redshift estimate, with an 80 per cent success rate, significantly larger than what is observed in similar programs of spectroscopic follow-up of red QSOs. We report the detection of broad and shifted components in the [O III] λλ5007, 4959 complexes for six out of eight sources with these lines observable in regions free from strong atmospheric absorptions. The full width at half-maximum (FWHM) associated with the broad components are in the range FWHM ˜ 900-1600 km s-1, larger than the average value observed in Sloan Digital Sky Survey type 2 AGN samples at similar observed [O III] luminosity, but comparable to those observed for QSO/ultraluminous infrared galaxies systems for which the presence of kpc scale outflows has been revealed through integral field unit spectroscopy. Although the total outflow energetics (inferred under reasonable assumptions) may be consistent with winds accelerated by stellar processes, we favour an AGN origin for the outflows given the high outflow velocities observed (v > 1000 km s-1) and the presence of strong winds also in objects undetected in the far-infrared.

  15. FUNDAMENTAL PARAMETERS AND SPECTRAL ENERGY DISTRIBUTIONS OF YOUNG AND FIELD AGE OBJECTS WITH MASSES SPANNING THE STELLAR TO PLANETARY REGIME

    SciTech Connect

    Filippazzo, Joseph C.; Rice, Emily L.; Faherty, Jacqueline; Cruz, Kelle L.; Van Gordon, Mollie M.; Looper, Dagny L.

    2015-09-10

    We combine optical, near-infrared, and mid-infrared spectra and photometry to construct expanded spectral energy distributions for 145 field age (>500 Myr) and 53 young (lower age estimate <500 Myr) ultracool dwarfs (M6-T9). This range of spectral types includes very low mass stars, brown dwarfs, and planetary mass objects, providing fundamental parameters across both the hydrogen and deuterium burning minimum masses for the largest sample assembled to date. A subsample of 29 objects have well constrained ages as probable members of a nearby young moving group. We use 182 parallaxes and 16 kinematic distances to determine precise bolometric luminosities (L{sub bol}) and radius estimates from evolutionary models give semi-empirical effective temperatures (T{sub eff}) for the full range of young and field age late-M, L, and T dwarfs. We construct age-sensitive relationships of luminosity, temperature, and absolute magnitude as functions of spectral type and absolute magnitude to disentangle the effects of degenerate physical parameters such as T{sub eff}, surface gravity, and clouds on spectral morphology. We report bolometric corrections in J for both field age and young objects and find differences of up to a magnitude for late-L dwarfs. Our correction in Ks shows a larger dispersion but not necessarily a different relationship for young and field age sequences. We also characterize the NIR–MIR reddening of low gravity L dwarfs and identify a systematically cooler T{sub eff} of up to 300 K from field age objects of the same spectral type and 400 K cooler from field age objects of the same M{sub H} magnitude.

  16. Stellar evolution.

    NASA Technical Reports Server (NTRS)

    Chiu, H.-Y. (Editor); Muriel, A.

    1972-01-01

    Aspects of normal stellar evolution are discussed together with evolution near the main sequence, stellar evolution from main sequence to white dwarf or carbon ignition, the structure of massive main-sequence stars, and problems of stellar stability and stellar pulsation. Other subjects considered include variable stars, white dwarfs, close binaries, novae, early supernova luminosity, neutron stars, the photometry of field horizontal-branch stars, and stellar opacity. Transport mechanisms in stars are examined together with thermonuclear reactions and nucleosynthesis, the instability problem in nuclear burning shells, stellar coalescence, and intense magnetic fields in astrophysics. Individual items are announced in this issue.

  17. VizieR Online Data Catalog: Young stellar structures in NGC 6503 (Gouliermis+, 2015)

    NASA Astrophysics Data System (ADS)

    Gouliermis, D. A.; Thilker, D.; Elmegreen, B. G.; Elmegreen, D. M.; Calzetti, D.; Lee, J. C.; Adamo, A.; Aloisi, A.; Cignoni, M.; Cook, D. O.; Dale, D. A.; Gallagher, J. S. Iii; Grasha, K.; Grebel, E. K.; Davo, A. H.; Hunter, D. A.; Johnson, K. E.; Kim, H.; Nair, P.; Nota, A.; Pellerin, A.; Ryon, J.; Sabbi, E.; Sacchi, E.; Smith, L. J.; Tosi, M.; Ubeda, L.; Whitmore, B.

    2016-03-01

    LEGUS is an HST panchromatic stellar survey of 50 nearby star-forming dwarf and spiral galaxies with an emphasis on UV-enabled science applications. Images in a wide waveband coverage from the near-UV (NUV) to the I band are being collected with WFC3 and ACS in parallel, and combined with archival optical ACS data. The survey, its scientific objectives and the data reduction are described in Calzetti et al. (2015AJ....149...51C). We present a detailed clustering analysis of the young blue stellar population identified with LEGUS across the star-forming ring galaxy NGC 6503. We construct stellar surface density maps and apply a contour-based analysis technique to identify the stellar complexes' population of the galaxy. We identify 244 distinct structures at various stellar density (significance) levels. The complete catalogue of 244 structures is available online at LEGUS site https://legus.stsci.edu/. (1 data file).

  18. Investigation of the behaviour of the eruptive young stellar object V1647 Ori since its outburst in 2008

    NASA Astrophysics Data System (ADS)

    Venkataraman, V.

    V1647 Ori is a young eruptive low mass pre-main sequence star that illuminates McNeil's nebula. The object has undergone two outbursts in the recent years - first in November 2003 and the second in mid 2008. While the first outburst lasted for about 2 years before it briefly recovered to its quiescent state, the object is still active since its second eruption in 2008. The nature of the V1647 ori outburst and its similarity with other pre-main sequence eruptive objects, namely FUors and EXors, are still debated. Both types of outburst are thought to be driven by a sudden increase of accretion through a circumstellar disk that feeds through a circumstellar envelope. Follow-up photometric and spectroscopic observations in the near-IR(NIR) JHK bands were being made at Mt. Abu observatory using NICS and NICMOS. The NIR observations taken on several occasions during 2008 to 2012 show mean values of brightness in J, H and K bands of 10.82(sigma=0.146), 9.02(0.189) and 7.58(0.234) mags respectively. During the period, occasional brightening or fading by about 2-3 sigma was also noticed which can be attributed to disk accretion rate variations. The NIR spectra obtained in the K band showed Brackett gamma in emission with non-systematic variability. Our observations indicate slight fading out of V1647 ori during the early part of 2012. Modelling of the spectral energy distribution (SED) in visible to sub-mm region (compiled from archival data) suggests increased disk mass accretion rate as compared to its quiescent state. The model parameters are in good agreement with those derived from observations. These results will be discussed in detail.

  19. A search for stellar remnants of supernovae

    NASA Technical Reports Server (NTRS)

    Fesen, R. A.; Kirshner, R. P.; Winkler, P. F., Jr.

    1979-01-01

    The slitless spectra of the stars in the central regions of six galactic supernova remnants Cas A, Kepler, Tycho, SN 1006, RCW 86, and the Cygnus Loop were obtained with the prime focus transmission gratings at the 4M telescopes on Kitt Peak and Cerro Tololo. It was found that no stellar remnant with an unusually blue or peculiar spectrum is present in any of the remnants down to the limit of m sub pg of 18.5. Except for the Cygnus Loop, the area searched in each remnant is large enough that objects with transverse velocities of 1000 km/s would be well within the field. The results are also compared with a computation of emission from gas near a neutron star and with the unpulsed emission from the Crab pulsar; in both cases upper limits were set which place constraints on a possible condensed stellar remnant.

  20. Surveying the agents of galaxy evolution in the tidally stripped, low metallicity small Magellanic Cloud (SAGE-SMC). III. Young stellar objects

    SciTech Connect

    Sewiło, M.; Carlson, L. R.; Seale, J. P.; Meixner, M.; Gordon, K.; Shiao, B. E-mail: carlson@strw.leidenuniv.nl E-mail: meixner@stsci.edu E-mail: shiao@stsci.edu; and others

    2013-11-20

    The Spitzer Space Telescope Legacy Program SAGE-SMC allows global studies of resolved stellar populations in the SMC in a different environment than our Galaxy. Using the SAGE-SMC IRAC (3.6-8.0 μm) and MIPS (24 and 70 μm) catalogs and images combined with near-infrared (JHK {sub s}) and optical (UBVI) data, we identified a population of ∼1000 intermediate- to high-mass young stellar objects (YSOs) in the SMC (three times more than previously known). Our method of identifying YSO candidates builds on the method developed for the Large Magellanic Cloud by Whitney et al. with improvements based on what we learned from our subsequent studies and techniques described in the literature. We perform (1) color-magnitude cuts based on five color-magnitude diagrams (CMDs), (2) visual inspection of multi-wavelength images, and (3) spectral energy distribution (SED) fitting with YSO models. For each YSO candidate, we use its photometry to calculate a measure of our confidence that the source is not a non-YSO contaminant, but rather a true YSO, based on the source's location in the color-magnitude space with respect to non-YSOs. We use this CMD score and the SED fitting results to define two classes of sources: high-reliability YSO candidates and possible YSO candidates. We found that, due to polycyclic aromatic hydrocarbon emission, about half of our sources have [3.6]-[4.5] and [4.5]-[5.8] colors not predicted by previous YSO models. The YSO candidates are spatially correlated with gas tracers.

  1. Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud (SAGE-SMC). III. Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Sewiło, M.; Carlson, L. R.; Seale, J. P.; Indebetouw, R.; Meixner, M.; Whitney, B. A.; Robitaille, T. P.; Oliveira, J. M.; Gordon, K.; Meade, M. R.; Babler, B. L.; Hora, J. L.; Block, M.; Misselt, K.; van Loon, J. Th.; Chen, C.-H. R.; Churchwell, E.; Shiao, B.

    2013-11-01

    The Spitzer Space Telescope Legacy Program SAGE-SMC allows global studies of resolved stellar populations in the SMC in a different environment than our Galaxy. Using the SAGE-SMC IRAC (3.6-8.0 μm) and MIPS (24 and 70 μm) catalogs and images combined with near-infrared (JHK s ) and optical (UBVI) data, we identified a population of ~1000 intermediate- to high-mass young stellar objects (YSOs) in the SMC (three times more than previously known). Our method of identifying YSO candidates builds on the method developed for the Large Magellanic Cloud by Whitney et al. with improvements based on what we learned from our subsequent studies and techniques described in the literature. We perform (1) color-magnitude cuts based on five color-magnitude diagrams (CMDs), (2) visual inspection of multi-wavelength images, and (3) spectral energy distribution (SED) fitting with YSO models. For each YSO candidate, we use its photometry to calculate a measure of our confidence that the source is not a non-YSO contaminant, but rather a true YSO, based on the source's location in the color-magnitude space with respect to non-YSOs. We use this CMD score and the SED fitting results to define two classes of sources: high-reliability YSO candidates and possible YSO candidates. We found that, due to polycyclic aromatic hydrocarbon emission, about half of our sources have [3.6]-[4.5] and [4.5]-[5.8] colors not predicted by previous YSO models. The YSO candidates are spatially correlated with gas tracers.

  2. 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.

  3. Development of a Virtual Observatory Tool for the Characterization of Stellar Objects in the DUNES Project Framework

    NASA Astrophysics Data System (ADS)

    Gutiérrez-Sánchez, Raúl; Solano, Enrique; Arévalo, María; Eiroa, Carlos

    Most of the projects that aim at detecting extrasolar planets require a careful selection of the central stars as well as an extremely detailed knowledge of their properties and environment. However, gathering information in a wide variety of types and formats from a large number of heterogeneous astronomical data services can be a tedious, very time-consuming task, even for a modest dataset. To overcome this situation the LAEFF Scientific Data Centre, in the framework of the Spanish Virtual Observatory1, has developed a VO-compliant discovery tool for DUNES2. This tool allows accessing, visualizing, filtering and retrieving relevant information of lists of objects. In this poster we describe the main characteristics and functionalities of the system.

  4. The VLTI/MIDI survey of massive young stellar objects . Sounding the inner regions around intermediate- and high-mass young stars using mid-infrared interferometry

    NASA Astrophysics Data System (ADS)

    Boley, Paul A.; Linz, Hendrik; van Boekel, Roy; Henning, Thomas; Feldt, Markus; Kaper, Lex; Leinert, Christoph; Müller, André; Pascucci, Ilaria; Robberto, Massimo; Stecklum, Bringfried; Waters, L. B. F. M.; Zinnecker, Hans

    2013-10-01

    Context. Because of inherent difficulties involved in observations and numerical simulations of the formation of massive stars, an understanding of the early evolutionary phases of these objects remains elusive. In particular, observationally probing circumstellar material at distances ≲100 AU from the central star is exceedingly difficult, as such objects are rare (and thus, on average, far away) and typically deeply embedded. Long-baseline mid-infrared interferometry provides one way of obtaining the necessary spatial resolution at appropriate wavelengths for studying this class of objects; however, interpreting such observations is often difficult due to sparse spatial-frequency coverage. Aims: We aim to characterize the distribution and composition of circumstellar material around young massive stars and to investigate exactly which physical structures in these objects are probed by long-baseline mid-infrared interferometric observations. Methods: We used the two-telescope interferometric instrument MIDI of the Very Large Telescope Interferometer of the European Southern Observatory to observe a sample of 24 intermediate- and high-mass young stellar objects in the N band (8-13 μm). We had successful fringe detections for 20 objects and present spectrally-resolved correlated fluxes and visibility levels for projected baselines of up to 128 m. We fit the visibilities with geometric models to derive the sizes of the emitting regions, as well as the orientation and elongation of the circumstellar material. Fourteen objects in the sample show the 10 μm silicate feature in absorption in the total and correlated flux spectra. For 13 of these objects, we were able to fit the correlated flux spectra with a simple absorption model, allowing us to constrain the composition and absorptive properties of the circumstellar material. Results: Nearly all of the massive young stellar objects observed show significant deviations from spherical symmetry at mid

  5. Intermittent maser flare around the high-mass young stellar object G353.273+0.641

    NASA Astrophysics Data System (ADS)

    Motogi, Kazuhito; Sorai, Kazuo; Fujisawa, Kenta; Sugiyama, Koichiro; Honma, Mareki

    2012-07-01

    The water maser site associated with G353.273+0.641 is classified as a dominant blueshifted H2O maser, which shows an extremely wide velocity range (+/- 100 km s-1) with almost all flux concentrated in the highly blueshifted emission. The previous study has proposed that this peculiar H2O maser site is excited by a pole-on jet from high mass protostellar object. We report on the monitoring of 22-GHz H2O maser emission from G353.273+0.641 with the VLBI Exploration of Radio Astrometry (VERA) and the Tomakamai 11-m radio telescope. Our VLBI imaging has shown that all maser features are distributed within a very small area of 200 × 200 au2, in spite of the wide velocity range (> 100 km s-1). The light curve obtained by weekly single-dish monitoring shows notably intermittent variation. We have detected three maser flares during three years. Frequent VLBI monitoring has revealed that these flare activities have been accompanied by a significant change of the maser alignments. We have also detected synchronized linear acceleration (-5 km s-1yr-1) of two isolated velocity components, suggesting a lower-limit momentum rate of 10-3 M⊙ km s-1yr-1 for the maser acceleration. All our results support the previously proposed pole-on jet scenario, and finally, a radio jet itself has been detected in our follow-up ATCA observation. If highly intermittent maser flares directly reflect episodic jet-launchings, G353.273+0.641 and similar dominant blueshifted water maser sources can be suitable targets for a time-resolved study of high mass protostellar jet.

  6. A FIRST LOOK AT THE AURIGA-CALIFORNIA GIANT MOLECULAR CLOUD WITH HERSCHEL AND THE CSO: CENSUS OF THE YOUNG STELLAR OBJECTS AND THE DENSE GAS

    SciTech Connect

    Harvey, Paul M.; Fallscheer, Cassandra; Ginsburg, Adam; Terebey, Susan; Andre, Philippe; Koenyves, Vera; Di Francesco, James; Matthews, Brenda C.; Peterson, Dawn E. E-mail: Cassandra.Fallscheer@nrc-cnrc.gc.ca E-mail: sterebe@calstatela.edu E-mail: vera.konyves@cea.fr E-mail: James.DiFrancesco@nrc-cnrc.gc.ca E-mail: dpeterson@spacescience.org

    2013-02-20

    We have mapped the Auriga/California molecular cloud with the Herschel PACS and SPIRE cameras and the Bolocam 1.1 mm camera on the Caltech Submillimeter Observatory with the eventual goal of quantifying the star formation and cloud structure in this giant molecular cloud (GMC) that is comparable in size and mass to the Orion GMC, but which appears to be forming far fewer stars. We have tabulated 60 compact 70/160 {mu}m sources that are likely pre-main-sequence objects and correlated those with Spitzer and WISE mid-IR sources. At 1.1 mm, we find 18 cold, compact sources and discuss their properties. The most important result from this part of our study is that we find a modest number of additional compact young objects beyond those identified at shorter wavelengths with Spitzer. We also describe the dust column density and temperature structure derived from our photometric maps. The column density peaks at a few Multiplication-Sign 10{sup 22} cm{sup -2} (N {sub H2}) and is distributed in a clear filamentary structure along which nearly all of the pre-main-sequence objects are found. We compare the young stellar object surface density to the gas column density and find a strong nonlinear correlation between them. The dust temperature in the densest parts of the filaments drops to {approx}10 K from values {approx}14-15 K in the low-density parts of the cloud. We also derive the cumulative mass fraction and probability density function of material in the cloud, which we compare with similar data on other star-forming clouds.

  7. The multiple young stellar objects of HBC 515: An X-ray and millimeter-wave imaging study in (pre-main sequence) diversity

    NASA Astrophysics Data System (ADS)

    Principe, D. A.; Sacco, G. G.; Kastner, J. H.; Wilner, D.; Stelzer, B.; Micela, G.

    2017-01-01

    We present Chandra X-ray Observatory and Submillimeter Array (SMA) imaging of HBC 515, a system consisting of multiple young stellar objects (YSOs). The five members of HBC 515 represent a remarkably diverse array of YSOs, ranging from the low-mass Class I/II protostar HBC 515B, through Class II and transition disk objects (HBC 515D and C, respectively), to the "diskless", intermediate-mass, pre-main sequence (pre-MS) binary HBC 515A. Our Chandra/ACIS imaging establishes that all five components are X-ray sources, with HBC 515A - a subarcsecond-separation binary that is partially resolved by Chandra - being the dominant X-ray source. We detect an X-ray flare associated with HBC 515B. In the SMA imaging, HBC 515B is detected as a strong 1.3 mm continuum emission source; a second, weaker mm continuum source is coincident with the position of the transition disk object HBC 515C. These results strongly support the protostellar nature of HBC 515B, and firmly establish HBC 515A as a member of the rare class of relatively massive, X-ray luminous weak-lined T Tauri stars that are binaries and have shed their disks at very early stages of pre-MS evolution. The coexistence of two such disparate objects within a single, presumably coeval multiple YSO system highlights the influence of pre-MS star mass, binarity, and X-ray luminosity in regulating the lifetimes of circumstellar, planet-forming disks, and the timescales of star-disk interactions.

  8. [Fe II] 1.64 μm FEATURES OF JETS AND OUTFLOWS FROM YOUNG STELLAR OBJECTS IN THE CARINA NEBULA

    SciTech Connect

    Shinn, Jong-Ho; Lee, Jae-Joon; Chun, Moo-Young; Lyo, A.-Ran; Moon, Dae-Sik; Kyeong, Jaemann; Park, Byeong-Gon; Pyo, Tae-Soo; Lee, Ho-Gyu; Kim, Hyun-Jeong; Koo, Bon-Chul; Lee, Yong-Hyun; Sung, Hwankyung; Hur, Hyeonoh

    2013-11-01

    We present [Fe II] 1.64 μm imaging observations for jets and outflows from young stellar objects (YSOs) over the northern part (∼24' × 45') of the Carina Nebula, a massive star-forming region. The observations were performed with IRIS2 of the Anglo-Australian Telescope and the seeing was ∼1.''5 ± 0.''5. Eleven jet and outflow features are detected at eight different regions and are termed ionized Fe objects (IFOs). One Herbig-Haro candidate that was missed in Hubble Space Telescope Hα observations is newly identified as HHc-16, referring to our [Fe II] images. IFOs have knotty or longish shapes, and the detection rate of IFOs against previously identified YSOs is 1.4%, which should be treated as a lower limit. Four IFOs show anti-correlated peak intensities in [Fe II] and Hα, where the ratio I([Fe II])/I(Hα) is higher for longish IFOs than for knotty IFOs. We estimate the outflow mass loss rate from the [Fe II] flux using two different methods. The jet-driving objects are identified for three IFOs (IFO-2, -4, and -7) for which we study the relations between the outflow mass loss rate and the YSO physical parameters from the radiative transfer model fitting. The ratios of the outflow mass loss rate over the disk accretion rate for IFO-4 and -7 are consistent with the previously reported values (10{sup –2}-10{sup +1}), while the ratio is higher for IFO-2. This excess may result from underestimating the disk accretion rate. The jet-driving objects are likely to be low- or intermediate-mass stars. Other YSO physical parameters, such as luminosity and age, show reasonable relations or trends.

  9. THE SPITZER ATLAS OF STELLAR SPECTRA (SASS)

    SciTech Connect

    Ardila, David R.; Van Dyk, Schuyler D.; Makowiecki, Wojciech; Stauffer, John; Rho, Jeonghee; Fajardo-Acosta, Sergio; Hoard, D. W.; Wachter, Stefanie; Song, Inseok

    2010-12-15

    We present the Spitzer Atlas of Stellar Spectra, which includes 159 stellar spectra (5-32 {mu}m; R {approx} 100) taken with the Infrared Spectrograph on the Spitzer Space Telescope. This Atlas gathers representative spectra of a broad section of the Hertzsprung-Russell diagram, intended to serve as a general stellar spectral reference in the mid-infrared. It includes stars from all luminosity classes, as well as Wolf-Rayet (WR) objects. Furthermore, it includes some objects of intrinsic interest, such as blue stragglers and certain pulsating variables. All of the spectra have been uniformly reduced, and all are available online. For dwarfs and giants, the spectra of early-type objects are relatively featureless, characterized by the presence of hydrogen lines in A spectral types. Besides these, the most noticeable photospheric features correspond to water vapor and silicon monoxide in late-type objects and methane and ammonia features at the latest spectral types. Most supergiant spectra in the Atlas present evidence of circumstellar gas and/or dust. The sample includes five M supergiant spectra, which show strong dust excesses and in some cases polycyclic aromatic hydrocarbon features. Sequences of WR stars present the well-known pattern of lines of He I and He II, as well as forbidden lines of ionized metals. The characteristic flat-top shape of the [Ne III] line is evident even at these low spectral resolutions. Several Luminous Blue Variables and other transition stars are present in the Atlas and show very diverse spectra, dominated by circumstellar gas and dust features. We show that the [8]-[24] Spitzer colors (IRAC and MIPS) are poor predictors of spectral type for most luminosity classes.

  10. Water in star-forming regions with Herschel (WISH). VI. Constraints on UV and X-ray irradiation from a survey of hydrides in low- to high-mass young stellar objects

    NASA Astrophysics Data System (ADS)

    Benz, A. O.; Bruderer, S.; van Dishoeck, E. F.; Melchior, M.; Wampfler, S. F.; van der Tak, F.; Goicoechea, J. R.; Indriolo, N.; Kristensen, L. E.; Lis, D. C.; Mottram, J. C.; Bergin, E. A.; Caselli, P.; Herpin, F.; Hogerheijde, M. R.; Johnstone, D.; Liseau, R.; Nisini, B.; Tafalla, M.; Visser, R.; Wyrowski, F.

    2016-05-01

    Context. Hydrides are simple compounds containing one or a few hydrogen atoms bonded to a heavier atom. They are fundamental precursor molecules in cosmic chemistry and many hydride ions have become observable in high quality for the first time thanks to the Herschel Space Observatory. Ionized hydrides such as CH+ and OH+ (and also HCO+), which affect the chemistry of molecules such as water, provide complementary information on irradiation by far-UV (FUV) or X-rays and gas temperature. Aims: We explore hydrides of the most abundant heavier elements in an observational survey covering young stellar objects (YSOs) with different mass and evolutionary state. The focus is on hydrides associated with the dense protostellar envelope and outflows, contrary to previous work that focused on hydrides in diffuse foreground clouds. Methods: Twelve YSOs were observed with HIFI on Herschel in six spectral settings providing fully velocity-resolved line profiles as part of the Water in star-forming regions with Herschel (WISH) program. The YSOs include objects of low (Class 0 and I), intermediate, and high mass, with luminosities ranging from 4 L⊙ to 2 × 105 L⊙. Results: The targeted lines of CH+, OH+, H2O+, C+, and CH are detected mostly in blue-shifted absorption. H3O+ and SH+ are detected in emission and only toward some high-mass objects. The observed line parameters and correlations suggest two different origins related to gas entrained by the outflows and to the circumstellar envelope. The derived column densities correlate with bolometric luminosity and envelope mass for all molecules, best for CH, CH+, and HCO+. The column density ratios of CH+/OH+ are estimated from chemical slab models, assuming that the H2 density is given by the specific density model of each object at the beam radius. For the low-mass YSOs the observed ratio can be reproduced for an FUV flux of 2-400 times the interstellar radiation field (ISRF) at the location of the molecules. In two high

  11. Differences between work and leisure in temporal patterns of objectively measured physical activity among blue-collar workers.

    PubMed

    Hallman, David M; Mathiassen, Svend Erik; Gupta, Nidhi; Korshøj, Mette; Holtermann, Andreas

    2015-09-28

    Leisure time physical activity (LTPA) is generally associated with favorable cardiovascular health outcomes, while occupational physical activity (OPA) shows less clear, or even opposite, cardiovascular effects. This apparent paradox is not sufficiently understood, but differences in temporal patterns of OPA and LTPA have been suggested as one explanation. Our aim was to investigate the extent to which work and leisure (non-occupational time) differ in temporal activity patterns among blue-collar workers, and to assess the modification of these patterns by age and gender. This study was conducted on a cross-sectional sample of male (n = 108) and female (n = 83) blue-collar workers, aged between 21 and 65 years. Physical activity and sedentary behavior were assessed using accelerometers (Actigraph GT3X+) worn on the thigh and trunk for four consecutive days. Temporal patterns of OPA and LTPA were retrieved using Exposure Variation Analysis (EVA), and expressed in terms of percentage of work and leisure time spent in uninterrupted periods of different durations (<1 min, 1-5 min, 5-10 min, 10-30 min, 30-60 min and > 60 min) of sitting, standing, and walking. Repeated measures ANOVA and linear regression analyses were used to test a) possible differences between OPA and LTPA in selected EVA derivatives, and b) the modification of these differences by age and gender. OPA showed a larger percentage time walking in brief (<5 min) periods [mean (SD): 33.4 % (12.2)], and less time in prolonged (>30 min) sitting [7.0 % (9.3)] than LTPA [walking 15.4 % (5.0); sitting 31.9 % (15.3)], even after adjustment for the difference between work and leisure in total time spent in each activity type. These marked differences in the temporal pattern of OPA and LTPA were modified by gender, but not age. We found that the temporal patterns of OPA and LTPA among blue-collar workers were markedly different even after adjustment for total physical activity time, and that this

  12. The slow ionized wind and rotating disklike system that are associated with the high-mass young stellar object G345.4938+01.4677

    SciTech Connect

    Guzmán, Andrés E.; Garay, Guido; Bronfman, Leonardo; Mardones, Diego; Rodríguez, Luis F.; Moran, James; Brooks, Kate J.; Nyman, Lars-Åke; Sanhueza, Patricio

    2014-12-01

    We report the detection, made using ALMA, of the 92 GHz continuum and hydrogen recombination lines (HRLs) H40α, H42α, and H50β emission toward the ionized wind associated with the high-mass young stellar object G345.4938+01.4677. This is the luminous central dominating source located in the massive and dense molecular clump associated with IRAS 16562–3959. The HRLs exhibit Voigt profiles, which is a strong signature of Stark broadening. We successfully reproduce the observed continuum and HRLs simultaneously using a simple model of a slow ionized wind in local thermodynamic equilibrium, with no need for a high-velocity component. The Lorentzian line wings imply electron densities of 5 × 10{sup 7} cm{sup –3} on average. In addition, we detect SO and SO{sub 2} emission arising from a compact (∼3000 AU) molecular core associated with the central young star. The molecular core exhibits a velocity gradient that is perpendicular to the jet-axis, which we interpret as evidence of rotation. The set of observations toward G345.4938+01.4677 are consistent with it being a young high-mass star associated with a slow photo-ionized wind.

  13. An EXES Medium Resolution Search for Formaldehyde Gas in the Class I/II Young Stellar Object IRAS 04278+2253

    NASA Astrophysics Data System (ADS)

    Sargent, Benjamin

    2015-10-01

    We propose to obtain high resolution mid-infrared spectroscopy at 5.8 microns wavelength of the Class I/II Young Stellar Object (YSO) IRAS 04278+2253 using EXES on SOFIA to search for absorption from formaldehyde (H2CO) gas. Low spectral resolution (R~90) Spitzer-IRS spectra of this YSO and a number of T Tauri stars (TTSs) show an unresolved band of absorption of full width half maximum (FWHM) of ~0.6 microns centered around 5.7 microns wavelength. Modeling of the Spitzer-IRS spectrum of IRAS 04278+2253 and the other TTSs indicates this band may be due to formaldehyde. Detection of individual absorption lines in high spectral resolution mid-infrared spectra of YSOs would be a significant finding, as the relatively recent mid-infrared spectral studies of TTSs that have found evidence for circumstellar gas in protoplanetary disks have found emission lines from gases such as H2O, OH, CO, CO2, HCN, and C2H2 (e.g., Carr & Najita 2008, Salyk et al 2008; Salyk et al 2009; Carr & Najita 2011; Pontoppidan et al 2011), but they do not find absorption lines, and they do not find H2CO.

  14. Introduction to Stellar Winds

    NASA Astrophysics Data System (ADS)

    Lamers, Henny J. G. L. M.; Cassinelli, Joseph P.

    1999-06-01

    Preface; 1. Historical overview; 2. Observations of stellar winds; 3. Basic concepts: isothermal winds; 4. Basic concepts: non-isothermal winds; 5. Coronal winds; 6. Sound wave driven winds; 7. Dust driven winds; 8. Line driven winds; 9. Magnetic rotator theory; 10. Alfvén wave driven winds; 11. Outflowing disks from rotating stars; 12. Winds colliding with the interstellar medium; 13. The effects of mass loss on stellar evolution; 14. Problems; Appendices; Bibliography; Object index; Index.

  15. Intermittent maser flare around the high-mass young stellar object G353.273+0.641 - I. Data and overview

    NASA Astrophysics Data System (ADS)

    Motogi, K.; Sorai, K.; Honma, M.; Minamidani, T.; Takekoshi, T.; Akiyama, K.; Tateuchi, K.; Hosaka, K.; Ohishi, Y.; Watanabe, Y.; Habe, A.; Kobayashi, H.

    2011-10-01

    We have performed very long baseline interferometry (VLBI) and single-dish monitoring of 22-GHz H2O maser emission from the high-mass young stellar object G353.273+0.641 with the VLBI Exploration of Radio Astrometry (VERA) and the Tomakamai 11-m radio telescope. Two maser flares have been detected, separated by almost two years. Frequent VLBI monitoring has revealed that the flare activity has been accompanied by structural change of the prominent shock front traced by H2O maser alignments. We have detected only blueshifted emission and all maser features have been distributed within a very small area of 200 × 200 au2, in spite of a wide velocity range (>100 km s-1). The light curve shows notably intermittent variation and suggests that the H2O masers in G353.273+0.641 are excited by an episodic radio jet. The time-scale of ˜2 yr and characteristic velocity of ˜500 km s-1 also support this interpretation. Two isolated velocity components, C50 (-53 ± 7 km s-1) and C70 (-73 ± 7 km s-1), have shown synchronized linear acceleration of the flux-weighted ? values (˜ -5 km s-1 yr-1) during the flare phase. This can be converted to the lower-limit momentum rate of 1.1 × 10-3 M⊙ km s-1 yr-1. The maser properties are quite similar to those of IRAS 20126+4104 especially. This corroborates the previous suggestion that G353.273+0.641 is a candidate high-mass protostellar object. The possible pole-on geometry of the disc-jet system may be suitable for direct imaging of the accretion disc in this case.

  16. Herschel-PACS observations of far-IR lines in young stellar objects. I. [OI] and H2O at 63 μm

    NASA Astrophysics Data System (ADS)

    Riviere-Marichalar, P.; Merín, B.; Kamp, I.; Eiroa, C.; Montesinos, B.

    2016-10-01

    Context. Gas plays a major role in the dynamical evolution of young stellar objects (YSOs). Its interaction with the dust is the key to our understanding planet formation later on in the protoplanetary disc stage. Studying the gas content is therefore a crucial step towards understanding YSO and planet formation. Such a study can be made through spectroscopic observations of emission lines in the far-infrared, where some of the most important gas coolants emit, such as the [OI] 3P1 →3P2 transition at 63.18 μm. Aims: We provide a compilation of observations of far-IR lines in 362 YSOs covering all evolutionary stages, from Class 0 to Class III with debris discs. In the present paper we focus on [OI] and o-H2O emission at 63 μm. Methods: We retrieved all the available Herschel-PACS spectroscopic observations at 63 μm that used the dominant observing mode, the chop-nod technique. We provide measurements of line fluxes for the [OI] 3P1 →3P2 and o-H2O808 → 717 transitions at 63 μm computed using different methods. Taking advantage of the PACS IFU, we checked for spatially extended emission and also studied multiple dynamical components in line emission. Results: The final compilation consists of line and continuum fluxes at 63 μm for a total of 362 young stellar objects (YSOs). We detect [OI] line emission at 63 μm in 194 sources out of 362, and line absorption in another five sources. o-H2O was detected in 42 sources. We find evidence of extended [OI] emission in 77 sources, and detect 3σ residual emission in 71 of them. The number of sources showing extended emission decays from Class 0 to Class II. We also searched for different components contributing to the line emission, and found evidence for multiple components in 30 sources. We explored correlations between line emission and continuum emission and found a clear correlation between WISE fluxes from 4.6 to 22 μm and [OI] line emission. We conclude that the observed emission is typically a

  17. Results from a triple chord stellar occultation and far-infrared photometry of the trans-Neptunian object (229762) 2007 UK126

    NASA Astrophysics Data System (ADS)

    Schindler, K.; Wolf, J.; Bardecker, J.; Olsen, A.; Müller, T.; Kiss, C.; Ortiz, J. L.; Braga-Ribas, F.; Camargo, J. I. B.; Herald, D.; Krabbe, A.

    2017-04-01

    Context. A stellar occultation by a trans-Neptunian object (TNO) provides an opportunity to probe the size and shape of these distant solar system bodies. In the past seven years, several occultations by TNOs have been observed, but mostly from a single location. Only very few TNOs have been sampled simultaneously from multiple locations. Sufficient data that enable a robust estimation of shadow size through an ellipse fit could only be obtained for two objects. Aims: We present the first observation of an occultation by the TNO 2007 UK126 on 15 November 2014, measured by three observers, one nearly on and two almost symmetrical to the shadow's centerline. This is the first multi-chord dataset obtained for a so-called detached object, a TNO subgroup with perihelion distances so large that the giant planets have likely not perturbed their orbits. We also revisit Herschel/PACS far-infrared data, applying a new reduction method to improve the accuracy of the measured fluxes. Combining both datasets allows us to comprehensively characterize 2007 UK126. Methods: We use error-in-variable regression to solve the non-linear problem of propagating timing errors into uncertainties of the ellipse parameters. Based on the shadow's size and a previously reported rotation period, we expect a shape of a Maclaurin spheroid and derive a geometrically plausible size range. To refine our size estimate of 2007 UK126, we model its thermal emission using a thermophysical model code. We conduct a parametric study to predict far-infrared fluxes and compare them to the Herschel/PACS measurements. Results: The favorable geometry of our occultation chords, combined with minimal dead-time imaging, and precise GPS time measurements, allow for an accurate estimation of the shadow size (best-fitting ellipse with axes 645.80 ± 5.68 km × 597.81 ± 12.74 km) and the visual geometric albedo (pV = 15.0 ± 1.6%). By combining our analyses of the occultation and the far-infrared data, we can

  18. The c2d Spitzer Spectroscopic Survey of Ices Around Low-mass Young Stellar Objects. IV. NH3 and CH3OH

    NASA Astrophysics Data System (ADS)

    Bottinelli, Sandrine; Boogert, A. C. Adwin; Bouwman, Jordy; Beckwith, Martha; van Dishoeck, Ewine F.; Öberg, Karin I.; Pontoppidan, Klaus M.; Linnartz, Harold; Blake, Geoffrey A.; Evans, Neal J., II; Lahuis, Fred

    2010-08-01

    NH3 and CH3OH are key molecules in astrochemical networks leading to the formation of more complex N- and O-bearing molecules, such as CH3CN and CH3OCH3. Despite a number of recent studies, little is known about their abundances in the solid state. This is particularly the case for low-mass protostars, for which only the launch of the Spitzer Space Telescope has permitted high-sensitivity observations of the ices around these objects. In this work, we investigate the ~8-10 μm region in the Spitzer IRS (InfraRed Spectrograph) spectra of 41 low-mass young stellar objects (YSOs). These data are part of a survey of interstellar ices in a sample of low-mass YSOs studied in earlier papers in this series. We used both an empirical and a local continuum method to correct for the contribution from the 10 μm silicate absorption in the recorded spectra. In addition, we conducted a systematic laboratory study of NH3- and CH3OH-containing ices to help interpret the astronomical spectra. We clearly detect a feature at ~9 μm in 24 low-mass YSOs. Within the uncertainty in continuum determination, we identify this feature with the NH3 ν2 umbrella mode and derive abundances with respect to water between ~2% and 15%. Simultaneously, we also revisited the case of CH3OH ice by studying the ν4 C-O stretch mode of this molecule at ~9.7 μm in 16 objects, yielding abundances consistent with those derived by Boogert et al. based on a simultaneous 9.75 and 3.53 μm data analysis. Our study indicates that NH3 is present primarily in H2O-rich ices, but that in some cases, such ices are insufficient to explain the observed narrow FWHM. The laboratory data point to CH3OH being in an almost pure methanol ice, or mixed mainly with CO or CO2, consistent with its formation through hydrogenation on grains. Finally, we use our derived NH3 abundances in combination with previously published abundances of other solid N-bearing species to find that up to 10%-20% of nitrogen is locked up in known

  19. The Effect of Broadband Soft X-Rays in SO2-Containing Ices: Implications on the Photochemistry of Ices toward Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Pilling, S.; Bergantini, A.

    2015-10-01

    We investigate the effects produced mainly by broadband soft X-rays up to 2 keV (plus fast (˜keV) photoelectrons and low-energy (˜eV) induced secondary electrons) in the ice mixtures containing H2O:CO2:NH3:SO2 (10:1:1:1) at two different temperatures (50 and 90 K). The experiments are an attempt to simulate the photochemical processes induced by energetic photons in SO2-containing ices present in cold environments in the ices surrounding young stellar objects (YSO) and in molecular clouds in the vicinity of star-forming regions, which are largely illuminated by soft X-rays. The measurements were performed using a high-vacuum portable chamber from the Laboratório de Astroquímica e Astrobiologia (LASA/UNIVAP) coupled to the spherical grating monochromator beamline at the Brazilian Synchrotron Light Source (LNLS) in Campinas, Brazil. In situ analyses were performed by a Fourier transform infrared spectrometer. Sample processing revealed the formation of several organic molecules, including nitriles, acids, and other compounds such as H2O2, H3O+, SO3, CO, and OCN-. The dissociation cross section of parental species was on the order of (2-7) × 10-18 cm2. The ice temperature does not seem to affect the stability of SO2 in the presence of X-rays. Formation cross sections of new species produced were also determined. Molecular half-lives at ices toward YSOs due to the presence of incoming soft X-rays were estimated. The low values obtained employing two different models of the radiation field of YSOs (TW Hydra and typical T-Tauri star) reinforce that soft X-rays are indeed a very efficient source of molecular dissociation in such environments.

  20. THE SPITZER SPACE TELESCOPE SURVEY OF THE ORION A AND B MOLECULAR CLOUDS. II. THE SPATIAL DISTRIBUTION AND DEMOGRAPHICS OF DUSTY YOUNG STELLAR OBJECTS

    SciTech Connect

    Megeath, S. T.; Kryukova, E.; Gutermuth, R.; Muzerolle, J.; Hora, J. L.; Myers, P. C.; Fazio, G. G.; Allen, L. E.; Flaherty, K.; Hartmann, L.; Pipher, J. L.; Stauffer, J.; Young, E. T.

    2016-01-15

    We analyze the spatial distribution of dusty young stellar objects (YSOs) identified in the Spitzer Survey of the Orion Molecular clouds, augmenting these data with Chandra X-ray observations to correct for incompleteness in dense clustered regions. We also devise a scheme to correct for spatially varying incompleteness when X-ray data are not available. The local surface densities of the YSOs range from 1 pc{sup −2} to over 10,000 pc{sup −2}, with protostars tending to be in higher density regions. This range of densities is similar to other surveyed molecular clouds with clusters, but broader than clouds without clusters. By identifying clusters and groups as continuous regions with surface densities ≥10 pc{sup −2}, we find that 59% of the YSOs are in the largest cluster, the Orion Nebula Cluster (ONC), while 13% of the YSOs are found in a distributed population. A lower fraction of protostars in the distributed population is evidence that it is somewhat older than the groups and clusters. An examination of the structural properties of the clusters and groups shows that the peak surface densities of the clusters increase approximately linearly with the number of members. Furthermore, all clusters with more than 70 members exhibit asymmetric and/or highly elongated structures. The ONC becomes azimuthally symmetric in the inner 0.1 pc, suggesting that the cluster is only ∼2 Myr in age. We find that the star formation efficiency (SFE) of the Orion B cloud is unusually low, and that the SFEs of individual groups and clusters are an order of magnitude higher than those of the clouds. Finally, we discuss the relationship between the young low mass stars in the Orion clouds and the Orion OB 1 association, and we determine upper limits to the fraction of disks that may be affected by UV radiation from OB stars or dynamical interactions in dense, clustered regions.

  1. Deriving the Extinction to Young Stellar Objects using [Fe II] Near-infrared Emission Lines: Prescriptions from GIANO High-resolution Spectra

    NASA Astrophysics Data System (ADS)

    Pecchioli, T.; Sanna, N.; Massi, F.; Oliva, E.

    2016-07-01

    The near-infrared (NIR) emission lines of Fe+ at 1.257, 1.321, and 1.644 μm share the same upper level; their ratios can then be exploited to derive the extinction to a line emitting region once the relevant spontaneous emission coefficients are known. This is commonly done, normally from low-resolution spectra, in observations of shocked gas from jets driven by Young Stellar Objects. In this paper we review this method, provide the relevant equations, and test it by analyzing high-resolution (R ∼ 50,000) NIR spectra of two young stars, namely the Herbig Be star HD 200775 and the Be star V1478 Cyg, which exhibit intense emission lines. The spectra were obtained with the new GIANO echelle spectrograph at the Telescopio Nazionale Galileo. Notably, the high-resolution spectra allowed checking the effects of overlapping telluric absorption lines. A set of various determinations of the Einstein coefficients are compared to show how much the available computations affect extinction derivation. The most recently obtained values are probably good enough to allow reddening determination within 1 visual mag of accuracy. Furthermore, we show that [Fe ii] line ratios from low-resolution pure emission-line spectra in general are likely to be in error due to the impossibility to properly account for telluric absorption lines. If low-resolution spectra are used for reddening determinations, we advice that the ratio 1.644/1.257, rather than 1.644/1.321, should be used, being less affected by the effects of telluric absorption lines.

  2. The Spitzer Space Telescope Survey of the Orion A and B Molecular Clouds. II. The Spatial Distribution and Demographics of Dusty Young Stellar Objects

    NASA Astrophysics Data System (ADS)

    Megeath, S. T.; Gutermuth, R.; Muzerolle, J.; Kryukova, E.; Hora, J. L.; Allen, L. E.; Flaherty, K.; Hartmann, L.; Myers, P. C.; Pipher, J. L.; Stauffer, J.; Young, E. T.; Fazio, G. G.

    2016-01-01

    We analyze the spatial distribution of dusty young stellar objects (YSOs) identified in the Spitzer Survey of the Orion Molecular clouds, augmenting these data with Chandra X-ray observations to correct for incompleteness in dense clustered regions. We also devise a scheme to correct for spatially varying incompleteness when X-ray data are not available. The local surface densities of the YSOs range from 1 pc-2 to over 10,000 pc-2, with protostars tending to be in higher density regions. This range of densities is similar to other surveyed molecular clouds with clusters, but broader than clouds without clusters. By identifying clusters and groups as continuous regions with surface densities ≥10 pc-2, we find that 59% of the YSOs are in the largest cluster, the Orion Nebula Cluster (ONC), while 13% of the YSOs are found in a distributed population. A lower fraction of protostars in the distributed population is evidence that it is somewhat older than the groups and clusters. An examination of the structural properties of the clusters and groups shows that the peak surface densities of the clusters increase approximately linearly with the number of members. Furthermore, all clusters with more than 70 members exhibit asymmetric and/or highly elongated structures. The ONC becomes azimuthally symmetric in the inner 0.1 pc, suggesting that the cluster is only ˜2 Myr in age. We find that the star formation efficiency (SFE) of the Orion B cloud is unusually low, and that the SFEs of individual groups and clusters are an order of magnitude higher than those of the clouds. Finally, we discuss the relationship between the young low mass stars in the Orion clouds and the Orion OB 1 association, and we determine upper limits to the fraction of disks that may be affected by UV radiation from OB stars or dynamical interactions in dense, clustered regions.

  3. THE HIGH A{sub V} Quasar Survey: Reddened Quasi-Stellar Objects selected from optical/near-infrared photometry. II

    SciTech Connect

    Krogager, J.-K.; Fynbo, J. P. U.; Vestergaard, M.; Geier, S.; Venemans, B. P.; Ledoux, C.; Møller, P.; Noterdaeme, P.; Kangas, T.; Pursimo, T.; Smirnova, O.; Saturni, F. G.

    2015-03-15

    Quasi-stellar objects (QSOs) whose spectral energy distributions (SEDs) are reddened by dust either in their host galaxies or in intervening absorber galaxies are to a large degree missed by optical color selection criteria like the ones used by the Sloan Digital Sky Survey (SDSS). To overcome this bias against red QSOs, we employ a combined optical and near-infrared (near-IR) color selection. In this paper, we present a spectroscopic follow-up campaign of a sample of red candidate QSOs which were selected from the SDSS and the UKIRT Infrared Deep Sky Survey (UKIDSS). The spectroscopic data and SDSS/UKIDSS photometry are supplemented by mid-infrared photometry from the Wide-field Infrared Survey Explorer. In our sample of 159 candidates, 154 (97%) are confirmed to be QSOs. We use a statistical algorithm to identify sightlines with plausible intervening absorption systems and identify nine such cases assuming dust in the absorber similar to Large Magellanic Cloud sightlines. We find absorption systems toward 30 QSOs, 2 of which are consistent with the best-fit absorber redshift from the statistical modeling. Furthermore, we observe a broad range in SED properties of the QSOs as probed by the rest-frame 2 μm flux. We find QSOs with a strong excess as well as QSOs with a large deficit at rest-frame 2 μm relative to a QSO template. Potential solutions to these discrepancies are discussed. Overall, our study demonstrates the high efficiency of the optical/near-IR selection of red QSOs.

  4. Unveiling the near-infrared structure of the massive-young stellar object NGC 3603 IRS 9A* with sparse aperture masking and spectroastrometry

    NASA Astrophysics Data System (ADS)

    Sanchez-Bermudez, J.; Hummel, C. A.; Tuthill, P.; Alberdi, A.; Schödel, R.; Lacour, S.; Stanke, T.

    2016-04-01

    Context. Contemporary theory holds that massive stars gather mass during their initial phases via accreting disk-like structures. However, conclusive evidence for disks has remained elusive for most massive young objects. This is mainly due to significant observational challenges: objects are rare and located at great distances within dusty, highly opaque environments. Incisive studies, even targeting individual objects, are therefore relevant to the progression of the field. NGC 3603 IRS 9A* is a young massive stellar object that is still surrounded by an envelope of molecular gas for which previous mid-infrared observations with long-baseline interferometry have provided evidence of a plausible disk of 50 mas diameter at its core. Aims: This work aims at a comprehensive study of the physics and morphology of IRS 9A at near-infrared wavelengths. Methods: New sparse aperture-masking interferometry data, taken with the near-infrared camera NACO of the Very Large Telescope (VLT) at Ks and L' wavelengths, were analyzed together with archival high-resolution H2 and Brγ lines obtained with the cryogenic high-resolution infrared schelle spectrograph (CRIRES). Results: The trends in the calibrated visibilities at Ks and L'-bands suggest the presence of a partially resolved compact object with an angular size of ≤30 mas at the core of IRS 9A, together with the presence of over-resolved flux. The spectroastrometric signal of the H2 line, obtained from the CRIRES spectra, shows that this spectral feature proceeds from the large-scale extended emission (~300 mas), while the Brγ line appears to be formed at the core of the object (~20 mas). To better understand the physics that drive IRS 9A, we have performed continuum radiative transfer modeling. Our best model supports the existence of a compact disk with an angular diameter of 20 mas, together with an outer envelope of 1'' exhibiting a polar cavity with an opening angle of ~30°. This model reproduces the MIR morphology

  5. A high-NA solid immersion objective for imaging a Blue-ray disc and investigating subsurface damage

    NASA Astrophysics Data System (ADS)

    Densmore, Victor; Kim, Young Sik; Milster, Tom; Watson, Matt; Kwok, Dolaphine

    2014-09-01

    Nano-scale resolution in miniature optical systems has been realized in the optical data storage industry. Numerical apertures greater than unity have been achieved in by utilizing the high index material of a hemispherical Solid Immersion Lens (SIL), which increases the resolution of the backing objective by a factor that is related to the refractive index of the SIL. In this research, a custom Hyper-Blu-Disc (HBD) NA=1.4 SIL objective is utilized for high-fidelity readout of data pits beneath a 100μm thick cover layer on an optical Blu-Ray Disc. If realized commercially, the increase in data density could be 3X today's Blu-Ray technology. A distinct difference between this work and other work with SILs in optical data storage is the relatively thick cover layer of 100μm. Recently, there has been interest in discovering new ways to apply the technology and methods used in optical data storage for other means. The inherent design of the HBD objective to image through a shallow layer of dielectric material may lend itself to be used as an effective means for characterizing subsurface damage in optical materials. This research will furthermore investigate the HBD objective as a means of detecting subsurface damage.

  6. Stellar Dynamos

    NASA Astrophysics Data System (ADS)

    Charbonneau, Paul

    This chapter steps finally away from the sun and towards the stars, the idea being to apply the physical insight gained so far to see how much of stellar magnetism can be understood in terms of dynamo action. Dynamo action in the convective core of massive main-sequence stars is first considered and shown viable. For intermediate-mass main-sequence stars the fossil field hypothesis will carry the day, although possible dynamo alternatives are also briefly discussed. The extension of the solar dynamo models investigated in Chap. 3 (10.1007/978-3-642-32093-4_3) to other solar-type stars will first take us through an important detour in first having to understand rotational evolution in response to angular momentum loss in a magnetized wind. Dynamo action in fully convective stars comes next, and the chapter closes with an overview of the situation for pre- and post-main-sequence stars and compact objects, leading finally to the magnetic fields of galaxies and beyond.

  7. Surface Abundances of NGC 188 Blue Stragglers as a Clue to Formation History

    NASA Astrophysics Data System (ADS)

    Milliman, Katelyn; Mathieu, R. D.; Schuler, S. C.

    2013-06-01

    Studies of the old open cluster NGC 188 have discovered a blue straggler binary frequency nearly three times the binary fraction of main-sequence stars, and a secondary mass distribution peaking at 0.5 solar masses for long-period blue stragglers. These features suggest that asymptotic giant branch mass transfer in binary stars dominates the production of blue stragglers in open clusters. However, sophisticated N-body simulations point toward stellar collisions being the dominant formation process. These two mechanisms are expected to result in measurably different blue straggler surface abundances. Blue stragglers resulting from stellar collisions of main-sequence stars are predicted to retain roughly the same surface abundance as the more massive star in the collision. On the other hand, blue stragglers formed by mass transfer from an evolved companion will have a surface abundance altered by the nucleosynthesis that occurred within the evolved donor star. We present first results of a surface abundance study of 21 blue stragglers in NGC 188 using the Hydra multi-object spectrograph on the WIYN 3.5 m telescope. These results include measurements of barium, oxygen, and carbon and offer a clue to the formation history of blue stragglers in open clusters. We gratefully acknowledge funding from the National Science Foundation under grant AST-0908082.

  8. Are forward bending of the trunk and low back pain associated among Danish blue-collar workers? A cross-sectional field study based on objective measures.

    PubMed

    Villumsen, Morten; Samani, Afshin; Jørgensen, Marie Birk; Gupta, Nidhi; Madeleine, Pascal; Holtermann, Andreas

    2015-01-01

    The aim of this cross-sectional study was to investigate the association between the duration of objectively measured forward bending of the trunk and low back pain (LBP) intensity among 198 Danish blue-collar workers (male = 115; female = 83). The duration of forward bending of ≥ 30°, ≥ 60° and ≥ 90° was divided into high (the highest tertile) and low-moderate (the remaining tertiles) categories. High (>5) and low ( ≤ 5) pain intensities were categorised from a self-reported 0-9 scale. Results of multi-adjusted logistic regressions indicated no significant positive associations between forward bending and LBP intensity. On the contrary, higher duration of forward bending of ≥ 30° was associated with lower LBP intensity during all day (OR = 0.40; 95% CI, 0.15-1.02; p = 0.05) and work (OR = 0.44; 95% CI, 0.17-1.15; p = 0.09). This indication of a negative association may be explained by fear-avoidance behaviour of the blue-collar worker, job crafting or healthy worker effect.

  9. Stellar chromospheres

    NASA Technical Reports Server (NTRS)

    Linsky, J. L.

    1980-01-01

    Developments in the understanding and use of chromospheric diagnostics are discussed with emphasis on the following aspects: (1) trends emerging from semiempirical models of single stars; (2) the validity of claims that theoretical models of chromospheres are becoming realistic; (3) the correlation between the widths of Ca 2 H and K line emission cores and stellar absolute luminosity extending over 15 magnitudes (Wilson-Bappu relation); and (4) the existence of systematic flow patterns in stellar chromospheres.

  10. THE EFFECT OF BROADBAND SOFT X-RAYS IN SO{sub 2}-CONTAINING ICES: IMPLICATIONS ON THE PHOTOCHEMISTRY OF ICES TOWARD YOUNG STELLAR OBJECTS

    SciTech Connect

    Pilling, S.; Bergantini, A.

    2015-10-01

    We investigate the effects produced mainly by broadband soft X-rays up to 2 keV (plus fast (∼keV) photoelectrons and low-energy (∼eV) induced secondary electrons) in the ice mixtures containing H{sub 2}O:CO{sub 2}:NH{sub 3}:SO{sub 2} (10:1:1:1) at two different temperatures (50 and 90 K). The experiments are an attempt to simulate the photochemical processes induced by energetic photons in SO{sub 2}-containing ices present in cold environments in the ices surrounding young stellar objects (YSO) and in molecular clouds in the vicinity of star-forming regions, which are largely illuminated by soft X-rays. The measurements were performed using a high-vacuum portable chamber from the Laboratório de Astroquímica e Astrobiologia (LASA/UNIVAP) coupled to the spherical grating monochromator beamline at the Brazilian Synchrotron Light Source (LNLS) in Campinas, Brazil. In situ analyses were performed by a Fourier transform infrared spectrometer. Sample processing revealed the formation of several organic molecules, including nitriles, acids, and other compounds such as H{sub 2}O{sub 2}, H{sub 3}O{sup +}, SO{sub 3}, CO, and OCN{sup −}. The dissociation cross section of parental species was on the order of (2–7) × 10{sup −18} cm{sup 2}. The ice temperature does not seem to affect the stability of SO{sub 2} in the presence of X-rays. Formation cross sections of new species  produced were also determined. Molecular half-lives at ices toward YSOs due to the presence of incoming soft X-rays were estimated. The low values obtained employing two different models of the radiation field of YSOs (TW Hydra and typical T-Tauri star) reinforce that soft X-rays are indeed a very efficient source of molecular dissociation in such environments.

  11. Census of Blue Stars in SDSS DR8

    NASA Astrophysics Data System (ADS)

    Scibelli, Samantha; Newberg, Heidi Jo; Carlin, Jeffrey L.; Yanny, Brian

    2014-12-01

    We present a census of the 12,060 spectra of blue objects ((g - r)0 < -0.25) in the Sloan Digital Sky Survey (SDSS) Data Release 8 (DR8). As part of the data release, all of the spectra were cross-correlated with 48 template spectra of stars, galaxies, and QSOs to determine the best match. We compared the blue spectra by eye to the templates assigned in SDSS DR8. 10,856 of the objects matched their assigned template, 170 could not be classified due to low signal-to-noise ratio, and 1034 were given new classifications. We identify 7458 DA white dwarfs, 1145 DB white dwarfs, 273 rarer white dwarfs (including carbon, DZ, DQ, and magnetic), 294 subdwarf O stars, 648 subdwarf B stars, 679 blue horizontal branch stars, 1026 blue stragglers, 13 cataclysmic variables, 129 white dwarf-M dwarf binaries, 36 objects with spectra similar to DO white dwarfs, 179, quasi-stellar objects (QSOs), and 10 galaxies. We provide two tables of these objects, sample spectra that match the templates, figures showing all of the spectra that were grouped by eye, and diagnostic plots that show the positions, colors, apparent magnitudes, proper motions, etc., for each classification. Future surveys will be able to use templates similar to stars in each of the classes we identify to automatically classify blue stars, including rare types.

  12. CENSUS OF BLUE STARS IN SDSS DR8

    SciTech Connect

    Scibelli, Samantha; Newberg, Heidi Jo; Carlin, Jeffrey L.; Yanny, Brian

    2015-01-01

    We present a census of the 12,060 spectra of blue objects ((g – r){sub 0} < –0.25) in the Sloan Digital Sky Survey (SDSS) Data Release 8 (DR8). As part of the data release, all of the spectra were cross-correlated with 48 template spectra of stars, galaxies, and QSOs to determine the best match. We compared the blue spectra by eye to the templates assigned in SDSS DR8. 10,856 of the objects matched their assigned template, 170 could not be classified due to low signal-to-noise ratio, and 1034 were given new classifications. We identify 7458 DA white dwarfs, 1145 DB white dwarfs, 273 rarer white dwarfs (including carbon, DZ, DQ, and magnetic), 294 subdwarf O stars, 648 subdwarf B stars, 679 blue horizontal branch stars, 1026 blue stragglers, 13 cataclysmic variables, 129 white dwarf-M dwarf binaries, 36 objects with spectra similar to DO white dwarfs, 179, quasi-stellar objects (QSOs), and 10 galaxies. We provide two tables of these objects, sample spectra that match the templates, figures showing all of the spectra that were grouped by eye, and diagnostic plots that show the positions, colors, apparent magnitudes, proper motions, etc., for each classification. Future surveys will be able to use templates similar to stars in each of the classes we identify to automatically classify blue stars, including rare types.

  13. Advanced stellarators

    NASA Astrophysics Data System (ADS)

    Schlüter, Arnulf

    1983-03-01

    Toroidal confinement of a plasma by an external magnetic field is not compatible with axisymmetry, in contrast to confinement by the pinch effect of induced electric currents as in a tokomak or by the reversed field pinch configuration. The existence of magnetic surfaces throughout the region in which grad p ≠ 0 is therefore not guaranteed in such configurations, though it is necessary for MHD-equilibrium when the lines of force possess a finite twist (or "rotational transform"). These twisted equilibria are called stellarators. The other type of external confinement requires all lines of force to be closed upon themselves and p to be function of the well defined quantity Q = φ d l/ B only. The resulting "bumpy" tori are sometimes also referred to as being M + S like. By discussing specific examples it is shown that stellarator configurations exist which retain as much as possible the properties of M + S like configurations, combine these with the magnetic well, and with an approximation to the isodynamic requirement of D. Palumbo. These so-called Advanced Stellarators shown an improvement in predicted particle confinement and beta-limit compared to the classical stellarators. They can also be viewed as forming a system of linked stabilized mirrors of small mirror ratio. These fields can be produced by modular coils. A prototype of such a configuration is being designed by the stellarator division of IPP under the name of Wendelstein VII-AS. Expected physical data and technical details of W VII-AS are given.

  14. Stellar Imager

    NASA Technical Reports Server (NTRS)

    Carpenter, Kenneth

    2007-01-01

    The Stellar Imager (SI) is one of NASA's "Vision Missions" - concepts for future, space-based, strategic missions that could enormously increase our capabilities for observing the Cosmos. SI is designed as a UV/Optical Interferometer which will enable 0.1 milli-arcsecond (mas) spectral imaging of stellar surfaces and, via asteroseismology, stellar interiors and of the Universe in general. The ultra-sharp images of the Stellar Imager will revolutionize our view of many dynamic astrophysical processes by transforming point sources into extended sources, and snapshots into evolving views. SI, with a characteristic angular resolution of 0.1 milli-arcseconds at 2000 Angstroms, represents an advance in image detail of several hundred times over that provided by the Hubble Space Telescope. The Stellar Imager will zoom in on what today-with few exceptions - we only know as point sources, revealing processes never before seen, thus providing a tool as fundamental to astrophysics as the microscope is to the study of life on Earth. SI's science focuses on the role of magnetism in the Universe, particularly on magnetic activity on the surfaces of stars like the Sun. It's prime goal is to enable long-term forecasting of solar activity and the space weather that it drives, in support of the Living With a Star program in the Exploration Era. SI will also revolutionize our understanding of the formation of planetary systems, of the habitability and climatology of distant planets, and of many magneto-hydrodynamically controlled processes in the Universe. Stellar Imager is included as a "Flagship and Landmark Discovery Mission" in the 2005 Sun Solar System Connection (SSSC) Roadmap and as a candidate for a "Pathways to Life Observatory" in the Exploration of the Universe Division (EUD) Roadmap (May, 2005) and as such is a candidate mission for the 2025-2030 timeframe. An artist's drawing of the current "baseline" concept for SI is presented.

  15. Using modern stellar observables to constrain stellar parameters and the physics of the stellar interior

    NASA Astrophysics Data System (ADS)

    van Saders, Jennifer L.

    2014-05-01

    stellar parameters and the physics of the interior. I examine how the acoustic signature of the location of the base of stellar convective envelopes can be used as an absolute abundance indicator, and describe a novel 3He-burning instability in low mass stars along with the observational signatures of such a process. Finally, I examine the manner in which stellar rotation, observed in a population of objects, can be used as a means to distinguish between different evolutionary states, masses, and ages. I emphasize that rotation periods can be used as age indicators (as often discussed in the literature), but that the interpretation of rotation periods must be made within the context of the full stellar population to arrive at accurate results.

  16. THE FIRST DETECTION OF BLUE STRAGGLER STARS IN THE MILKY WAY BULGE

    SciTech Connect

    Clarkson, W. I.; Rich, R. Michael; Sahu, Kailash C.; Anderson, Jay; Smith, T. Ed.; Brown, Thomas M.; Bond, Howard E.; Livio, Mario; Minniti, Dante; Zoccali, Manuela; Renzini, Alvio

    2011-07-01

    We report the first detections of Blue Straggler Stars (BSS) in the bulge of the Milky Way. Proper motions from extensive space-based observations along a single sight line allow us to separate a sufficiently clean and well-characterized bulge sample such that we are able to detect a small population of bulge objects in the region of the color-magnitude diagram commonly occupied by young objects and blue stragglers. Variability measurements of these objects clearly establish that a fraction of them are blue stragglers. Out of the 42 objects found in this region of the color-magnitude diagram, we estimate that at least 18 are genuine BSS. We normalize the BSS population by our estimate of the number of horizontal branch stars in the bulge in order to compare the bulge to other stellar systems. The BSS fraction is clearly discrepant from that found in stellar clusters. The blue straggler population of dwarf spheroidals remains a subject of debate; some authors claim an anticorrelation between the normalized blue straggler fraction and integrated light. If this trend is real, then the bulge may extend it by three orders of magnitude in mass. Conversely, we find that the genuinely young (<5 Gyr) population in the bulge, must be at most 3.4% under the most conservative scenario for the BSS population.

  17. Intermittent maser flare around the high-mass young stellar object G353.273 + 0.641 - II. Detection of a radio and molecular jet

    NASA Astrophysics Data System (ADS)

    Motogi, K.; Sorai, K.; Niinuma, K.; Sugiyama, K.; Honma, M.; Fujisawa, K.

    2013-01-01

    We report the first detection of a radio continuum and molecular jet associated with a dominant blue-shifted maser source, G353.273+0.641. A radio jet is extended 3000 au along the north-west-south-east (NW-SE) direction. H2O masers are found to be clustered in the root of a bipolar radio jet. A molecular jet is detected by thermal SiO ( \\upsilon = 0, J = 2-1) emission. The SiO spectrum is extremely wide ( - 120 to +87 km s- 1) and significantly blue-shift dominated, similar to the maser emission. The observed geometry and remarkable spectral similarity between H2O maser and SiO strongly suggest the existence of a maser-scale ( ˜ 340 au) molecular jet that is enclosed by the extended radio jet. We propose a disc-masking scenario as the origin of the strong blue-shift dominance, where an optically thick disc obscures a red-shifted lobe of a compact jet.

  18. Hydrodynamic stellar interactions in dense star clusters

    NASA Technical Reports Server (NTRS)

    Rasio, Frederic A.

    1993-01-01

    Highly detailed HST observations of globular-cluster cores and galactic nuclei motivate new theoretical studies of the violent dynamical processes which govern the evolution of these very dense stellar systems. These processes include close stellar encounters and direct physical collisions between stars. Such hydrodynamic stellar interactions are thought to explain the large populations of blue stragglers, millisecond pulsars, X-ray binaries, and other peculiar sources observed in globular clusters. Three-dimensional hydrodynamics techniques now make it possible to perform realistic numerical simulations of these interactions. The results, when combined with those of N-body simulations of stellar dynamics, should provide for the first time a realistic description of dense star clusters. Here I review briefly current theoretical work on hydrodynamic stellar interactions, emphasizing its relevance to recent observations.

  19. Properties of Open Clusters Containing Blue Stragglers

    NASA Astrophysics Data System (ADS)

    Lee, Hyun-Uk; Chang, Heon-Young

    2017-06-01

    The presence of blue stragglers pose challenges to standard stellar evolution theory, in the sense that explaining their presence demands a complex interplay between stellar evolution and cluster dynamics. In the meantime, mass transfer in binary systems and stellar collisions are widely studied as a blue straggler formation channel. We explore properties of the Galactic open clusters where blue stragglers are found, in attempting to estimate the relative importance of these two favored processes, by comparing them with those resulting from open clusters in which blue stragglers are absent as of now. Unlike previous studies which require a sophisticated process in understanding the implication of the results, this approach is straightforward and has resulted in a supplementary supporting evidence for the current view on the blue straggler formation mechanism. Our main findings are as follows: (1) Open clusters in which blue stragglers are present have a broader distribution with respect to the Z-axis pointing towards the North Galactic Pole than those in which blue stragglers are absent. The probability that two distributions with respect to the Z-axis are drawn from the same distribution is 0.2%. (2) Average values of log_{10}(t) of the clusters with blue stragglers and those without blue stragglers are 8.58 ± 0.232 and 7.52 ± 0.285, respectively. (3) The clusters with blue stragglers tend to be relatively redder than the others, and are distributed broader in colors. (4) The clusters with blue stragglers are likely brighter than those without blue stragglers. (5) Finally, blue stragglers seem to form in condensed clusters rather than simply dense clusters. Hence, we conclude that mass transfer in binaries seems to be a relatively important physical mechanism of the generation of blue stragglers in open clusters, provided they are sufficiently old.

  20. Extragalactic Stellar Spectroscopy

    NASA Astrophysics Data System (ADS)

    Lennon, D. J.; Smartt, S. J.; Dufton, P. L.; Herrero, A.; Kudritzki, R.-P.; Venn, K.; McCarthy, J.

    1999-09-01

    The advent of large 8-10m telescopes heralds a new age in stellar astronomy. It is now possible to carry out detailed spectroscopic observations at high resolution of the brightest stars of galaxies in the Local Group, and it is envisaged that intermediate resolution observations will be extended to stars in the nearest galaxy clusters such as Virgo and Fornax. For some years the authors have been carrying out the groundwork involved in identifying young massive supergiant stars in nearby resolved galaxies, with a view to performing follow-up detailed studies of selected samples. In this article we summarize the contribution that the William Herschel Telescope has made to this project, and further, show that even a 4.2m telescope with a blue sensitive, large format CCD at a good site with dependable sub-arcsecond seeing can make an important contribution to the detailed study of our nearest spiral neighbours M31 and M33.

  1. Radial velocities of blue stragglers in the old open cluster NGC 7789

    NASA Astrophysics Data System (ADS)

    Drilling, J. S.; Schoenberner, D.

    NGC 7789 is a populous, old galactic cluster with a large number of blue stragglers. In an attempt to determine the stellar parameters of as many of these objects as possible in order to unravel their origin, the brighter blue stragglers of NGC 7789 were observed with the 4-meter echelle spectrograph at Kitt Peak and the 2.2-meter coude spectrograph at Calar Alto. This paper reports on the determination of radial velocities from these high resolution spectra. The results are compared with the previous radial velocity studies of Strom and Strom (1970) and Stryker and Hrivnak (1984).

  2. [Maternity blues].

    PubMed

    Gonidakis, F

    2007-04-01

    Maternity blues is a transient change of mood that occurs mainly between the 1st and 10th day of puerpartum and is characterized by bursts of tears, mild depressive mood, anxiety and liability of mood. The frequency of maternity blues varies in different studies form 4% to 80%. A number of biological and psychosocial parameters have been studied in order to determine their correlation with maternity blues. The most well studied biological parameters are progesterone and cortizol although their relation with maternity blues has not yet been clearly defined. Stress and the emotional state of the woman during pregnancy as well as history of mood disorders or maternity blues in a previous birth are the psychosocial parameters that are more likely to correlate with the occurrence of maternity blues. Most of the authors suggest that information on maternity blues and reassurance of the woman are the best way to deal with maternity blues both on preventive and therapeutical basis.

  3. Stellar shrapnel

    NASA Image and Video Library

    2016-08-15

    Several thousand years ago, a star some 160 000 light-years away from us exploded, scattering stellar shrapnel across the sky. The aftermath of this energetic detonation is shown here in this striking image from the NASA/ESA Hubble Space Telescope’s Wide Field Camera 3. The exploding star was a white dwarf located in the Large Magellanic Cloud, one of our nearest neighbouring galaxies. Around 97% of stars within the Milky Way that are between a tenth and eight times the mass of the Sun are expected to end up as white dwarfs. These stars can face a number of different fates, one of which is to explode as supernovae, some of the brightest events ever observed in the Universe. If a white dwarf is part of a binary star system, it can siphon material from a close companion. After gobbling up more than it can handle — and swelling to approximately one and a half times the size of the Sun — the star becomes unstable and ignites as a Type Ia supernova. This was the case for the supernova remnant pictured here, which is known as DEM L71. It formed when a white dwarf reached the end of its life and ripped itself apart, ejecting a superheated cloud of debris in the process. Slamming into the surrounding interstellar gas, this stellar shrapnel gradually diffused into the separate fiery filaments of material seen scattered across this skyscape.

  4. Stellar cannibalism

    NASA Astrophysics Data System (ADS)

    Astronomers have obtained evidence that stars can literally swallow other stars, leading to the ejection of stellar material into space and the formation of extremely close pairs of stars, according to the National Science Foundation (NSF). The discovery supports theoretical predictions of the evolution of double stars.While studying the central stars of planetary nebulae—disk-shaped gas clouds that vaguely resemble planets—Albert D. Grauer of the University of Arkansas at Little Rock and Howard E. Bond of Louisiana State University at Baton Rouge found that several of these central stars are actually very close stellar pairs. Previously, it had been thought that the central star in a planetary nebula was a single star that expelled a gas cloud as it neared the end of its life. Their latest discovery, the central star of planetary nebula Abell 41, consists of a pair of stars that orbit each other in 2 hours and 43 minutes. The researchers also have found three other central star pairs that have orbital periods of between 11 and 16 hours.

  5. Modelling realistic horizontal branch morphologies and their impact on spectroscopic ages of unresolved stellar systems

    NASA Astrophysics Data System (ADS)

    Percival, Susan M.; Salaris, Maurizio

    2011-04-01

    The presence of an extended blue horizontal branch (HB) in a stellar population is known to affect the age inferred from spectral fitting to stellar population synthesis models. This is due to the hot blue component which increases the strength of the Balmer lines and can make an old population look spuriously young. However, most population synthesis models still rely on theoretical isochrones, which do not include realistic modelling of extended HBs. In this work, we create detailed models for a range of old simple stellar populations (SSPs), with metallicities ranging from [Fe/H]=-1.3 to solar, to create a variety of realistic HB morphologies, from extended red clumps, to extreme blue HBs. We achieve this by utilizing stellar tracks from the BaSTI data base and implementing a different mass-loss prescription for each SSP created. This includes setting an average mass and a Gaussian spread in masses of individual stars coming on to the zero-age HB for each model, and hence resulting in different HB morphologies. We find that, for each metallicity, there is some HB morphology which maximizes Hβ, making an underlying 14-Gyr population look ˜5-6 Gyr old for the low- and intermediate-metallicity cases, and as young as 2 Gyr in the case of the solar metallicity SSP. We explore whether there are any spectral indices capable of breaking the degeneracy between an old SSP with extended blue HB and a truly young or intermediate-age SSP, and find that the Ca II index of Rose and the strength of the Mg II doublet at 2800 Å are promising candidates, in combination with Hβ and other metallicity indicators, such as Mgb and Fe5406. We also run Monte Carlo simulations to investigate the level of statistical fluctuations in the spectra of typical stellar clusters. We find that fluctuations in spectral indices are significant even for average to large globular clusters and that various spectral indices are affected in different ways, which has implications for full

  6. STELLARATOR INJECTOR

    DOEpatents

    Post, R.F.

    1962-09-01

    A method and means are described for injecting energetic neutral atoms or molecular ions into dense magnetically collimated plasma columns of stellarators and the like in such a manner that the atoms or ions are able to significantly penetrate the column before being ionized by collision with the plasma constituent particles. Penetration of the plasma column by the neutral atoms or molecular ions is facilitated by superposition of two closely spaced magnetic mirrors on the plasma confinement field. The mirrors are moved apart to magnetically sweep plasma from a region between the mirrors and establish a relatively low plasma density therein. By virture of the low density, neutral atoms or molecular ions injected into the region significantly penetrate the plasma column before being ionized. Thereafter, the mirrors are diminished to permit the injected material to admix with the plasma in the remainder of the column. (AEC)

  7. A Study of the Stellar Population in Selected SO Galaxies

    NASA Technical Reports Server (NTRS)

    Perez, M.; Danks, A.

    1997-01-01

    The goal of this program was to observe at least two SO galaxies with abnormal colors in the blue and clear optical signatures of dust and gas. The galaxies NGC 2217 and NGC 1808 were observed at least in one of the IUE cameras (1200-200 and 2000-3200 A) during the 13th episode, using the 4 US1 shifts assigned to this program. The galaxy NGC 2217 had been found to be part of a subgroup of SO galaxies with external gas rotating in retrograde motion with respect to the stars. This galaxy is a face-on object with indications of large amount of gas, quite rare for a SO galaxy. We observed this object on three different occasions with IUE at different positions of the large aperture (spacecraft roll angle) with respect to the nuclear region. These exposures allowed us to take full advantage of the spatial resolution of IUE by mapping nuclear and bulge region of this galaxy. We found that the data point to a marginally earlier stellar population toward the central region. The UV light as a whole is dominated by a late-type stellar population of principally G and K stars. The almost face-on view of this galaxy appears optically thick to UV light. It is conceivable that in analogy to out own Galaxy, the stellar populations weakly detected in NGC 2217, are mostly halo and late-type stars in the center with an increasing contribution of dust and early stellar populations (so far undetected) as we move outward along the faint spiral arms. This result is contrary to our initial expectation, since the counterrotating gas does not appear to be enhancing star formation in this galaxy. Even more interesting were the observations of NGC 1808; galaxy which has been classified, with a handful of other objects, both as a starburst and Seyfert galaxy. Attachment: 'The White-Dwarf Companions of 56 Persei and HR 3643.'

  8. Blue Note

    ScienceCinema

    Murray Gibson

    2016-07-12

    Argonne's Murray Gibson is a physicist whose life's work includes finding patterns among atoms. The love of distinguishing patterns also drives Gibson as a musician and Blues enthusiast."Blue" notes are very harmonic notes that are missing from the equal temperament scale.The techniques of piano blues and jazz represent the melding of African and Western music into something totally new and exciting.

  9. Blue Note

    SciTech Connect

    Murray Gibson

    2007-04-27

    Argonne's Murray Gibson is a physicist whose life's work includes finding patterns among atoms. The love of distinguishing patterns also drives Gibson as a musician and Blues enthusiast."Blue" notes are very harmonic notes that are missing from the equal temperament scale.The techniques of piano blues and jazz represent the melding of African and Western music into something totally new and exciting.

  10. Chaotic pulsations in stellar models

    SciTech Connect

    Buchler, J.R. )

    1990-12-01

    The irregular behavior of large-amplitude pulsating stars undergoing radial oscillations is examined theoretically, with a focus on hydrodynamic simulations of the W Virginis population II Cepheids (stars which show both regular and RV Tau characteristics). Sequences of models are constructed as one-parameter families (with luminosity, mass, and composition fixed and Teff as the control parameter) and analyzed to derive a systematic map of the bifurcation set; i.e., of the possible types of pulsations. The results are presented graphically, and it is shown that both cascades of period doubling (via destabilization of an overtone through a half-integer-type resonance) and tangent bifurcation are possible routes to chaos in these systems, depending on the stellar parameters. The general robustness of the chaotic behavior and the existence of a 'chaotic blue edge' in stellar-parameter space are demonstrated. 55 refs.

  11. Trends of stellar entropy along stellar evolution

    NASA Astrophysics Data System (ADS)

    de Avellar, Guilherme Bronzato, Marcio; Alvares de Souza, Rodrigo; Horvath, Jorge Ernesto

    2016-02-01

    This paper is devoted to discussing the difference in the thermodynamic entropy budget per baryon in each type of stellar object found in the Universe. We track and discuss the actual decrease of the stored baryonic thermodynamic entropy from the most primitive molecular cloud up to the final fate of matter in black holes, passing through evolved states of matter as found in white dwarfs and neutron stars. We then discuss the case of actual stars with different masses throughout their evolution, clarifying the role of the virial equilibrium condition for the decrease in entropy and related issues. Finally, we discuss the role of gravity in driving the composition and the structural changes of stars with different Main Sequence masses during their evolution up to the final product. Particularly, we discuss the entropy of a black hole in this context arguing that the dramatic increase in its entropy, differently from the other cases, is due to the gravitational field itself.

  12. Stellar Snowflake Cluster

    NASA Technical Reports Server (NTRS)

    2005-01-01

    from the same cloud. The blue dots sprinkled across the image represent older Milky Way stars at various distances along this line of sight. This image is a five-channel, false-color composite, showing emission from wavelengths of 3.6 and 4.5 microns (blue), 5.8 microns (cyan), 8 microns (green), and 24 microns (red).

    The top right (fig. 2) image from the infrared array camera show that the nebula is still actively forming stars. The wisps of red (represented as green in the combined image) are organic molecules mixed with dust, which has been illuminated by nearby star formation. The infrared array camera picture is a four-channel, false-color composite, showing emission from wavelengths of 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8.0 microns (red).

    The bottom right image (fig. 3) from the multiband imaging photometer shows the colder dust of the nebula and unwraps the youngest stellar babies from their dusty covering. This is a false-color image showing emission at 24 microns (red).

  13. Stellar Snowflake Cluster

    NASA Technical Reports Server (NTRS)

    2005-01-01

    from the same cloud. The blue dots sprinkled across the image represent older Milky Way stars at various distances along this line of sight. This image is a five-channel, false-color composite, showing emission from wavelengths of 3.6 and 4.5 microns (blue), 5.8 microns (cyan), 8 microns (green), and 24 microns (red).

    The top right (fig. 2) image from the infrared array camera show that the nebula is still actively forming stars. The wisps of red (represented as green in the combined image) are organic molecules mixed with dust, which has been illuminated by nearby star formation. The infrared array camera picture is a four-channel, false-color composite, showing emission from wavelengths of 3.6 microns (blue), 4.5 microns (green), 5.8 microns (orange) and 8.0 microns (red).

    The bottom right image (fig. 3) from the multiband imaging photometer shows the colder dust of the nebula and unwraps the youngest stellar babies from their dusty covering. This is a false-color image showing emission at 24 microns (red).

  14. Blue bubble in Carina

    NASA Image and Video Library

    2016-02-22

    Sparkling at the centre of this beautiful NASA/ESA Hubble Space Telescope image is a Wolf–Rayet star known as WR 31a, located about 30 000 light-years away in the constellation of Carina (The Keel). The distinctive blue bubble appearing to encircle WR 31a, and its uncatalogued stellar sidekick, is a Wolf–Rayet nebula — an interstellar cloud of dust, hydrogen, helium and other gases. Created when speedy stellar winds interact with the outer layers of hydrogen ejected by Wolf–Rayet stars, these nebulae are frequently ring-shaped or spherical. The bubble — estimated to have formed around 20 000 years ago — is expanding at a rate of around 220 000 kilometres per hour! Unfortunately, the lifecycle of a Wolf–Rayet star is only a few hundred thousand years — the blink of an eye in cosmic terms. Despite beginning life with a mass at least 20 times that of the Sun, Wolf–Rayet stars typically lose half their mass in less than 100 000 years. And WR 31a is no exception to this case. It will, therefore, eventually end its life as a spectacular supernova, and the stellar material expelled from its explosion will later nourish a new generation of stars and planets.

  15. Stellar Ro

    NASA Astrophysics Data System (ADS)

    Featherstone, Nicholas

    2017-05-01

    Our understanding of the interior dynamics that give rise to a stellar dynamo draws heavily from investigations of similar dynamics in the solar context. Unfortunately, an outstanding gap persists in solar dynamo theory. Convection, an indispensable component of the dynamo, occurs in the midst of rotation, and yet we know little about how the influence of that rotation manifests across the broad range of convective scales present in the Sun. We are nevertheless well aware that the interaction of rotation and convection profoundly impacts many aspects of the dynamo, including the meridional circulation, the differential rotation, and the helicity of turbulent EMF. The rotational constraint felt by solar convection ultimately hinges on the characteristic amplitude of deep convective flow speeds, and such flows are difficult to measure helioseismically. Those measurements of deep convective power which do exist disagree by orders of magnitude, and until this disagreement is resolved, we are left with the results of models and those less ambiguous measurements derived from surface observations of solar convection. I will present numerical results from a series of nonrotating and rotating convection simulations conducted in full 3-D spherical geometry. This presentation will focus on how convective spectra differ between the rotating and non-rotating models and how that behavior changes as simulations are pushed toward more turbulent and/or more rotationally-constrained regimes. I will discuss how the surface signature of rotationally-constrained interior convection might naturally lead to observable signatures in the surface convective pattern, such as supergranulation and a dearth of giant cells.

  16. RESOLVING THE DYNAMICAL MASS OF A z {approx} 1.3 QUASI-STELLAR OBJECT HOST GALAXY USING SINFONI AND LASER GUIDE STAR ASSISTED ADAPTIVE OPTICS

    SciTech Connect

    Inskip, K. J.; Jahnke, K.; Rix, H.-W.; Van de Ven, G.

    2011-10-01

    Recent studies of the tight scaling relations between the masses of supermassive black holes (BHs) and their host galaxies have suggested that in the past BHs constituted a larger fraction of their host galaxies' mass. However, these arguments are limited by selection effects and difficulties in determining robust host galaxy masses at high redshifts. Here we report the first results of a new, complementary diagnostic route: we directly determine a dynamical host galaxy mass for the z = 1.3 luminous quasar J090543.56+043347.3 through high spatial resolution (0.''47, 4 kpc FWHM) observations of the host galaxy gas kinematics over 30 x 40 kpc using the European Southern Observatory/Very Large Telescope/SINFONI with laser guide star adaptive optics. Combining our result of M{sub dyn} = 2.05{sup +1.68}{sub -0.74} x 10{sup 11} M{sub sun} (within a radius 5.25 {+-} 1.05 kpc) with M{sub BH,MgII} = 9.02 {+-} 1.43 x 10{sup 8} M{sub sun}, M{sub BH,H{alpha}} = 2.83{sup +1.93}{sub -1.13} x 10{sup 8} M{sub sun}, we find that the ratio of BH mass to host galaxy dynamical mass for J090543.56+043347.3 matches the present-day relation for M{sub BH} versus M{sub Bulge,Dyn}, well within the IR scatter, and deviating at most by a factor of two from the mean. J090543.56+043347.3 displays clear signs of an ongoing tidal interaction and of spatially extended star formation at a rate of 50-100 M{sub sun} yr{sup -1}, above the cosmic average for a galaxy of this mass and redshift. We argue that its subsequent evolution may move J090543.56+043347.3 even closer to the z = 0 relation for M{sub BH} versus M{sub Bulge,Dyn}. Our results support the picture in which any substantive evolution in these relations must occur prior to z {approx} 1.3. Having demonstrated the power of this modeling approach, we are currently analyzing similar data on seven further objects to better constrain such evolution.

  17. Stellar Astrophysics for the Local Group

    NASA Astrophysics Data System (ADS)

    Aparicio, A.; Herrero, A.; Sánchez, F.

    2011-06-01

    1. Fundamentals of stellar evolution theory: understanding the HRD C. Chiosi; 2. Observations of the most luminous stars in local group galaxies P. Massey; 3. Quantitative spectroscopy of the brightest blue supergiant stars in galaxies R. P. Kudritzki; 4. Calibration of the extragalactic distance scale B. F. Madore and W. L. Freedman; 5. Dwarf galaxies G. S. Da Costa; 6. Resolved stellar populations of the luminous galaxies in the local group M. Mateo; 7. Chemical evolution of the ISM in nearby galaxies E. D. Skillman; 8. Populations of massive stars and the interstellar medium C. Leitherer.

  18. Detailed Analysis of Starburst and AGN Activity in Blue E/S0 Galaxies in RESOLVE

    NASA Astrophysics Data System (ADS)

    Bittner, Ashley; Snyder, Elaine M.; Kannappan, Sheila; Norman, Dara J.; Norris, Mark A.; Moffett, Amanda J.; Hoversten, Erik A.; Stark, David; RESOLVE Team

    2016-01-01

    We identify a population of ~120 blue E/S0 galaxies among the ~1350 galaxies that are targeted for spectroscopy and have measured morphologies in the highly complete REsolved Spectroscopy Of a Local Volume (RESOLVE) survey. Blue E/S0s are identified as being early type objects morphologically classified between E and S0/a that fall on the blue sequence. Most (~85%) of our blue E/S0s have stellar masses <10^10 M_sun. Using pPXF, we have measured the stellar velocity dispersions (sigma values) from high resolution 485 - 550 nm spectroscopy for ~15% of the blue E/S0 sample. Using three variations of the M_BH -- sigma relation, this kinematic subsample is estimated to typically host central black holes within the range log M_BH = 4-6 M_sun. Following up on previous suggestions of nuclear activity in the blue E/S0 population, we investigate nuclear starburst and/or AGN activity occurring within the full sample. Preliminary results from cross-checking known AGN catalogs with the blue E/S0 sample have revealed nuclear activity in ~20 of these galaxies based on heterogeneous criteria (BPT line ratio analysis, spectral line broadening, etc.), some of which may not entirely distinguish starburst from AGN activity. In an attempt to break the degeneracy between AGN and starburst activity, we perform detailed spectral analysis for a few of the galaxies with kinematic data. We also consider the viability of alternate AGN detection methods based on L_Edd estimates calculated from the M_BH estimates. This research has been supported by the National Science Foundation through the CAP REU Program (ACI-1156614) and the RESOLVE Survey (AST-0955368) as well as the National Space Grant College and Fellowship Program and the NC Space Grant Consortium.

  19. Devastated Stellar Neighborhood

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This image from NASA's Spitzer Space Telescope shows the nasty effects of living near a group of massive stars: radiation and winds from the massive stars (white spot in center) are blasting planet-making material away from stars like our sun. The planetary material can be seen as comet-like tails behind three stars near the center of the picture. The tails are pointing away from the massive stellar furnaces that are blowing them outward.

    The picture is the best example yet of multiple sun-like stars being stripped of their planet-making dust by massive stars.

    The sun-like stars are about two to three million years old, an age when planets are thought to be growing out of surrounding disks of dust and gas. Astronomers say the dust being blown from the stars is from their outer disks. This means that any Earth-like planets forming around the sun-like stars would be safe, while outer planets like Uranus might be nothing more than dust in the wind.

    This image shows a portion of the W5 star-forming region, located 6,500 light-years away in the constellation Cassiopeia. It is a composite of infrared data from Spitzer's infrared array camera and multiband imaging photometer. Light with a wavelength of 3.5 microns is blue, while light from the dust of 24 microns is orange-red.

  20. The status of blue straggler studies (II): observational properties

    NASA Astrophysics Data System (ADS)

    Xin, Yu; Deng, Li-Cai; Liang, Yan-Chun

    2006-09-01

    The obervational features of blue stragglers (BSs) show great differences among the different stellar systems, such as Galactic halo, open clusters, globular clusters, and dwarf galaxies. These differences reveal the distinctive formation of BSs and the physical conditions of the systems and their stellar populations. Therefore, studying the observational properties of BSs could be an effective method for studying the formation mechanisms of BSs, the evolution of single stars and binary systems, and the dynamical evolution of stellar systems.

  1. Blue Laser.

    DTIC Science & Technology

    1985-12-01

    HOLLOW CATHODE LASER FABRICATION 13 4. EXPERIENCE WITH THE BLUE LASER 18 4.1 Operational and Processing Experience 18 4.2 Performance Testing 20 5...34 -. - . •. SECTION 3 BLUE HOLLOW CATHODE LASER FABRICATION This section presents an overview of the steps taken in creating a HCL. There is...to the laser assembly. These steps can actually be considered as the final steps in laser fabrication because some of them involve adding various

  2. The stellar population in the core of M15

    NASA Technical Reports Server (NTRS)

    De Marchi, Guido; Paresce, Francesco

    1994-01-01

    The inner core of the globular cluster M15 within approximately 2 sec of the geometrical center has been explored with high-resolution images taken through several broad-band UV filter with the Faint Object Camera (FOC) on board the Hubble Space Telescope (HST). Approximately 210 stars in this region down to a 5 sigma detection limit of m(sub 220) = 21.5 were reliably identified and located on a UV - U color magnitude diagram for the first time. A majority of stars (about 70% of the total) observed this way lie above the expected main-sequence turn-off of this cluster and below the sparsely populated horizontal branch. The extension of the main sequence above the turn-off separates this population in two roughly equal components situated to the right and left of this line. Most of the former must be classical blue stragglers while the rest belong to a new, as yet unidentified, population of very blue stars. Possibilities include, but are not restricted to, well-mixed single stars, subdwarfs, and helium white dwarfs. Similar objects are also found just outside the core out to approximately 6 sec from the center, but the brighter, presumably more massive ones, are sharply confined to the core itself. The measured excess of bright blue stars and the relative deficiency of bright red giants in the core are consistent with the blue inward color gradient measured from the ground and imply that dynamical evolution can significantly affect the stellar population in the very dense central regions of a high-concentration globular cluster like M15.

  3. GRAVITATIONAL WAVES FROM STELLAR COLLAPSE

    SciTech Connect

    C. L. FRYER

    2001-01-01

    Stellar core-collapse plays an important role in nearly all facets of astronomy: cosmology (as standard candles), formation of compact objects, nucleosynthesis and energy deposition in galaxies. In addition, they release energy in powerful explosions of light over a range of energies, neutrinos, and the subject of this meeting, gravitational waves. Because of this broad range of importance, astronomers have discovered a number of constraints which can be used to help them understand the importance of stellar core-collapse as gravitational wave sources.

  4. Stellar Evolution

    NASA Astrophysics Data System (ADS)

    Christensen-Dalsgaard, J.; Murdin, P.

    2002-01-01

    Stars evolve because they lose energy through radiation from their hot surfaces. As a result, there is a general tendency for the star to contract under gravity. This is partly stopped by the release of energy from nuclear reactions. However, once the nuclear fuel is exhausted, gravity gets the upper hand and the star ends its life as a compact object: a white dwarf, a neutron star or a black hol...

  5. Stellar metallicity of the extended disk and distance of the spiral galaxy NGC 3621

    SciTech Connect

    Kudritzki, Rolf-Peter; Bresolin, Fabio; Hosek, Matthew W. Jr.; Urbaneja, Miguel A.; Przybilla, Norbert E-mail: bresolin@ifa.hawaii.edu E-mail: Miguel.Urbaneja-Perez@uibk.ac.at

    2014-06-10

    Low resolution (∼4.5 Å) ESO VLT/FORS spectra of blue supergiant stars are analyzed to determine stellar metallicities (based on elements such as iron, titanium, and magnesium) in the extended disk of the spiral galaxy, NGC 3621. Mildly subsolar metallicity (–0.30 dex) is found for the outer objects beyond 7 kpc, independent of galactocentric radius and compatible with the absence of a metallicity gradient, confirming the results of a recent investigation of interstellar medium H II region gas oxygen abundances. The stellar metallicities are slightly higher than those from the H II regions when based on measurements of the weak forbidden auroral oxygen line at 4363 Å but lower than the ones obtained with the R {sub 23} strong line method. It is shown that the present level of metallicity in the extended disk cannot be the result of chemical evolution over the age of the disk with the present rate of in situ star formation. Additional mechanisms must be involved. In addition to metallicity, stellar effective temperatures, gravities, interstellar reddening, and bolometric magnitudes are determined. After the application of individual reddening corrections for each target, the flux-weighted gravity-luminosity relationship of blue supergiant stars is used to obtain a distance modulus of 29.07 ± 0.09 mag (distance D = 6.52 ± 0.28 Mpc). This new distance is discussed in relation to Cepheid and the tip of the red giant branch distances.

  6. The Evolution of Stellar Populations

    NASA Astrophysics Data System (ADS)

    DÍaz, Angeles I.; Hardy, Eduardo

    We summarize the discussion section on `Evolution of Stellar Populations' we led on May 27, 2000 in Granada, Spain, as part of the Euroconference on The Evolution of Galaxies. I- Observational Clues. The discussion was organized around two groups of topics. In the first, Population Synthesis, the accent was partially placed on the use of tools and techniques centered around the question of the unicity of the models, their sensitivity to input and the question of the age-metallicity degeneracy. In the second group, Stellar Systems a stronger accent was placed on astrophysical questions, although we included there the need for `truth tests' that apply spectral synthesis techniques to objects for which there is detailed a priori knowledge of their stellar populations. We also provide a partial comparison between the present knowledge of these topics and that which existed at the time of the Crete Conference of 1995.

  7. Spectroscopy of Blue Horizontal Branch Stars in the Globular Cluster NGC 6752

    NASA Astrophysics Data System (ADS)

    Cote, P.; Bolte, M.; Wilson, C. D.; Patel, K.

    1993-12-01

    Optical spectra (at 0.9 Angstroms /pixel dispersion) for 24 candidate blue horizontal branch stars in the globular cluster NGC 6752 have been obtained with ARGUS, the multi-object spectrograph on the CTIO 4.0m telescope. In addition to strong hydrogen lines, ten of the stars exhibit the 4471 Angstroms line of neutral helium. The equivalent widths of this line, the full widths of H_γ and H_δ at the 20% absorption level and BV CCD photometry have been used to derive effective temperatures, surface gravities and surface helium abundances for our program objects. With the exception of one star which has an exceptionally strong 4471 Angstroms line, all of the objects with detected helium are consistent with the rather low value of N(He)/N(H) =~ 0.008, suggesting that neither enhanced atmospheric helium nor increased stellar rotation is responsible for the extremely blue horizontal branch observed in this intermediate metallicity cluster.

  8. The HST quasar absorption line key project. 4: HST faint-object spectrograph and ground-based observations of the unusual low-redshift broad absorption-line quasi-stellar object PG 0043+039

    NASA Technical Reports Server (NTRS)

    Turnshek, David A.; Espey, Brian R.; Kopko, Michael, Jr.; Rauch, Michael; Weymann, Ray J.; Jannuzi, Buell T.; Boksenberg, Alec; Bergeron, Jacqueline; Hartig, George F.; Sargent, W. L. W.

    1994-01-01

    Hubble Space Telescope Faint Object Spectrograph (HST FOS) observations have shown that the spectrum of the low-redshift (z(sub em) approximately equal to 0.384) QSO PG 0043+039 exhibits weak broad absorption lines (BALs). The BALs were discovered during the course of UV spectrophotometry made for the HST Quasar Absorption Line Key Project. The HST data are analyzed along with ground-based optical and IUE spectrophotometry. The object is found to have a number of atypical properties relative to normal non-BAL QSOs. The observed continuum is atypical in the sense that it is much weaker than that of a normal optically selected QSO at rest wavelengths approximately less than 2200 A. Intrinsic reddening of E(B-V) approximately equal to 0.11 mag by dust similar to that found in the SMC at the redshift of PG 0043+039 conservatively accounts for the observed continuum shape moderately well. These observed characteristics are typical of low-ionization BAL QSOs, but convincing evidence for BALs due to low-ionization transitions of Mg II, Al III, Al II, or C II does not exist. Therefore, this object may be a misaligned BAL QSO having many of the characteristics of low-ionization BAL QSOs with the sight line passing through a putative dusty region, but evidently missing clouds of high enough column density to produce observable low-ionization BALs. If the intrinsic dust-extinction model is correct, the observations suggest that the dust is not confined to the presumably higher density, low-ionization BAL clouds, but that it has drifted to nearby high-ionization BAL regions. We also consider other possible mechanisms for producing the shape of the continuous energy distribution which cannot be ruled out. We compare the Fe II emission in PG 0043+039 with that in another Key Project QSO, NGC 2841-UB 3, which has optical Fe II emission comparable in strength to that in PG 0043+039, but has anomalously weak UV Fe II emission. In addition, from an analysis of UV and optical

  9. Advanced stellarator power plants

    SciTech Connect

    Miller, R.L.

    1994-07-01

    The stellarator is a class of helical/toroidal magnetic fusion devices. Recent international progress in stellarator power plant conceptual design is reviewed and comparisons in the areas of physics, engineering, and economics are made with recent tokamak design studies.

  10. Catalog of Non-Stellar Objects

    DTIC Science & Technology

    1977-09-12

    Nebula (a planetary nebulae), the Horsehead Nebula (a reflection-emission nebulosity), the Crab Nebula (a supernova remnant), the nebulosity around...Their motion is a combination of their revolution about the Sun as well as the motion of the Earth . Their magnitude variations are due to a...0) = !• The apparent magnitude of an asteroid with phase angle a, a distance r A.U. from the Sun, A A.U. from the Earth , with geometric albedo p

  11. VizieR Online Data Catalog: Census of blue stars in SDSS DR8 (Scibelli+, 2014)

    NASA Astrophysics Data System (ADS)

    Scibelli, S.; Newberg, H. J.; Carlin, J. L.; Yanny, B.

    2015-02-01

    We present a census of the 12060 spectra of blue objects ((g-r)0<-0.25) in the Sloan Digital Sky Survey (SDSS) Data Release 8 (DR8). As part of the data release, all of the spectra were cross-correlated with 48 template spectra of stars, galaxies, and QSOs to determine the best match. We compared the blue spectra by eye to the templates assigned in SDSS DR8. 10856 of the objects matched their assigned template, 170 could not be classified due to low signal-to-noise ratio, and 1034 were given new classifications. We identify 7458 DA white dwarfs, 1145 DB white dwarfs, 273 rarer white dwarfs (including carbon, DZ, DQ, and magnetic), 294 subdwarf O stars, 648 subdwarf B stars, 679 blue horizontal branch stars, 1026 blue stragglers, 13 cataclysmic variables, 129 white dwarf-M dwarf binaries, 36 objects with spectra similar to DO white dwarfs, 179, quasi-stellar objects (QSOs), and 10 galaxies. We provide two tables of these objects, sample spectra that match the templates, figures showing all of the spectra that were grouped by eye, and diagnostic plots that show the positions, colors, apparent magnitudes, proper motions, etc., for each classification. (3 data files).

  12. Stellarator status, 1989

    SciTech Connect

    Lyon, J.F. ); Grieger, G.; Rau, F. ); Iiyoshi, A. ); Navarro, A.P. ); Kovrizhnykh, L.M. . Inst. Obshchey Fiziki); Pavlichenko, O.S. (AN Ukrain

    1990-07-01

    The present status of stellarator experiments and recent progress in stellarator research (both experimental and theoretical) are reported by groups in the United States, the USSR, Japan, Australia, and the European Community (the Federal Republic of Germany and Spain). Experiments under construction and studies of large, next-generation stellarators are also described. 73 refs., 11 figs., 4 tabs.

  13. Hunting for Stellar Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Korhonen, Heidi; Vida, Krisztián; Leitzinger, Martin; Odert, Petra; Kovács, Orsolya Eszter

    2017-10-01

    Coronal mass ejections (CMEs) are explosive events that occur basically daily on the Sun. It is thought that these events play a crucial role in the angular momentum and mass loss of late-type stars, and also shape the environment in which planets form and live. Stellar CMEs can be detected in optical spectra in the Balmer lines, especially in Hα, as blue-shifted extra emission/absorption. To increase the detection probability one can monitor young open clusters, in which the stars are due to their youth still rapid rotators, and thus magnetically active and likely to exhibit a large number of CMEs. Using ESO facilities and the Nordic Optical Telescope we have obtained time series of multi-object spectroscopic observations of late-type stars in six open clusters with ages ranging from 15 Myrs to 300 Myrs. Additionally, we have studied archival data of numerous active stars. These observations will allow us to obtain information on the occurrence rate of CMEs in late-type stars with different ages and spectral types. Here we report on the preliminary outcome of our studies.

  14. Recent advances in modeling stellar interiors

    NASA Astrophysics Data System (ADS)

    Guzik, Joyce Ann

    2011-11-01

    Advances in stellar interior modeling are being driven by new data from large-scale surveys and high-precision photometric and spectroscopic observations. Here we focus on single stars in normal evolutionary phases; we will not discuss the many advances in modeling star formation, interacting binaries, supernovae, or neutron stars. We review briefly: (1) updates to input physics of stellar models; (2) progress in two and three-dimensional evolution and hydrodynamic models; (3) insights from oscillation data used to infer stellar interior structure and validate model predictions (asteroseismology). We close by highlighting a few outstanding problems, e.g., the driving mechanisms for hybrid γ Dor/ δ Sct star pulsations, the cause of giant eruptions seen in luminous blue variables such as η Car and P Cyg, and the solar abundance problem.

  15. Recent advances in modeling stellar interiors (u)

    SciTech Connect

    Guzik, Joyce Ann

    2010-01-01

    Advances in stellar interior modeling are being driven by new data from large-scale surveys and high-precision photometric and spectroscopic observations. Here we focus on single stars in normal evolutionary phases; we will not discuss the many advances in modeling star formation, interacting binaries, supernovae, or neutron stars. We review briefly: (1) updates to input physics of stellar models; (2) progress in two and three-dimensional evolution and hydrodynamic models; (3) insights from oscillation data used to infer stellar interior structure and validate model predictions (asteroseismology). We close by highlighting a few outstanding problems, e.g., the driving mechanisms for hybrid {gamma} Dor/{delta} Sct star pulsations, the cause of giant eruptions seen in luminous blue variables such as {eta} Car and P Cyg, and the solar abundance problem.

  16. The Hibernating Stellar Magnet

    NASA Astrophysics Data System (ADS)

    2008-09-01

    First Optically Active Magnetar-Candidate Discovered Astronomers have discovered a most bizarre celestial object that emitted 40 visible-light flashes before disappearing again. It is most likely to be a missing link in the family of neutron stars, the first case of an object with an amazingly powerful magnetic field that showed some brief, strong visible-light activity. Hibernating Stellar Magnet ESO PR Photo 31/08 The Hibernating Stellar Magnet This weird object initially misled its discoverers as it showed up as a gamma-ray burst, suggesting the death of a star in the distant Universe. But soon afterwards, it exhibited some unique behaviour that indicates its origin is much closer to us. After the initial gamma-ray pulse, there was a three-day period of activity during which 40 visible-light flares were observed, followed by a brief near-infrared flaring episode 11 days later, which was recorded by ESO's Very Large Telescope. Then the source became dormant again. "We are dealing with an object that has been hibernating for decades before entering a brief period of activity", explains Alberto J. Castro-Tirado, lead author of a paper in this week's issue of Nature. The most likely candidate for this mystery object is a 'magnetar' located in our own Milky Way galaxy, about 15 000 light-years away towards the constellation of Vulpecula, the Fox. Magnetars are young neutron stars with an ultra-strong magnetic field a billion billion times stronger than that of the Earth. "A magnetar would wipe the information from all credit cards on Earth from a distance halfway to the Moon," says co-author Antonio de Ugarte Postigo. "Magnetars remain quiescent for decades. It is likely that there is a considerable population in the Milky Way, although only about a dozen have been identified." Some scientists have noted that magnetars should be evolving towards a pleasant retirement as their magnetic fields decay, but no suitable source had been identified up to now as evidence for

  17. Weighing Stars: The Identification of an Evolved Blue Straggler Star in the Globular Cluster 47 Tucanae

    NASA Astrophysics Data System (ADS)

    Ferraro, F. R.; Lapenna, E.; Mucciarelli, A.; Lanzoni, B.; Dalessandro, E.; Pallanca, C.; Massari, D.

    2016-01-01

    Globular clusters are known to host peculiar objects named blue straggler stars (BSSs), significantly heavier than the normal stellar population. While these stars can be easily identified during their core hydrogen-burning phase, they are photometrically indistinguishable from their low-mass sisters in advanced stages of the subsequent evolution. A clear-cut identification of these objects would require the direct measurement of the stellar mass. We used the detailed comparison between chemical abundances derived from neutral and from ionized spectral lines as a powerful stellar “weighing device” to measure stellar mass and to identify an evolved BSS in 47 Tucanae. In particular, high-resolution spectra of three bright stars, located slightly above the level of the “canonical” horizontal branch (HB) sequence in the color-magnitude diagram of 47 Tucanae, have been obtained with the UVES spectrograph. The measurements of iron and titanium abundances performed separately from neutral and ionized lines reveal that two targets have stellar parameters fully consistent with those expected for low-mass post-HB objects, while for the other target the elemental ionization balance is obtained only by assuming a mass of ˜ 1.4{M}⊙ , which is significantly larger than the main sequence turn-off mass of the cluster (˜ 0.85{M}⊙ ). The comparison with theoretical stellar tracks suggests that this is a BSS descendant possibly experiencing its core helium-burning phase. The large applicability of the proposed method to most of the globular clusters in our Galaxy opens the possibility to initiate systematic searches for evolved BSSs, thus giving access to still unexplored phases of their evolution. Based on UVES-FLAMES observations collected under Program 193.D-0232.

  18. Blue gods, blue oil, and blue people.

    PubMed

    Fairbanks, V F

    1994-09-01

    Studies of the composition of coal tar, which began in Prussia in 1834, profoundly affected the economies of Germany, Great Britain, India, and the rest of the world, as well as medicine and surgery. Such effects include the collapse of the profits of the British indigo monopoly, the growth in economic power of Germany based on coal tar chemistry, and an economic crisis in India that led to more humane tax laws and, ultimately, the independence of India and the end of the British Empire. Additional consequences were the development of antiseptic surgery and the synthesis of a wide variety of useful drugs that have eradicated infections and alleviated pain. Many of these drugs, particularly the commonly used analgesics, sulfonamides, sulfones, and local anesthetics, are derivatives of aniline, originally called "blue oil" or "kyanol." Some of these aniline derivatives, however, have also caused aplastic anemia, agranulocytosis, and methemoglobinemia (that is, "blue people"). Exposure to aniline drugs, particularly when two or three aniline drugs are taken concurrently, seems to be the commonest cause of methemoglobinemia today.

  19. Models of Individual Blue Stragglers

    NASA Astrophysics Data System (ADS)

    Sills, Alison

    This chapter describes the current state of models of individual blue stragglers. Stellar collisions, binary mergers (or coalescence), and partial or ongoing mass transfer have all been studied in some detail. The products of stellar collisions retain memory of their parent stars and are not fully mixed. Very high initial rotation rates must be reduced by an unknown process to allow the stars to collapse to the main sequence. The more massive collision products have shorter lifetimes than normal stars of the same mass, while products between low mass stars are long-lived and look very much like normal stars of their mass. Mass transfer can result in a merger, or can produce another binary system with a blue straggler and the remnant of the original primary. The products of binary mass transfer cover a larger portion of the colour-magnitude diagram than collision products for two reasons: there are more possible configurations which produce blue stragglers, and there are differing contributions to the blended light of the system. The effects of rotation may be substantial in both collision and merger products, and could result in significant mixing unless angular momentum is lost shortly after the formation event. Surface abundances may provide ways to distinguish between the formation mechanisms, but care must be taken to model the various mixing mechanisms properly before drawing strong conclusions. Avenues for future work are outlined.

  20. THE SPITZER SPACE TELESCOPE SURVEY OF THE ORION A AND B MOLECULAR CLOUDS. I. A CENSUS OF DUSTY YOUNG STELLAR OBJECTS AND A STUDY OF THEIR MID-INFRARED VARIABILITY

    SciTech Connect

    Megeath, S. T.; Kryukova, E.; Gutermuth, R.; Muzerolle, J.; Flaherty, K.; Hora, J. L.; Myers, P. C.; Fazio, G. G.; Allen, L. E.; Hartmann, L.; Pipher, J. L.; Stauffer, J.; Young, E. T.

    2012-12-01

    We present a survey of the Orion A and B molecular clouds undertaken with the IRAC and MIPS instruments on board Spitzer. In total, five distinct fields were mapped, covering 9 deg{sup 2} in five mid-IR bands spanning 3-24 {mu}m. The survey includes the Orion Nebula Cluster, the Lynds 1641, 1630, and 1622 dark clouds, and the NGC 2023, 2024, 2068, and 2071 nebulae. These data are merged with the Two Micron All Sky Survey point source catalog to generate a catalog of eight-band photometry. We identify 3479 dusty young stellar objects (YSOs) in the Orion molecular clouds by searching for point sources with mid-IR colors indicative of reprocessed light from dusty disks or infalling envelopes. The YSOs are subsequently classified on the basis of their mid-IR colors and their spatial distributions are presented. We classify 2991 of the YSOs as pre-main-sequence stars with disks and 488 as likely protostars. Most of the sources were observed with IRAC in two to three epochs over six months; we search for variability between the epochs by looking for correlated variability in the 3.6 and 4.5 {mu}m bands. We find that 50% of the dusty YSOs show variability. The variations are typically small ({approx}0.2 mag) with the protostars showing a higher incidence of variability and larger variations. The observed correlations between the 3.6, 4.5, 5.8, and 8 {mu}m variability suggests that we are observing variations in the heating of the inner disk due to changes in the accretion luminosity or rotating accretion hot spots.

  1. Mg II ABSORPTION SYSTEMS WITH W{sub 0} >= 0.1 A FOR A RADIO SELECTED SAMPLE OF 77 QUASI-STELLAR OBJECTS AND THEIR ASSOCIATED MAGNETIC FIELDS AT HIGH REDSHIFT

    SciTech Connect

    Bernet, M. L.; Miniati, F.; Lilly, S. J. E-mail: fm@phys.ethz.c

    2010-03-01

    We present a catalog of Mg II absorption systems obtained from high-resolution Ultraviolet and Visual Echelle Spectrograph/VLT data of 77 quasi-stellar objects in the redshift range 0.6 < z < 2.0, and down to an equivalent width W{sub 0} >= 0.1 A. The statistical properties of our sample are found to be in agreement with those from the previous work in the literature. However, we point out that the previously observed increase with redshift of partial derivN/partial derivz for weak absorbers pertains exclusively to very weak absorbers with W{sub 0} < 0.1 A. Instead, partial derivN/partial derivz for absorbers with W{sub 0} in the range 0.1-0.3 A actually decreases with redshift, similar to the case of strong absorbers. We then use this catalog to extend our earlier analysis of the links between the Faraday rotation measure (RM) of the quasars and the presence of intervening Mg II absorbing systems in their spectra. In contrast to the case with strong Mg II absorption systems (W{sub 0} > 0.3 A), the weaker systems do not contribute significantly to the observed RM of the background quasars. This is possibly due to the higher impact parameters of the weak systems compared to strong ones, suggesting that the high column density magnetized material that is responsible for the Faraday rotation is located within about 50 kpc of the galaxies. Finally, we show that this result also rules out the possibility that some unexpected secondary correlation between the quasar redshift and its intrinsic RM is responsible for the association of high RM and strong intervening Mg II absorption that we have presented elsewhere, since this would have produced an equal effect for the weak absorption line systems, which exhibit a very similar distribution of quasar redshifts.

  2. The Spitzer Space Telescope Survey of the Orion A and B Molecular Clouds. I. A Census of Dusty Young Stellar Objects and a Study of Their Mid-infrared Variability

    NASA Astrophysics Data System (ADS)

    Megeath, S. T.; Gutermuth, R.; Muzerolle, J.; Kryukova, E.; Flaherty, K.; Hora, J. L.; Allen, L. E.; Hartmann, L.; Myers, P. C.; Pipher, J. L.; Stauffer, J.; Young, E. T.; Fazio, G. G.

    2012-12-01

    We present a survey of the Orion A and B molecular clouds undertaken with the IRAC and MIPS instruments on board Spitzer. In total, five distinct fields were mapped, covering 9 deg2 in five mid-IR bands spanning 3-24 μm. The survey includes the Orion Nebula Cluster, the Lynds 1641, 1630, and 1622 dark clouds, and the NGC 2023, 2024, 2068, and 2071 nebulae. These data are merged with the Two Micron All Sky Survey point source catalog to generate a catalog of eight-band photometry. We identify 3479 dusty young stellar objects (YSOs) in the Orion molecular clouds by searching for point sources with mid-IR colors indicative of reprocessed light from dusty disks or infalling envelopes. The YSOs are subsequently classified on the basis of their mid-IR colors and their spatial distributions are presented. We classify 2991 of the YSOs as pre-main-sequence stars with disks and 488 as likely protostars. Most of the sources were observed with IRAC in two to three epochs over six months; we search for variability between the epochs by looking for correlated variability in the 3.6 and 4.5 μm bands. We find that 50% of the dusty YSOs show variability. The variations are typically small (~0.2 mag) with the protostars showing a higher incidence of variability and larger variations. The observed correlations between the 3.6, 4.5, 5.8, and 8 μm variability suggests that we are observing variations in the heating of the inner disk due to changes in the accretion luminosity or rotating accretion hot spots.

  3. Virtual Observatory for stellar astronomy

    NASA Astrophysics Data System (ADS)

    Malkov, O.; Zolotukhin, I.

    2013-10-01

    The principal idea of the Virtual Observatory is to achieve real transparency for astronomical data, similar to transparency for all the world's documents in the World Wide Web. In the Virtual Observatory, all the world's astronomical data is available from one's desktop. All archives understand the same query language, can be accessed through a uniform interface, and diverse data can be analyzed with the same tools. In particular, facilities of the Virtual Observatory allow users to make a fast and correct analysis of objects from various surveys. It yields multi-photometry data on registered objects and makes it possible to determine stellar parameters. Methods of astronomical data analysis as well as their application to various areas of stellar astronomy are discussed in this paper.

  4. BLUE LUMINOUS STARS IN NEARBY GALAXIES-UIT 005: A POSSIBLE LINK TO THE LUMINOUS BLUE VARIABLE STAGE

    SciTech Connect

    Urbaneja, M. A.; Herrero, A.; Corral, L. J.; Meynet, G.

    2011-07-01

    A detailed study of the blue supergiant UIT 005 (B2-2.5Ia{sup +}) in M 33 is presented. The results of our quantitative spectral analysis indicate that the star is a very luminous (log L/L{sub sun} {approx} 5.9 dex) and massive (M {approx} 50 M{sub sun}) object, showing a very high nitrogen-to-oxygen ratio in its surface (N/O{approx}8, by mass). Based on the derived Mg and Si abundances, we argue that this high N/O ratio cannot be the result of an initial low O content due to its location on the disk of M 33, a galaxy known to present a steep metallicity gradient. In combination with the He abundance, the most plausible interpretation is that UIT 005 is in an advanced stage of evolution, showing in its surface N enrichment and O depletion resulting from mixing with CNO processed material from the stellar interior. A comparison with the predictions of current stellar evolutionary models indicates that there are significant discrepancies, in particular with regard to the degree of chemical processing, with the models predicting a much lower degree of O depletion than observed. At the same time, the mass-loss rate derived in our analysis is an order of magnitude lower than the values considered in the evolutionary calculations. Based on a study of the surrounding stellar population and the nearby cluster, NGC 588, using Hubble Space Telescope/WFPC2 photometry, we suggest that UIT 005 could be in fact a runaway star from this cluster. Regardless of its origin, the derived parameters place the star in a region of the Hertzsprung-Russell diagram where luminous blue variables (LBVs) are usually found, but we find no evidence supporting photometric or spectroscopic variability, except for small H{alpha} changes, otherwise observed in Galactic B-type supergiants. Whether UIT 005 is an LBV in a dormant state or a regular blue supergiant could not be discerned in this study. Subsequent monitoring would help us to improve our knowledge of the more massive stars, bridging the

  5. Blue Saturn

    NASA Image and Video Library

    2004-03-19

    Bands and spots in Saturn's atmosphere, including a dark band south of the equator with a scalloped border, are visible in this image from the Cassini-Huygens spacecraft. The narrow angle camera took the image in blue light on Feb. 29, 2004. The distance to Saturn was 59.9 million kilometers (37.2 million miles). The image scale is 359 kilometers (223 miles) per pixel. Three of Saturn's moons are seen in the image: Enceladus (499 kilometers, or 310 miles across) at left; Mimas (398 kilometers, or 247 miles across) left of Saturn's south pole; and Rhea (1,528 kilometers, or 949 miles across) at lower right. The imaging team enhanced the brightness of the moons to aid visibility. The BL1 broadband spectral filter (centered at 451 nanometers) allows Cassini to "see" light in a part of the spectrum visible as the color blue to human eyes. Scientist can combine images made with this filter with those taken with red and green filters to create full-color composites. Scientists can also assess cloud heights by combining images from the blue filter with images taken in other spectral regions. For example, the bright clouds that form the equatorial zone are the highest in altitude and have pressures at their tops of about one quarter of Earth's atmospheric pressure at sea level. The cloud tops at middle latitudes are lower in altitude and have higher pressures of about half that found at sea level. Analysis of Saturn images like this one will be extremely useful to researchers assessing cloud altitudes during the Cassini-Huygens mission. http://photojournal.jpl.nasa.gov/catalog/PIA05383

  6. Stability in straight stellarators

    SciTech Connect

    Kulsrud, R.M.; Yoshikawa, S.

    1981-07-01

    The stability of the straight stellarator against localized interchange modes is investigated employing the Mercier-Greene-Johnson criterion. Critical values of ..beta.. are obtained both numerically and analytically. The conclusion is that for classical helical stellarators the average limiting ..beta..'s are quite low of order three to four percent.

  7. Observation of stellar remnants from recent supernovae

    NASA Technical Reports Server (NTRS)

    Helfand, D. J.; Becker, R. H.

    1984-01-01

    The current observational situation regarding the presence or absence of collapsed stellar objects associated with supernova remnants is reviewed. The theoretical expectations and observational evidence for the various possible classes of stellar remnants are discussed. The results of searches for these objects in the radio, optical, X-ray and gamma-ray regions of the spectrum are outlined with the conclusion that nine bona fide candidates are currently known. The implications of these results for the origin and evolution of compact objects are summarized.

  8. PRIMUS: The Dependence of AGN Accretion on Host Stellar Mass and Color

    NASA Astrophysics Data System (ADS)

    Aird, James; Coil, Alison L.; Moustakas, John; Blanton, Michael R.; Burles, Scott M.; Cool, Richard J.; Eisenstein, Daniel J.; Smith, M. Stephen M.; Wong, Kenneth C.; Zhu, Guangtun

    2012-02-01

    We present evidence that the incidence of active galactic nuclei (AGNs) and the distribution of their accretion rates do not depend on the stellar masses of their host galaxies, contrary to previous studies. We use hard (2-10 keV) X-ray data from three extragalactic fields (XMM-LSS, COSMOS, and ELAIS-S1) with redshifts from the Prism Multi-object Survey to identify 242 AGNs with L 2-10 keV = 1042-44 erg s-1 within a parent sample of ~25,000 galaxies at 0.2 < z < 1.0 over ~3.4 deg2 and to i ~ 23. We find that although the fraction of galaxies hosting an AGN at fixed X-ray luminosity rises strongly with stellar mass, the distribution of X-ray luminosities is independent of mass. Furthermore, we show that the probability that a galaxy will host an AGN can be defined by a universal Eddington ratio distribution that is independent of the host galaxy stellar mass and has a power-law shape with slope -0.65. These results demonstrate that AGNs are prevalent at all stellar masses in the range 9.5 and that the same physical processes regulate AGN activity in all galaxies in this stellar mass range. While a higher AGN fraction may be observed in massive galaxies, this is a selection effect related to the underlying Eddington ratio distribution. We also find that the AGN fraction drops rapidly between z ~ 1 and the present day and is moderately enhanced (factor ~2) in galaxies with blue or green optical colors. Consequently, while AGN activity and star formation appear to be globally correlated, we do not find evidence that the presence of an AGN is related to the quenching of star formation or the color transformation of galaxies.

  9. Stellar structures in Extended Gravity

    NASA Astrophysics Data System (ADS)

    Capozziello, S.; De Laurentis, M.

    2016-09-01

    Stellar structures are investigated by considering the modified Lané-Emden equation coming out from Extended Gravity. In particular, this equation is obtained in the Newtonian limit of f ( R) -gravity by introducing a polytropic relation between the pressure and the density into the modified Poisson equation. The result is an integro-differential equation, which, in the limit f ( R) → R , becomes the standard Lané-Emden equation usually adopted in the stellar theory. We find the radial profiles of gravitational potential by solving for some values of the polytropic index. The solutions are compatible with those coming from General Relativity and could be physically relevant in order to address peculiar and extremely massive objects.

  10. DuOCam: A Two-Channel Camera for Simultaneous Photometric Observations of Stellar Clusters

    NASA Astrophysics Data System (ADS)

    Maier, Erin R.; Witt, Emily; Depoy, Darren L.; Schmidt, Luke M.

    2017-01-01

    We have designed the Dual Observation Camera (DuOCam), which uses commercial, off-the-shelf optics to perform simultaneous photometric observations of astronomical objects at red and blue wavelengths. Collected light enters DuOCam’s optical assembly, where it is collimated by a negative doublet lens. It is then separated by a 45 degree blue dichroic filter (transmission bandpass: 530 - 800 nm, reflection bandpass: 400 - 475 nm). Finally, the separated light is focused by two identical positive doublet lenses onto two independent charge-coupled devices (CCDs), the SBIG ST-8300M and the SBIG STF-8300M. This optical assembly converts the observing telescope to an f/11 system, which balances maximum field of view with optimum focus. DuOCam was commissioned on the McDonald Observatory 0.9m, f/13.5 telescope from July 21st - 24th, 2016. Observations of three globular and three open stellar clusters were carried out. The resulting data were used to construct R vs. B-R color magnitude diagrams for a selection of the observed clusters. The diagrams display the characteristic evolutionary track for a stellar cluster, including the main sequence and main sequence turn-off.

  11. Stellar Nuclear Structure

    SciTech Connect

    Champagne, A.E.

    2005-04-05

    It is possible to measure some stellar cross sections without worrying too much about why the nuclei are built the way that they are. At the same time, many cross sections are impossible to measure because they are either too small or involve short-lived nuclei. Also, at high temperatures and densities, nucleosynthesis is governed by masses, shell structure, etc., not by individual reaction rates. Thus, at the limits, nuclear astrophysics can be thought of as nuclear structure applied to large objects. One area where there is a clear convergence between nuclear structure and nuclear astrophysics is the r-process. Here, advances in observation, experiment and theory point towards real progress on what has been a long-standing problem in astrophysics. Although the r-process is perhaps the most recognized astrophysical venue for nuclear structure, it is by no means the only one. This talk will highlight some of the areas where nuclear structure plays a leading role in addressing questions in astrophysics.

  12. Double-helix stellarator

    SciTech Connect

    Moroz, P.E.

    1997-09-01

    A new stellarator configuration, the Double-Helix Stellarator (DHS), is introduced. This novel configuration features a double-helix center post as the only helical element of the stellarator coil system. The DHS configuration has many unique characteristics. One of them is the extreme low plasma aspect ratio, A {approx} 1--1.2. Other advantages include a high enclosed volume, appreciable rotational transform, and a possibility of extreme-high-{beta} MHD equilibria. Moreover, the DHS features improved transport characteristics caused by the absence of the magnetic field ripple on the outboard of the torus. Compactness, simplicity and modularity of the coil system add to the DHS advantages for fusion applications.

  13. Spectroscopy of Stellar Coronae

    NASA Astrophysics Data System (ADS)

    Laming, J. Martin

    I review the important spectroscopic results that have come from observations of stellar coronae, mainly by EUVE and ASCA, but also from HST. The plasma parameters that can be determined from such spectra include the electron density and temperature distributions, and relative element abundances. With high resolution spectra dynamical information can be obtained. Such parameters can then be used to put constraints on models of the heating and structure of stellar coronae. Throughout, I try to emphasise the similarities and differences between stellar coronal spectroscopy and that of the solar corona.

  14. Frontiers of stellar evolution

    NASA Technical Reports Server (NTRS)

    Lambert, David L. (Editor)

    1991-01-01

    The present conference discusses theoretical and observational views of star formation, spectroscopic constraints on the evolution of massive stars, very low mass stars and brown dwarfs, asteroseismology, globular clusters as tests of stellar evolution, observational tests of stellar evolution, and mass loss from cool evolved giant stars. Also discussed are white dwarfs and hot subdwarfs, neutron stars and black holes, supernovae from single stars, close binaries with evolved components, accretion disks in interacting binaries, supernovae in binary systems, stellar evolution and galactic chemical evolution, and interacting binaries containing compact components.

  15. The BlueTides simulation: first galaxies and reionization

    NASA Astrophysics Data System (ADS)

    Feng, Yu; Di-Matteo, Tiziana; Croft, Rupert A.; Bird, Simeon; Battaglia, Nicholas; Wilkins, Stephen

    2016-01-01

    We introduce the BlueTides simulation and report initial results for the luminosity functions of the first galaxies and active galactic nuclei (AGN), and their contribution to reionization. BlueTides was run on the BlueWaters cluster at National Center for Super-computing Applications from z = 99 to 8.0 and includes 2 × 70403 particles in a 400 h-1 Mpc per side box, making it the largest hydrodynamic simulation ever performed at high redshift. BlueTides includes a pressure-entropy formulation of smoothed particle hydrodynamics, gas cooling, star formation (including molecular hydrogen), black hole growth and models for stellar and AGN feedback processes, and a fluctuating ultraviolet background from a patchy reionization model. The predicted star formation rate density is a good match to current observational data at z ˜ 8-10. We find good agreement between observations and the predicted galaxy luminosity function in the currently observable range -18 ≤ MUV ≤ -22.5 with some dust extinction required to match the abundance of brighter objects. The predicted number counts for galaxies fainter than current observational limits are consistent with extrapolating the faint-end slope of the luminosity function with a power-law index α ˜ -1.8 at z ˜ 8 and redshift dependence of α ˜ (1 + z)-0.4. The AGN population has a luminosity function well fit by a power law with a slope α ˜ -2.4 that compares favourably with the deepest CANDELS GOODS fields. We investigate how these luminosity functions affect the progress of reionization, and find that a high Lyman α escape fraction (fesc ˜ 0.5) is required if galaxies dominate the ionizing photon budget during reionization. Smaller galaxy escape fractions imply a large contribution from faint AGN (down to MUV = -12) which results in a rapid reionization, disfavoured by current observations.

  16. Measuring Doppler Shifts of X-Ray Lines to Determine the Stellar Wind X-Ray Locations in OB Stars

    NASA Astrophysics Data System (ADS)

    Waldron, Wayne

    1999-09-01

    For almost 20 years we have been trying to determine the source of the X-ray emission in OB stars. It is generally believed that this emission is caused by a distribution of stellar wind shocks. The AXAF grating spectrometers will provide the ultimate test of X-ray models. The shock model predicts that X-ray lines must be Doppler blue-shifted, hence, our primary objective is to measure these blue-shifts. MARX simulations show that the expected X-ray line shifts will be at least 4 times the MEG1 energy resolution limit. ASCA observations have provided stronger constraints on X-ray models, but they have also raised additional questions (e.g., X-ray abundance anomalies). The large number of X-ray lines predicted by MARX simulations will allow us to probe X-ray densities and abundances.

  17. COS Spectroscopy of White Dwarf Companions to Blue Stragglers

    NASA Astrophysics Data System (ADS)

    Gosnell, Natalie M.; Geller, Aaron M.; Knigge, Christian; Mathieu, Robert D.; Sills, Alison; Leiner, Emily; Leigh, Nathan

    2017-01-01

    Complete membership studies of open stellar clusters reveal that 25% of the evolved stars follow alternative pathways in stellar evolution, meaning something in the history of these stars changed their composition or mass (or both). In order to draw a complete picture of stellar evolution we must include these canonically "strange" stars in our definition of standard stellar populations. The formation mechanism of blue straggler stars, traditionally defined to be brighter and bluer than the main sequence turnoff in a star cluster, has been an outstanding question for almost six decades. Recent Hubble Space Telescope (HST) far-ultraviolet (far-UV) observations directly reveal that the blue straggler stars in the old (7 Gyr) open cluster NGC 188 are predominantly formed through mass transfer. We will present HST far-UV COS spectroscopy of white dwarf companions to blue stragglers. These white dwarfs are the remnants of the mass transfer formation process. The effective temperatures and surface gravities of the white dwarfs delineate the timeline of blue straggler formation in this cluster. The existence of these binaries in a well-studied cluster environment provides an unprecedented opportunity to observationally constrain mass transfer models and inform our understanding of many other alternative pathway stellar products.

  18. Evolving sparse stellar populations

    NASA Astrophysics Data System (ADS)

    Bruzual, Gustavo; Gladis Magris, C.; Hernández-Pérez, Fabiola

    2017-03-01

    We examine the role that stochastic fluctuations in the IMF and in the number of interacting binaries have on the spectro-photometric properties of sparse stellar populations as a function of age and metallicity.

  19. Stellar atmospheric structural patterns

    NASA Technical Reports Server (NTRS)

    Thomas, R. N.

    1983-01-01

    The thermodynamics of stellar atmospheres is discussed. Particular attention is given to the relation between theoretical modeling and empirical evidence. The characteristics of distinctive atmospheric regions and their radical structures are discussed.

  20. The Blue Bottle Revisited.

    ERIC Educational Resources Information Center

    Vandaveer, Walter R., IV; Mosher, Mel

    1997-01-01

    Presents a modification of the classic Blue Bottle demonstration that involves the alkaline glucose reduction of methylene blue. Uses other indicators in the classic Blue Bottle to produce a rainbow of colors. (JRH)

  1. The Blue Bottle Revisited.

    ERIC Educational Resources Information Center

    Vandaveer, Walter R., IV; Mosher, Mel

    1997-01-01

    Presents a modification of the classic Blue Bottle demonstration that involves the alkaline glucose reduction of methylene blue. Uses other indicators in the classic Blue Bottle to produce a rainbow of colors. (JRH)

  2. Oscillations in stellar atmospheres

    NASA Technical Reports Server (NTRS)

    Costa, A.; Ringuelet, A. E.; Fontenla, J. M.

    1989-01-01

    Atmospheric excitation and propagation of oscillations are analyzed for typical pulsating stars. The linear, plane-parallel approach for the pulsating atmosphere gives a local description of the phenomenon. From the local analysis of oscillations, the minimum frequencies are obtained for radially propagating waves. The comparison of the minimum frequencies obtained for a variety of stellar types is in good agreement with the observed periods of the oscillations. The role of the atmosphere in the globar stellar pulsations is thus emphasized.

  3. Oscillations in stellar atmospheres

    NASA Technical Reports Server (NTRS)

    Costa, A.; Ringuelet, A. E.; Fontenla, J. M.

    1989-01-01

    Atmospheric excitation and propagation of oscillations are analyzed for typical pulsating stars. The linear, plane-parallel approach for the pulsating atmosphere gives a local description of the phenomenon. From the local analysis of oscillations, the minimum frequencies are obtained for radially propagating waves. The comparison of the minimum frequencies obtained for a variety of stellar types is in good agreement with the observed periods of the oscillations. The role of the atmosphere in the globar stellar pulsations is thus emphasized.

  4. STELLAR ENCOUNTER RATE IN GALACTIC GLOBULAR CLUSTERS

    SciTech Connect

    Bahramian, Arash; Heinke, Craig O.; Sivakoff, Gregory R.; Gladstone, Jeanette C.

    2013-04-01

    The high stellar densities in the cores of globular clusters cause significant stellar interactions. These stellar interactions can produce close binary mass-transferring systems involving compact objects and their progeny, such as X-ray binaries and radio millisecond pulsars. Comparing the numbers of these systems and interaction rates in different clusters drives our understanding of how cluster parameters affect the production of close binaries. In this paper we estimate stellar encounter rates ({Gamma}) for 124 Galactic globular clusters based on observational data as opposed to the methods previously employed, which assumed 'King-model' profiles for all clusters. By deprojecting cluster surface brightness profiles to estimate luminosity density profiles, we treat 'King-model' and 'core-collapsed' clusters in the same way. In addition, we use Monte Carlo simulations to investigate the effects of uncertainties in various observational parameters (distance, reddening, surface brightness) on {Gamma}, producing the first catalog of globular cluster stellar encounter rates with estimated errors. Comparing our results with published observations of likely products of stellar interactions (numbers of X-ray binaries, numbers of radio millisecond pulsars, and {gamma}-ray luminosity) we find both clear correlations and some differences with published results.

  5. Binary Populations and Stellar Dynamics in Young Clusters

    NASA Astrophysics Data System (ADS)

    Vanbeveren, D.; Belkus, H.; Van Bever, J.; Mennekens, N.

    2008-06-01

    We first summarize work that has been done on the effects of binaries on theoretical population synthesis of stars and stellar phenomena. Next, we highlight the influence of stellar dynamics in young clusters by discussing a few candidate UFOs (unconventionally formed objects) like intermediate mass black holes, η Car, ζ Pup, γ2 Velorum and WR 140.

  6. Stellar and Gaseous Properties of Tidal Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Duc, P.-A.; Mirabel, I. F.; Brinks, E.

    Small galaxies may form as a result of interactions between galaxies. This idea is consistent with a number of observations of the outer regions of interacting systems: optical condensations, as luminous as dwarf galaxies, are often found at the end of tidal tails. We will present multi--wavelength observations of a few systems and highlight the existence of a new class of objects, which have been named ``tidal dwarf galaxies'', that are made of material pulled out from colliding galaxies. They are gas--rich, associated with massive HI clouds and, like traditional dwarf irregular and blue compact dwarf galaxies, they host active star formation regions. However, they have a high metallicity for their mass. This is the very result of their peculiar mode of formation which is based on cosmic recycling. Part of their stellar populations consists of young stars formed from the collapse in the intergalactic medium of tidally expelled HI clouds, while another fraction is composed of old stars pulled out from the disks of the parent galaxies. We have found for the first time evidence that some tidal dwarfs might already be gravitationally bound and therefore have become independent galaxies. Systematic studies of the properties of dwarf galaxies in different environments are underway in order to estimate the fraction of recycled objects among them.

  7. PREFACE: A Stellar Journey A Stellar Journey

    NASA Astrophysics Data System (ADS)

    Asplund, M.

    2008-10-01

    The conference A Stellar Journey was held in Uppsala, Sweden, 23 27June 2008, in honour of Professor Bengt Gustafsson's 65th birthday. The choice of Uppsala as the location for this event was obvious given Bengt's long-standing association with the city stemming back to his school days. With the exception of a two-year postdoc stint in Copenhagen, five years as professor at Stockholm University and two years as director of the Sigtuna foundation, Bengt has forged his illustrious professional career at Uppsala University. The symposium venue was Museum Gustavianum, once the main building of the oldest university in Scandinavia. The title of the symposium is a paraphrasing of Bengt's popular astronomy book Kosmisk Resa (in English: Cosmic Journey) written in the early eighties. I think this aptly symbolizes his career that has been an astronomical voyage from near to far, from the distant past to the present. The original book title was modified slightly to reflect that most of his work to date has dealt with stars in one way or another. In addition it also gives credit to Bengt's important role as a guiding light for a very large number of students, colleagues and collaborators, indeed for several generations of astronomers. For me personally, the book Kosmisk Resa bears particular significance as it has shaped my life rather profoundly. Although I had already decided to become an astronomer, when I first read the book as a 14-year-old I made up my mind then and there that I would study under Bengt Gustafsson and work on stars. Indeed I have remained true to this somewhat audacious resolution. I suspect that a great number of us have similar stories how Bengt has had a major influence on our lives, whether on the professional or personal level. Perhaps Bengt's most outstanding characteristic is his enthralling enthusiasm. This is equally true whether he is pondering some scientific conundrum, supervising students or performing in front of an audience, be it an

  8. Las Campanas Stellar Library

    NASA Astrophysics Data System (ADS)

    Chilingarian, Igor; Zolotukhin, Ivan; Beletsky, Yuri; Worthey, Guy

    2015-08-01

    Stellar libraries are fundamental tools required to understand stellar populations in star clusters and galaxies as well as properties of individual stars. Comprehensive libraries exist in the optical domain, but the near-infrared (NIR) domain stays a couple of decades behind. Here we present the Las Campanas Stellar Library project aiming at obtaining high signal-to-noise intermediate-resolution (R=8000) NIR spectra (0.83<λ<2.5μm) for a sample of 1200 stars in the Southern sky using the Folded-port InfraRed Echelette spectrograph at the 6.5-m Magellan Baade telescope. We developed a dedicated observing strategy and customized the telescope control software in order to achieve the highest possible level of data homogeniety. As of 2015, we observed about 600 stars of all spectral types and luminosity classes making our library the largest homogeneous collection of stellar spectra covering the entire NIR domain. We also re-calibrated in flux and wavelength the two existing optical stellar libraries, INDO-US and UVES-POP and followed up about 400 non-variable stars in the NIR in order to get complete optical-NIR coverage. Worth mentioning that our current sample includes about 80 AGB stars and a few dozens of bulge/LMC/SMC stars.

  9. Origins of Stellar Halos

    NASA Astrophysics Data System (ADS)

    Johnston, Kathryn V.

    2016-08-01

    This contribution reviews ideas about the origins of stellar halos. It includes discussion of the theoretical understanding of and observational evidence for stellar populations formed ``in situ'' (meaning formed in orbits close to their current ones), ``kicked-out'' (meaning formed in the inner galaxy in orbits unlike their current ones) and ``accreted'' (meaning formed in a dark matter halo other than the one they currently occupy). At this point there is general agreement that a significant fraction of any stellar halo population is likely ``accreted''. There is modest evidence for the presence of a ``kicked-out'' population around both the Milky Way and M31. Our theoretical understanding of and the observational evidence for an ``in situ'' population are less clear.

  10. The Galactic stellar disc

    NASA Astrophysics Data System (ADS)

    Feltzing, S.; Bensby, T.

    2008-12-01

    The study of the Milky Way stellar discs in the context of galaxy formation is discussed. In particular, we explore the properties of the Milky Way disc using a new sample of about 550 dwarf stars for which we have recently obtained elemental abundances and ages based on high-resolution spectroscopy. For all the stars we also have full kinematic information as well as information about their stellar orbits. We confirm results from previous studies that the thin and the thick discs have distinct abundance patterns. But we also explore a larger range of orbital parameters than what has been possible in our previous studies. Several new results are presented. We find that stars that reach high above the Galactic plane and have eccentric orbits show remarkably tight abundance trends. This implies that these stars formed out of well-mixed gas that had been homogenized over large volumes. We find some evidence that suggest that the event that most likely caused the heating of this stellar population happened a few billion years ago. Through a simple, kinematic exploration of stars with super-solar [Fe/H], we show that the solar neighbourhood contains metal-rich, high velocity stars that are very likely associated with the thick disc. Additionally, the HR1614 moving group and the Hercules and Arcturus stellar streams are discussed and it is concluded that, probably, a large fraction of the groups and streams so far identified in the disc are the result of evolution and interactions within the stellar disc rather than being dissolved stellar clusters or engulfed dwarf galaxies. This paper includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile. Also based on observations collected at the Nordic Optical Telescope on La Palma, Spain, and at the European Southern Observatories on La Silla and Paranal, Chile, Proposals no. 65.L-0019(B), 67.B-0108(B), 69.B-0277.

  11. Young and Exotic Stellar Zoo

    NASA Astrophysics Data System (ADS)

    2005-03-01

    constellation Ara (the Altar). It was discovered in 1961 from Australia by Swedish astronomer Bengt Westerlund, who later moved from there to become ESO Director in Chile (1970 - 74). This cluster is behind a huge interstellar cloud of gas and dust, which blocks most of its visible light. The dimming factor is more than 100,000 - and this is why it has taken so long to uncover the true nature of this particular cluster. In 2001, the team of astronomers identified more than a dozen extremely hot and peculiar massive stars in the cluster, so-called "Wolf-Rayet" stars. They have since studied Westerlund 1 extensively with various ESO telescopes. They used images from the Wide Field Imager (WFI) attached to the 2.2-m ESO/MPG as well as from the SUperb Seeing Imager 2 (SuSI2) camera on the ESO 3.5-m New Technology Telescope (NTT). From these observations, they were able to identify about 200 cluster member stars. To establish the true nature of these stars, the astronomers then performed spectroscopic observations of about one quarter of them. For this, they used the Boller & Chivens spectrograph on the ESO 1.52-m telescope and the ESO Multi-Mode Instrument (EMMI) on the NTT. An Exotic Zoo These observations have revealed a large population of very bright and massive, quite extreme stars. Some would fill the solar system space within the orbit of Saturn (about 2,000 times larger than the Sun!), others are as bright as a million Suns. Westerlund 1 is obviously a fantastic stellar zoo, with a most exotic population and a true astronomical bonanza. All stars identified are evolved and very massive, spanning the full range of stellar oddities from Wolf-Rayet stars, OB supergiants, Yellow Hypergiants (nearly as bright as a million Suns) and Luminous Blue Variables (similar to the exceptional Eta Carinae object - see ESO PR 31/03). All stars so far analysed in Westerlund 1 weigh at least 30-40 times more than the Sun. Because such stars have a rather short life - astronomically speaking

  12. Stellar Astrophysical Fluid Dynamics

    NASA Astrophysics Data System (ADS)

    Thompson, Michael J.; Christensen-Dalsgaard, Jørgen

    2008-02-01

    Preface; 1. A selective overview Jørgen Christensen-Dalsgaard and Michael J. Thompson; Part I. Stellar Convection and Oscillations: 2. On the diversity of stellar pulsations Wojciech A. Dziembowski; 3. Acoustic radiation and mode excitation by turbulent convection Günter Houdek; 4. Understanding roAp stars Margarida S. Cunha; 5. Waves in the magnetised solar atmosphere Colin S. Rosenthal; Part II. Stellar Rotation and Magnetic Fields: 6. Stellar rotation: a historical survey Leon Mestel; 7. The oscillations of rapidly rotating stars Michel Rieutord; 8. Solar tachocline dynamics: eddy viscosity, anti-friction, or something in between? Michael E. McIntyre; 9. Dynamics of the solar tachocline Pascale Garaud; 10. Dynamo processes: the interaction of turbulence and magnetic fields Michael Proctor; 11. Dynamos in planets Chris Jones; Part III. Physics and Structure of Stellar Interiors: 12. Solar constraints on the equation of state Werner Däppen; 13. 3He transport and the solar neutrino problem Chris Jordinson; 14. Mixing in stellar radiation zones Jean-Paul Zahn; 15. Element settling and rotation-induced mixing in slowly rotating stars Sylvie Vauclair; Part IV. Helio- and Asteroseismology: 16. Solar structure and the neutrino problem Hiromoto Shibahashi; 17. Helioseismic data analysis Jesper Schou; 18. Seismology of solar rotation Takashi Sekii; 19. Telechronohelioseismology Alexander Kosovichev; Part V. Large-Scale Numerical Experiments: 20. Bridges between helioseismology and models of convection zone dynamics Juri Toomre; 21. Numerical simulations of the solar convection zone Julian R. Elliott; 22. Modelling solar and stellar magnetoconvection Nigel Weiss; 23. Nonlinear magnetoconvection in the presence of a strong oblique field Keith Julien, Edgar Knobloch and Steven M. Tobias; 24. Simulations of astrophysical fluids Marcus Brüggen; Part VI. Dynamics: 25. A magic electromagnetic field Donald Lynden-Bell; 26. Continuum equations for stellar dynamics Edward A

  13. Stellar Astrophysical Fluid Dynamics

    NASA Astrophysics Data System (ADS)

    Thompson, Michael J.; Christensen-Dalsgaard, Jørgen

    2003-05-01

    Preface; 1. A selective overview Jørgen Christensen-Dalsgaard and Michael J. Thompson; Part I. Stellar Convection and Oscillations: 2. On the diversity of stellar pulsations Wojciech A. Dziembowski; 3. Acoustic radiation and mode excitation by turbulent convection Günter Houdek; 4. Understanding roAp stars Margarida S. Cunha; 5. Waves in the magnetised solar atmosphere Colin S. Rosenthal; Part II. Stellar Rotation and Magnetic Fields: 6. Stellar rotation: a historical survey Leon Mestel; 7. The oscillations of rapidly rotating stars Michel Rieutord; 8. Solar tachocline dynamics: eddy viscosity, anti-friction, or something in between? Michael E. McIntyre; 9. Dynamics of the solar tachocline Pascale Garaud; 10. Dynamo processes: the interaction of turbulence and magnetic fields Michael Proctor; 11. Dynamos in planets Chris Jones; Part III. Physics and Structure of Stellar Interiors: 12. Solar constraints on the equation of state Werner Däppen; 13. 3He transport and the solar neutrino problem Chris Jordinson; 14. Mixing in stellar radiation zones Jean-Paul Zahn; 15. Element settling and rotation-induced mixing in slowly rotating stars Sylvie Vauclair; Part IV. Helio- and Asteroseismology: 16. Solar structure and the neutrino problem Hiromoto Shibahashi; 17. Helioseismic data analysis Jesper Schou; 18. Seismology of solar rotation Takashi Sekii; 19. Telechronohelioseismology Alexander Kosovichev; Part V. Large-Scale Numerical Experiments: 20. Bridges between helioseismology and models of convection zone dynamics Juri Toomre; 21. Numerical simulations of the solar convection zone Julian R. Elliott; 22. Modelling solar and stellar magnetoconvection Nigel Weiss; 23. Nonlinear magnetoconvection in the presence of a strong oblique field Keith Julien, Edgar Knobloch and Steven M. Tobias; 24. Simulations of astrophysical fluids Marcus Brüggen; Part VI. Dynamics: 25. A magic electromagnetic field Donald Lynden-Bell; 26. Continuum equations for stellar dynamics Edward A

  14. The Resolved Stellar Population of Leo A

    NASA Astrophysics Data System (ADS)

    Tolstoy, Eline

    1996-05-01

    New observations of the resolved stellar population of the extremely metal-poor Magellanic dwarf irregular galaxy Leo A in Thuan-Gunn r, g, i, and narrowband Hα filters are presented. Using the recent Cepheid variable star distance determination to Leo A by Hoessel et al., we are able to create an accurate color-magnitude diagram (CMD). We have used the Bavesian inference method described by Tolstoy & Saha to calculate the likelihood of a Monte Carlo simulation of the stellar population of Leo A being a good match to the data within the well understood errors in the data. The magnitude limits on our data are sensitive enough to look back at ~1 Gyr of star formation history at the distance of Leo A. To explain the observed ratio of red to blue stars in the observed CMD, it is necessary to invoke either a steadily decreasing star formation rate toward the present time or gaps in the star formation history. We also compare the properties of the observed stellar population with the known spatial distribution of the H I gas and H II regions to support the conclusions from CMD modeling. We consider the possibility that currently there is a period of diminished star formation in Leo A, as evidenced by the lack of very young stars in the CMD and the faint H II regions. How the chaotic H I distribution, with no observable rotation, fits into our picture of the evolution of Leo A is as yet unclear.

  15. Galaxy bimodality versus stellar mass and environment

    NASA Astrophysics Data System (ADS)

    Baldry, I. K.; Balogh, M. L.; Bower, R. G.; Glazebrook, K.; Nichol, R. C.; Bamford, S. P.; Budavari, T.

    2006-12-01

    We analyse a z < 0.1 galaxy sample from the Sloan Digital Sky Survey focusing on the variation in the galaxy colour bimodality with stellar mass and projected neighbour density Σ, and on measurements of the galaxy stellar mass functions. The characteristic mass increases with environmental density from about 1010.6 to (Kroupa initial mass function, H0 = 70) for Σ in the range 0.1-10Mpc-2. The galaxy population naturally divides into a red and blue sequence with the locus of the sequences in colour-mass and colour-concentration indices not varying strongly with environment. The fraction of galaxies on the red sequence is determined in bins of 0.2 in logΣ and bins). The red fraction fr generally increases continuously in both Σ and such that there is a unified relation: . Two simple functions are proposed which provide good fits to the data. These data are compared with analogous quantities in semi-analytical models based on the Millennium N-body simulation: the Bower et al. and Croton et al. models that incorporate active galactic nucleus feedback. Both models predict a strong dependence of the red fraction on stellar mass and environment that is qualitatively similar to the observations. However, a quantitative comparison shows that the Bower et al. model is a significantly better match; this appears to be due to the different treatment of feedback in central galaxies.

  16. Galactic stellar populations with APOGEE and Kepler

    NASA Astrophysics Data System (ADS)

    Johnson, J. A.; APOKASC Collaboration

    2016-09-01

    Understanding the history of baryons is key to understanding galaxy formation, as galaxies with very similar stellar mass and/or dark matter halo mass can have markedly different morphologies in their stellar light. Stars are a useful way to study this history, because properties such as their composition, age, and orbital motion can map galaxy formation and evolution. Lightcurves from the Kepler mission, both original and extended, provide asteroseismic parameters, such as Δ ν and ν_max, and rotation periods. The high-resolution near-infrared APOGEE spectroscopic survey is observing an extensive sample of red giants and cool dwarfs in both the Kepler and K2 fields to provide composition and effective temperature measurements. These spectroscopic and seismic parameters can be combined to yield ages, important for dissecting the history of the Milky Way. Results based on this combination have already been published in the first APOKASC catalog. Among the interesting results about stellar populations so far are the presence of a large metallicity spread in the young secondary red clump population at the solar circle, the identification of young, yet α-rich stars, and the detection of a field blue straggler descendant. The K2 fields along the ecliptic will extend the possibilities of these techniques to new lines of sight in the Galaxy and provide a much more representative sample of Galactic populations with seismic and spectroscopic information.

  17. Determination of Stellar Parameters Through the Use of All Available Flux Data and Model Spectral Energy Distributions

    NASA Astrophysics Data System (ADS)

    Ekanayake, Gemunu

    2017-05-01

    Basic stellar atmospheric parameters, such as effective temperature, surface gravity, and metallicity plays a vital role in the characterization of various stellar populations in the Milky Way. The Stellar parameters can be measured by adopting one or more observational techniques, such as spectroscopy, photometry, interferometry, etc. Finding new and innovative ways to combine these observational data to derive reliable stellar parameters and to use them to characterize some of the stellar populations in our galaxy is the main goal of this thesis. Our initial work, based on the spectroscopic and photometric data available in literature, had the objective of calibrating the stellar parameters from a range of available flux observations from far-UV to far-IR. Much effort has been made to estimate probability distributions of the stellar parameters using Bayesian inference, rather than point estimates. We applied these techniques to blue straggler stars (BSSs) in the galactic field, which are thought to be a product of mass transfer mechanism associated with binary stars. Using photometry available in SDSS and GALEX surveys we identified 85 stars with UV excess in their spectral energy distribution (SED) : indication of a hot white dwarf companion to BSS. To determine the parameter distributions (mass, temperature and age) of the WD companions, we developed algorithms that could fit binary model atmospheres to the observed SED. The WD mass distribution peaks at 0.4 solar mass, suggests the primary formation channel of field BSSs is Case-B mass transfer, i.e. when the donor star is in red giant phase of its evolution. Based on stellar evolutionary models, we estimate the lower limit of binary mass transfer efficiency beta 0.5. Next, we have focused on the Canis Major overdensity (CMO), a substructure located at low galactic latitude in the Milky Way, where the interstellar reddening (E(B-V)) due to dust is significantly high. In this study we estimated the reddening

  18. Active Luminous Blue Variables in the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Walborn, Nolan R.; Gamen, Roberto C.; Morrell, Nidia I.; Barbá, Rodolfo H.; Fernández Lajús, Eduardo; Angeloni, Rodolfo

    2017-07-01

    We present extensive spectroscopic and photometric monitoring of two famous and currently highly active luminous blue variables (LBVs) in the Large Magellanic Cloud (LMC), together with more limited coverage of three further, lesser known members of the class. R127 was discovered as an Ofpe/WN9 star in the 1970s but entered a classical LBV outburst in or about 1980 that is still in progress, thus enlightening us about the minimum state of such objects. R71 is currently the most luminous star in the LMC and continues to provide surprises, such as the appearance of [Ca ii] emission lines, as its spectral type becomes unprecedentedly late. Most recently, R71 has developed inverse P Cyg profiles in many metal lines. The other objects are as follows: HDE 269582, now a “second R127” that has been followed from Ofpe/WN9 to A type in its current outburst; HDE 269216, which changed from late B in 2014 to AF in 2016, its first observed outburst; and R143 in the 30 Doradus outskirts. The light curves and spectroscopic transformations are correlated in remarkable detail and their extreme reproducibility is emphasized, both for a given object and among all of them. It is now believed that some LBVs proceed directly to core collapse. One of these unstable LMC objects may thus oblige in the near future, teaching us even more about the final stages of massive stellar evolution.

  19. MOCK OBSERVATIONS OF BLUE STRAGGLERS IN GLOBULAR CLUSTER MODELS

    SciTech Connect

    Sills, Alison; Glebbeek, Evert; Chatterjee, Sourav; Rasio, Frederic A. E-mail: e.glebbeek@astro.ru.nl E-mail: rasio@northwestern.edu

    2013-11-10

    We created artificial color-magnitude diagrams of Monte Carlo dynamical models of globular clusters and then used observational methods to determine the number of blue stragglers in those clusters. We compared these blue stragglers to various cluster properties, mimicking work that has been done for blue stragglers in Milky Way globular clusters to determine the dominant formation mechanism(s) of this unusual stellar population. We find that a mass-based prescription for selecting blue stragglers will select approximately twice as many blue stragglers than a selection criterion that was developed for observations of real clusters. However, the two numbers of blue stragglers are well-correlated, so either selection criterion can be used to characterize the blue straggler population of a cluster. We confirm previous results that the simplified prescription for the evolution of a collision or merger product in the BSE code overestimates their lifetimes. We show that our model blue stragglers follow similar trends with cluster properties (core mass, binary fraction, total mass, collision rate) as the true Milky Way blue stragglers as long as we restrict ourselves to model clusters with an initial binary fraction higher than 5%. We also show that, in contrast to earlier work, the number of blue stragglers in the cluster core does have a weak dependence on the collisional parameter Γ in both our models and in Milky Way globular clusters.

  20. From stellar nebula to planetesimals

    NASA Astrophysics Data System (ADS)

    Marboeuf, Ulysse; Thiabaud, Amaury; Alibert, Yann; Cabral, Nahuel; Benz, Willy

    2014-10-01

    Context. Solar and extrasolar comets and extrasolar planets are the subject of numerous studies in order to determine their chemical composition and internal structure. In the case of planetesimals, their compositions are important as they govern in part the composition of future planets. Aims: The present works aims at determining the chemical composition of icy planetesimals, believed to be similar to present day comets, formed in stellar systems of solar chemical composition. The main objective of this work is to provide valuable theoretical data on chemical composition for models of planetesimals and comets, and models of planet formation and evolution. Methods: We have developed a model that calculates the composition of ices formed during the cooling of the stellar nebula. Coupled with a model of refractory element formation, it allows us to determine the chemical composition and mass ratio of ices to rocks in icy planetesimals throughout in the protoplanetary disc. Results: We provide relationships for ice line positions (for different volatile species) in the disc, and chemical compositions and mass ratios of ice relative to rock for icy planetesimals in stellar systems of solar chemical composition. From an initial homogeneous composition of the nebula, a wide variety of chemical compositions of planetesimals were produced as a function of the mass of the disc and distance to the star. Ices incorporated in planetesimals are mainly composed of H2O, CO, CO2, CH3OH, and NH3. The ice/rock mass ratio is equal to 1 ± 0.5 in icy planetesimals following assumptions. This last value is in good agreement with observations of solar system comets, but remains lower than usual assumptions made in planet formation models, taking this ratio to be of 2-3.

  1. The galaxy population of Abell 1367: the stellar mass-metallicity relation

    NASA Astrophysics Data System (ADS)

    Mouhcine, M.; Kriwattanawong, W.; James, P. A.

    2011-04-01

    Using wide baseline broad-band photometry, we analyse the stellar population properties of a sample of 72 galaxies, spanning a wide range of stellar masses and morphological types, in the nearby spiral-rich and dynamically young galaxy cluster Abell 1367. The sample galaxies are distributed from the cluster centre out to approximately half the cluster Abell radius. The optical/near-infrared colours are compared with simple stellar population synthesis models from which the luminosity-weighted stellar population ages and metallicities are determined. The locus of the colours of elliptical galaxies traces a sequence of varying metallicity at a narrow range of luminosity-weighted stellar ages. Lenticular galaxies in the red sequence, however, exhibit a substantial spread of luminosity-weighted stellar metallicities and ages. For red-sequence lenticular galaxies and blue cloud galaxies, low-mass galaxies tend to be on average dominated by stellar populations of younger luminosity-weighted ages. Sample galaxies exhibit a strong correlation between integrated stellar mass and luminosity-weighted stellar metallicity. Galaxies with signs of morphological disturbance and ongoing star formation activity, tend to be underabundant with respect to passive galaxies in the red sequence of comparable stellar masses. We argue that this could be due to tidally driven gas flows towards the star-forming regions, carrying less enriched gas and diluting the pre-existing gas to produce younger stellar populations with lower metallicities than would be obtained prior to the interaction. Finally, we find no statistically significant evidence for changes in the luminosity-weighted ages and metallicities for either red-sequence or blue-cloud galaxies, at fixed stellar mass, with location within the cluster. We dedicate this work to the memory of our friend and colleague C. Moss who died suddenly recently.

  2. The Stellar Imager (SI)"Vision Mission"

    NASA Technical Reports Server (NTRS)

    Carpenter, Ken; Danchi, W.; Leitner, J.; Liu, A.; Lyon, R.; Mazzuca, L.; Moe, R.; Chenette, D.; Karovska, M.; Allen, R.

    2004-01-01

    The Stellar Imager (SI) is a "Vision" mission in the Sun-Earth Connection (SEC) Roadmap, conceived for the purpose of understanding the effects of stellar magnetic fields, the dynamos that generate them, and the internal structure and dynamics of the stars in which they exist. The ultimate goal is to achieve the best possible forecasting of solar/stellar magnetic activity and its impact on life in the Universe. The science goals of SI require an ultra-high angular resolution, at ultraviolet wavelengths, on the order of 100 micro-arcsec and thus baselines on the order of 0.5 km. These requirements call for a large, multi-spacecraft (less than 20) imaging interferometer, utilizing precision formation flying in a stable environment, such as in a Lissajous orbit around the Sun-Earth L2 point. SI's resolution will make it an invaluable resource for many other areas of astrophysics, including studies of AGN s, supernovae, cataclysmic variables, young stellar objects, QSO's, and stellar black holes. ongoing mission concept and technology development studies for SI. These studies are designed to refine the mission requirements for the science goals, define a Design Reference Mission, perform trade studies of selected major technical and architectural issues, improve the existing technology roadmap, and explore the details of deployment and operations, as well as the possible roles of astronauts and/or robots in construction and servicing of the facility.

  3. ESTIMATION OF DISTANCES TO STARS WITH STELLAR PARAMETERS FROM LAMOST

    SciTech Connect

    Carlin, Jeffrey L.; Newberg, Heidi Jo; Liu, Chao; Deng, Licai; Li, Guangwei; Luo, A-Li; Wu, Yue; Yang, Ming; Zhang, Haotong; Beers, Timothy C.; Chen, Li; Hou, Jinliang; Smith, Martin C.; Guhathakurta, Puragra; Lépine, Sébastien; Yanny, Brian; Zheng, Zheng

    2015-07-15

    We present a method to estimate distances to stars with spectroscopically derived stellar parameters. The technique is a Bayesian approach with likelihood estimated via comparison of measured parameters to a grid of stellar isochrones, and returns a posterior probability density function for each star’s absolute magnitude. This technique is tailored specifically to data from the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) survey. Because LAMOST obtains roughly 3000 stellar spectra simultaneously within each ∼5° diameter “plate” that is observed, we can use the stellar parameters of the observed stars to account for the stellar luminosity function and target selection effects. This removes biasing assumptions about the underlying populations, both due to predictions of the luminosity function from stellar evolution modeling, and from Galactic models of stellar populations along each line of sight. Using calibration data of stars with known distances and stellar parameters, we show that our method recovers distances for most stars within ∼20%, but with some systematic overestimation of distances to halo giants. We apply our code to the LAMOST database, and show that the current precision of LAMOST stellar parameters permits measurements of distances with ∼40% error bars. This precision should improve as the LAMOST data pipelines continue to be refined.

  4. Estimation of distances to stars with stellar parameters from LAMOST

    DOE PAGES

    Carlin, Jeffrey L.; Liu, Chao; Newberg, Heidi Jo; ...

    2015-06-05

    Here, we present a method to estimate distances to stars with spectroscopically derived stellar parameters. The technique is a Bayesian approach with likelihood estimated via comparison of measured parameters to a grid of stellar isochrones, and returns a posterior probability density function for each star's absolute magnitude. We tailor this technique specifically to data from the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) survey. Because LAMOST obtains roughly 3000 stellar spectra simultaneously within each ~5-degree diameter "plate" that is observed, we can use the stellar parameters of the observed stars to account for the stellar luminosity function and targetmore » selection effects. This removes biasing assumptions about the underlying populations, both due to predictions of the luminosity function from stellar evolution modeling, and from Galactic models of stellar populations along each line of sight. Using calibration data of stars with known distances and stellar parameters, we show that our method recovers distances for most stars within ~20%, but with some systematic overestimation of distances to halo giants. We apply our code to the LAMOST database, and show that the current precision of LAMOST stellar parameters permits measurements of distances with ~40% error bars. This precision should improve as the LAMOST data pipelines continue to be refined.« less

  5. Estimation of distances to stars with stellar parameters from LAMOST

    SciTech Connect

    Carlin, Jeffrey L.; Liu, Chao; Newberg, Heidi Jo; Beers, Timothy C.; Chen, Li; Deng, Licai; Guhathakurta, Puragra; Hou, Jinliang; Hou, Yonghui; Lépine, Sébastien; Li, Guangwei; Luo, A-Li; Smith, Martin C.; Wu, Yue; Yang, Ming; Yanny, Brian; Zhang, Haotong; Zheng, Zheng

    2015-06-05

    Here, we present a method to estimate distances to stars with spectroscopically derived stellar parameters. The technique is a Bayesian approach with likelihood estimated via comparison of measured parameters to a grid of stellar isochrones, and returns a posterior probability density function for each star's absolute magnitude. We tailor this technique specifically to data from the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) survey. Because LAMOST obtains roughly 3000 stellar spectra simultaneously within each ~5-degree diameter "plate" that is observed, we can use the stellar parameters of the observed stars to account for the stellar luminosity function and target selection effects. This removes biasing assumptions about the underlying populations, both due to predictions of the luminosity function from stellar evolution modeling, and from Galactic models of stellar populations along each line of sight. Using calibration data of stars with known distances and stellar parameters, we show that our method recovers distances for most stars within ~20%, but with some systematic overestimation of distances to halo giants. We apply our code to the LAMOST database, and show that the current precision of LAMOST stellar parameters permits measurements of distances with ~40% error bars. This precision should improve as the LAMOST data pipelines continue to be refined.

  6. Blue Supergiant X-Ray Binaries in the Nearby Dwarf Galaxy IC 10

    NASA Astrophysics Data System (ADS)

    Laycock, Silas G. T.; Christodoulou, Dimitris M.; Williams, Benjamin F.; Binder, Breanna; Prestwich, Andrea

    2017-02-01

    In young starburst galaxies, the X-ray population is expected to be dominated by the relics of the most massive and short-lived stars, black hole and neutron-star high-mass X-ray binaries (XRBs). In the closest such galaxy, IC 10, we have made a multi-wavelength census of these objects. Employing a novel statistical correlation technique, we have matched our list of 110 X-ray point sources, derived from a decade of Chandra observations, against published photometric data. We report an 8σ correlation between the celestial coordinates of the two catalogs, with 42 X-ray sources having an optical counterpart. Applying an optical color-magnitude selection to isolate blue supergiant (SG) stars in IC 10, we find 16 matches. Both cases show a statistically significant overabundance versus the expectation value for chance alignments. The blue objects also exhibit systematically higher {f}x/{f}v ratios than other stars in the same magnitude range. Blue SG-XRBs include a major class of progenitors of double-degenerate binaries, hence their numbers are an important factor in modeling the rate of gravitational-wave sources. We suggest that the anomalous features of the IC 10 stellar population are explained if the age of the IC 10 starburst is close to the time of the peak of interaction for massive binaries.

  7. Dawes Review 6: The Impact of Companions on Stellar Evolution

    NASA Astrophysics Data System (ADS)

    De Marco, Orsola; Izzard, Robert G.

    2017-01-01

    Astrophysicists are increasingly taking into account the effects of orbiting companions on stellar evolution. New discoveries have underlined the role of binary star interactions in a range of astrophysical events, including some that were previously interprete