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Microwave emission from late-type dwarf stars UV Ceti and YZ Canis Minoris  

NASA Astrophysics Data System (ADS)

Simultaneous high-resolution observations of two late-type dwarf stars, UV Cet and YZ CMi, at 6 and 20 cm are presented. These observations put sufficient constraints on existing interpretations to conclude that the quiescent microwave emission from these stars is due to gyrosynchrotron radiation of nonthermal electrons having a power-law energy distribution. From the lifetime of 1 hr of the nonthermal particles against radiation and collision losses, a magnetic field of a few thousand gauss on the photosphere of these stars is estimated. The observations indicate that the ambient density in the coronae of YZ CMi is an order of magnitude higher than that of UV Cet.

Kundu, M. R.; Shevgaonkar, R. K.



Driving in ZZ Ceti stars - Problem solved? .  

NASA Astrophysics Data System (ADS)

There is a fairly tight correlation between the pulsation periods and effective temperatures of ZZ Ceti stars (cooler stars have longer periods). This seems to fit the theoretical picture, where driving occurs in the partial ionization zone, which lies deeper and deeper within the star as it cools. It is reasonable to assume that the pulsation periods should be related to the thermal timescale in the region where driving occurs. As that region sinks further down below the surface, that thermal timescale increases. Assuming this connection, the pulsation periods could provide an additional way to determine effective temperatures, independent of spectroscopy. We explore this idea and find that in practice, things are not so simple.

Kim, A.; Winget, D. E.; Montgomery, M. H.; Kepler, S. O.


FV Serpentis is a Mira Ceti-type variable star.  

NASA Astrophysics Data System (ADS)

The examination of about hundred plates (1974 - 1982) showed absence of R Coronae Borealis type variability. The star is a Mira Ceti-type variable with the period of 365d. Photographic (B) observations and a finding chart with comparison stars magnitudes are given.

Pogosyants, A. Yu.



SciTech Connect

We compute new chemical profiles for the core and envelope of white dwarfs appropriate for pulsational studies of ZZ Ceti stars. These profiles are extracted from the complete evolution of progenitor stars, evolved through the main sequence and the thermally pulsing asymptotic giant branch (AGB) stages, and from time-dependent element diffusion during white dwarf evolution. We discuss the importance of the initial-final mass relationship for the white dwarf carbon-oxygen composition. In particular, we find that the central oxygen abundance may be underestimated by about 15% if the white dwarf mass is assumed to be the hydrogen-free core mass before the first thermal pulse. We also discuss the importance for the chemical profiles expected in the outermost layers of ZZ Ceti stars of the computation of the thermally pulsing AGB phase and of the phase in which element diffusion is relevant. We find a strong dependence of the outer layer chemical stratification on the stellar mass. In particular, in the less massive models, the double-layered structure in the helium layer built up during the thermally pulsing AGB phase is not removed by diffusion by the time the ZZ Ceti stage is reached. Finally, we perform adiabatic pulsation calculations and discuss the implications of our new chemical profiles for the pulsational properties of ZZ Ceti stars. We find that the whole g-mode period spectrum and the mode-trapping properties of these pulsating white dwarfs as derived from our new chemical profiles are substantially different from those based on chemical profiles widely used in existing asteroseismological studies. Thus, we expect the asteroseismological models derived from our chemical profiles to be significantly different from those found thus far.

Althaus, L. G.; Corsico, A. H.; Romero, A. D.; Miller Bertolami, M. M. [Facultad de Ciencias Astronomicas y Geofisicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, (1900) La Plata (Argentina); Bischoff-Kim, A. [Department of Chemistry, Physics and Astronomy, CBX 82, Georgia College and State University, Milledgeville, GA 31061 (United States); Renedo, I.; Garcia-Berro, E., E-mail: [Departament de Fisica Aplicada, Universitat Politecnica de Catalunya, c/Esteve Terrades 5, 08860 Castelldefels (Spain)



14 Ceti: a probable Ap-star-descendant entering the Hertzsprung gap  

NASA Astrophysics Data System (ADS)

Context. 14 Ceti is a subgiant star of F spectral class that displays variations in the S-index of its Ca ii H & K lines and an X-ray emission that is stronger than the mean observed for its spectral class, which may be due to some magnetic activity. Aims: We attempt to Zeeman-detect and study the magnetic field of 14 Ceti and to infer its origin. Methods: We used the spectropolarimeter Narval at the Telescope Bernard Lyot, Pic du Midi Observatory, and the least squares deconvolution method to create high signal-to-noise ratio Stokes V profiles. We derived the surface-averaged longitudinal magnetic field Bl. We also measured the S-index, and the radial velocity for each observation. Results: 14 Ceti is Zeeman-detected for the 30 observed dates spanning from August 2007 to January 2012. The average longitudinal magnetic field does not reverse its sign, reaches about -35 G, and shows some month-long-timescale variations in our 2008 and 2011-2012 observations. The S-index follows the same long-term trend as Bl. 14 Ceti is confirmed as a single star without H-K emission cores. The strength of the observed surface magnetic field of 14 Ceti is one order of magnitude greater than the observed one for late F main-sequence stars, and is comparable to the values measured in the active late F pre-main-sequence star HR 1817. On the other hand, taking into account the post-main-sequence evolution of an Ap star, an oblique rotator model can explain the strength of the magnetic field of 14 Ceti. The variations with a timescale of months observed for both the Bl and S-index could be due to the rotation. Conclusions: The most probable scenario to explain our observations appears to be that 14 Ceti is the descendant of a cool Ap star. Based on data obtained using the Télescope Bernard Lyot at Observatoire du Pic du Midi, CNRS/INSU and Université de Toulouse, France.

Aurière, M.; Konstantinova-Antova, R.; Petit, P.; Charbonnel, C.; Van Eck, S.; Donati, J.-F.; Lignières, F.; Roudier, T.



The effective temperature of Wolf 485A and the statistics of ZZ Ceti stars  

Microsoft Academic Search

High-speed photometry shows that the bright DA white dwarf Wolf 485A is not a variable star, with an upper limit on the semi-amplitudes of luminosity variations of 0.0005 mag in the period range characteristic of the ZZ Ceti stars. However, its time-averaged multichannel color index (G-R) places it in the instability strip. If confirmed, this result would make Wolf 485A

F. Wesemael; G. Fontaine



Asteroseismology of the ZZ Ceti star HS 0507+0434B  

NASA Astrophysics Data System (ADS)

The pulsating DA white dwarfs (ZZ Ceti stars) are g-mode non-radial pulsators. Asteroseismology provides strong constraints on their global parameters and internal structure. Since all the DA white dwarfs falling in the ZZ Ceti instability strip do pulsate, the internal structure derived from asteroseismology brings knowledge for the DA white dwarfs as a whole group. HS 0507+0434B is one of the ZZ Ceti stars which lies approximately in the middle of the instability strip for which we have undertaken a detailed asteroseismological study. We carried out multisite observation campaigns in 2007 and from 2009 December to 2010 January. In total, 206 h of photometric time series have been collected. They have been analysed by means of Fourier analysis and simultaneous multifrequency sine wave fitting. In total, 39 frequency values are resolved including six triplets and a number of linear combinations. We identify the triplets as ? = 1 g modes split by rotation. We derived the period spacing, the rotational splitting and the rotation rate. From the comparison of the observed periods with the theoretical periods of a series of models, we estimate the fundamental parameters of the star: its total mass M*/M? = 0.675, its luminosity L/L? = 3.5 × 10-3, and its hydrogen mass fraction MH/M* = 10-8.5.

Fu, J.-N.; Dolez, N.; Vauclair, G.; Fox-Machado, L.; Kim, S.-L.; Li, C.; Chen, L.; Alvarez, M.; Su, J.; Charpinet, S.; Chevreton, M.; Michel, R.; Yang, X. H.; Li, Y.; Zhang, Y. P.; Molnar, L.; Plachy, E.




SciTech Connect

We infer the structure of the ZZ Ceti stars L 19-2 and GD 165 by comparing the observed periods with periods predicted from an extensive grid of evolutionary white dwarf models. The observed period structure of these two stars is similar, and the models for both stars have a helium layer mass of about 10{sup {minus}2}M* and a hydrogen layer mass of about 10{sup {minus}4}M*. The core of these models is 20:80 C/O that extends to 0.60 to 0.65M* with a linear ramp to pure carbon by 0.90M*. The differences in the observed effective temperature, log g, and periods imply different stellar masses for these two stars. L 19-2 has a favored stellar mass of 0.72M{circle_dot} and GD 165 has a favored stellar mass range of 0.65 to 0.68M*.




Seismological procedures for ZZ Ceti stars and an application to G 117-B15A  

SciTech Connect

In this paper, we outline the procedure for seismological analysis of the ZZ Ceti stars, which are pulsating white dwarfs with hydrogen atmospheres. We use G 117-B15A as the example for this process and derive constraints on the mass and internal structure. The hydrogen layer mass is either about 10(-4)M* or 10(-7)M* depending on whether the l = 1 mode near 215 s is k = 2 or k = 1, respectively. In both cases, the best fitting mass is 0.60M solar, in agreement with spectroscopic log g values.

Bradley, P.A.



The cool ZZ Ceti star PG 2303+243: observations and analysis of variability in 2004  

NASA Astrophysics Data System (ADS)

PG 2303+243 is a cool DA variable (also called ZZ Ceti) star with a rich pulsation spectrum and variable amplitudes. A mini-campaign involving six observatories yielded time-resolved photometric measurements of PG 2303+243 during the period 2004 September 5-20. A duty cycle of 35 per cent was achieved. We detected 24 possible independent frequencies, their amplitudes and phases for future mode identification. We confirm the occurrence of short-term amplitude and frequency variations. Our analysis suggests an l= 1 rotational splitting around 8.4 ?Hz, implying a rotation period of 16.5 h.

Pakštien?, E.; Solheim, J.-E.; Handler, G.; Reed, M.; Bognár, Zs.; Rodler, F.; Paparó, M.; Zdanavi?ius, J.; Steininger, B.; Wolf, G.



Shock-induced polarized hydrogen emission lines in the Mira star o Ceti  

NASA Astrophysics Data System (ADS)

Context. In the spectra of variable pulsating stars, especially Mira stars, the detection of intense hydrogen emission lines has been explained by the presence of a radiative and hypersonic shock wave, periodically propagating throughout the stellar atmosphere. Previous observation of the Mira star o Ceti around one of its brightest maximum light led to the detection of a strong level of linear polarization associated to Balmer emissions, although the origin of this phenomenon is not fully explained yet. Aims: With the help of spectropolarimetry, we propose to investigate the nature of shock waves propagating throughout the stellar atmosphere and present, for o Ceti (the prototype of Mira stars), a full observational study of hydrogen emission lines formed in the radiative region of such a shock. Methods: Using the instrument NARVAL mounted on the Télescope Bernard Lyot (TBL) in Pic du Midi Observatory (France), we performed a spectropolarimetric monitoring of o Ceti during three consecutive pulsation cycles. For this survey, the four Stokes parameters (I for intensity, Q and U for linear polarization, and V for circular polarization) were systematically collected, with a particular emphasis on the maxima of luminosity, i.e. when a radiative shock wave is supposed to emerge from the photosphere and starts to propagate outward. Results: On hydrogen Balmer lines, over a large part of the luminosity cycle, we report clear detection of polarimetric structures in Q and U Stokes spectra (and also in V Stokes spectra but to a lesser extent). We report a temporal evolution of these spectropolarimetric signatures, which appear strongly correlated to the presence of an intense shock wave responsible for the hydrogen emission lines. We establish that the hydrogen lines are polarized by a physical process inherent to the mechanism responsible for the emission line formation: the shock wave itself. Two mechanisms are thus considered: a global one that implies a polarization induced by some giant convective cells located around the photosphere and a local one that implies a charge separation due to the passage of the shock wave, inducing an electrical current. Combined with the existing turbulence, this may generate a magnetic field, hence polarization. Based on spectropolarimetric observations obtained at the Télescope Bernard Lyot (TBL at Observatoire du Pic du Midi, CNRS and Université de Toulouse, France).

Fabas, N.; Lèbre, A.; Gillet, D.



Whole Earth telescope observations of the ZZ Ceti star HL Tau 76  

NASA Astrophysics Data System (ADS)

This paper analyses the Whole Earth Telescope observations of HL Tau 76, the first discovered pulsating DA white dwarf. The star was observed during two Whole Earth Telescope campaigns. It was a second priority target during the XCOV13 campaign in 1996 and the first priority one during the XCOV18 campaign in 1999. The 1999 campaign reached 66.5% duty cycle. With a total duration of 18 days, the frequency resolution achieved is 0.68 ?Hz. With such a frequency resolution, we were able to find as many as 78 significant frequencies in the power spectrum, of which 34 are independent frequencies after removal of all linear combinations. In taking into account other frequencies present during the 1996 WET campaign and those present in earlier data, which do not show up in the 1999 data set, we find a total of 43 independent frequencies. This makes HL Tau 76 the richest ZZ Ceti star in terms of number of observed pulsation modes. We use those pulsation frequencies to determine as much as possible of the internal structure of HL Tau 76. The pulsations in HL Tau 76 cover a wide range of periods between 380 s and 1390 s. We propose an identification for 39 of those 43 frequencies in terms of ?=1 and ?=2 non-radial g-modes split by rotation. We derive an average rotation period of 2.2 days. The period distribution of HL Tau 76 is best reproduced if the star has a moderately "thick" hydrogen mass fraction log qH ? -7.0. The results presented in this paper constitute a starting point for a detailed comparison of the observed periods with the periods calculated for models as representative as possible of HL Tau 76.

Dolez, N.; Vauclair, G.; Kleinman, S. J.; Chevreton, M.; Fu, J. N.; Solheim, J.-E.; González Perez, J. M.; Ulla, A.; Fraga, L.; Kanaan, A.; Reed, M.; Kawaler, S.; O'Brien, M. S.; Metcalfe, T. S.; Nather, R. E.; Sanwal, D.; Klumpe, E. W.; Mukadam, A.; Wood, M. A.; Ahrens, T. J.; Silvestri, N.; Sullivan, D.; Sullivan, T.; Jiang, X. J.; Xu, D. W.; Ashoka, B. N.; Leibowitz, E.; Ibbetson, P.; Ofek, E.; Kilkenny, D.; Meištas, E. G.; Alisauskas, D.; Janulis, R.; Kalytis, R.; Moskalik, P.; Zola, S.; Krzesinski, J.; Ogloza, W.; Handler, G.; Silvotti, R.; Bernabei, S.



A 40 Myr Old Gaseous Circumstellar Disk at 49 Ceti: Massive CO-rich Comet Clouds at Young A-type Stars  

NASA Astrophysics Data System (ADS)

The gaseous molecular disk that orbits the main-sequence A-type star 49 Ceti has been known since 1995, but the stellar age and the origin of the observed carbon monoxide molecules have been unknown. We now identify 49 Ceti as a member of the 40 Myr old Argus Association and present a colliding comet model to explain the high CO concentrations seen at 49 Ceti and the 30 Myr old A-type star HD 21997. The model suggests that massive—400 Earth mass—analogs of the Sun's Kuiper Belt are in orbit around some A-type stars, that these large masses are composed primarily of comet-like objects, and that these objects are rich in CO and perhaps also CO2. We identify additional early-type members of the Argus Association and the Tucana/Horologium and Columba Associations; some of these stars display excess mid-infrared emission as measured with the Widefield Infrared Survey Explorer.

Zuckerman, B.; Song, Inseok



No first ionization potential fractionation in the active stars AR Piscium and AY Ceti  

NASA Astrophysics Data System (ADS)

Context: The comparison of coronal and photospheric abundances in cool stars is an essential question to resolve. In the Sun an enhancement of the elements with low first ionization potential (FIP) is observed in the corona with respect to the photosphere. Stars with high levels of activity seem to show a depletion of elements with low FIP when compared to solar standard values; however, the few cases of active stars in which photospheric values are available for comparison lead to confusing results, and an enlargement of the sample is mandatory for solving this longstanding problem. Aims: We calculate in this paper the photospheric and coronal abundances of two well known active binary systems, AR Psc and AY Cet, to get further insight into the complications of coronal abundances. Methods: Coronal abundances of 9 elements were calculated by means of the reconstruction of a detailed emission measure distribution, using a line-based method that considers the lines from different elements separately. Photospheric abundances of 8 elements were calculated using high-resolution optical spectra of the stars. Results: The results once again show a lack of any FIP-related effect in the coronal abundances of the stars. The presence of metal abundance depletion (MAD) or inverse FIP effects in some stars could stem from a mistaken comparison to solar photospheric values or from a deficient calculation of photospheric abundances in fast-rotating stars. Conclusions: The lack of FIP fractionation seems to confirm that Alfvén waves combined with pondermotive forces are dominant in the corona of active stars. Tables 2 and 3 are only available in electronic form at

Sanz-Forcada, J.; Affer, L.; Micela, G.



School-Seminar on CETI Program (Participants Report).  

National Technical Information Service (NTIS)

Methods for the discovery of planets around the nearest stars, for the detection of amino acids in the lunar soil, and for detection of relatively complex organic molecules in cosmic clouds were discussed. Concrete CETI (Communication with Extraterrestria...

Y. Kukharenko



UV habitable zones around M stars  

Microsoft Academic Search

During the last decade there was a change in paradigm, which led to consider that terrestrial-type planets within liquid-water habitable zones (LW-HZ) around M stars can also be suitable places for the emergence and evolution of life. Since many dMe stars emit large amount of UV radiation during flares, in this work we analyze the UV constrains for living systems

Andrea P. Buccino; Guillermo A. Lemarchand; Pablo J. D. Mauas



An Empirical Study of the ZZ Ceti Instability Strip  

NASA Astrophysics Data System (ADS)

ZZ Ceti stars are pulsating hydrogen-line (DA) white dwarfs, which are found in a rather narrow strip within the Teff-log g plane: the ZZ Ceti instability strip. Historically, the instability strip has been studied by analyzing the ZZ Ceti stars themselves. However, an analysis of the photometrically constant DA white dwarfs that lie near the instability strip can be just as insightful. Therefore, in an effort to delineate better the boundaries of the ZZ Ceti instability strip, we have gathered optical spectra for all known constant DA white dwarfs near the instability strip. By comparing the Balmer-line profiles to synthetic spectra generated from model atmospheres, it is possible to determine with great accuracy the atmospheric parameters of these stars. These spectra have been secured as part of a broader observing campaign during which we are hoping to identify new candidate ZZ Ceti stars as well. Indeed, already two of our program stars have showed themselves to be genuine ZZ Ceti pulsators, PB 520 and G232-38. Luminosity variations in the latter were recently discovered by us at the Observatoire du mont Mégantic.

Gianninas, Alexandros; Bergeron, Pierre; Fontaine, Gilles



Constraining the Axion Mass through the Asteroseismology of the ZZ Ceti Star G117-B15A  

NASA Astrophysics Data System (ADS)

We perform an asteroseismological study on the DAV star G117-B15A on the basis of a modern set of fully evolutionary DA white dwarf models that have consistent chemical profiles at the core and the envelope. We found an asteroseismological model for G117-B15A that closely reproduces its observed pulsation periods. Then, we use the most recently measured value of the rate of period change for the dominant mode of this pulsating star to impose a preliminary upper limit to the mass of the axion.

Córsico, A. H.; Althaus, L. G.; Romero, A. D.; Miller Bertolami, M. M.; García-Berro, E.; Isern, J.



The Cosmic Star-Formation History: The UV Finds Most  

Microsoft Academic Search

This is a summary of arguments in favor of observing high-redshift star formation in the UV as presented at the Ringberg meeting in September 2000. The most rapidly star-forming galaxies are very dusty, easier to detect at 850um than in the UV, but less rapidly star-forming galaxies are less obscured by dust and as a result the comparatively faint galaxies

Kurt Adelberger



Long-Period Variability in o Ceti  

NASA Astrophysics Data System (ADS)

We carried out a new and sensitive search for long-period variability in the prototype of the Mira class of long-period pulsating variables, o Ceti (Mira A), the closest and brightest Mira variable. We conducted this search using an unbroken light curve from 1902 to the present, assembled from the visual data archives of five major variable star observing organizations from around the world. We applied several time-series analysis techniques to search for two specific kinds of variability: long secondary periods (LSPs) longer than the dominant pulsation period of ~333 days, and long-term period variation in the dominant pulsation period itself. The data quality is sufficient to detect coherent periodic variations with photometric amplitudes of 0.05 mag or less. We do not find evidence for coherent LSPs in o Ceti to a limit of 0.1 mag, where the amplitude limit is set by intrinsic, stochastic, low-frequency variability of approximately 0.1 mag. We marginally detect a slight modulation of the pulsation period similar in timescale to that observed in the Miras with meandering periods, but with a much lower period amplitude of ±2 days. However, we do find clear evidence of a low-frequency power-law component in the Fourier spectrum of o Ceti's long-term light curve. The amplitude of this stochastic variability is approximately 0.1 mag at a period of 1000 days, and it exhibits a turnover for periods longer than this. This spectrum is similar to the red noise spectra observed in red supergiants.

Templeton, Matthew R.; Karovska, Margarita



Why UV Observatories are crucial to understand massive stars ?  

NASA Astrophysics Data System (ADS)

Each Ultraviolet (UV) mission has brought a breakthrough to our knowledge of massive stars. The first rocket UV spectra of O-type stars showed powerful P-Cygni profiles, which revealed that O stars have an expanding atmosphere or stellar wind. After IUE, FUSE and HST-STIS we now know that these winds are not static nor homogeneous, with shocks and mechanisms for extra ionization in the outflow. Radiation driven winds are actually one of the main pillars of the current paradigm of massive stars, as through mass-removal they dictate the sequence of evolutionary stages, duration, ionizing power and yields to the ISM, and the fate of the star as supernova. But many questions remain open: the weak-wind problem, the driving mechanism of very metal-poor massive stars (our connection to the first stars), and a proper characterization of wind inhomogeneities and shocks, to name a few. HST-COS and the up-coming WSO spectrographs will play a crucial role in solving these issues --crucial to calculate massive star feedback to the Universe-- thanks to the wealth of UV metallic transitions that offer many diagnostics to these physical phenomena.

Garcia Garcia, Miriam



Pre main sequence stars as UV sources for the World Space Observatory-UV mission  

NASA Astrophysics Data System (ADS)

Pre-main sequence stars are bright UV (UV) sources compared with their main sequence analogues. The source of this excess is the high energy processes associated with the physics of accretion/outflow during early stellar evolution. In this review, the main sources of UV excess are described as well as the most significant "unknowns" in the field. Special emphasis is made on the results from the last observations carried out with the Hubble Space Telescope and on the relevance of future dedicated monitoring programs with the World Space Observatory-UV.

Gomez de Castro, Ana I.; Lamzin, Sergei A.



Complete UV Atlas of Standard Stars.  

National Technical Information Service (NTIS)

The general objective of this project is to provide a comprehensive ultraviolet spectral atlas of stars based on the data in the IUE Final Archive. The data have been uniformly processed by the IUE NEWSIPS pipeline system. The NEWSIPS gives an improved si...

C. C. Wu



A Complete UV Atlas of Standard Stars  

Microsoft Academic Search

The general objective of this project is to provide a comprehensive ultraviolet spectral atlas of stars based on the data in the IUE Final Archive. The data have been uniformly processed by the IUE NEWSIPS pipeline system. The NEWSIPS gives an improved signal to noise ratio for the data that will be especially beneficial to low signal portions of the

Chi-Chao Wu



Shock-Induced Polarized Hydrogen Emission Lines in Omicron Ceti  

NASA Astrophysics Data System (ADS)

We have performed a spectropolarimetric survey of the variable Mira star omicron Ceti along three pulsation cycles. We present those new data collected with the Narval instrument mounted on the Telescope Bernard Lyot (TBL) in Pic du Midi, France. We have detected time variable polarimetric signatures (on QUV Stokes spectra) associated with Balmer hydrogen emission lines supposed to be formed behind the front of a shock wave propagating throughout the stellar atmosphere. We associate the linear polarization of Balmer emission lines in Mira stars to the presence and the structure of the radiative shock wave.

Fabas, N.; Lèbre, A.; Gillet, D.



Shock-Induced Polarized Hydrogen Emission Lines in omicron Ceti  

NASA Astrophysics Data System (ADS)

We have performed a spectropolarimetric survey of the variable Mira star omicron Ceti along three pulsation cycles. We present those new data collected with the Narval instrument mounted on the Telescope Bernard Lyot (TBL) in Pic du Midi, France. We have detected time variable polarimetric signatures (on QUV Stokes spectra) associated with Balmer hydrogen emission lines supposed to be formed behind the front of a shock wave propagating throughout the stellar atmosphere. We associate the linear polarization of Balmer emission lines in Mira stars to the presence and the structure of the radiative shock wave.

Lèbre, A.; Fabas, N.; Gillet, D.



UV Spectral Properties of O and B Stars Versus Metallicity  

NASA Astrophysics Data System (ADS)

Metallicity is the most fundamental parameter governing both stellar and galactic evolution. Yet, little is known observationally about how metallicity affects the physics of massive stars. To explore this connection, we will use the STIS to obtain slitless UV spectroscopy of bright OB associations in three Local Group galaxies that span a factor of 30 in metallicity. Our targets are star-forming regions in M31, NGC 6822, and Sextans A. Nebular O/H abundances indicate Sextans A is the most metal deficient galaxy in the Local Group, with a metallicity 30x below the Galaxy and 3x below the SMC. The STIS UV slitless spectra will resolve numerous O and B stars in a single exposure. This study will use the unique spectral imaging capabilities of STIS to probe stellar populations spanning the widest range of metallicity possible. Theoretical synthetic spectra will be constructed in an attempt to match the strengths and shapes of both strong photospheric and wind features. In th is way we will derive approximate abundances, mass loss rates, and terminal velocities. We will also apply our new UV stellar classification criteria and probe the variation with metallicity of mass-loss characteristics through the H-R diagram. Our goal is to answer one of the most fundamental questions in astrophysics: ``What is the impact of chemical abundance upon stellar mass loss?"

Bruhweiler, Frederick



The CP Galium Stars in the UV. I. HD 168733  

NASA Astrophysics Data System (ADS)

HD 168733 is a magnetic CP star with an unusual spectrum. It was not possible to assign this star to the Si or HgMn group. Jaschek & Jaschek (A&A, 171, 380, 1987) have included this star in a list of objects having strong UV Gallium lines. In order to get some clues about the real nature of this star, we are performing an elemental abundance analysis of this star using spectrograms obtained with EBASIM spectrograph attached to CASLEO 2.15 m telescope. The reduction of the observational material and the measurements of the equivalent widths were carried out using the appropriate IRAF tasks. The atmospheric parameters Teff and log g were determined using uvbybeta photometry and TemLogG code with the corrections suggested by Adelman & Rayle (A&A 447, 685, 2000) for magnetic CP stars. The adopted values are: Teff = 13274 K, log g = 3.58. The chemical abundances are being calculating using WIDTH9 code.

Collado, A.; López García, Z.; Levato, H.; Malaroda, S.


Shock-induced polarized hydrogen emission lines in omicron Ceti  

NASA Astrophysics Data System (ADS)

Hydrogen emission lines in Mira variable stars are a well-known phenomenon whose origin has been established as related to the propagation of radiative hypersonic shock waves throughout the stellar atmosphere. A polarimetric observation by McLean and Coyne [1] made on omicron Ceti (the prototype of Mira variable stars) has revealed the existence of linear polarization signatures associated with Balmer emission lines. However, the polarizing mechanism has never been properly explained so far. The study presented here is the first of its kind since it displays the results of a spectropolarimetric survey of omicron Ceti in the Balmer lines. The survey was made with the NARVAL spectropolarimeter (Telescope Bernard Lyot, France) in full Stokes mode. We did not just confirm the appearance of this polarization but we also and above all showed the temporal variation of the linear polarization in the lines. We conclude that the polarizing mechanism is definitely intrinsic to the shock wave propagation throughout the stellar atmosphere of Mira and give some leads about the nature of this mechanism.

Fabas, N.; Lèbre, A.; Gillet, D.



Gershberg Flare Star Catalogue (Shakhovskaya 1971)  

NASA Astrophysics Data System (ADS)

This catalog groups the flare stars as presented in the IAU Colloquium 15 (combined Colloquium of Commisions 27 and 42) held at Bamberg 31-Aug to 03-Sep 1971 entitled "New Directions and New Frontiers in Variable Star Research" The following definition of the UV Cet-type variables was given in Kukarkin's General Catalogue of Variable Stars (1969): "dMe stars, sometimes subject to flares with the amplitude from 1 to 6mag. Maximum brightness is attained in seconds or dozens of seconds after the commencement of the flare; the star returns to its normal brightness after several minutes, or dozens of minutes. A typical representative is UV Ceti." Now it is impossible to consider this definition as a quite right because: 1) There are a number of M-dwarf stars affected by the flares similar to the UV Ceti flares, but in their quiet state spectra, no emission lines are observed. For example, BD+43 44A, BD+43 44 B, and SZ UMa, the flare activity of these stars were detected in Crimea; and probably BD-04 4048B is suspected as a flare star by HERBIG. 2) The lower limit of flare amplitude cited in Kukarkin's corresponds to visual observations, but the modern photoelectric observations register flares with amplitudes to 0.02-0.05mag. Therefore we suppose, that UV Cet-type variables are K-M dwarfs, which show quick flares with amplitudes exceeding the observational errors, and duration of the flares are from a few seconds up to a few hundred minutes. The "catalog" file includes only such variable K-M dwarf stars, for which existing observations allow to construct flare light curves. All stars in "catalog", except V371 Ori, have photoelectric flare light curves. The strong flare of V371 Ori was observed in radio region, but simultaneous optical observations were carried out photographically and visually only. (1 data file).

Shakhovskaya, N. I.



Morphologies and Substructures of UV Star-Forming Galaxies at Intermediate-z  

NASA Astrophysics Data System (ADS)

Exploring potential links between the internal physical processes of galaxies with respect to their external morphologies can reveal connections between past and present populations. One primary physical driver of galaxy evolution is star formation, which is directly detected from UV emission. Here, we summarize a study investigating the optical and UV morphologies of rest-frame UV-detected star-forming galaxies at intermediate redshifts (0.1UV) and Wide Field PlanetaryCamera 2 (WFPC2; U-band) in the Great Observatories Origins Deep Survey fields.

Voyer, E. N.; de Mello, D. F.; Blevins, S. M.; Teplitz, H. I.; Gardner, J. P.; Siana, B. D.; Soto, E.




SciTech Connect

Taking into account results obtained from models and from statistical analyses of obtained parameters, we discuss flare activity levels and flare characteristics of five UV Ceti stars. We present the parameters of unpublished flares detected over two years of observations of V1005 Ori. We compare parameters of the U-band flares detected over several seasons of observations of AD Leo, EV Lac, EQ Peg, V1054 Oph, and V1005 Ori. Flare frequencies calculated for all program stars and maximum energy levels of the flares are compared, and we consider which is the most correct parameter as an indicator of flare activity levels. Using the One Phase Exponential Association function, the distributions of flare equivalent duration versus flare total duration are modeled for each program star. We use the Independent Samples t-Test in the statistical analyses of the parameters obtained from the models. The results reveal some properties of flare processes occurring on the surfaces of UV Ceti type stars. (1) Flare energies cannot be higher than a specific value regardless of the length of the flare total duration. This must be a saturation level for white-light flares occurring in flare processes observed in the U band. Thus, for the first time it is shown that white-light flares have a saturation in a specific energy range. (2) The span values, which are the difference between the equivalent durations of flares with the shortest and longest total durations, are almost equal for each star. (3) The half-life values, minimum flare durations for saturation, increase toward the later spectral types. (4) Both maximum total durations and maximum rise times computed from the observed flares decrease toward the later spectral types among the UV Ceti stars. According to the maximum energy levels obtained from the models, both EV Lac and EQ Peg are more active than the other three program stars, while AD Leo is the most active flare star according to the flare frequencies.

Dal, H. A.; Evren, S., E-mail: [Department of Astronomy and Space Sciences, University of Ege, Bornova, 35100 Izmir (Turkey)



Infant Mortality of Star Clusters: on the Origin of the Diffuse UV Emission  

NASA Astrophysics Data System (ADS)

We present HST images in which we discovered the presence of a large number of massive stars in the field of the two galaxies NGC 1313 and NGC 4449. These massive stars, not in obvious groups or clusters, are known to produce a significant amount of UV radiation, and to live for at most 25 Myr. We think that these stars are the main source of diffuse UV emission first observed by Meurer et al. (1995) in starburst galaxies. We also propose that the infant mortality of star clusters, an early evolutionary stage of star clusters which kills 90% of them within 10 Myr, is a physical process that can explain how these young stars could end up in the field so quickly. We will also present preliminary stellar 2-points correlation functions for the two galaxies.

Pellerin, A.; Meyer, M. J.; Harris, J.; Calzetti, D.



Stroemgren photometry of ZZ Ceti and other DA white dwarfs  

SciTech Connect

Stroemgren colors for a sample of 71 stars classified as DA white dwarfs are presented. Comparison with the recent model atmospheres of the Kiel group indicates that the average gravity of 63 stars of the sample is log g = 7.98 +- 0.31, with no indication of a dependence on the effective temperature. This is consistent with the theoretical expectation that white dwarfs evolve at constant gravity. Correlations between Stroemgren colors and Greenstein multichannel colors are also given, using 52 stars that have been observed in common in the two systems. These correlations are used to compare the data with a second set of model atmospheres computed by Shipman. Contrary to what has been suggested in the past, no fundamental differences are found when confronting the Stroemgren data with the DA model atmospheres of Shipman or those of the Kiel group. Finally, observations of 11 pulsating objects reveal the existence of a narrow instability strip in the range 13 000 K> or approx. =T/sub e/> or approx. =11 000 K in a ((u-b), (b-y)) two-color diagram. The present results add evidence to the contention that all DA white dwarfs evolve to become ZZ Ceti pulsators in the instability strip.

Fontaine, G.; Bergeron, P.; Lacombe, P.; Lamontagne, R.; Talon, A.



Binary Stars as the Source of the Far-UV Excess in Elliptical Galaxies  

NASA Astrophysics Data System (ADS)

The discovery of an excess of light in the far-ultraviolet (UV) spectrum in elliptical galaxies was a major surprise in 1969. While it is now clear that this UV excess is caused by an old population of hot helium-burning stars without large hydrogen-rich envelopes rather than young stars, their origin has remained a mystery. Here we show that these stars most likely lost their envelopes because of binary interactions, similar to the hot subdwarf population in our own Galaxy. This has major implications for understanding the evolution of the UV excess and of elliptical galaxies in general. In particular, it implies that the UV excess is not a sign of age, as had been postulated previously, and predicts that it should not be strongly dependent on the metallicity of the population.

Han, Z.; Podsiadlowski, P.; Lynas-Gray, A. E.




SciTech Connect

As part of the Panchromatic Hubble Andromeda Treasury multi-cycle program, we observed a 12' Multiplication-Sign 6.'5 area of the bulge of M31 with the WFC3/UVIS filters F275W and F336W. From these data we have assembled a sample of {approx}4000 UV-bright, old stars, vastly larger than previously available. We use updated Padova stellar evolutionary tracks to classify these hot stars into three classes: Post-AGB stars (P-AGB), Post-Early AGB (PE-AGB) stars, and AGB-manque stars. P-AGB stars are the end result of the asymptotic giant branch (AGB) phase and are expected in a wide range of stellar populations, whereas PE-AGB and AGB-manque (together referred to as the hot post-horizontal branch; HP-HB) stars are the result of insufficient envelope masses to allow a full AGB phase, and are expected to be particularly prominent at high helium or {alpha} abundances when the mass loss on the red giant branch is high. Our data support previous claims that most UV-bright sources in the bulge are likely hot (extreme) horizontal branch (EHB) stars and their progeny. We construct the first radial profiles of these stellar populations and show that they are highly centrally concentrated, even more so than the integrated UV or optical light. However, we find that this UV-bright population does not dominate the total UV luminosity at any radius, as we are detecting only the progeny of the EHB stars that are the likely source of the UV excess. We calculate that only a few percent of main-sequence stars in the central bulge can have gone through the HP-HB phase and that this percentage decreases strongly with distance from the center. We also find that the surface density of hot UV-bright stars has the same radial variation as that of low-mass X-ray binaries. We discuss age, metallicity, and abundance variations as possible explanations for the observed radial variation in the UV-bright population.

Rosenfield, Philip; Johnson, L. Clifton; Dalcanton, Julianne J.; Williams, Benjamin F.; Gilbert, Karoline M. [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Girardi, Leo [Osservatorio Astronomico di Padova-INAF, Vicolo dell'Osservatorio 5, I-35122 Padova (Italy); Bressan, Alessandro [SISSA, Via Bonomea 265, 34136 Trieste (Italy); Lang, Dustin [Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States); Guhathakurta, Puragra; Dorman, Claire E. [UCO/Lick Observatory and Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Howley, Kirsten M. [Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 (United States); Lauer, Tod R.; Olsen, Knut A. G. [National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Bell, Eric F. [Department of Astronomy, University of Michigan, 500 Church St., Ann Arbor, MI 48109 (United States); Bianchi, Luciana [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States); Caldwell, Nelson [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street Cambridge, MA 02138 (United States); Dolphin, Andrew [Raytheon Company, 1151 East Hermans Road, Tucson, AZ 85756 (United States); Kalirai, Jason [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Larsen, Soren S. [Astronomical Institute, University of Utrecht, Princetonplein 5, 3584 CC Utrecht (Netherlands); Rix, Hans-Walter [Max Planck Institute for Astronomy, Koenigstuhl 17, D-69117 Heidelberg (Germany); and others



The Panchromatic Hubble Andromeda Treasury: Bright UV Stars in the Bulge of M31  

NASA Astrophysics Data System (ADS)

As part of the Panchromatic Hubble Andromeda Treasury (PHAT) multi-cycle program, we observed a 12? × 6.5? area of the bulge of M31 with the WFC3/UVIS filters F275W and F336W . From these data we have assembled a sample of UV-bright, old stars, vastly larger than previously available. We use updated Padova stellar evolutionary tracks to classify these hot stars into three classes, including Post-AGB stars (P-AGB), Post-Early AGB (PE-AGB) stars and AGB-manque stars. P-AGB stars are the end result of the AGB phase and are expected in a wide range of stellar populations, whereas PE-AGB and AGB-manque (together referred to as hot post-horizontal branch HP-HB) stars are the result of insufficient envelope masses to allow a full AGB phase, and are expected to be particularly prominent at high helium or ? abundances when the mass loss on the RGB is high. Our data support previous claims that most UV-bright sources in the bulge are likely hot horizontal branch stars (EHB) and their progeny. We construct the first radial profiles of these stellar populations, and show that they are highly centrally concentrated, even more so than the integrated UV or optical light. However, we find that this UV-bright population does not dominate the total UV luminosity at any radius, as we are detecting the progeny of the EHB stars that are the likely source of the UVX. We calculate that only a few percent of MS stars in the central bulge can have gone through the HP-HB phase and that this percentage decreases strongly with distance from the center. We also find that the surface density of hot UV-bright stars has the same radial variation as that of LMXBs. We discuss age, metallicity, and abundance variations as possible explanations for the observed radial variation in the UV-bright population.

Rosenfield, Philip; Johnson, L.; Girardi, L.; Dalcanton, J. J.; Bressan, A.; Lang, D.; Williams, B. F.; Howley, K. M.; Guhathakurta, P.; Panchromatic Hubble Andromeda Treasury Survey Team



Mid-IR Luminosities and UV\\/Optical Star Formation Rates at z < 1.4  

Microsoft Academic Search

Ultraviolet (UV) nonionizing continuum and mid-infrared (IR) emission constitute the basis of two widely used star formation (SF) indicators at intermediate and high redshifts. We study 2430 galaxies with z < 1.4 in the Extended Groth Strip with deep MIPS 24 mum observations from FIDEL, spectroscopy from DEEP2, and UV, optical, and near-IR photometry from the AEGIS. The data are

Samir Salim; R. Michael Rich; Stéphane Charlot; Janice C. Lee; David Schiminovich; Pablo G. Pérez-González; Matthew L. N. Ashby; Casey Papovich; S. M. Faber; Rob J. Ivison; David T. Frayer; Josiah M. Walton; Benjamin J. Weiner; Ranga-Ram Chary; Kevin Bundy; Kai Noeske; Anton M. Koekemoer



Habitable zones and UV habitable zones around host stars  

NASA Astrophysics Data System (ADS)

Ultraviolet radiation is a double-edged sword to life. If it is too strong, the terrestrial biological systems will be damaged. And if it is too weak, the synthesis of many biochemical compounds cannot go along. We try to obtain the continuous ultraviolet habitable zones, and compare the ultraviolet habitable zones with the habitable zones of host stars. Using the boundary ultraviolet radiation of ultraviolet habitable zone, we calculate the ultraviolet habitable zones of host stars with masses from 0.08 to 4.00 M ?. For the host stars with effective temperatures lower than 4,600 K, the ultraviolet habitable zones are closer than the habitable zones. For the host stars with effective temperatures higher than 7,137 K, the ultraviolet habitable zones are farther than the habitable zones. For a hot subdwarf as a host star, the distance of the ultraviolet habitable zone is about ten times more than that of the habitable zone, which is not suitable for the existence of life.

Guo, Jianpo; Zhang, Fenghui; Zhang, Xianfei; Han, Zhanwen



Atlas of Far UV and Optical Spectra of Be Stars.  

National Technical Information Service (NTIS)

An atlas based on IUE (International Ultraviolet Explorer) high resolution spectra of the Be stars and their Balmer emission line profiles published by ESA in 1990 is described. It is intended to serve as a tool for future research and planning of both gr...

V. Doazan G. Sedmak M. Barylak L. Rusconi



The instability strip of ZZ Ceti white dwarfs. I. Introduction of time-dependent convection  

NASA Astrophysics Data System (ADS)

Aims: The determination of the location of the theoretical ZZ Ceti instability strip in the log g - Teff diagram has remained a challenge over the years due to the lack of a suitable treatment for convection in these stars. For the first time, a full nonadiabatic approach including time-dependent convection is applied to ZZ Ceti pulsators, and we provide the appropriate details related to the inner workings of the driving mechanism. Methods: We used the nonadiabatic pulsation code MAD with a representative evolutionary sequence of a 0.6 M? DA white dwarf. This sequence is made of state-of-the-art models that include a detailed modeling of the feedback of convection on the atmospheric structure. The assumed convective efficiency in these models is the so-called ML2/? = 1.0 version. We also carried out, for comparison purposes, nonadiabatic computations within the frozen convection approximation, as well as calculations based on models with standard grey atmospheres. Results: We find that pulsational driving in ZZ Ceti stars is concentrated at the base of the superficial H convection zone, but at depths, near the blue edge of the instability strip, somewhat larger than those obtained with the frozen convection approach. Despite the fact that this approach is formally invalid in such stars, particularly near the blue edge of the instability strip, the predicted boundaries are not dramatically different in both cases. The revised blue edge for a 0.6 M? model is found to be around Teff = 11 970 K, some 240 K hotter than the value predicted within the frozen convection approximation, in rather good agreement with the empirical value. On the other hand, our predicted red edge temperature for the same stellar mass is only about 5600 K (80 K hotter than with the frozen convection approach), much lower than the observed value. Conclusions: We correctly understand the development of pulsational instabilities of a white dwarf as it cools at the blue edge of the ZZ Ceti instability strip. Our current implementation of time-dependent convection however still lacks important ingredients to fully account for the observed red edge of the strip. We will explore a number of possibilities in the future papers of this series.

Van Grootel, V.; Dupret, M.-A.; Fontaine, G.; Brassard, P.; Grigahcène, A.; Quirion, P.-O.



Elemental abundance analyses with DAO spectrograms: XXX. The middle B through early A stars ?2 Ceti (B9 III), 21 Aquilae (B8 II-III), ? Aquilae (B5 III), and ? Delphini (A2V)  

NASA Astrophysics Data System (ADS)

This series of high quality elemental abundance analyses of mostly main-sequence band normal and peculiar B, A, and F stars defines their properties and provides data for the comparison with the analyses of somewhat similar stars and with theoretical predictions. Most use high dispersion and high S/N (? 200) spectrograms obtained with CCD detectors at the long camera of the Coudé spectrograph of the 1.22-m Dominion Astrophysical Observatory telescope. Here we reanalyze 21 Aql with better quality spectra and increase the number of stars consistently analyzed in the spectral range B5 to A2 by analyzing three new stars for this series. In the early A stars the normal and non-mCP stars have abundances with overlapping ranges. But more stars are needed especially in the B5 to B9 range. ?2 Cet on average has a solar composition with a few abundances outside the solar range while both 21 Aql and ? Aql have abundances marginally less than solar. The abundances of ? Del are greater than solar with a few elements such as Ca being less than solar. It is an Am star. Table 3 is only available in electronic form at the CDS via

Adelman, S. J.; Westbrook, P. C.; Gulliver, A. F.



Be Star Atlas of Far UV and Optical High-Resolution Spectra.  

National Technical Information Service (NTIS)

An overview of the spectral characteristics of Be stars in both the far UV and optical wavelength ranges is provided and details of their variable behavior are given when data are available. Line profiles of H alpha and/or H beta are given for the majorit...

V. Doazan G. Sedmak M. Barylak L. Rusconi B. Battrick



Quantifying Star Formation in Early-Type Galaxies using Spatially-Resolved UV-Optical Photometry  

NASA Astrophysics Data System (ADS)

Our understanding of star formation in nearby early-type galaxies (ETGs) has evolved rapidly in recent years, due to new UV data from GALEX and HST. Contrary to the classical notion of them being old, passively-evolving systems, recent work has demonstrated widespread late-epoch star formation in ETGs, which builds ~20% of their stellar mass after 1, via minor mergers between ETGs and gas-rich dwarfs. While survey data from GALEX has indicated the average properties of star formation in the ETG population as a whole, I demonstrate how spatially-resolved UV studies can offer detailed insights into the star formation histories of individual galaxies, using an HST-WFC3 case study of NGC 4150. Using a pixel-by-pixel analysis in 5 WFC3 filters, spanning UV to i-band, reveals a central 0.9 Gyr old young stellar population, with a median metallicity of 0.5 solar, that contributes around 3% of the stellar mass and coincides spatially with a small, kinematically-decoupled core (indicating a recent minor merger). Assuming that the metallicity of the young stars traces the gas-phase metallicity of the satellite that fuels the star formation, we use the mass-metallicity relation to estimate the mass ratio of the merger to be ~1:20. An WFC3 study of globular clusters reveals a substantial population of young star clusters coincident with the central region of star formation and indicates that the bulk of the stellar mass in this galaxy probably formed 6-8 Gyrs in the past. This study demonstrates the utility of high-resolution imaging from future instruments such as the extremely large telescopes. (Based on Early Release Science observations by the WFC3 Scientific Oversight Committee. We are grateful to the Director of the Space Telescope Science Institute for awarding Director's Discretionary time for this program.)

Kaviraj, Sugata



Habitable zones and UV habitable zones around host stars  

Microsoft Academic Search

Ultraviolet radiation is a double-edged sword to life. If it is too strong, the terrestrial biological systems will be damaged.\\u000a And if it is too weak, the synthesis of many biochemical compounds cannot go along. We try to obtain the continuous ultraviolet\\u000a habitable zones, and compare the ultraviolet habitable zones with the habitable zones of host stars. Using the boundary

Jianpo Guo; Fenghui Zhang; Xianfei Zhang; Zhanwen Han



The Duty Cycle of Star Formation : Far-UV imaging of the Hubble Deep Field  

NASA Astrophysics Data System (ADS)

We propose deep far-UV imaging of the Hubble Deep Field {HDF} with the ACS-SBC . Previously, we surveyed 1/5 of the HDF in the UV and now propose to complete the area. Near- and far-UV number counts suggest that there is a large population of UV- bright starbursts at moderate redshifts {z<0.6}, and our proposed observations will investigate their nature. We will measure the star formation properties of these galaxies and their morphologies in the UV, optical, and near-IR. This catalog of starbursts will also be important to the astronomical community after Cycle 11 in interpreting planned SIRTF observations of the field. We will also set strict limits on the flux escaping in intermediate redshift {1star forming galaxies at z 5 to the metagalactic ionizing radiation. Finally, we will measure the diffuse far-UV background at 1600 Angstrom. The HDF is the best field in the sky for the background measurements, given the legacy of ultra-deep observations at other wavelengths. In the spirit of the Hubble Deep Fields, we waive proprietary rights to these data.

Teplitz, Harry



Comparing H-alpha, UV, and Far-IR Star Formation Rates of Galaxies at 2  

NASA Astrophysics Data System (ADS)

We use a unique sample of 262 star-forming galaxies selected during the epoch of peak cosmic star formation to infer star-formation rates and dust reddening, and to investigate the validity of the local star-formation calibrations at high redshift. The sample contains galaxies at redshifts 2.08UV continuum and Spitzer/MIPS 24 micron measurements in order to examine the bolometric star-formation rates and dust attenuation. We discuss the comparison of these three complementary star-formation rate indicators in the context of the star-formation histories of the galaxies, and the implications for inferring star-formation rates and reddening at high redshift.

Shivaei, Irene; Reddy, N.



StarCAT: STIS UV echelle spectra of stars (Ayres, 2010)  

NASA Astrophysics Data System (ADS)

StarCAT is a Cycle 14 Legacy Archival project supported by the Guest Investigator program of Hubble Space Telescope (HST). The objective of StarCAT was to create an easily accessible catalog of high resolution spectral observations of targets broadly identified as "stars," collected by Space Telescope Imaging Spectrograph (STIS) from the time of its installation in 1997, during Hubble Servicing Mission 2, to its shutdown in 2004 August. StarCAT is available through an interface maintained at the Multimission Archive at Space Telescope (MAST): (3 data files).

Ayres, T. R.



Spectral classification criteria for some early type stars in the UV region/atl>  

NASA Astrophysics Data System (ADS)

The aim of this paper is to get new critertia for spectral classification of some early type stars which depend on the flux in the UV region ? ? 1500-2500 by carrying out spectrophotometric analysis of observational ultraviolet data of stars obtained by the S2/68 Ultraviolet Sky Survey Telescope (UVSST) aboard the European Space Research Organization (ESRO) Satellite TD1. We have developed these new criteria based on the Intrinsic Ultraviolet Colour Index (IUI), and the Intrinsic Flux Ratio (IFR). Using these quantities we are going to represent the results of spectral classification of 323 early type stars mainly from spectral type B and A. The results of calculations of the Intrinsic Flux Ratios for the stars under investigation together with their Colour Temperatures (Tc) are given. Comparison between our suggested two new criteria with the MK classification system and Cucchairo (1980) classification system was carried out.

Hamdy, M. A.; Abo Elazm, M. S.; Saad, S. M.; Nafie, H. O.; Abdel Baeth, H. E.


Structural Relations of a Sulfate-bearing Unit near Ceti Mensa, Candor Chasma, Mars  

NASA Astrophysics Data System (ADS)

A mapped kieserite unit within Ceti Mensa is unconformable to units that comprise Ceti Mensa. This fits a model of ILD deposition in which Ceti Mensa is a fault-bound block emplaced during ancestral basin formation, while kieserite units are late.

Fueten, F.; Stesky, R.; MacKinnon, P.; Hauber, E.; Gwinner, K.; Scholten, F.; Zegers, T. E.



Testing the Effectiveness of the H-alpha\\/UV flux Ratio in Determining Star Formation Rates in Dwarf Galaxies  

Microsoft Academic Search

We use an N-body\\/smoothed particle hydrodynamic simulation to study the evolution of H-alpha and UV star formation indicators in a starbursting dwarf galaxy. H-alpha based observations of star-formation under-predict the star formation rate (SFR) relative to the FUV determined SFR. The two implied scenarios: bursty star formation in dwarf galaxies or a non-uniform stellar initial mass function (IMF), cannot currently

Ferah Munshi; C. Christensen; F. Governato; T. Quinn; J. Wadsley



GD 244: asteroseismology of a pulsator in the middle of the ZZ Ceti instability strip  

NASA Astrophysics Data System (ADS)

We present our preliminary results on the asteroseismological investigations of the ZZ Ceti star GD 244. We used literature values of the effective temperature and surface gravity and utilized the White Dwarf Evolution Code of Bischoff-Kim, Montgomery and Winget (2008, ApJ, 675, 1512) to build our model grid for the seismological analysis. Five observed pulsational modes published up to now were used to find acceptable model solutions. We found that the best model fits have masses between 0.61 and 0.74 Msolar and constitute two groups with hydrogen layer masses of either ~10-5 or 10-6 Msolar. Based on a statistical analysis of a larger sample of possible model solutions, we assume that the mass of the star is below ~0.68 Msolar and the oxygen content in the centre is less than 60 percent.

Bognár, Zs.; Paparó, M.



UV-derived Star Formation Rates in a Survey of Nearby Starburst Dwarf Galaxies  

NASA Astrophysics Data System (ADS)

We present an analysis of new and archival GALEX FUV and NUV images and archival SPITZER MIPS (24 micron, 70 micron and 160 micron) images of 19 nearby starburst dwarf galaxies from the sample studied by McQuinn et al. (2010a,b). These galaxies all have recent star formation histories derived from Hubble Space Telescope (HST) imaging of resolved stars. We perform background subtractions, cropping to fit HST fields of view, re-sampling of images for matched-resolution comparisons across wavelengths, and masking of foreground stars and background galaxies. Additionally, we have created a multi-wavelength archive providing the astronomical community with access to processed data sets. We compare the current star formation rates, derived from the UV emission and corrected for extinction using total IR flux estimates, to the average star formation rates derived from the optically resolved stellar populations for a variety of timescales. Our results show very good agreement for star formation rates averaged over the past 150 Myr. Partial support for this work was provided by a NASA ADAP grant (No. NNX10AD57G), a NASA GALEX grant (No. 00015662) and the NSF REU program (PHY-0851820) at the University of Minnesota.

Mitchell, Noah P.; McQuinn, K. B. W.; Skillman, E. D.



Correlation of MgII(h+k) UV Resonance Lines and Rotational Period in G-type Stars  

NASA Astrophysics Data System (ADS)

We present preliminary results of an investigation aimed at establishing the correlation between the mid-UV MgII h and k lines and the rotational period of G-Type stars. We collected the high resolution spectra of a small sample of stars extracted from the International Ultraviolet Explorer (IUE) and the Hubble Space Telescope (HST) archives. The far more intense MgII lines with respect to CaII appear well correlated with rotational period, showing very little scatter. These UV features seems to be a promising tool for dating stars on the main sequence.

Olmedo, M.; Chávez, M.; Bertone, E.



Unveiling and Dereddening Classical T Tauri Stars Using Simultaneous UV and Optical Spectra  

NASA Astrophysics Data System (ADS)

T Tauri stars (TTSs) are low-mass, pre-main sequence stars that exhibit a variety of interesting spectral characteristics. One of the defining features of a classical TTS (CTTS) is the presence of an ultraviolet and optical excess continuum that is believed to form as the result of accreting circumstellar disk material that shocks at the photosphere of the star, heating the material to ~106 K. The excess emission results in the TTS spectrum being veiled, i.e. the photospheric absorption features appear to be filled in and are thus shallower than they would be in an unveiled spectrum. Correctly de-veiling TTSs is vital in determining the extinction to these systems. The amount of extinction in turn determines the correction that must be applied to emission at shorter wavelengths where veiling measurements are not possible due to the lack of stellar continuum. We present veiling and extinction measurements to a small sample of CTTS using low resolution, flux calibrated spectra that are simultaneous across the wavelengths 1800-8500 Å. By measuring the extinction with optical data taken simultaneously with the UV observations, we are able to generate accurate estimates of the extinction-corrected UV flux that is unaffected by variability, which in turn places more precise constraints on relationships between single colors and accretion luminosity.

Cauley, Paul W.; Hartigan, P. M.; Johns-Krull, C. M.




SciTech Connect

Ultraviolet (UV) nonionizing continuum and mid-infrared (IR) emission constitute the basis of two widely used star formation (SF) indicators at intermediate and high redshifts. We study 2430 galaxies with z < 1.4 in the Extended Groth Strip with deep MIPS 24 {mu}m observations from FIDEL, spectroscopy from DEEP2, and UV, optical, and near-IR photometry from the AEGIS. The data are coupled with dust-reddened stellar population models and Bayesian spectral energy distribution (SED) fitting to estimate dust-corrected star formation rates (SFRs). In order to probe the dust heating from stellar populations of various ages, the derived SFRs were averaged over various timescales-from 100 Myr for 'current' SFR (corresponding to young stars) to 1-3 Gyr for long-timescale SFRs (corresponding to the light-weighted age of the dominant stellar populations). These SED-based UV/optical SFRs are compared to total IR luminosities extrapolated from 24 {mu}m observations, corresponding to 10-18 {mu}m rest frame. The total IR luminosities are in the range of normal star-forming galaxies and luminous IR galaxies (10{sup 10}-10{sup 12} L{sub sun}). We show that the IR luminosity can be estimated from the UV and optical photometry to within a factor of 2, implying that most z < 1.4 galaxies are not optically thick. We find that for the blue, actively star-forming galaxies the correlation between the IR luminosity and the UV/optical SFR shows a decrease in scatter when going from shorter to longer SFR-averaging timescales. We interpret this as the greater role of intermediate age stellar populations in heating the dust than what is typically assumed. Equivalently, we observe that the IR luminosity is better correlated with dust-corrected optical luminosity than with dust-corrected UV light. We find that this holds over the entire redshift range. Many so-called green valley galaxies are simply dust-obscured actively star-forming galaxies. However, there exist 24 {mu}m detected galaxies, some with L{sub IR}>10{sup 11} L{sub sun}, yet with little current SF. For them a reasonable amount of dust absorption of stellar light (but presumably higher than in nearby early-type galaxies) is sufficient to produce the observed levels of IR, which includes a large contribution from intermediate and old stellar populations. In our sample, which contains very few ultraluminous IR galaxies, optical and X-ray active galactic nuclei do not contribute on average more than {approx}50% to the mid-IR luminosity, and we see no evidence for a large population of 'IR excess' galaxies.

Salim, Samir; Dickinson, Mark [National Optical Astronomy Observatory, 950 North Cherry Ave., Tucson, AZ 85719 (United States); Michael Rich, R. [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States); Charlot, Stephane [Institut d'Astrophysique de Paris, CNRS, 98 bis boulevard Arago, F-75014 Paris (France); Lee, Janice C. [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Schiminovich, David [Department of Astronomy, Columbia University, New York, NY 10027 (United States); Perez-Gonzalez, Pablo G. [Departamento de AstrofIsica, Facultad de CC. FIsicas, Universidad Complutense de Madrid, E-28040 Madrid (Spain); Ashby, Matthew L. N.; Noeske, Kai [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Papovich, Casey; Weiner, Benjamin J. [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Faber, S. M. [University of California Observatories/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States); Ivison, Rob J. [UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ (United Kingdom); Frayer, David T. [Infrared Processing and Analysis Center, California Institute of Technology 100-22, Pasadena, CA 91125 (United States); Walton, Josiah M. [University of Arkansas, Fayetteville, AR 72701 (United States); Chary, Ranga-Ram [Spitzer Science Center, California Institute of Technology 220-6, Pasadena, CA 91125 (United States); Bundy, Kevin [Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, ON M5S 3H4 (Canada); Koekemoer, Anton M. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)], E-mail:



Constraints provided by star cluster spectra on the nature of the UV turn-up in giant elliptical galaxies  

NASA Astrophysics Data System (ADS)

We have linked available ultraviolet observations to the visible and near infrared spectra of some objects from our star cluster and galaxy nucleus samples. We have analyzed the nature of the UV turn-up in giant elliptical galaxies (gE) in the light of our recent population synthesis results which are based upon a library of star cluster integrated spectra in the visible and near infrared. We also investigate how star clusters can provide information on the frequency of occurrence of particular types of stars with respect to the associated populations of a given age and metallicity. We definitely exclude the possibility that the UV turn-up in gE is caused by blue horizontal branch (BHB) stars associated with metal-poor components: even if they were a major contributor to the optical spectrum, their UV turn-up would be unable to account for that observed in gE, simply because it is not steep enough. Furthermore, our previous visible-near infrared synthesis has shown that only 10% of the flux originates from low metallicity components. On the contrary we find strong evidence that this UV turn-up is a result of on-going star formation in gE nuclei. Indeed, young blue clusters and/or H II region spectra match the UV turn-up quite well, without affecting much the optical range where their contribution is less than 2% at 5870 Å. Another possibility would be that the UV turn-up in gE is caused by post AGB stars from metal-rich components: data presently available about their frequency of occurrence in metal-rich galactic clusters, as well as about that of planetary nebulae in the bulge of M31 do not favour this interpretation however.

Bica, E.; Alloin, D.




SciTech Connect

We investigate the average physical properties and star formation histories (SFHs) of the most UV-luminous star-forming galaxies at z {approx} 3.7. Our results are based on the average spectral energy distributions (SEDs), constructed from stacked optical-to-infrared photometry, of a sample of the 1913 most UV-luminous star-forming galaxies found in 5.3 deg{sup 2} of the NOAO Deep Wide-Field Survey. We find that the shape of the average SED in the rest optical and infrared is fairly constant with UV luminosity, i.e., more UV-luminous galaxies are, on average, also more luminous at longer wavelengths. In the rest UV, however, the spectral slope {beta} ({identical_to} dlogF{sub {lambda}}/dlog{lambda}; measured at 0.13 {mu}m < {lambda}{sub rest} < 0.28 {mu}m) rises steeply with the median UV luminosity from -1.8 at L {approx} L* to -1.2 (L {approx} 4-5L*). We use population synthesis analyses to derive their average physical properties and find that (1) L{sub UV} and thus star formation rates (SFRs) scale closely with stellar mass such that more UV-luminous galaxies are also more massive, (2) the median ages indicate that the stellar populations are relatively young (200-400 Myr) and show little correlation with UV luminosity, and (3) more UV-luminous galaxies are dustier than their less-luminous counterparts, such that L {approx} 4-5L* galaxies are extincted up to A(1600) = 2 mag while L {approx} L* galaxies have A(1600) = 0.7-1.5 mag. We argue that the average SFHs of UV-luminous galaxies are better described by models in which SFR increases with time in order to simultaneously reproduce the tight correlation between the UV-derived SFR and stellar mass and their universally young ages. We demonstrate the potential of measurements of the SFR-M{sub *} relation at multiple redshifts to discriminate between simple models of SFHs. Finally, we discuss the fate of these UV-brightest galaxies in the next 1-2 Gyr and their possible connection to the most massive galaxies at z {approx} 2.

Lee, Kyoung-Soo; Glikman, Eilat [Yale Center for Astronomy and Astrophysics, Department of Physics, Yale University, New Haven, CT 06520 (United States); Dey, Arjun; Reddy, Naveen; Jannuzi, Buell T. [National Optical Astronomy Observatory, Tucson, AZ 85726 (United States); Brown, Michael J. I. [School of Physics, Monash University, Clayton, Victoria 3800 (Australia); Gonzalez, Anthony H. [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Cooper, Michael C.; Fan Xiaohui; Bian Fuyan [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Stern, Daniel [Jet Propulsion Laboratory, California Institute of Technology, MS 169-327, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Brodwin, Mark [Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States); Cooray, Asantha [School of Physical Sciences, University of California, Irvine, CA 92697 (United States)



Preparation of a Far-UV Spectral and Line Atlas for B stars near the Main Sequence  

Microsoft Academic Search

B type stars are major contributors to the total far-UV (949-1225 Å) flux produced in the Milky Way and external galaxies. The final reprocessing of the FUSE satellite dataset, together with the existing archives of the HST\\/STIS, IUE, and the Copernicus Atlas of tau Sco, permit the construction of a high dispersion atlas of 10 sharp-lined B stars near the

Myron A. Smith



Preparation of a Far-UV Spectral and Line Atlas for B stars near the Main Sequence  

Microsoft Academic Search

B type stars are major contributors to the total far-UV (949–1225 Å) flux produced in the Milky Way and external galaxies. The final reprocessing of the FUSE satellite dataset, together with the existing archives of the HST?STIS, IUE, and the Copernicus Atlas of ? Sco, permit the construction of a high dispersion atlas of 10 sharp-lined B stars near the

Myron A. Smith



Measuring the Evolutionary Rate of Cooling of ZZ Ceti  

NASA Astrophysics Data System (ADS)

We have finally measured the evolutionary rate of cooling of the pulsating hydrogen atmosphere white dwarf ZZ Ceti (R548), as reflected by the 213.13260694 s period. Using 41 years of time-series photometry from 1970 to 2011, we determine its rate of change of period with time to be dP/dt = (3.0 ± 1.4) × 10-15 s/s with the O-C method and (3.23 ± 0.87) × 10-15 s/s using the nonlinear least squares fit, after correcting for proper motion. We augment the uncertainty to a more realistic value and arrive at the evolutionary cooling rate of (3.2 ± 1.2) × 10-15 s/s for ZZ Ceti, consistent with the measurement of (4.19 ± 0.73) × 10-15 s/s for G117-B15A.

Mukadam, A. S.; Kim, A.; Montgomery, M. H.; Córsico, A. H.; Kepler, S. O.; Romero, A. D.; Winget, D. E.; Fraser, O.; Riecken, T. S.; Kronberg, M. E.; Hermes, J. J.; Winget, K. I.; Falcon, R. E.; Chandler, D. W.; Kuehne, J. W.; Sullivan, D. J.; Reaves, D.; von Hippel, T.; Mullally, F.; Shipman, H.; Thompson, S. E.; Silvestri, N. M.; Hynes, R. I.



UV Spectroscopy of Hydrogen-Deficient Post-AGB Stars: PG 1144+005 and PG 1520+525  

NASA Astrophysics Data System (ADS)

We present preliminary results of an ongoing spectral analysis by means of fully metal-line blanketed NLTE model atmospheres of two PG 1159-type stars, namely PG 1144+005 and PG 1520+525, that is based on UV spectra obtained with FUSE, HST/GHRS, and IUE.

Müller, U. C.; Rauch, T.; Werner, K.; Kruk, J. W.



Presence of dust with a UV bump in massive, star-forming galaxies at 1 < z < 2.5  

NASA Astrophysics Data System (ADS)

Aims:Fundamental properties of the extinction curve, like the slope in the rest-frame ultraviolet (UV) and the presence/absence of a broad absorption excess centred at 2175 Å (the UV bump), are investigated for a sample of 108 massive, star-forming galaxies at 1 < z < 2.5, selected from the FDF Spectroscopic Survey, the K20 survey, and the GDDS. Methods: These characteristics are constrained from a parametric description of the UV spectral energy distribution (SED) of a galaxy, as enforced by combined stellar population and radiative transfer models for different geometries, dust/stars configurations, and dust properties. Results: In at least one third of the sample, there is a robust evidence for extinction curves with at least a moderate UV bump. The presence of the carriers of the UV bump is more evident in galaxies with UV SEDs suffering from heavy reddening. We interpret these results as follows. The sample objects possess different mixtures of dust grains and molecules producing extinction curves in between the average ones of the Small and Large Magellanic Cloud, where the UV bump is absent or modest, respectively. Most of the dust embeds the UV-emitting stellar populations or is distributed out of the galaxy mid-plane. Alternatively, even dust with a pronounced UV bump, as for the average Milky-Way extinction curve, can be present and distributed in the galaxy mid-plane. In this case, variations of the continuum scattering albedo with wavelength or an age-dependent extinction are not sufficient to explain the previous trend with reddening. Hence, additional extraplanar dust has to be invoked. The data suggest that the carriers of the UV bump are associated with intermediate-age stellar populations, while they survive in the harshest UV-radiation fields owing to dust self-shielding. Conclusions: The existence of different extinction curves implies that different patterns of evolution and reprocessing of dust exist at high redshift. Ignoring this may produce a non-negligible uncertainty on the star-formation rate estimated from the rest-frame UV. Table 1 is only available in electronic form at

Noll, S.; Pierini, D.; Pannella, M.; Savaglio, S.



The photometric period in ES Ceti  

NASA Astrophysics Data System (ADS)

We present ULTRACAM photometry of ES Cet, an ultracompact binary with a 620-s orbital period. The mass transfer in systems such as this one is thought to be driven by gravitational radiation, which causes the binary to evolve to longer periods since the semidegenerate donor star expands in size as it loses mass. We supplement these ULTRACAM+William Herschel Telescope (WHT) data with observations made with smaller telescopes around the world over a 9-yr baseline. All of the observations show variation on the orbital period, and by timing this variation we track the period evolution of this system. We do not detect any significant departure from a linear ephemeris, implying a donor star that is of small mass and close to a fully degenerate state. This finding favours the double white dwarf formation channel for this AM Canum Venaticorum (AM CVn) star. An alternative explanation is that the system is in the relatively short-lived phase in which the mass transfer rate climbs towards its long-term value.

Copperwheat, C. M.; Marsh, T. R.; Dhillon, V. S.; Littlefair, S. P.; Woudt, P. A.; Warner, B.; Patterson, J.; Steeghs, D.; Kemp, J.; Armstrong, E.; Rea, R.



Stellar Population Models of the Outer Disks of Spiral Galaxies Using Representative Star Formation Histories: Implications for UV, Optical and NIR Colors  

NASA Astrophysics Data System (ADS)

We generate star formation histories representative of the low present and past star formation rates in the outer disks of spiral galaxies. The model star formation histories consist of episodic sampling of exponentially declining star formation rates. We study the effects of these star formation histories on UV, optical and NIR colors using stellar population models from Bruzual and Charlot (2003). We find significant dispersion in the UV colors, and negligible dispersion in both the optical and NIR colors. We compare our Monte Carlo simulations to recent observations of the outer disks of nearby spiral galaxies. Our results indicate that the large dispersion in UV colors in outer disks may be a result of low star formation frequency.

Barnes, Kate L.; van Zee, L.; Dowell, J. D.



New Optical/UV Counterparts, Astrometry and the Spectral Energy Distributions of Nearby, Thermally Emitting, Isolated Neutron Stars  

NASA Astrophysics Data System (ADS)

Seven of the nearby isolated neutron stars (INS) known till date show predominantly thermal spectrum with 106 K temperatures. Being relatively nearby and isolated makes them particularly attractive to constrain important NS properties such as mass, radius, cooling and possibly the equation of state of matter at ultra-high densities. However, interpreting their thermal spectra has turned out to be far more difficult than thought initially : The blackbody radius inferred from X-ray spectra, while ignoring optical/UV measurements, turns out to be too small to be a NS - even leading to immature speculations that the object might be a 'quark star'. Therefore, we carried out HST observations of these INSs to identify their optical/UV counterparts. We now have clearly identified optical and UV counterparts to all seven INSs. When compared to their X-ray spectra most of these sources appear to be brighter in optical/UV, in one case by a factor of 40 ! We find that the optical/UV SEDs show a range of slopes that are inconsistent with that expected from thermal (Rayleigh-Jeans) emission. We consider several explanations for this ranging from atmospheric effects, magnetospheric emission, and resonant scattering, but find that none is sufficient. These observations show that the puzzle of INSs, and possibly of all NSs, is far from over. Support for this work was provided by NASA (HST award GO-11564.05), and NSF (under grants PHY 05-51164 and AST 07-07633).

Kamble, Atish; Kaplan, D. L.; Kerkwijk, M. H. v.; Ho, W. C. G.



The Newly Discovered Pulsating Low-mass White Dwarfs: An Extension of the ZZ Ceti Instability Strip  

NASA Astrophysics Data System (ADS)

In light of the exciting discovery of g-mode pulsations in extremely low-mass, He-core DA white dwarfs, we report on the results of a detailed stability survey aimed at explaining the existence of these new pulsators as well as their location in the spectroscopic Hertzsprung-Russell diagram. To this aim, we calculated some 28 evolutionary sequences of DA models with various masses and chemical layering. These models are characterized by the so-called ML2/? = 1.0 convective efficiency and take into account the important feedback effect of convection on the atmospheric structure. We pulsated the models with the nonadiabatic code MAD, which incorporates a detailed treatment of time-dependent convection. On the other hand, given the failure of all nonadiabatic codes, including MAD, to account properly for the red edge of the strip, we resurrect the idea that the red edge is due to energy leakage through the atmosphere. We thus estimated the location of that edge by requiring that the thermal timescale in the driving region—located at the base of the H convection zone—be equal to the critical period beyond which l = 1 g-modes cease to exist. Using this approach, we find that our theoretical ZZ Ceti instability strip accounts remarkably well for the boundaries of the empirical strip, including the low-gravity, low-temperature regime where the three new pulsators are found. We also account for the relatively long periods observed in these stars, and thus conclude that they are true ZZ Ceti stars, but with low masses.

Van Grootel, V.; Fontaine, G.; Brassard, P.; Dupret, M.-A.




SciTech Connect

We present UV broadband photometry and optical emission-line measurements for a sample of 32 brightest cluster galaxies (BCGs) in clusters of the Representative XMM-Newton Cluster Structure Survey (REXCESS) with z = 0.06-0.18. The REXCESS clusters, chosen to study scaling relations in clusters of galaxies, have X-ray measurements of high quality. The trends of star formation and BCG colors with BCG and host properties can be investigated with this sample. The UV photometry comes from the XMM-Newton Optical Monitor, supplemented by existing archival Galaxy Evolution Explorer photometry. We detected H{alpha} and forbidden line emission in seven (22%) of these BCGs, in optical spectra obtained using the Southern Astrophysical Research Goodman spectrograph. All of these emission-line BCGs occupy clusters classified as cool cores (CCs) based on the central cooling time in the cluster core, for an emission-line incidence rate of 70% for BCGs in REXCESS CC clusters. Significant correlations between the H{alpha} equivalent widths, excess UV production in the BCG, and the presence of dense, X-ray bright intracluster gas with a short cooling time are seen, including the fact that all of the H{alpha} emitters inhabit systems with short central cooling times and high central intracluster medium densities. Estimates of the star formation rates based on H{alpha} and UV excesses are consistent with each other in these seven systems, ranging from 0.1to8 solar masses per year. The incidence of emission-line BCGs in the REXCESS sample is intermediate, somewhat lower than in other X-ray-selected samples ({approx}35%), and somewhat higher than but statistically consistent with optically selected, slightly lower redshift BCG samples ({approx}10%-15%). The UV-optical colors (UVW1 - R {approx}4.7 {+-} 0.3) of REXCESS BCGs without strong optical emission lines are consistent with those predicted from templates and observations of ellipticals dominated by old stellar populations. We see no trend in UV-optical colors with optical luminosity, R-K color, X-ray temperature, redshift, or offset between X-ray centroid and X-ray peak ((w)). The lack of such trends in these massive galaxies, particularly the ones lacking emission lines, suggests that the proportion of UV-emitting (200-300 nm) stars is insensitive to galaxy mass, cluster mass, cluster relaxation, and recent evolution, over the range of this sample.

Donahue, Megan; Bruch, Seth; Wang, Emily; Voit, G. Mark; Hicks, Amalia K. [Physics and Astronomy Department, Michigan State University, East Lansing, MI 48824-2320 (United States); Haarsma, Deborah B. [Calvin College, 1734 Knollcrest Circle SE, Grand Rapids, MI 48546 (United States); Croston, Judith H. [School of Physics and Astronomy, University of Southampton, Southampton SO17 1SJ (United Kingdom); Pratt, Gabriel W. [Laboratoire AIM, IRFU/Service dAstrophysique-CEA/DSM-CNRS-Universite Paris Diderot, Bt. 709, CEA-Saclay, F-91191, Gif-sur-Yvette Cedex (France); Pierini, Daniele; Boehringer, Hans [Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstr., 85748 Garching (Germany); O'Connell, Robert W., E-mail: donahue@pa.msu.ed [Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325 (United States)



Multiwavelength Investigations of Hickson Compact Groups of Galaxies: Evolution of Star Formation with UV, IR and X-ray Diagnostics  

NASA Astrophysics Data System (ADS)

Nearby (? Mpc) compact groups of galaxies represent a special high-density environment, which, thanks to their relative proximity, can be studied in detail. The similarity of compact groups to dense environments at high redshift makes them an ideal laboratory for gaining insight on galaxy evolution and transformation in the distant Universe, where merging and interactions are prevalent. We have selected a diverse sample of 12 Hickson Compact Groups (HCGs), and performed observations in the X-ray (Chandra), the UV (Swift/UVOT), the optical (CTIO imaging/spectroscopy), and the IR (2MASS, Spitzer IRAC and MIPS). Until recently, large HCG samples were relatively unexplored in the UV, IR and X-ray wavelength regions. We aim to fully characterize star formation in galaxies of different morphological types and groups of different evolutionary stages. I will present Swift/UVOT 3-color UV data, which we combine with Spitzer and 2MASS IR data, to obtain, for the first time, dust maps and specific star-formation rate (SSFR) estimates for HCGs. I will discuss the interpretation of the 'gap' in mid-IR and SSFR space and how it relates to the proposed evolutionary schemes for compact groups. The X-ray regime also provides valuable information on the evolutionary stage of HCGs. I will discuss results on 5 HCGs from our sample and discuss the relative importance of the diffuse emission and X-ray binary contribution, as a function of stellar mass.

Tzanavaris, Panayiotis; Hornschemeier, A.; Gallagher, S.; Johnson, K.; Gronwall, C.; Immler, S.; Reines, A.; Hoversten, E.; Charlton, J.



Proprietes Adiabatiques des Naines Blanches Pulsantes de Type ZZ Ceti  

NASA Astrophysics Data System (ADS)

Cette these a pour but d'etudier les proprietes des oscillation non-radiales des etoiles ZZ Ceti, appelees aussi etoiles DA variables, dans le contexte de la theorie adiabatique des petites oscillations. Ces oscillations sont observables, pour ce type d'etoiles, sous forme de variations periodiques de la luminosite. A partir d'une analyse de modeles stellaires, analyse qui consiste principalement a calculer et a interpreter les periodes d'oscillations des modeles, nous voulons mieux connai tre les proprietes physiques fondamentales des ZZ Ceti. Nous developpons tout d'abord divers outils pour entreprendre cette etude. Apres avoir presente le formalisme mathematique de base decrivant les oscillations non-radiales d'une etoile, nous discutons des difficultes pouvant etre rencontrees dans le calcul de la frequence de Brunt-Vaisala, une quantite fondamentale pour le calcul des periodes d'oscillations. Par la suite, nous developpons un modele theorique simple permettant d'analyser et d'interpreter la structure des periodes calculees (ou observees) en termes des proprietes de structure de l'etoile. Nous presentons aussi les outils numeriques tout a fait originaux utilises pour calculer nos periodes a partir de modeles stellaires. Finalement, nous presentons les resultats d'ensemble de l'analyse de nos modeles, et discutons de l'interpretation des observations de periodes et du taux de variation de ces periodes en termes de structure de l'etoile et de composition du noyau de l'etoile, respectivement. Ces resultats representent l'etude la plus complete a ce jour de la seismologie des naines blanches.

Brassard, Pierre



The First Look at the Rest-Frame Optical Morphology of the Most UV-Luminous Star-Forming Galaxies at High Redshift  

NASA Astrophysics Data System (ADS)

We present preliminary results of comparative morphological studies of high-redshift star-forming galaxies observed over a wide range of UV luminosities. Our main sample represents the most actively star-forming (thus most UV-luminous; L>L*) galaxies selected over a 5.3 square-degree area in the Bootes field of the NOAO Deep Wide-Field Survey. On the other hand, the control sample derives from similarly selected, but significantly less UV-luminous, galaxies observed by the CANDELS program. Based on the HST imaging data (CANDELS + existing archival data) available for the two samples, we employ both visual inspection and quantitative classification techniques to investigate whether or not the galaxy morphology varies significantly with UV luminosity (or star formation rates).

Wilson, Christian; Lee, K.



Oscillations in solar-type stars: recent observational results  

NASA Astrophysics Data System (ADS)

The past few years have seen a breakthrough in observing oscillations in solar-type stars. We now have moved from ambiguous detections to firm measurements, and there are now several stars for which numerous oscillation frequencies have been measured. I will review the recent results from high-precision Doppler measurements on stars such as ? Centauri A and B, ? Ceti and the planet-hosting star ? Arae. Asteroseismology has moved from dream to reality and the prospects are very exciting.

Bedding, T. R.; Kjeldsen, H.



The helium-to-hydrogen ratio of the UV-bright star Barnard 29 of Messier 13  

NASA Astrophysics Data System (ADS)

Barnard 29 is the most luminous UV-bright star of the globular cluster Messier 13. Comparison of its reddening corrected optical region spectrophotometry and IUE low dispersion fluxes and its H-gamma profile with the predictions of metal-poor model atmospheres having the metallicity of M 13 indicated Teff = 20250 K, log g = 3.15. Observations of He I lambda(4026) taken with echelle spectrograph of the Multi-Mirror telescope using a Reticon detector show that He/H = 0.055 +/- 0.020. Some astrophysical implications of this result are discussed.

Adelman, S. J.; Aikman, G. C. L.; Hayes, D. S.; Philip, A. G. D.; Sweigart, A. V.



GMASS ultradeep spectroscopy of galaxies at z ~ 2. VI. Star formation, extinction, and gas outflows from UV spectra  

NASA Astrophysics Data System (ADS)

Aims: We use rest-frame UV spectroscopy to investigate the properties related to large-scale gas outflow, and both the dust extinction and star-formation rates (SFRs) of a sample of z ~ 2 star-forming galaxies from the Galaxy Mass Assembly ultradeep Spectroscopic Survey (GMASS). Methods: Dust extinction is estimated from the rest-frame UV continuum slope and used to obtain dust-corrected SFRs for the galaxies in the sample. A composite spectrum is created by averaging all the single spectra of our sample, and the equivalent widths and centroids of the absorption lines associated with the interstellar medium are measured. We then calculate the velocity offsets of these lines relative to the composite systemic velocity, which is obtained from photospheric stellar absorption lines and nebular emission lines. Finally, to investigate correlations between galaxy UV spectral characteristics and galaxy general properties, the sample is divided into two bins that are equally populated, according to the galaxy properties of stellar mass, color excess, and SFR. A composite spectrum for each group of galaxies is then created, and both the velocity offsets and the equivalent widths of the interstellar absorption lines are measured. Results: For the entire sample, we derive a mean value of the continuum slope ??? = -1.11 ± 0.44 (rms). For each galaxy, we calculate the dust extinction from the UV spectrum and then use this to correct the flux measured at 1500 Å (rest-frame), before converting the corrected UV flux into a SFR. We find that our galaxies have an average SFR of ?SFR? = 52 ± 48 M? yr-1 (rms) and that there is a positive correlation between SFR and stellar mass, in agreement with other works, the logarithmic slope of the relation being 1.10 ± 0.10. We discover that the low-ionization absorption lines associated with the interstellar medium measured in the composite spectrum, are blueshifted with respect to the rest frame of the system, which indicates that there is outflowing gas with typical velocities of about ~100 km s-1. Finally, investigating the correlations between the galaxy UV spectral characteristics and general galaxy properties, we find a possible correlation between the equivalent width of the interstellar absorption lines and SFR, stellar mass, and color excess similar to that previously reported to hold at different redshifts.

Talia, M.; Mignoli, M.; Cimatti, A.; Kurk, J.; Berta, S.; Bolzonella, M.; Cassata, P.; Daddi, E.; Dickinson, M.; Franceschini, A.; Halliday, C.; Pozzetti, L.; Renzini, A.; Rodighiero, G.; Rosati, P.; Zamorani, G.



Synthetic UV Lines of Si IV, C IV, and He II from a Population of Massive Stars in Starburst Galaxies  

NASA Astrophysics Data System (ADS)

We present the first results of our study of the massive star population in starburst galaxies based on UV data. We have synthesized the Si IV 1400, C IV 1550 and He II 1640 lines for both a continuous and an instantaneous burst of star formation with approximately solar chemical composition. Our code uses the latest generation of stellar evolutionary models, stellar atmosphere codes, and a library of high-dispersion lUE spectra of hot stars. Models were computed for various values of the IMF parameters. Si IV ?1400 and C IV ?1550 develop P Cygni profiles when formed in strong stellar winds from the most massive stars. The velocity shifts predicted for these lines give a tight constraint on the value of the IMF upper mass cutoff: strong blueshifts in both lines are produced if stars with an initial mass larger than 30-60 Msun are included in the models. Based on the line velocity shifts, it also seems possible to put limits on the burst age. The models show only a small dependence of the line velocity shifts on the IMF slope. We also find a significant dependence of the equivalent widths of Si IV ?1400 and C IV ?1550 on the burst age, the IMF upper cutoff mass, and the IMF slope. The He II ?1640 line shows a strong broad emission profile when formed in winds from evolved massive stars. It offers additional important clues to the burst age and the IMF upper cutoff mass. We have compared the model parameters with data obtained for an average galaxy spectrum formed by combining low-dispersion IUE spectra of 13 starburst galaxies with nearly solar chemical composition. The most interesting result, based on the Si IV ?1400 and C IV ?1550 line velocity shifts and the strength of the broad He II ?1640 emission line, is that evolved massive stars with an initial mass larger than 30 Msun must be present in most of these galaxies. We find a good fit to the data for a model of an instantaneous burst of age ?5 × 106 yr or a model for which star formation is proceeding at a constant rate for ?107 yr. Hubble Space Telescope data with higher spectral resolution will be required to test these ideas and to allow us to fully exploit our method.

Robert, Carmelle; Leitherer, Claus; Heckman, Timothy M.



The spectral energy distributions of K+A galaxies from the UV to the mid-IR: stellar populations, star formation and hot dust  

NASA Astrophysics Data System (ADS)

We present spectrum synthesis fits to 808 K+A galaxies selected from the Sloan Digital Sky Survey (SDSS) and population synthesis of their spectral energy distributions, extending from the far-UV (0.15 ?m) to the mid-IR (22 ?m), based on the results of STARLIGHT code fitting to the SDSS spectra. Our modelling shows that K+A galaxies have undergone a large starburst, involving a median 50 per cent of their present stellar masses, superposed over an older stellar population. The metal abundance of the intermediate-age stars shows that star formation did not take place in pristine gas, but was part of a dramatic increase in the star formation rates for originally gas-rich objects. We find no evidence for ongoing QSO activity in the UV, which is well modelled by the emission of intermediate-age stars. We use K+A galaxies as local counterparts of high-redshift objects to test for the presence of thermally pulsing asymptotic giant branch (TP-AGB) stars in similarly aged populations and find no excess in the infrared due to emission from such stars, arguing that more distant galaxies are indeed old and massive at their redshift. All of our galaxies show significant excesses in the mid-IR compared to the light from their stars. We fit this ad hoc with a 300 K blackbody. Possible sources include TP-AGB stars, obscured young star clusters and hidden AGNs, heating a significant dust component.

Melnick, J.; De Propris, R.



Herschel Observations of Gas and Dust in the Unusual 49 Ceti Debris Disk  

NASA Astrophysics Data System (ADS)

We present far-IR/sub-mm imaging and spectroscopy of 49 Ceti, an unusual circumstellar disk around a nearby young A1V star. The system is famous for showing the dust properties of a debris disk, but the gas properties of a low-mass protoplanetary disk. The data were acquired with the Herschel Space Observatory PACS and SPIRE instruments, largely as part of the "Gas in Protoplanetary Systems" (GASPS) Open Time Key Programme. Disk dust emission is detected in images at 70, 160, 250, 350, and 500 ?m 49 Cet is significantly extended in the 70 ?m image, spatially resolving the outer dust disk for the first time. Spectra covering small wavelength ranges centered on eight atomic and molecular emission lines were obtained, including [O I] 63 ?m and [C II] 158 ?m. The C II line was detected at the 5? level—the first detection of atomic emission from the disk. No other emission lines were seen, despite the fact that the O I line is the brightest one observed in Herschel protoplanetary disk spectra. We present an estimate of the amount of circumstellar atomic gas implied by the C II emission. The new far-IR/sub-mm data fills in a large gap in the previous spectral energy distribution (SED) of 49 Cet. A simple model of the new SED confirms the two-component structure of the disk: warm inner dust and cold outer dust that produces most of the observed excess. Finally, we discuss preliminary thermochemical modeling of the 49 Cet gas/dust disk and our attempts to match several observational results simultaneously. Although we are not yet successful in doing so, our investigations shed light on the evolutionary status of the 49 Cet gas, which might not be primordial gas but rather secondary gas coming from comets.

Roberge, A.; Kamp, I.; Montesinos, B.; Dent, W. R. F.; Meeus, G.; Donaldson, J. K.; Olofsson, J.; Moór, A.; Augereau, J.-C.; Howard, C.; Eiroa, C.; Thi, W.-F.; Ardila, D. R.; Sandell, G.; Woitke, P.



Luminosities and Star Formation Rates Of Galaxies Observed With the Ultraviolet Imaging Telescope: A Comparison of Far-UV, H-alpha, and Far-IR Diagnostics  

Microsoft Academic Search

During the UIT\\/Astro Spacelab missions, the Ultraviolet Imaging Telescope\\u000aobtained spatially resolved far-UV (lambda 1500 A) imagery of ~35 galaxies\\u000aexhibiting recent massive star formation. The sample includes disk systems,\\u000airregular, dwarf, and blue compact galaxies. The objects span an observed FUV\\u000aluminosity range from -17 to -22 magnitudes. We estimate global star formation\\u000arates by comparing the observed FUV

Michael N. Fanelli; Theodore P. Stecher



Meningoencephalitis and arthritis associated with Brucella ceti in a short-beaked common dolphin (Delphinus delphis).  


Brucella species infection in marine mammal species has been reported to have a global distribution. In 2007, the description of Brucella ceti was published and formally adopted for those isolates originating from cetaceans and pathologic lesions similar to those seen in terrestrial mammals infected with Brucella spp. have been associated with its isolation. Brucella ceti infection specific to the central nervous system has been described in two species of cetacean: striped dolphins (Stenella coeruleoalba) in Europe and Costa Rica and an Atlantic white-sided dolphin (Lagenorhynchus acutus) in the UK. We describe the first report, to our knowledge, of B. ceti-associated meningitis and arthritis in a third species, the short-beaked common dolphin (Delphinus delphis), in an animal that stranded in the UK. PMID:23778612

Davison, Nicholas J; Barnett, James E F; Perrett, Lorraine L; Dawson, Claire E; Perkins, Matthew W; Deaville, Robert C; Jepson, Paul D



UV to IR SEDs of UV-Selected Galaxies in the ELAIS Fields: Evolution of Dust Attenuation and Star Formation Activity from z = 0.7 to 0.2  

NASA Astrophysics Data System (ADS)

We study the ultraviolet to far-infrared (hereafter UV-to-IR) SEDs of a sample of intermediate-redshift (0.2<=z<=0.7) UV-selected galaxies from the ELAIS N1 and ELAIS N2 fields by fitting a multi-wavelength data set to a library of GRASIL templates. Star formation related properties of the galaxies are derived from the library of models by using Bayesian statistics. We find a decreasing presence of galaxies with low attenuation and low total luminosity as redshift decreases, which does not hold for high total luminosity galaxies. In addition, the dust attenuation of low-mass galaxies increases as redshift decreases, and this trend seems to disappear for galaxies with M*>=1011 Msolar. This result is consistent with a mass-dependent evolution of the dust-to-gas ratio, which could be driven by a mass-dependent efficiency of star formation in star-forming galaxies. The specific star formation rates (SSFR) decrease with increasing stellar mass at all redshifts, and for a given stellar mass the SSFR decreases with decreasing redshift. The differences in the slope of the M*-SSFR relation found between this work and others at similar redshift could be explained by the adopted selection criteria of the samples, which for a UV-selected sample, favors blue, star-forming galaxies.

Iglesias-Páramo, J.; Buat, V.; Hernández-Fernández, J.; Xu, C. K.; Burgarella, D.; Takeuchi, T. T.; Boselli, A.; Shupe, D.; Rowan-Robinson, M.; Babbedge, T.; Conrow, T.; Fang, F.; Farrah, D.; González-Solares, E.; Lonsdale, C.; Smith, G.; Surace, J.; Barlow, T. A.; Forster, K.; Friedman, P. G.; Martin, D. C.; Morrissey, P.; Neff, S. G.; Schiminovich, D.; Seibert, M.; Small, T.; Wyder, T. K.; Bianchi, L.; Donas, J.; Heckman, T. M.; Lee, Y.-W.; Madore, B. F.; Milliard, B.; Rich, R. M.; Szalay, A. S.; Welsh, B. Y.; Yi, S. K.



Analysis of far-UV data of central stars of planetary nebulae: Occurrence and variability of stellar winds  

NASA Astrophysics Data System (ADS)

The occurrence of stellar wind in the central star of a planetary nebula (CSPN) can be revealed by the presence of P Cygni profiles of high-excitation lines overimposed on its stellar continuum. We examined the entire Far-Ultraviolet Spectroscopic Explorer (FUSE) archive and merged all useful spectroscopic observations of CSPNe to produce the highest quality spectra that can be used to assess the frequency of stellar winds. Furthermore, the individual spectra of each CSPN were compared to search for variability in the P Cygni profile. P Cygni profiles of high-excitation lines have been found in 44 CSPNe, with a clear correlation between the ionization potential of the lines and the effective temperature of the star. We introduce a prescription to derive the terminal wind velocity (v?) from saturated and unsaturated P Cygni profiles and provide new values of v? for these stars. Another 23 CSPNe do not show P Cygni profiles, or else their data in the FUSE archive are not conclusive enough to determine the occurrence of P Cygni profiles. Variability in the P Cygni profile of high-excitation, far-UV lines is found for the first time in six CSPNe, namely Hen 2-131, NGC 40, NGC 1535, NGC 2392, Sp 3, and SwSt 1. This increases up to 13 the number of CSPNe with variable P Cygni profiles in the UV, including those previously reported using IUE or FUSE observations. Variability is seen primarily in the unsaturated P v and Si iv lines, but also in saturated C iii and O vi lines. The CSPNe with variable P Cygni profiles have similar stellar properties (relatively low log (g) and Teff) that suggest they are less evolved CSPNe. Some of the CSPNe with variable P Cygni profiles show O vi lines, while their effective temperature is insufficient to produce this ion. We suggest that this ion is produced by Auger ionization from X-rays associated to shocks in their stellar winds, as is the case in massive OB stars of high ionization potential ions that cannot be abundantly produced by photoionizations. ASCII tables of wavelengths and fluxes are available at the CDS via anonymous ftp to ( or via

Guerrero, M. A.; De Marco, O.



UV survey of central stars of planetary nebulae: occurence and variability of stellar winds  

NASA Astrophysics Data System (ADS)

The occurrence of a stellar wind in the central star of a planetary nebula (CSPN) is revealed by the presence of P Cygni profiles of high-excitation lines overimposed on its stellar continuum. We have used the entire Far-Ultraviolet Spectroscopic Explorer (FUSE) archive to investigate the occurrence and variability of P Cygni profiles of high-excitation lines. All useful spectroscopic observations have been merged to produce the highest quality spectra that can be used to assess the occurrence of stellar winds through the P Cygni profiles of high-excitation lines. The individual spectra have been compared to search for variability in the P Cygni profile. P Cygni profiles of high-excitation lines have been found in more than 40 CSPNe, with a clear correlation between the ionization potential of the lines and the effective temperature of the star. Ten CSPNe show variability in the P Cygni profile of high-excitation lines, preferentially in the unsaturated P V and Si IV lines, but also in saturated C III and O VI lines. The CSPNe with variable P Cygni profiles have similar stellar and wind properties that suggests they are not in an evolved evolutionary status. Some of the CSPNe with variable P Cygni profile show O VI lines, while their effective temperature are insufficient to produce this ion. We suggest that this ion is produced by Auger ionization from X-rays associated to shocks in their stellar winds as is the case of super-ions in OB stars.

Guerrero, M. A.; de Marco, O.



Mass loss from inhomogeneous hot star winds. II. Constraints from a combined optical/UV study  

NASA Astrophysics Data System (ADS)

Context. Mass loss is essential for massive star evolution, thus also for the variety of astrophysical applications relying on its predictions. However, mass-loss rates currently in use for hot, massive stars have recently been seriously questioned, mainly because of the effects of wind clumping. Aims: We investigate the impact of clumping on diagnostic ultraviolet resonance and optical recombination lines often used to derive empirical mass-loss rates of hot stars. Optically thick clumps, a non-void interclump medium, and a non-monotonic velocity field are all accounted for in a single model. The line formation is first theoretically studied, after which an exemplary multi-diagnostic study of an O-supergiant is performed. Methods: We used 2D and 3D stochastic and radiation-hydrodynamic wind models, constructed by assembling 1D snapshots in radially independent slices. To compute synthetic spectra, we developed and used detailed radiative transfer codes for both recombination lines (solving the "formal integral") and resonance lines (using a Monte-Carlo approach). In addition, we propose an analytic method to model these lines in clumpy winds, which does not rely on optically thin clumping. Results: The importance of the "vorosity" effect for line formation in clumpy winds is emphasized. Resonance lines are generally more affected by optically thick clumping than recombination lines. Synthetic spectra calculated directly from current radiation-hydrodynamic wind models of the line-driven instability are unable to in parallel reproduce strategic optical and ultraviolet lines for the Galactic O-supergiant ? Cep. Using our stochastic wind models, we obtain consistent fits essentially by increasing the clumping in the inner wind. A mass-loss rate is derived that is approximately two times lower than what is predicted by the line-driven wind theory, but much higher than the corresponding rate derived when assuming optically thin clumps. Our analytic formulation for line formation is used to demonstrate the potential importance of optically thick clumping in diagnostic lines in so-called weak-winded stars and to confirm recent results that resonance doublets may be used as tracers of wind structure and optically thick clumping. Conclusions: We confirm earlier results that a re-investigation of the structures in the inner wind predicted by line-driven instability simulations is needed. Our derived mass-loss rate for ? Cep suggests that only moderate reductions of current mass-loss predictions for OB-stars are necessary, but this nevertheless prompts investigations on feedback effects from optically thick clumping on the steady-state, NLTE wind models used for quantitative spectroscopy.

Sundqvist, J. O.; Puls, J.; Feldmeier, A.; Owocki, S. P.



Evolution of Dust Attenuation and Star Formation Activity from z=0.7 to z=0.2 for a Sample of UV-selected Galaxies  

NASA Astrophysics Data System (ADS)

We study the ultraviolet to far-infrared spectral energy distributions of a sample of intermediate-redshift (0.2 ? z ? 0.7) UV-selected galaxies from the ELAIS-N1 and ELAIS-N2 fields by fitting a multiwavelength dataset to a library of GRASIL templates. The dust attenuation of low mass galaxies increases as redshift decreases, and this trend seems to disappear for galaxies with M* ? 1011 M?. This result is consistent with a mass-dependent evolution of the dust to gas ratio, which could be driven by a mass-dependent efficiency of star formation in star-forming galaxies. The specific star formation rates decrease with increasing stellar mass at all redshifts, and for a given stellar mass the specific star formation rate decreases with decreasing redshift.

Iglesias-Páramo, J.; Hernández-Fernández, J.; Buat, V.; Burgarella, D.; Boselli, A.; Xu, C. K.; Takeuchi, T. T.



Results from Hubble COS Far-UV Spectroscopy of Warm DAZ Stars  

NASA Astrophysics Data System (ADS)

I will present results from a Hubble Snapshot Survey of 17,000 - 25,000K DA white dwarfs to search for atmospheric silicon absorption. This approach is 2 orders of magnitude more sensitive than targeting calcium K in the optical for this range of effective temperatures, probing relatively low metal abundances achievable for cooler stars from the ground. Roughly half of our 80 observed targets show metal pollution, about 10% of which are truly spectacular. These objects have no convection zones and thus very short diffusion time scales, assuring that accretion is currently ongoing. I will discuss the overall results, some outstanding cases, and what they reveal about the nature of the circumstellar debris.

Farihi, Jay; Gänsicke, B.; Koester, D.



Modeling the near-UV Band of GK Stars. II. Non-LTE Models  

NASA Astrophysics Data System (ADS)

We present a grid of atmospheric models and synthetic spectral energy distributions (SEDs) for late-type dwarfs and giants of solar and 1/3 solar metallicity with many opacity sources computed in self-consistent non-local thermodynamic equilibrium (NLTE), and compare them to the LTE grid of Short & Hauschildt (Paper I). We describe, for the first time, how the NLTE treatment affects the thermal equilibrium of the atmospheric structure (T(?) relation) and the SED as a finely sampled function of T eff, log g, and [A/H] among solar metallicity and mildly metal-poor red giants. We compare the computed SEDs to the library of observed spectrophotometry described in Paper I across the entire visible band, and in the blue and red regions of the spectrum separately. We find that for the giants of both metallicities, the NLTE models yield best-fit T eff values that are 30-90 K lower than those provided by LTE models, while providing greater consistency between log g values, and, for Arcturus, T eff values, fitted separately to the blue and red spectral regions. There is marginal evidence that NLTE models give more consistent best-fit T eff values between the red and blue bands for earlier spectral classes among the solar metallicity GK giants than they do for the later classes, but no model fits the blue-band spectrum well for any class. For the two dwarf spectral classes that we are able to study, the effect of NLTE on derived parameters is less significant. We compare our derived T eff values to several other spectroscopic and photometric T eff calibrations for red giants, including one that is less model dependent based on the infrared flux method (IRFM). We find that the NLTE models provide slightly better agreement to the IRFM calibration among the warmer stars in our sample, while giving approximately the same level of agreement for the cooler stars.

Short, C. Ian; Campbell, Eamonn A.; Pickup, Heather; Hauschildt, Peter H.



Signals embedded in the radial velocity noise. Periodic variations in the ? Ceti velocities  

NASA Astrophysics Data System (ADS)

Context. The abilities of radial velocity exoplanet surveys to detect the lowest-mass extra-solar planets are currently limited by a combination of instrument precision, lack of data, and "jitter". Jitter is a general term for any unknown features in the noise, and reflects a lack of detailed knowledge of stellar physics (asteroseismology, starspots, magnetic cycles, granulation, and other stellar surface phenomena), as well as the possible underestimation of instrument noise. Aims: We study an extensive set of radial velocities for the star HD 10700 (? Ceti) to determine the properties of the jitter arising from stellar surface inhomogeneities, activity, and telescope-instrument systems, and perform a comprehensive search for planetary signals in the radial velocities. Methods: We performed Bayesian comparisons of statistical models describing the radial velocity data to quantify the number of significant signals and the magnitude and properties of the excess noise in the data. We reached our goal by adding artificial signals to the "flat" radial velocity data of HD 10700 and by seeing which one of our statistical noise models receives the greatest posterior probabilities while still being able to extract the artificial signals correctly from the data. We utilised various noise components to assess properties of the noise in the data and analyse the HARPS, AAPS, and HIRES data for HD 10700 to quantify these properties and search for previously unknown low-amplitude Keplerian signals. Results: According to our analyses, moving average components with an exponential decay with a timescale from a few hours to few days, and Gaussian white noise explains the jitter the best for all three data sets. Fitting the corresponding noise parameters results in significant improvements of the statistical models and enables the detection of very weak signals with amplitudes below 1 m s-1 level in our numerical experiments. We detect significant periodicities that have no activity-induced counterparts in the combined radial velocities. Three of these signals can be seen in the HARPS data alone, and a further two can be inferred by utilising the AAPS and Keck data. These periodicities could be interpreted as corresponding to planets on dynamically stable close-circular orbits with periods of 13.9, 35.4, 94, 168, and 640 days and minimum masses of 2.0, 3.1, 3.6, 4.3, and 6.6 M?, respectively. Radial velocities are only available in electronic form at the CDS via anonymous ftp to or via

Tuomi, M.; Jones, H. R. A.; Jenkins, J. S.; Tinney, C. G.; Butler, R. P.; Vogt, S. S.; Barnes, J. R.; Wittenmyer, R. A.; O'Toole, S.; Horner, J.; Bailey, J.; Carter, B. D.; Wright, D. J.; Salter, G. S.; Pinfield, D.




SciTech Connect

We present a grid of atmospheric models and synthetic spectral energy distributions (SEDs) for late-type dwarfs and giants of solar and 1/3 solar metallicity with many opacity sources computed in self-consistent non-local thermodynamic equilibrium (NLTE), and compare them to the LTE grid of Short and Hauschildt (Paper I). We describe, for the first time, how the NLTE treatment affects the thermal equilibrium of the atmospheric structure (T({tau}) relation) and the SED as a finely sampled function of T{sub eff}, log g, and [A/H] among solar metallicity and mildly metal-poor red giants. We compare the computed SEDs to the library of observed spectrophotometry described in Paper I across the entire visible band, and in the blue and red regions of the spectrum separately. We find that for the giants of both metallicities, the NLTE models yield best-fit T{sub eff} values that are 30-90 K lower than those provided by LTE models, while providing greater consistency between log g values, and, for Arcturus, T{sub eff} values, fitted separately to the blue and red spectral regions. There is marginal evidence that NLTE models give more consistent best-fit T{sub eff} values between the red and blue bands for earlier spectral classes among the solar metallicity GK giants than they do for the later classes, but no model fits the blue-band spectrum well for any class. For the two dwarf spectral classes that we are able to study, the effect of NLTE on derived parameters is less significant. We compare our derived T{sub eff} values to several other spectroscopic and photometric T{sub eff} calibrations for red giants, including one that is less model dependent based on the infrared flux method (IRFM). We find that the NLTE models provide slightly better agreement to the IRFM calibration among the warmer stars in our sample, while giving approximately the same level of agreement for the cooler stars.

Ian Short, C.; Campbell, Eamonn A. [Department of Astronomy and Physics and Institute for Computational Astrophysics, Saint Mary's University, Halifax, NS B3H 3C3 (Canada); Pickup, Heather [Department of Physics and Astronomy, University of Waterloo, Waterloo, ON (Canada); Hauschildt, Peter H., E-mail:, E-mail: [Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg (Germany)



How Much Dusty Star Formation Has Been Missed at z˜2 through UV/Optical Selections?  

NASA Astrophysics Data System (ADS)

We apply the UV/optical criteria BM/BX, BzK and IRAC Peakers to a sample of 24? m selected galaxies from the COSMOS field with the goal of quantifying their contribution to the 8? m rest-frame Luminosity Function (LF) at z˜2. We slightly modify the BM/BX and BzK criteria to adapt them to the COSMOS filters. 93% of the MIPS sources with 1.4 < z < 2.5 are properly selected as BzK and 68% of the MIPS sources with 1.5 < z < 3 are IRAC Peakers while only 50% of those with 1.5 < z < 2.8 are selected as BM/BX. The BzK criterion is independent of dust extinction while the BM/BX is highly affected by this phenomenon. We compute the 8? m rest-frame LF for all the sources and we find the same proportions for the contribution of these different selections to the LF at z˜2.

Riguccini, L.; Le Floc'h, E.




SciTech Connect

Using a complete sample of approx300 star-forming galaxies within 11 Mpc of the Milky Way, we evaluate the consistency between star formation rates (SFRs) inferred from the far ultraviolet (FUV) non-ionizing continuum and Halpha nebular emission, assuming standard conversion recipes in which the SFR scales linearly with luminosity at a given wavelength. Our analysis probes SFRs over 5 orders of magnitude, down to ultra-low activities on the order of approx10{sup -4} M{sub sun} yr{sup -1}. The data are drawn from the 11 Mpc Halpha and Ultraviolet Galaxy Survey (11HUGS), which has obtained Halpha fluxes from ground-based narrowband imaging, and UV fluxes from imaging with GALEX. For normal spiral galaxies (SFR approx 1 M{sub sun} yr{sup -1}), our results are consistent with previous work which has shown that FUV SFRs tend to be lower than Halpha SFRs before accounting for internal dust attenuation, but that there is relative consistency between the two tracers after proper corrections are applied. However, a puzzle is encountered at the faint end of the luminosity function. As lower luminosity dwarf galaxies, roughly less active than the Small Magellanic Cloud, are examined, Halpha tends to increasingly underpredict the total SFR relative to the FUV. The trend is evident prior to corrections for dust attenuation, which affects the FUV more than the nebular Halpha emission, so this general conclusion is robust to the effects of dust. Although past studies have suggested similar trends, this is the first time this effect is probed with a statistical sample for galaxies with SFR approx< 0.1 M{sub sun} yr{sup -1}. By SFR approx 0.003 M{sub sun} yr{sup -1}, the average Halpha-to-FUV flux ratio is lower than expected by a factor of two, and at the lowest SFRs probed, the ratio exhibits an order of magnitude discrepancy for the handful of galaxies that remain in the sample. A range of standard explanations does not appear to be able to fully account for the magnitude of the systematic. Some recent work has argued for a stellar initial mass function which is deficient in high-mass stars in dwarf and low surface brightness galaxies, and we also consider this scenario. Under the assumption that the FUV traces the SFR in dwarf galaxies more robustly, the prescription relating Halpha luminosity to SFR is re-calibrated for use in the low SFR regime when FUV data are not available.

Lee, Janice C. [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Gil de Paz, Armando [Departmento de Astrofisica, Universidad Complutense de Madrid, Madrid 28040 (Spain); Tremonti, Christy; Walter, Fabian [Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Kennicutt, Robert C.; Bothwell, Matthew; Johnson, Benjamin [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Salim, Samir [NOAO, 950 North Cherry Ave., Tucson, AZ 85719 (United States); Calzetti, Daniela [Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States); Dalcanton, Julianne [Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195 (United States); Dale, Daniel [Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States); Engelbracht, Chad [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Funes, S. J. Jose G. [Vatican Observatory, Specola Vaticana, V00120 (Vatican City State, Holy See); Sakai, Shoko [Division of Astronomy and Astrophysics, University of California, Los Angeles, CA 90095-1562 (United States); Skillman, Evan; Weisz, Daniel [Department of Astronomy, University of Minnesota, Minneapolis, MN 55455 (United States); Van Zee, Liese, E-mail: jlee@ociw.ed [Astronomy Department, Indiana University, Bloomington, IN 47405 (United States)



Asteroseismology of DAV White Dwarf Stars  

SciTech Connect

The author reviews the seismological structural determinations of ZZ Ceti stars done to date, and supplement these with additional preliminary determinations of his own. He compares the constraints on the hydrogen layer mass to see what trends emerge and also determines if the observed hydrogen layer masses are consistent with proposed theories. He then looks ahead to the prospects of further DAV white dwarf seismology.

Bradley, Paul A.



The Effect of Crystallization on the Pulsations of White Dwarf Stars  

Microsoft Academic Search

We consider the pulsational properties of white dwarf star models with temperatures appropriate for the ZZ Ceti instability strip and with masses large enough that they should be substantially crystallized. Our work is motivated by the existence of a potentially crystallized DA variable (DAV), BPM 37093, and the expectation that digital surveys in progress will yield many more such massive

M. H. Montgomery; D. E. Winget



Herschel Detection of Dust Emission from UV-luminous Star-forming Galaxies at 3.3 <~ z <~ 4.3  

NASA Astrophysics Data System (ADS)

We report the Herschel/SPIRE detection of dust emission arising from UV-luminous (L >~ L*) star-forming galaxies at 3.3 <~ z <~ 4.3. Our sample of 1913 Lyman break galaxy (LBG) candidates is selected over an area of 5.3 deg2 in the Boötes field of the NOAO Deep Wide-Field Survey. This is one of the largest samples of UV-luminous galaxies at this epoch and enables an investigation of the bright end of the galaxy luminosity function. We divide our sample into three luminosity bins and stack the Herschel/SPIRE data to measure the average spectral energy distribution (SED) of LBGs at far-infrared (FIR) wavelengths. We find that these galaxies have average IR luminosities of (3-5) × 1011 L ? and 60%-70% of their star formation obscured by dust. The FIR SEDs peak at ?rest >~ 100 ?m suggesting dust temperatures (Td = 27-30 K) significantly colder than that of local galaxies of comparable IR luminosities. The observed IR-to-UV luminosity ratio (IRX ? L IR/L UV) is low (?3-4) compared with that observed for z ? 2 LBGs (IRXz ~ 2 ? 7.1 ± 1.1). The correlation between the slope of the UV continuum and IRX for galaxies in the two lower luminosity bins suggests dust properties similar to those of local starburst galaxies. However, the galaxies in the highest luminosity bin appear to deviate from the local relation, suggesting that their dust properties may differ from those of their lower-luminosity and low-redshift counterparts. We speculate that the most UV-luminous galaxies at this epoch are being observed in a short-lived and young evolutionary phase.

Lee, Kyoung-Soo; Alberts, Stacey; Atlee, David; Dey, Arjun; Pope, Alexandra; Jannuzi, Buell T.; Reddy, Naveen; Brown, Michael J. I.



Herschel Detection of Dust Emission from UV-Luminous Star-Forming Galaxies at 3.3  

NASA Astrophysics Data System (ADS)

We report the Herschel SPIRE detection of dust emission arising from UV-luminous (L> L*) star-forming galaxies at 3.3UV-luminous galaxies at this epoch and enables an investigation of the bright end of the galaxy luminosity function. We divide our sample into three luminosity bins and stack the Herschel SPIRE data to measure the average spectral energy distribution (SED) of LBGs at far-infrared (FIR) wavelengths. We find that these galaxies have average IR luminosities of 3-5x 10^11L_sun and 60-70% of their star-formation obscured by dust. The FIR SEDs peak at lambda_res 100um, suggesting dust temperatures (T_d=27-30K) significantly colder than that of local galaxies of comparable IR luminosities. The observed IR-to-UV luminosity ratio (IRX=L_IR/L_UV) is low 3-4) compared with that observed for 2 LBGs (IR 7.1+/-1.1). The correlation between the slope of the UV continuum and IRX for galaxies in the two lower luminosity bins suggests dust properties similar to those of local starburst galaxies. However, the galaxies in the highest luminosity bin appear to deviate from the local relation, suggesting that their dust properties may differ from those of their lower-luminosity and low-redshift counterparts. We speculate that the most UV luminous galaxies at this epoch are being observed in a short-lived and young evolutionary phase.

Lee, Kyoung-Soo; Alberts, S.; Atlee, D. W.; Dey, A.; Pope, A.; Jannuzi, B.; Reddy, N. A.; Brown, M. J.




NSDL National Science Digital Library

This section of the Windows to the Universe web site provides information and images about stars including star statistics, and a star gallery. Windows to the Universe is a user-friendly learning system pertaining to the Earth and Space sciences. The objective of this project is to develop an innovative and engaging web site that spans the Earth and Space sciences and includes a rich array of documents, including images, movies, animations, and data sets that explore the Earth and Space sciences and the historical and cultural ties between science, exploration and the human experience. Links at the top of each page allow users to navigate between beginner, intermediate and advanced levels.

Johnson, Roberta



Searching for the Most Stable Pulsating Stars  

NASA Astrophysics Data System (ADS)

Certain modes in the hot ZZ Ceti stars (HDAVs) exhibit extreme pulsational stability; their periods have been observed to show a slow increase, which is theoretically accounted for by evolutionary cooling of the star. These modes are super-stable, more stable than atomic clocks and most pulsars; they will lose one cycle in a few billion years. We have begun a program to find 100 new HDAVs to do ensemble asteroseismology and to search for planetary companions. HDAVs with an orbiting planet should show a measurable reflex motion around the center of mass of the system, easily distinguishable from their slow evolutionary cooling.

Mukadam, A.; Mullally, F.; Winget, D. E.; Nather, R. E.; Salviander, S.; von Hippel, T.; Reaves, D.; Slaughter, D.; Kepler, S. O.; Sullivan, D. J.; Homeier, D.


Flavobacterium anatoliense sp. nov., isolated from fresh water, and emended description of Flavobacterium ceti.  


A Gram-staining-negative, catalase- and oxidase-positive, strictly aerobic, rod-shaped bacterial strain isolated from fresh water in Trabzon, Turkey and designated MK3(T) was characterized by phenotypic and molecular methods in order to determine its phylogenetic position. On the basis of 16S rRNA gene sequence similarity, strain MK3(T) was shown to belong to the genus Flavobacterium, being most closely related to Flavobacterium ceti CECT 7184(T) (93.6%). Sequence similarity with other species of the genus Flavobacterium with validly published names was less than 91.6%. Phenotypic and chemotaxonomic data supported the affiliation of strain MK3(T) to the genus Flavobacterium. The only menaquinone was MK-6; the major fatty acids were iso-C15:0 (45.2%), summed feature 9 (C16:0 10-methyl and/or iso-C17:1?9c; 20.4%) and summed feature 3 (C16:1?7c and/or C16:1?6c; 13.3%) and the major polar lipids were phosphatidylethanolamine, one unidentified aminophospholipid and two unidentified phospholipids. The G+C content of the genomic DNA was 38.6 mol%. The results of physiological and biochemical tests allowed strain MK3(T) to be distinguished phenotypically from Flavobacterium ceti CECT 7184(T). Strain MK3(T), therefore, represents a novel species of the genus Flavobacterium, for which the name Flavobacterium anatoliense sp. nov. is proposed. The type strain is MK3(T) (=LMG 26441(T)=NCCB 100384(T)). An emended description of Flavobacterium ceti is also proposed. PMID:23064353

Kacagan, Murat; Inan, Kadriye; Belduz, Ali Osman; Canakci, Sabriye




SciTech Connect

We report the Herschel/SPIRE detection of dust emission arising from UV-luminous (L {approx}> L*) star-forming galaxies at 3.3 {approx}< z {approx}< 4.3. Our sample of 1913 Lyman break galaxy (LBG) candidates is selected over an area of 5.3 deg{sup 2} in the Booetes field of the NOAO Deep Wide-Field Survey. This is one of the largest samples of UV-luminous galaxies at this epoch and enables an investigation of the bright end of the galaxy luminosity function. We divide our sample into three luminosity bins and stack the Herschel/SPIRE data to measure the average spectral energy distribution (SED) of LBGs at far-infrared (FIR) wavelengths. We find that these galaxies have average IR luminosities of (3-5) Multiplication-Sign 10{sup 11} L{sub Sun} and 60%-70% of their star formation obscured by dust. The FIR SEDs peak at {lambda}{sub rest} {approx}> 100 {mu}m suggesting dust temperatures (T{sub d} = 27-30 K) significantly colder than that of local galaxies of comparable IR luminosities. The observed IR-to-UV luminosity ratio (IRX {identical_to} L{sub IR}/L{sub UV}) is low ( Almost-Equal-To 3-4) compared with that observed for z Almost-Equal-To 2 LBGs (IRX{sub z{approx}2} Almost-Equal-To 7.1 {+-} 1.1). The correlation between the slope of the UV continuum and IRX for galaxies in the two lower luminosity bins suggests dust properties similar to those of local starburst galaxies. However, the galaxies in the highest luminosity bin appear to deviate from the local relation, suggesting that their dust properties may differ from those of their lower-luminosity and low-redshift counterparts. We speculate that the most UV-luminous galaxies at this epoch are being observed in a short-lived and young evolutionary phase.

Lee, Kyoung-Soo [Department of Physics, Purdue University, 525 Northwestern Avenue, West Lafayette, IN 47907 (United States); Alberts, Stacey; Pope, Alexandra [Department of Astronomy, University of Massachusetts, 710 North Pleasant Street, Amherst, MA 01003 (United States); Atlee, David; Dey, Arjun; Jannuzi, Buell T. [National Optical Astronomy Observatory, Tucson, AZ 85726 (United States); Reddy, Naveen [Department of Physics and Astronomy, University of California, Riverside, 900 University Avenue, Riverside, CA 92521 (United States); Brown, Michael J. I. [School of Physics, Monash University, Clayton, Victoria 3800 (Australia)




SciTech Connect

We present a new analysis of the dust obscuration in starburst galaxies at low and high redshifts. This study is motivated by our unique sample of the most extreme UV-selected starburst galaxies in the nearby universe (z < 0.3), found to be good analogs of high-redshift Lyman break galaxies (LBGs) in most of their physical properties. We find that the dust properties of the Lyman break analogs (LBAs) are consistent with the relation derived previously by Meurer et al. (M99) that is commonly used to dust-correct star formation rate (SFR) measurements at a very wide range of redshifts. We directly compare our results with high-redshift samples (LBGs, 'BzK', and submillimeter galaxies at z {approx} 2-3) having IR data either from Spitzer or Herschel. The attenuation in typical LBGs at z {approx} 2-3 and LBAs is very similar. Because LBAs are much better analogs to LBGs compared to previous local star-forming samples, including M99, the practice of dust-correcting the SFRs of high-redshift galaxies based on the local calibration is now placed on a much more solid ground. We illustrate the importance of this result by showing how the locally calibrated relation between UV measurements and extinction is used to estimate the integrated, dust-corrected SFR density at z {approx_equal} 2-6.

Overzier, Roderik A.; Wang Jing [Max-Planck-Institut for Astrophysics, D-85748 Garching (Germany); Heckman, Timothy M. [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Armus, Lee; Howell, Justin [Spitzer Science Center, Caltech, MS 220-6, Pasadena, CA 91125 (United States); Buat, Veronique [Laboratoire d'Astrophysique de Marseille, OAMP, Universite Aix-marseille, CNRS, 38 rue Frederic Joliot-Curie, 13388 Marseille Cedex 13 (France); Meurer, Gerhardt [ICRAR/University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia); Seibert, Mark [Observatories of the Carnegie Institution of Washington, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Siana, Brian; Goncalves, Thiago S.; Martin, D. Christopher; Neill, James D. [California Institute of Technology, MS 249-17, Pasadena, CA 91125 (United States); Basu-Zych, Antara [NASA Goddard Space Flight Center, Laboratory for X-ray Astrophysics, Greenbelt, MD 20771 (United States); Charlot, Stephane [PMC Univ Paris 06, UMR7095, Institut d'Astrophysique de Paris, F-75014 Paris (France); Rich, R. Michael [Department of Physics and Astronomy, Division of Astronomy and Astrophysics, University of California, Los Angeles, CA 90095-1562 (United States); Salim, Samir [National Optical Astronomical Observatories, 950 N. Cherry Avenue, Tucson, AZ 85719 (United States); Schiminovich, David, E-mail: [Department of Astronomy, Columbia University, MC 2457, 550 West 120th Street, New York, NY 10027 (United States)



A Comparison of H-alpha and UV Star Formation Rates in the Local Volume: Systematic Discrepancies in Dwarf Galaxies  

Microsoft Academic Search

Using a complete, statistical sample of star-forming galaxies within the Local Volume, we evaluate the consistency between star formation rates (SFRs) inferred from H-alpha nebular emission and the far ultraviolet non-ionizing continuum. Our analysis probes activities ranging from those that characteristic of the Milky Way to ultra-low SFRs of 0.0001 M&sun;\\/yr. We establish that there is a systematic decline of

Janice Lee



Magnetic field and activity of the single late-type giant ? Ceti  

NASA Astrophysics Data System (ADS)

We present the behavior of the magnetic field and activity indicators of the single late-type giant ? Ceti in the period June 19, 2010 - December 14, 2010. We used spectropolarimetric data obtained with two telescopes -- the NARVAL spectropolarimeter at Télescope Bernard Lyot, Pic du Midi, France and the ESPaDOnS spectropolarimeter at CFHT, Hawaii. The data were processed using the method of Least Square Deconvolution which enables to derive the mean photospheric profiles of Stokes I and V parameters. We measured the surface-averaged longitudinal magnetic field B_{l}, which varies in the interval 0.1 - 8.2 G, the line activity indicators CaII K, H?, CaII IR (854.2 nm), and radial velocity. By analyzing the B_{l} variations, a possible rotational period P = 118 days was identified. A single, large magnetic spot, which dominates the field topology, is a possible explanation for the B_{l} and activity indicator variations of ? Ceti.

Tsvetkova, S.; Aurière, M.; Konstantinova-Antova, R.; Wade, G. A.; Bogdanovski, R. G.; Petit, P.


Chemical composition of AY Ceti: A flaring, spotted star with a white dwarf companion  

NASA Astrophysics Data System (ADS)

The detailed chemical composition of the atmosphere AY Cet (HD 7672) is determined from a high-resolution spectrum in the optical region. The main atmospheric parameters and the abundances of 22 chemical elements, including key species such as 12C, 13C, N, and O, are determined. A differential line analysis gives T_eff=5080 K, log g=3.0, [Fe/H]=-0.33, [C/Fe]=-0.17, [N/Fe]=0.17, [O/Fe]=0.05, C/N=1.58, and 12C/13C=21. Despite the high chromospheric activity, the optical spectrum of AY Cet provides a chemical composition typical for first ascent giants after the first dredge-up.

Tautvaišien?, G.; Barisevi?ius, G.; Berdyugina, S.; Ilyin, I.; Chorniy, Y.




SciTech Connect

We provide a systematic measurement of the rest-frame UV continuum slope beta over a wide range in redshift (z approx 2-6) and rest-frame UV luminosity (0.1 L* {sub z} {sub =} {sub 3} to 2 L* {sub z={sub 3}}) to improve estimates of the star formation rate (SFR) density at high redshift. We utilize the deep optical and infrared data (Advanced Camera for Surveys/NICMOS) over the Chandra Deep Field-South and Hubble Deep Field-North Great Observatories Origins Deep Survey fields, as well as the UDF for our primary UBVi 'dropout' Lyman Break Galaxy sample. We also use strong lensing clusters to identify a population of very low luminosity, high-redshift dropout galaxies. We correct the observed distributions for both selection biases and photometric scatter. We find that the UV-continuum slope of the most luminous galaxies is substantially redder at z approx 2-4 than it is at z approx 5-6 (from approx-2.4 at z approx 6 to approx-1.5 at z approx 2). Lower luminosity galaxies are also found to be bluer than higher luminosity galaxies at z approx 2.5 and z approx 4. We do not find a large number of galaxies with beta's as red as -1 in our dropout selections at z approx 4, and particularly at z approx> 5, even though such sources could be readily selected from our data (and also from Balmer Break Galaxy searches at z approx 4). This suggests that star-forming galaxies at z approx> 5 almost universally have very blue UV-continuum slopes, and that there are not likely to be a substantial number of dust-obscured galaxies at z approx> 5 that are missed in 'dropout' searches. Using the same relation between UV-continuum slope and dust extinction as has been found to be appropriate at both z approx 0 and z approx 2, we estimate the average dust extinction of galaxies as a function of redshift and UV luminosity in a consistent way. As expected, we find that the estimated dust extinction increases substantially with cosmic time for the most UV luminous galaxies, but remains small (approx<2 times) at all times for lower luminosity galaxies. Because these same lower luminosity galaxies dominate the luminosity density in the UV continuum, the overall dust extinction correction remains modest at all redshifts and the evolution of this correction with redshift is only modest. We include the contribution from ultra-luminous IR galaxies in our SFR density estimates at z approx 2-6, but find that they contribute only approx20% of the total at z approx 2.5 and approx<10% at z approx> 4.

Bouwens, R. J.; Illingworth, G. D. [Astronomy Department, University of California, Santa Cruz, CA 95064 (United States); Franx, M. [Leiden Observatory, University of Leiden, Postbus 9513, 2300 RA Leiden (Netherlands); Chary, R.-R. [Divison of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA 91125 (United States); Meurer, G. R.; Ford, H. [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Conselice, C. J. [University of Nottingham, School of Physics and Astronomy, Nottinghm NG7 2RD (United Kingdom); Giavalisco, M. [Department of Astronomy, University of Massachusetts, Amherst, MA (United States); Van Dokkum, P. [Department of Astronomy, Yale University, New Haven, CT (United States)



The Spacelab1 Very Wide Field Survey of UV-excess objects. II - Analysis of 7 stars of various nature  

Microsoft Academic Search

Multiwavelength observations of seven stellar objects with strong UV excesses are presented. The observations are IUE spectrophotometry, Stromgren Vuvby optical photometry, Johnson JHK infrared photometry, intermediate resolution optical spectroscopy, and in one case a CORAVEL radial velocity survey. Three of the objects are field subdwarfs (one of which is helium-rich) with z-distances of from -150 to -300 pc from the

M. Viton; M. Deleuil; W. Tobin; L. Prevot; P. Bouchet



Irradiation of Dust in Molecular Clouds. III. Internal Sources of Stellar UV Photons from A-F-G Dwarf Stars  

NASA Astrophysics Data System (ADS)

The radiation fluxes inside interstellar gas-dust molecular clouds as stars of classes A, F, and G pass through the clouds are calculated. It is shown that radiation in the range 912stars cross the clouds that is high enough to initiate chemical reactions in the ice mantles of dust particles. The possible use of these results for astrophysical interpretation of published data from laboratory experiments on the irradiation of H2O:CH3OH:NH3:CO ice mixtures is discussed. The complex carbon-containing compounds formed during this radiation-induced chemical transformation may play an important role in the prebiological evolution of the dust component of molecular clouds.

Yeghikyan, A. G.



Dust-obscured star formation and the contribution of galaxies escaping UV/optical color selections at z ~ 2  

NASA Astrophysics Data System (ADS)

Context. A substantial amount of the stellar mass growth across cosmic time occurred within dust-enshrouded environments. So far, identification of complete samples of distant star-forming galaxies from the short wavelength range has been strongly biased by the effect of dust extinction. Nevertheless, the exact amount of star-forming activity that took place in high-redshift dusty galaxies but that has currently been missed by optical surveys has barely been explored. Aims: Our goal is to determine the number of luminous star-forming galaxies at 1.5 ? z ? 3 that are potentially missed by the traditional color selection techniques because of dust extinction. We also aim at quantifying the contribution of these sources to the IR luminosity and cosmic star formation density at high redshift. Methods: We based our work on a sample of 24 ?m sources brighter than 80 ?Jy and taken from the Spitzer survey of the COSMOS field. Almost all of these sources have accurate photometric redshifts. We applied to this mid-IR selected sample the BzK and BM/BX criteria, as well as the selections of the IRAC peakers and the Optically-Faint IR-bright (OFIR) galaxies. We analyzed the fraction of sources identified with these techniques. We also computed 8 ?m rest-frame luminosity from the 24 ?m fluxes of our sources, and considering the relationships between L8 ?m and LPa? and between L8 ?m and LIR, we derived ?IR and then ?SFR for our MIPS sources. Results: The BzK criterion offers an almost complete (~90%) identification of the 24 ?m sources at 1.4 < z < 2.5. In contrast, the BM/BX criterion misses 50% of the MIPS sources. We attribute this bias to the effect of extinction, which reddens the typical colors of galaxies. The contribution of these two selections to the IR luminosity density produced by all the sources brighter than 80 ?Jy are on the same order. Moreover the criterion based on the presence of a stellar bump in their spectra (IRAC peakers) misses up to 40% of the IR luminosity density, while only 25% of the IR luminosity density at z ~ 2 is produced by OFIR galaxies characterized by extreme mid-IR to optical flux ratios. Conclusions: Color selections of distant star-forming galaxies must be used with care given the substantial bias they can suffer. In particular, the effect of dust extinction strongly affects the completeness of identifications at the bright end of the bolometric luminosity function, which implies large and uncertain extrapolations to account for the contribution of dusty galaxies missed by these selections. In the context of forthcoming facilities that will operate at long wavelengths (e.g., JWST, ALMA, SAFARI, EVLA, SKA), this emphasizes the importance of minimizing the extinction biases when probing the activity of star formation in the early Universe.

Riguccini, L.; Le Floc'h, E.; Ilbert, O.; Aussel, H.; Salvato, M.; Capak, P.; McCracken, H.; Kartaltepe, J.; Sanders, D.; Scoville, N.




SciTech Connect

A new set of color selection criteria (VJL) analogous with the BzK method is designed to select both star-forming galaxies (SFGs) and passively evolving galaxies (PEGs) at 2.3 {approx}< z {approx}< 3.5 by using rest-frame UV-optical (V - J versus J - L) colors. The criteria are thoroughly tested with theoretical stellar population synthesis models and real galaxies with spectroscopic redshifts to evaluate their efficiency and contamination. We apply the well-tested VJL criteria to the HST/WFC3 Early Release Science field and study the physical properties of selected galaxies. The redshift distribution of selected SFGs peaks at z {approx} 2.7, slightly lower than that of Lyman break galaxies at z {approx} 3. Comparing the observed mid-infrared fluxes of selected galaxies with the prediction of pure stellar emission, we find that our VJL method is effective at selecting massive dusty SFGs that are missed by the Lyman break technique. About half of the star formation in massive (M{sub star} > 10{sup 10} M{sub Sun }) galaxies at 2.3 {approx}< z {approx}< 3.5 is contributed by dusty (extinction E(B - V) > 0.4) SFGs, which, however, only account for {approx}20% of the number density of massive SFGs. We also use the mid-infrared fluxes to clean our PEG sample and find that galaxy size can be used as a secondary criterion to effectively eliminate the contamination of dusty SFGs. The redshift distribution of the cleaned PEG sample peaks at z {approx} 2.5. We find six PEG candidates at z > 3 and discuss possible methods to distinguish them from dusty contamination. We conclude that at least part of our candidates are real PEGs at z {approx} 3, implying that these types of galaxies began to form their stars at z {approx}> 5. We measure the integrated stellar mass density (ISMD) of PEGs at z {approx} 2.5 and set constraints on it at z > 3. We find that the ISMD grows by at least about a factor of 10 in 1 Gyr at 3 < z <5 and by another factor of 10 in the next 3.5 Gyr (1 < z < 3).

Guo Yicheng; Giavalisco, Mauro; Cassata, Paolo; Williams, Christina C.; Salimbeni, Sara [Astronomy Department, University of Massachusetts, 710 N. Pleasant Street, Amherst, MA 01003 (United States); Ferguson, Henry C.; Koekemoer, Anton; Grogin, Norman A. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Dickinson, Mark [NOAO-Tucson, 950 North Cherry Avenue, Tucson, AZ 85719 (United States); Chary, Ranga-Ram [Spitzer Science Center, California Institute of Technology, MS 220-6, Pasadena, CA 91125 (United States); Messias, Hugo [Centro de Astronomia e Astrofisica da Universidade de Lisboa, Observatorio Astronomico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa (Portugal); Tundo, Elena [INAF-Osservatorio Astronomico di Trieste, Via Tiepolo 11, I-34131 Trieste (Italy); Lin Lihwai [Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 106, Taiwan (China); Lee, Seong-Kook [School of Physics, Korea Institute for Advanced Study, Hoegiro 87, Dongdaemun-Gu, Seoul 130-722 (Korea, Republic of); Fontana, Adriano; Grazian, Andrea [INAF-Osservatorio Astronomico di Roma, Via Frascati 33, I00040 Monteporzio (Italy); Kocevski, Dale [UCO/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States); Lee, Kyoung-Soo [Yale Center for Astronomy and Astrophysics, Department of Physics, Yale University, New Haven, CT 06520 (United States); Villanueva, Edward [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101-1292 (United States); Van der Wel, Arjen, E-mail: [Max-Planck Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)



Dust-obscured Star Formation And The Contribution Of Galaxies Escaping UV/optical Color Selections At z 2  

NASA Astrophysics Data System (ADS)

This poster focus on the luminous star-forming galaxies at 1.5 < z < 3 potentially missed by the traditional color selection techniques because of dust extinction. We quantify the fraction of these sources and their contribution to the IR luminosity and cosmic star formation density at high redshift. Our work is based on a sample of 24microns sources brighter than 80microJy taken from the Spitzer survey of the COSMOS field. Almost all of these sources have accurate photometric redshifts. I apply to this mid-IR selected sample the BzK and BM/BX criteria as well as the selections of the "IRAC peakers " and the "optically-faint IR-bright " galaxies, and I analyze the fraction of sources identified with these techniques. I also computed 8microns rest-frame luminosity from the 24microns fuxes of our sources, and considering the relationships between L8microns and LPaalpha and between L8microns and LIR, I derived the IR luminosity density and the SFR density for our MIPS sources. The BzK criterion offers an almost complete ( 90%) identification of the 24microns sources at 1.4 < z < 2.5. On the contrary, the BM/BX criterion miss 50% of the MIPS sources. We attribute this bias to the effect of extinction which redden the typical colors of galaxies. The contribution of these two selections to the IR luminosity density produced by all the sources brighter than 80microJy are from the same order. Moreover the criterion based on the presence of a stellar bump in their spectra ("IRAC peakers") miss up to 40% of the IR luminosity density while only 25% of the IR luminosity density at z 2 is produced by "optically-faint IR-bright" galaxies characterized by extreme mid-IR to optical flux ratios.

Riguccini, Laurie; Le Floc'h, E.; Ilbert, O.; Aussel, H.; Salvato, M.; Capak, P.; McCracken, H.; Kartaltepe, J.; Sanders, D.; Scoville, N.



The Effect of Crystallization on the Pulsations of White Dwarf Stars  

Microsoft Academic Search

We consider the pulsational properties of white dwarf star models with\\u000atemperatures appropriate for the ZZ Ceti instability strip and with masses\\u000alarge enough that they should be substantially crystallized. Our work is\\u000amotivated by the existence of a potentially crystallized DAV, BPM 37093, and\\u000athe expectation that digital surveys in progress will yield many more such\\u000amassive pulsators.\\u000a A

M. H. Montgomery; D. E. Winget



UV-to-FIR Analysis of Spitzer/IRAC Sources in the Extended Groth Strip. II. Photometric Redshifts, Stellar Masses, and Star Formation Rates  

NASA Astrophysics Data System (ADS)

Based on the ultraviolet to far-infrared photometry already compiled and presented in a companion paper (Paper I), we present a detailed spectral energy distribution (SED) analysis of nearly 80,000 IRAC 3.6 + 4.5 ?m selected galaxies in the Extended Groth Strip. We estimate photometric redshifts, stellar masses, and star formation rates (SFRs) separately for each galaxy in this large sample. The catalog includes 76,936 sources with [3.6] <= 23.75 (85% completeness level of the IRAC survey) over 0.48 deg2. The typical photometric redshift accuracy is ?z/(1 + z) = 0.034, with a catastrophic outlier fraction of just 2%. We quantify the systematics introduced by the use of different stellar population synthesis libraries and initial mass functions in the calculation of stellar masses. We find systematic offsets ranging from 0.1 to 0.4 dex, with a typical scatter of 0.3 dex. We also provide UV- and IR-based SFRs for all sample galaxies, based on several sets of dust emission templates and SFR indicators. We evaluate the systematic differences and goodness of the different SFR estimations using the deep FIDEL 70 ?m data available in the Extended Groth Strip. Typical random uncertainties of the IR-bases SFRs are a factor of two, with non-negligible systematic effects at z gsim 1.5 observed when only MIPS 24 ?m data are available. All data products (SEDs, postage stamps from imaging data, and different estimations of the photometric redshifts, stellar masses, and SFRs of each galaxy) described in this and the companion paper are publicly available, and they can be accessed through our the Web interface utility Rainbow-navigator.

Barro, G.; Pérez-González, P. G.; Gallego, J.; Ashby, M. L. N.; Kajisawa, M.; Miyazaki, S.; Villar, V.; Yamada, T.; Zamorano, J.



Star Journey  

NSDL National Science Digital Library

This National Geographic web-site contains information about the Hubble Space Telescope (HST) along with a star chart and facts about objects in the night sky. The HST section contains details about the building and structure of the HST, how it captures light, positioning the HST to targets, instruments used to record and measure infrared through UV wavelengths, how the HST is powered and communicates with the Earth. Star Attractions discusses properties of constellations, the Milky Way galaxy, other galaxies, star clusters and nebulae. This information is then put together on the National Geographic Star Chart. This chart contains maps of the heavens for the northern and southern hemispheres. The chart contains constellation names, location of stars and other objects, and links to HST images of various galaxies and objects on the chart with names and detailed descriptions. There is an image index to find HST images from the site, details about chart symbol meanings, and links for more information.

Anderson, Carolyn


A Steep Faint-End Slope of the UV Luminosity Function at z ~ 2-3: Implications for the Global Stellar Mass Density and Star Formation in Low-Mass Halos  

NASA Astrophysics Data System (ADS)

We use the deep ground-based optical photometry of the Lyman Break Galaxy (LBG) Survey to derive robust measurements of the faint-end slope (?) of the UV luminosity function (LF) at redshifts 1.9 <= z <= 3.4. Our sample includes >2000 spectroscopic redshifts and ?31000 LBGs in 31 spatially independent fields over a total area of 3261 arcmin2. These data allow us to select galaxies to 0.07L* and 0.10L* at z ~ 2 and z ~ 3, respectively. A maximum-likelihood analysis indicates steep values of ?(z = 2) = -1.73 ± 0.07 and ?(z = 3) = -1.73 ± 0.13. This result is robust to luminosity-dependent systematics in the Ly? equivalent width and reddening distributions, and is similar to the steep values advocated at z gsim 4, and implies that ?93% of the unobscured UV luminosity density at z ~ 2-3 arises from sub-L* galaxies. With a realistic luminosity-dependent reddening distribution, faint to moderately luminous galaxies account for gsim70% and gsim25% of the bolometric luminosity density and present-day stellar mass density, respectively, when integrated over 1.9 <= z < 3.4. We find a factor of 8-9 increase in the star-formation rate density between z ~ 6 and z ~ 2, due to both a brightening of L* and an increasing dust correction proceeding to lower redshifts. Combining the UV LF with stellar mass estimates suggests a relatively steep low-mass slope of the stellar mass function at high redshift. The previously observed discrepancy between the integral of the star-formation history and stellar mass density measurements at z ~ 2 may be reconciled by invoking a luminosity-dependent reddening correction to the star-formation history combined with an accounting for the stellar mass contributed by UV-faint galaxies. The steep and relatively constant faint-end slope of the UV LF at z gsim 2 contrasts with the shallower slope inferred locally, suggesting that the evolution in the faint-end slope may be dictated simply by the availability of low-mass halos capable of supporting star formation at z lsim 2. Based, in part, 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 NASA, and was made possible by the generous financial support of the W. M. Keck Foundation.

Reddy, Naveen A.; Steidel, Charles C.



The presence of Brucella ceti ST26 in a striped dolphin (Stenella coeruleoalba) with meningoencephalitis from the Mediterranean Sea.  


Brucella spp. was isolated from brain, lung and intestinal lymph nodes of a dead adult male striped dolphin (Stenella coeruleoalba) found stranded on the Tyrrhenian coast (Tuscany, Italy) of the Mediterranean Sea in February 2012. Brucella spp. was associated with moderate to severe lesions of meningoencephalitis. A co-infection by Toxoplasma gondii was also demonstrated at brain level by means of molecular and histopathologic methods. The Brucella isolate was further characterized based on a fragment-specific polymerase chain reaction (PCR) approach, consisting of a set of five specific PCRs, targeting specific chromosomal IS711 locations for marine mammal Brucellae, as described previously. The isolate was thus classified as Brucella ceti I; V fragment-positive (or B. ceti dolphin type), according to previous studies. Multi Locus Sequence Analysis demonstrated that the isolate belongs to Sequence Type 26, while omp2 (omp2a and omp2b genes) sequence analysis further confirmed the isolate belonged to this group of strains. This is the first report of Brucella spp. from marine mammals in the Mediterranean Sea, and represents a further observation that this strain group is associated with hosts of the Family Delphinidae, and particularly with the striped dolphins, also in the Mediterranean area, thus constituting a further biological hazard of concern for this vulnerable subpopulation. PMID:23419820

Alba, Patricia; Terracciano, Giuliana; Franco, Alessia; Lorenzetti, Serena; Cocumelli, Cristiano; Fichi, Gianluca; Eleni, Claudia; Zygmunt, Michel S; Cloeckaert, Axel; Battisti, Antonio



Further VLBA observations of SiO masers toward Mira variable stars  

NASA Astrophysics Data System (ADS)

We present the results of continued monitoring of the SiO masers at 7 mm wavelength in several of the Mira variable stars reported in Cotton et al. (2004, A&A, 414, 275) (o Ceti = Mira, U Orionis = U Ori, R Aquarii = R Aqr) over a period of 16 months, extending the observations to several pulsation cycles. The observed size of the maser rings varied by 3-14% with time but show no clear correlation with pulsation phase. In all cases, the SiO masers appear just outside the dense molecular layer indicated by near-IR observations. Rotation (or large scale motion) is possibly detected in o Ceti with a period of 89× sin(i) years. We find linear polarization up to ˜ 60% and at several epochs predominantly tangentially ordered polarization vectors indicate a radial magnetic field direction. Jet-like features are examined in o Ceti and R Aqr and in both cases, the magnetic field appears elongated with the masing structure. This suggests that the dynamic feature in the envelope is dragging the magnetic field or that the gas is constrained to follow magnetic field.

Cotton, W. D.; Vlemmings, W.; Mennesson, B.; Perrin, G.; Coudé du Foresto, V.; Chagnon, G.; Diamond, P. J.; van Langevelde, H. J.; Bakker, E.; Ridgway, S.; McAllister, H.; Traub, W.; Ragland, S.



Identification of new fluorescence processes in the UV spectra of cool stars from new energy levels of Fe II and CR II  

NASA Astrophysics Data System (ADS)

Two fluorescence processes operating in atmospheres of cool stars, symbiotic stars, and the Sun are presented. Two emission lines, at 1347.03 and 1360.17 A, are identified as fluorescence lines of Cr II and Fe II. The lines are due to transitions from highly excited levels, which are populated radiatively by the hydrogen Lyman alpha line due to accidental wavelength coincidences. Three energy levels, one in Cr II and two in Fe II, are reported.

Johansson, Sveneric; Carpenter, Kenneth G.



Analysis of Peculiarities of Star Velocity Distributions in the Solar Neighborhood  

NASA Astrophysics Data System (ADS)

Analysis of the velocities of ?17000 individual stars in the Solar neighborhood was performed based on the new version of the Hipparcos catalogue and updated Geneva-Copenhagen survey of F- and G-dwarfs. The main known condensations, streams and branches (Pleiades, Hyades, Sirius, Coma Berenices, ? Herculis, Wolf 630-? Ceti, Arcturus) were revealed using various methods. The evolution of the velocity field of F- and G-dwarfs was traced with respect to the ages of stars. We managed to prove the existence of the recently discovered stream KFR08. 19 Hipparcos stars - candidates to the membership in the stream KFR08 were found, and the isochronal estimate of the age of the stream - 13 billion years - was found using them. We demonstrate that the average ages of the streams Wolf 630-? Ceti and Hercules are comparable: 4-6 billion years. No essential differences in the metallicities of the stars of these streams were found. This is an argument in favor of the hypothesis that these streams have a common mechanism of origin.

Bobylev, V. V.; Bajkova, A. T.



UV Radiation  


... you see, infrared radiation that you feel as heat, and ultraviolet (UV) radiation that you can’t see or feel. UV radiation has a shorter wavelength and higher energy than visible light. It affects human health both ...


Predicting UV sky for future UV missions  

NASA Astrophysics Data System (ADS)

Software simulators are now widely used in all areas of science, especially in application to astronomical missions: from instrument design to mission planning, and to data interpretation. We present a simulator to model the diffuse ultraviolet sky, where the different contributors are separately calculated and added together to produce a sky image of the size specified by the instrument requirements. Each of the contributors to the background, instrumental dark current, airglow, zodiacal light and diffuse Galactic light, depends on different factors. Airglow is dependent on the time of day; zodiacal light depends on the time of year, angle from the Sun and from the ecliptic; diffuse UV emission depends on the line of sight. To provide a full description of the sky along any line of sight, we have also added stars. The UV background light can dominate in many areas of the sky and severely limit viewing directions due to overbrightness. The simulator, available as a downloadable package and as a web-based tool, can be applied to preparation of real space missions and instruments. For demonstration, we present the example use for the two near-future UV missions: UVIT instrument on the Indian Astrosat mission and a new proposed wide-field (?1000 square degrees) transient explorer satellite.

Safonova, M.; Mohan, R.; Sreejith, A. G.; Murthy, Jayant



The History of Variable Stars: A Fresh Look  

NASA Astrophysics Data System (ADS)

(Abstract only) For historians of astronomy, variable stars are important for a simple reason - stars change. But good evidence suggests this is a very modern idea. Over the millennia, our species has viewed stars as eternal and unchanging, forever fixed in time and space - indeed, the Celestial Dance was a celebration of order, reason, and stability. But everything changed in the period between Copernicus and Newton. According to tradition, two New Stars announced the birth of the New Science. Blazing across the celestial stage, Tycho's Star (1572) and Kepler's Star (1604) appeared dramatically - and just as unexpectedly - disappeared forever. But variable stars were different. Mira Ceti, the oldest, brightest, and most controversial variable star, was important because it appeared and disappeared again and again. Mira was important because it did not go away. The purpose of this essay is to take a fresh look at the history of variable stars. In re-thinking the traditional narrative, I begin with the first sightings of David Fabricius (1596) and his contemporaries - particularly Hevelius (1662) and Boulliau (1667) - to new traditions that unfolded from Newton and Maupertuis to Herschel (1780) and Pigott (1805). The essay concludes with important 19th-century developments, particularly by Argelander (1838), Pickering (1888), and Lockyer (1890). Across three centuries, variable stars prompted astronomers to re-think all the ways that stars were no longer "fixed." New strategies were needed. Astronomers needed to organize, to make continuous observations, to track changing magnitudes, and to explain stellar phases. Importantly - as Mira suggested from the outset - these challenges called for an army of observers with the discipline of Spartans. But recruiting that army required a strategy, a set of theories with shared expectations. Observation and theory worked hand-in-hand. In presenting new historical evidence from neglected printed sources and unpublished manuscripts, this essay aims to offer a fresh look at the history of variable stars.

Hatch, R. A.



High mass stars: starbursts  

NASA Astrophysics Data System (ADS)

Starbursts are the preferred place where massive stars form; the main source of thermal and mechanical heating in the interstellar medium, and the factory where the heavy elements form. Thus, starbursts play an important role in the origin and evolution of galaxies. Starbursts are bright at ultraviolet (UV) wavelengths, and after the pioneering IUE program, high spatial and spectral resolution UV observations of local starburst galaxies, mainly taken with HST and FUSE, have made relevant contributions to the following issues: a) The determination of the initial mass function in violent star forming systems in low and high metallicity environments, and in dense (e.g. in stellar clusters) and diffuse environments. b) The modes of star formation: Starburst clusters are an important mode of star formation. c) The role of starbursts in AGN. d) The interaction between massive stars and the interstellar and intergalactic media. e) The contribution of starbursts to the reionization of the universe. Despite the very significant progress obtained over the past two decades of UV observations of starbursts, there are important problems that still need to be solved. High-spatial resolution UV observations of nearby starbursts are crucial to further progress in understanding the violent star formation processes in galaxies, the interaction between the stellar clusters and the interstellar medium, and the variation of the IMF. Thus, a new UV mission furnished with an intermediate spectral resolution long-slit spectrograph with high spatial resolution and high UV sensitivity is required to further progress in the study of starburst galaxies and their impact on the evolution of galaxies.

González Delgado, R. M.



GALEX and star formation  

Microsoft Academic Search

Wide-field far-UV (FUV, 1344–1786 Å) and near-UV (NUV, 1771–2831 Å) imaging from GALEX provides a deep, comprehensive view of the young stellar populations in hundreds of nearby galaxies, shedding new light on\\u000a the process of star formation (SF) in different environments, and on the interplay between dust and SF. GALEX’s FUV-NUV color is extremely sensitive to stellar populations of ages up to

Luciana Bianchi



AM CVn stars  

Microsoft Academic Search

I review our observational and theoretical knowledge of AM CVn stars,\\u000afocusing on recent developments. These include newly discovered systems, the\\u000apossibility that two recently discovered extremely short period objects are AM\\u000aCVn stars and an update on X-ray, UV an optical studies. Theoretical advances\\u000ainclude the study of the details of both the donor and accretor, and the\\u000aphysics

Gijs Nelemans



Ce-Ti amorphous oxides for selective catalytic reduction of NO with NH3: confirmation of Ce-O-Ti active sites.  


The amorphous Ce-Ti mixed oxides were reported to be catalysts for selective catalytic reduction of NO(x) with NH(3), in which Ce and not Ti acts as their solvent in spite of the fact that Ce is low in content. The amorphous catalysts were characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) equipped with selective area electron diffraction (SAED). The Ce-Ti amorphous oxide shows higher activity than its crystalline counterpart at lower temperatures. Moreover, the presence of small CeO(2) crystallites as for the impregnated sample is deleterious to activity. The Ce-O-Ti short-range order species with the interaction between Ce and Ti in atomic scale was confirmed for the first time to be the active site using temperature programmed reduction with H(2) (H(2)-TPR), in situ FTIR spectra of NO adsorption, X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine-structure (XAFS). Lastly, the Ce-O-Ti structure was directly observed by field-emission TEM (FETEM). PMID:22888951

Li, Ping; Xin, Ying; Li, Qian; Wang, Zhongpeng; Zhang, Zhaoliang; Zheng, Lirong



Recent star formation in galaxies  

Microsoft Academic Search

In recent years the study of starburst galaxies has become a very popular subject because of their intimate connection with the global star formation history of the Universe. Current estimates of the star formation rate of the Unvierse have been interpreted on the basis of our understanding of local analogous galaxies, in particular through UV continuum and optical line emission.

Alessandro Bressan



Uv Throughput  

NASA Astrophysics Data System (ADS)

GRW+70d5824 is observed shortly before and after a DECON through all the UV filters in each chip and through F160BW crossed with F130LP, F185LP, and F165LP (where applicable) to determine the wavelength dependence of the throughput across the bandpass (hence color terms). Based on no particular cycle 4 program, this program is designed to better characterize the spectral response curve in the UV, and the spectral shape introduced by the contamination. Overall discrepencies between the updated synthetic photometric products and the results of this test should be 1-2% rms. This does not mean that the UV throughput will be known to this accuracy primarily because of uncertainties in the flux calibration of the standard used (5%) uncertainties in the UV flatfields (maybe 3% near the chip center), and time dependent contamination corrections (3% error), and uncertainties in the CTE correction (2%). The derived UV absolute photometry accuracy at the center of the chips should therefore be about 10%. After pipeline processing, each image will be reduced by aperture photometry. The throughput curves and their normalizations can be updated by trial and error. Expected to run 8/95. NOTE: crossed filters exposures should be observed in ALL chips after decontamination, but just in WF3 before decontamination.

Casertano, Stefano



A Marvelous Star in M33  

NASA Astrophysics Data System (ADS)

The end stages of stellar evolution release heavy element enriched dust into the interstellar medium where it is eventually incorporated into star formation regions and later generations of stars. As low mass stars go through this process they bloat in size, pulsate, and expel dust and gas before ultimately transforming into planetary nebulae (PNe). A classic example of this stage of evolution is the well studied class of pulsating stars, the Mira variables. Prior to expelling a PNe, these objects go through a short (tens of thousands of years) stage of evolution where they undergo episodic mass loss and become enshrouded in dust. We report the discovery of an unusual Mira star within the M33 galaxy; IRAC 0134+3029. The source is heavily obscured in the visible, indicating large amounts of enshrouding dust. In addition, Spitzer Space Telescope spectroscopy and imaging show strong thermal emission as well as absorption features from silicates. Examination of the properties of IRAC 0134 suggests that it is the extragalactic analog of the well known "extreme" Mira OH26.5+0.6. We compare spectra and photometry of IRAC 0134 to observations of OH26.5+.6 as well as to the prototype of the Mira class, Omicron Ceti. We also discuss some contradictory archival observations of these objects and suggest possible explanations. This work is based upon observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA contract 1407. The authors were supported in part through contracts 1256406 and 1215746 issued by JPL/Caltech to the University of Minnesota.

Polomski, Elisha; Gehrz, R. D.; McQuinn, K.; Paffel, F.; Woodward, C. E.



Solar UV dose patterns in Italy.  


Since 1992 solar ultraviolet (UV) spectral irradiance (290-325 nm) has been measured at two Italian stations of Rome (urban site) and Ispra (semirural site) using Brewer spectrophotometry. The data collected under all sky conditions, are compared with the output of a sophisticated radiative transfer model (System for Transfer of Atmospheric Radiation--STAR model). The STAR multiple scattering scheme is able to cope with all physical processes relevant to the UV transfer through the atmosphere. The experience so far acquired indicates that, in spite of the unavoidable uncertainties in the input parameters (ozone, aerosol, surface albedo, pressure, temperature, relative humidity, cloud cover), measured and computed clear sky iradiances are in reasonable agreement. The STAR model is applied to build up the solar UV geographic patterns in Italy: the daily dose in the range 290-325 nm is computed at about 70 sites where a thorough and homogeneous climatology is available. For each month the concept of an idealized "standard day" is introduced and the surface distribution of solar UV field determined. The map of solar UV patterns for Italy, available for the first time, meets the study requirements in the field of skin and eye epidemiology, as well as in other investigations dealing with the impact of UV on the biosphere. The results are interpreted in terms of atmospheric and meteorological parameters modulating UV radiation reaching the ground. PMID:10857363

Meloni, D; Casale, G R; Siani, A M; Palmieri, S; Cappellani, F



MLVA-16 typing of 295 marine mammal Brucella isolates from different animal and geographic origins identifies 7 major groups within Brucella ceti and Brucella pinnipedialis  

PubMed Central

Background Since 1994, Brucella strains have been isolated from a wide range of marine mammals. They are currently recognized as two new Brucella species, B. pinnipedialis for the pinniped isolates and B. ceti for the cetacean isolates in agreement with host preference and specific phenotypic and molecular markers. In order to investigate the genetic relationships within the marine mammal Brucella isolates and with reference to terrestrial mammal Brucella isolates, we applied in this study the Multiple Loci VNTR (Variable Number of Tandem Repeats) Analysis (MLVA) approach. A previously published assay comprising 16 loci (MLVA-16) that has been shown to be highly relevant and efficient for typing and clustering Brucella strains from animal and human origin was used. Results 294 marine mammal Brucella strains collected in European waters from 173 animals and a human isolate from New Zealand presumably from marine origin were investigated by MLVA-16. Marine mammal Brucella isolates were shown to be different from the recognized terrestrial mammal Brucella species and biovars and corresponded to 3 major related groups, one specific of the B. ceti strains, one of the B. pinnipedialis strains and the last composed of the human isolate. In the B. ceti group, 3 subclusters were identified, distinguishing a cluster of dolphin, minke whale and porpoise isolates and two clusters mostly composed of dolphin isolates. These results were in accordance with published analyses using other phenotypic or molecular approaches, or different panels of VNTR loci. The B. pinnipedialis group could be similarly subdivided in 3 subclusters, one composed exclusively of isolates from hooded seals (Cystophora cristata) and the two others comprising other seal species isolates. Conclusion The clustering analysis of a large collection of marine mammal Brucella isolates from European waters significantly strengthens the current view of the population structure of these two species, and their relative position with respect to the rest of the Brucella genus. MLVA-16 is confirmed as being a rapid, highly discriminatory and reproducible method to classify Brucella strains including the marine mammal isolates. The Brucella2009 MLVA-16 genotyping database available at is providing a detailed coverage of all 9 currently recognized Brucella species.




SciTech Connect

The early evolution of Earth's atmosphere and the origin of life took place at a time when physical conditions at the Earth were radically different from its present state. The radiative input from the Sun was much enhanced in the high-energy spectral domain, and in order to model early planetary atmospheres in detail, a knowledge of the solar radiative input is needed. We present an investigation of the atmospheric parameters, state of evolution, and high-energy fluxes of the nearby star {kappa}{sup 1} Cet, previously thought to have properties resembling those of the early Sun. Atmospheric parameters were derived from the excitation/ionization equilibrium of Fe I and Fe II, profile fitting of H{alpha}, and the spectral energy distribution. The UV irradiance was derived from Far-Ultraviolet Spectroscopic Explorer and Hubble Space Telescope data, and the absolute chromospheric flux from the H{alpha} line core. From careful spectral analysis and the comparison of different methods, we propose for {kappa}{sup 1} Cet the following atmospheric parameters: T{sub eff} = 5665 {+-} 30 K (H{alpha} profile and energy distribution), log g = 4.49 {+-} 0.05 dex (evolutionary and spectroscopic), and [Fe/H] = +0.10 {+-} 0.05 (Fe II lines). The UV radiative properties of {kappa}{sup 1} Cet indicate that its flux is some 35% lower than the current Sun's between 210 and 300 nm, it matches the Sun's at 170 nm, and increases to at least 2-7 times higher than the Sun's between 110 and 140 nm. The use of several indicators ascribes an age to {kappa}{sup 1} Cet in the interval {approx}0.4-0.8 Gyr and the analysis of the theoretical Hertzsprung-Russell diagram (H-R) suggests a mass {approx}1.04 M{sub sun}. This star is thus a very close analog of the Sun when life arose on Earth and Mars is thought to have lost its surface bodies of liquid water. Photochemical models indicate that the enhanced UV emission leads to a significant increase in photodissociation rates compared with those commonly assumed of the early Earth. Our results show that reliable calculations of the chemical composition of early planetary atmospheres need to account for the stronger solar photodissociating UV irradiation.

Ribas, I.; Garces, A. [Institut de Ciencies de l'Espai (CSIC-IEEC), Campus UAB, Facultat de Ciencies, Torre C5, parell, 2a pl., E-08193 Bellaterra (Spain); Porto de Mello, G. F.; Ferreira, L. D. [Universidade Federal do Rio de Janeiro, Observatorio do Valongo, Ladeira do Pedro Antonio 43, CEP: 20080-090, Rio de Janeiro, RJ (Brazil); Hebrard, E.; Selsis, F. [Universite de Bordeaux, Observatoire Aquitain des Sciences de l'Univers, 2 rue de l'Observatoire, BP 89, F-33271 Floirac Cedex (France); Catalan, S. [Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield AL10 9AB (United Kingdom); Do Nascimento, J. D.; De Medeiros, J. R., E-mail: iribas@ice.csic.e, E-mail: garces@ice.csic.e, E-mail: gustavo@astro.ufrj.b, E-mail: leticia@astro.ufrj.b, E-mail: franck.selsis@obs.u-bordeaux1.f, E-mail: eric.hebrard@obs.u-bordeaux1.f, E-mail:, E-mail: dias@dfte.ufrn.b, E-mail: renan@dfte.ufrn.b [Departamento de Fisica, Universidade Federal do Rio Grande do Norte, CEP: 59072-970, Natal, RN (Brazil)




SciTech Connect

We show that the UV spectrum (1280-3200 A) of the 'superficially normal' A-star Vega, as observed by the International Ultraviolet Explorer (IUE) satellite at a resolution comparable to the star's rotational broadening width, can be fit remarkably well by a single-temperature synthetic spectrum based on LTE atmosphere models and a newly constructed UV line list. If Vega were a normal, equator-on, slow-rotating star, then its spectrum and our analysis would indicate a temperature of T{sub eff} {approx_equal}9550 K, surface gravity of log g {approx_equal}3.7, general surface metallicity of [m/H] {approx_equal}-0.5, and a microturbulence velocity of v{sub turb} {approx_equal}2.0 km s{sup -1}. Given its rapid rotation and nearly pole-on orientation, however, these parameters must be regarded as representing averages across the observed hemisphere. Modeling the complex UV line spectrum has allowed us to determine the specific surface abundances for 17 different chemical elements, including CNO, the light metals, and the iron group elements. The resultant abundance pattern agrees in general with previous results, although there is considerable scatter in the literature. Despite its peculiarities, Vega has turned out to provide a powerful test of the extent of our abilities to model the atmospheric properties of the early A-stars, particularly the detailed UV line spectrum. The value of the measurements from this pilot study will increase as this analysis is extended to more objects in the rich high-dispersion IUE data archive, including both normal and peculiar objects.

Fitzpatrick, E. L., E-mail: edward.fitzpatrick@villanova.ed [Department of Astronomy and Astrophysics, Villanova University, 800 Lancaster Avenue, Villanova, PA 19085 (United States)



Magnetism in Massive Stars  

NASA Astrophysics Data System (ADS)

Stars with mass more than 8 solar masses end their lives as neutron stars, which we mostly observe as highly magnetized objects. Where does this magnetic field come from? Such a field could be formed during the collapse, or is a (modified) remnant of a fossil field since the birth of the star, or otherwise generated by a dynamo during its lifetime in the pre-collapse stages. The answer is unknown, but traditionally magnetic massive stars should not exist since they do not have a convective layer such as the Sun. In the last decade, however, a number of magnetic massive stars have been found, which likely possess a stable field from their birth, and indirect evidence is accumulating that localized fields can indeed be generated during the main-sequence lifetime and beyond. These observational facts opened a new field of research, which is the topic of this review. Among the indirect evidence is a large range of observational phenomena among O and B stars that cannot be explained without the presence of surface magnetic fields. These phenomena include photospheric turbulence, wind clumping, cyclic wind variability observed in UV lines, other types of wind variability in optical lines, anomalous X-ray emission, and non-thermal emission in the radio region. A summary of the properties of observed magnetic massive OB stars is given and the role of magnetic fields in massive stars will be discussed, including how to identify new magnetic candidates.

Henrichs, H. F.



Optical, UV and Radio Observations of RS Canum Venaticorum  

NASA Astrophysics Data System (ADS)

Preliminary results are reported on optical, UV and radio observations of the binary system RS Canum Venaticorum carried out in March 1984, as a part of the international coordinated programme on solar-like activity in late type stars.

Catalano, S.; Rodono, M.; Linsky, J. L.; Carpenter, K.; Gibson, D.; Gary, D.; Butler, J.


Observations of Circumstellar Material Around Evolved Stars with the ISI  

NASA Astrophysics Data System (ADS)

The U.C. Berkeley Infrared Spatial Interferometer (ISI) is a stellar interferometer operating in the 9-12 micron region and has been in operation from 1988 until the present. It utilizes heterodyne detection using CO2 laser local oscillators and currently includes two 1.65 m movable telescopes mounted in semi-trailers and baselines up to about 65 m in length. A third telescope is being integrated with the other two and within the next year will operate as an imaging interferometer providing data with three simultaneous baselines and a closure phase, and baselines up to about 75 m. During the past twelve years the ISI has been used extensively for studies of circumstellar material around evolved stars. Multi-epoch observations of a sample of prototypical sources have elucidated the location and time scales for dust formation around these stars. These time scales can be as short as 10 years for Mira stars and as long as 100 years for supergiants. For stars like Mira itself there is evidence for departure from spherical symmetry and episodes of dust formation and destruction. For some stars motion of dust has been observed -- IK Tau is one example, and NML Cyg is another. The molecules Silane and Ammonia were observed for the extreme carbon star IRC +10216 and the supergiant VY CMa pinpointing their location relative to the inner radius of the dust shell. Somehwat surprisingly, these molecules were found to form many stellar radii away from the inner radius of the dust shell, implying that they form by interactions with the surfaces of dust grains. Last year observations with the longest baselines lead to new precision diameters of o Ceti and ? Orionis, and are continuing on a somewhat larger set of Mira variable and supergiant stars.

Danchi, W.; Townes, C.



UV measurements of the local SFR  

NASA Astrophysics Data System (ADS)

Because of its strong interest in itself and for comparison to the hi-z Universe, the rest-UV approach to the global SFR in the local Universe has motivated a long standing effort to overcome the difficulties inherent to observations from space. This brief review focuses on the results obtained from wide-band observations on ``normally star forming" galaxies, which show only moderate dust attenuation and may well host the bulk of the star formation activity in the local Universe (Strong starbursts are addressed by Tim Heckman, this Session). The wide-band rest-UV approach is first illustrated with results on the major characteristics of star formation in nearby individual galaxies, their variations along the Hubble sequence and their links with the gas content and galaxy parameters. The availability of a few genuine rest-UV selected galaxies samples at reshifts below 0.5 has opened the door to the first statistical approaches to the global star formation parameters in the local Universe. The results address the derivation of the FUV luminosity function, the global star formation intensity, the influence of environment, and the amount of star formation that could be hidden to rest-UV selected samples. Along the talk, the rest-UV approach to SFR is compared to other young population tracers. We expose its strengths and weaknesses, and stress how complementary data available in the local Universe helps find a way around the major limitations to the accuracy (namely the dust attenuation-see also Daniella Calzetti this Session, the metallicity effects, the IMF scatter and the microhistory- see also Richard Ellis, this Session). We end with some perspectives promised by GALEX. Funding by CNES and CNRS is acknowledged.

Milliard, B.; Donas, J.; Buat, V.; Deharveng, J.-M.



Classification and properties of UV extinction curves  

Microsoft Academic Search

The catalog of Savage et al. (\\\\cite{ref27}) reporting colour excesses of 1415 stars from ANS photometry offers the opportunity to deeply investigate the characteristics of UV extinction curves which differ from the standard extinction of the diffuse interstellar medium. To this aim we have selected a sample of 252 curves, which have been compared with the relations derived by Cardelli

G. Barbaro; P. Mazzei; L. Morbidelli; P. Patriarchi; M. Perinotto



Stochastic Star Formation in Low Mass Galaxies: A case study of DDO 210  

Microsoft Academic Search

To address the longstanding question of whether dwarf galaxies have bursty star formation histories requires a large sample of dwarf galaxies and an accurate tracer of star formation. Here we explore the utility of using two common tracers, H-alpha and the ultraviolet (UV). H-alpha and UV photons are primarily produced by massive stars, so stochastic effects come into play when

Christina A. Tremonti; J. C. Lee; L. van Zee; R. C. Kennicutt; A. Gil de Paz; S. Sakai; J. Funes; S. Akiyama



UV emissions of Hot Jupiters  

NASA Astrophysics Data System (ADS)

In the solar system, the giant planets Jupiter and Saturn have bright aurorae due to particle precipitation in the upper atmospheres. The brightest optical auroral emissions are emitted by H and H2 in the UV and by H3+ in the IR. Due to the short distance to the parent stars, hot Jupiters are likely to be bombarded by intense stellar winds and UV fluxes and have strong emissions at the same wavelengths. When detected, their UV emissions could bring helpful information to characterize the upper atmospheres of the exoplanets. The first question to address is : are these emissions bright enough to be observed from Earth and distinguished from the stellar UV emissions ? We focus on Jupiter-like atmospheres, composed of H, H2 and He. Kinetic calculations allow to estimate the electron flux throughout the atmosphere and to calculate excitation rates of the upper levels of UV transitions of H and H2. Radiative transfer calculations are then done to estimate the intensity of the emergent lines and the profile of the H Lyman alpha line. Using the Yelle (2004) atmosphere model for HD209458b, we evaluate the H Lyman alpha dayglow of the planet. We also evaluate UV emissions of the planet caused by the precipitation of particles with and without an intrinsec magnetic field. We find that the Lyman alpha emission of the planet could reach 1/1000 of that of the star. It has been shown that the profile of the H Lyman alpha line is very sensitive to the atmospheric model and to the energy of the precipitating electrons (Menager et al. 2010). We see here a way to constrain the upper atmosphere of exoplanets and their particle environment, that could be used by future UV telescopes. References R. Yelle, Aeronomy of extra-solar giant planets at small orbital distances, Icarus, volume 170, 2004 H. Menager, M. Barthélemy, and J. Lilensten, H Lyman alpha line in Jovian aurorae : electron transport and radiative transfer coupled modelling, Astronomy & Astrophysics, accepted

Ménager, Hélène; Mathieu, Barthélemy; Jean, Lilensten



Photometry of faint blue stars - IX  

NASA Astrophysics Data System (ADS)

Stromgren uv by photometry is presented for 129 `faint blue' stars taken from various catalogues. The photometry is used to estimate photometric `classifications' for the stars, which indicate a mixture of hot subdwarfs, horizontal-branch stars, metal-weak subdwarfs and so on. Attention is drawn to stars (from this paper and previous papers in the series) which appear to be somewhat reddened. Some are probably binaries, and others might be objects with peculiar colours, such as cataclysmic variables. One star, LB 9963, almost certainly falls into the latter category. Two stars which, from their colours, are Population II A-F stars are variable; one of these, OM 89, is the known RR Lyrae star, VW Dor.

Kilkenny, D.



Extreme Stars  

Microsoft Academic Search

Over the past 200 years, our knowledge of stars has expanded enormously. From seeing myriad dots of different brightnesses, we haved moved on to measure their distances, temperatures, sizes, chemical compositions, and even ages, finding both young and ancient stars that dwarf our Sun and are dwarfed by it. Unique in its approach, Extreme Stars describes the lives of stars

James B. Kaler



Synthesis and photo physical properties of star shaped gold nanoparticles  

Microsoft Academic Search

Here, we report synthesis of star shape gold nanoparticles using seed mediated growth process. Ag+ ions have been used to catalyze the anisotropic growth of gold particles in the growth solution. Star like gold nanoparticles are characterized using UV–vis and TEM study. Excitation of localized surface plasmon of star shaped gold nanoparticles by the visible radiation results broad and intense

Gobinda Prasad Sahoo; Harekrishna Bar; Dipak Kumar Bhui; Priyanka Sarkar; Sadhan Samanta; Santanu Pyne; Sankarlal Ash; Ajay Misra



Stars and Star Myths.  

ERIC Educational Resources Information Center

|Myths and tales from around the world about constellations and facts about stars in the constellations are presented. Most of the stories are from Greek and Roman mythology; however, a few Chinese, Japanese, Polynesian, Arabian, Jewish, and American Indian tales are also included. Following an introduction, myths are presented for the following…

Eason, Oliver


Multi-Wavelength Constraints on the Cosmic Star Formation History from Spectroscopy: the Rest-Frame UV, H-alpha, and Infrared Luminosity Functions at Redshifts 1.9  

Microsoft Academic Search

We use a sample of rest-frame UV selected and spectroscopically observed\\u000agalaxies at redshifts 1.9UV, H-alpha, and infrared (IR) luminosity functions (LFs) at\\u000athese redshifts. Our sample is by far the largest of its kind, with over 2000\\u000aspectroscopic

Naveen A. Reddy; Charles C. Steidel; Max Pettini; Kurt L. Adelberger; Alice E. Shapley; Dawn K. Erb; Mark Dickinson



UVMag: a UV+visible spectropolarimeter to study stellar magnetospheres  

NASA Astrophysics Data System (ADS)

In the last decade magnetic fields have been detected in basically all types of stars. These discoveries gave rise to innovative studies on the mapping of magnetic fields and on their impact on stellar environment. To go even further, the UVMag international consortium proposes to combine UV and visible spectropolarimetry. The UV domain allows us to study stellar winds, while the optical domain allows us to study the stellar surface. With UV and visible spectropolarimetry we can then study magnetospheres as a whole and do this over a complete stellar rotation period thanks to a space mission. UV and visible spectropolarimetry can of course also address many other stellar physics issues.

Neiner, C.



A Comparison of UIT Far-Ultraviolet and H alpha Star Formation Rates  

Microsoft Academic Search

We have used archival ultraviolet (UV) imaging of 50 nearby star-forming\\u000agalaxies obtained with the Ultraviolet Imaging Telescope (UIT) to derive\\u000aintegrated near-UV and far-UV magnitudes, and have combined these data with H\\u000aalpha, far-infrared, and thermal radio continuum measurements to explore the\\u000aconsistency of UV and H alpha star formation rates (SFRs). In agreement with\\u000aprevious studies, we find

Eric F. Bell; Robert C. Kennicutt Jr.



Doppler Tomography of Massive Compact Binary Stars in Multiple Star Systems  

Microsoft Academic Search

I present a study of IUE spectra for three O stars in multiple star systems. These spectra were first subjected to cross-correlation analysis to find their radial velocity curves and hence their orbital elements. I then used Doppler tomographic methods to separate the individual component spectra in order to find their MK types, projected rotational velocities, and UV flux ratios,

J. A. Harvin



Variable stars  

SciTech Connect

This book covers the following topics: pulsating variables; eruptive variables; eclipsing stars; supplement to the classification; the discovery of variable stars; the significance of variable stars for research on the structure of the galaxy and stellar evolution; and observational methods and organizations.

Hoffmeister, C.; Richter, G.; Wenzel, W.



UV Disinfection Technology Assessment.  

National Technical Information Service (NTIS)

This document studies the effectiveness of ultra-violet (UV) disinfection systems for wastewater treatment. Discussed are the current UV systems in operation, trends in system design, configuration, and operations.



Optical and ultraviolet spectroscopy of three F + B binary stars  

NASA Astrophysics Data System (ADS)

Optical and ultraviolet spectroscopy is presented for three F + B objects that are members of the first group of strongly interacting, F II + B systems. The data obtained confirm that HD 59771, HD 242257, and CoD -30 5135 are all binary star systems consisting of a luminous F-type component and a B star. Strong, variable H-alpha emission is seen in all the stars. It is found that the UV spectrum of HD 59771 resembles the spectrum of HD 207739. CoD -30 5135 has the most dramatic mid-UV spectrum seen among the scores of observed cool + hot star systems.

Bopp, Bernard W.; Dempsey, Robert C.; Parsons, Sidney B.



The Origin of the Diffuse UV Light from Spiral Disks: The Case of M101  

NASA Astrophysics Data System (ADS)

Active star formation sites in the arms of spiral galaxies distinctly stand out in UV images, however, UV emission is also detected within inter-arm regions. Three sources for this emission are possible: 1) in-situ star formation, at a low specific SFR or with a top-light IMF 2) a quiescently aging young stellar population and 3) UV light scattered off dust grains. The possibility of substantial emission from these latter two sources calls into question the applicability of standard star-formation recipes to inter-arm regions as done in studies of resolved star-formation laws. Using HST FUV images of two inter-arm regions in M101, we use the FUV luminosity function of individual stars to constrain the recent star-formation histories of these regions. One of the two regions shows a recent SFH that must have quenched in the past 10-15 Myr, while the other region may have some ongoing star-formation. We also measure the amount of non-stellar UV luminosity (after a correction for sub-detection stars based on the derived star-formation history) and this accounts for a minimal fraction in one field (< 20%), but a substantial fraction in the other field (approximately 70%). This emission is likely to be scattered light from more actively star-forming regions; indeed, a higher surface density of this diffuse emission is observed in the field closer to an actively star-forming arm. Both the lack of current star-formation (confirmed in one field) and the sizable contribution from scattered UV light indicates that UV emission may not ideal for constraining the current SFR in all inter-arm regions of spiral galaxies.

Crocker, Alison F.; Chandar, R.



The Rest Frame UV Properties of Type IIn Supernovae  

NASA Astrophysics Data System (ADS)

Unlike other classes of supernovae (SNe), Type IIn's are very bright in the UV and can be used in z>2 optical surveys (Cooke et al. 2009). Their intrinsic brightness and long-lived emission also aid in spectroscopically confirming these SNe in such surveys (Cooke 2008). Since they are associated with massive stars and because of their intrinsic UV brightness, Type IIn's are potentially strong probes of star formation out to relatively large redshifts (z>2). Here we present the UV properties of nearby Swift Ultra-Violet/Optical Telescope observed Type IIn SNe from early epochs. The data are then compared against rest frame UV observations of high-z counterparts in order to test for evolution.

Roming, Peter; Pritchard, T.; Immler, S.; Brown, P.



A mid-UV stellar library for population synthesis  

NASA Astrophysics Data System (ADS)

A far-UV (lambda lambda 1230 to 1900A) stellar library was extended to the mid-UV wavelength range (lambda lambda 1900 to 3200A) using low resolution spectra obtained from the IUE Spectral Atlas and new cool (FGK) star spectra. A set of spectral energy distributions of common stellar types ranging from O3 to M0 is derived for this entire wavelength range. The usefulness of various spectral diagnostics in the mid-UV such as Mg I lambda 2852A, Mg II lambda 2798A, and the Fe II blend near lambda 2400 was examined. The library extends the analysis of the stellar populations in actively star-forming galaxies to cooler (A-F) spectral types, thereby probing the intermediate age (1-5 Gyr) stellar content in these galaxies. The library is also useful for synthesis of the mid-UV spectra of old stellar populations.

Fanelli, M. N.; Oconnell, R. W.; Thuan, T. X.; Burstein, D.; Wu, C.-C.



Star Formation in Atomic Gas  

NASA Astrophysics Data System (ADS)

Observations of nearby galaxies have firmly established, over a broad range of galactic environments and metallicities, that star formation occurs exclusively in the molecular phase of the interstellar medium (ISM). Theoretical models show that this association results from the correlation between chemical phase, shielding, and temperature. Interstellar gas converts from atomic to molecular only in regions that are well shielded from interstellar ultraviolet (UV) photons, and since UV photons are also the dominant source of interstellar heating, only in these shielded regions does the gas become cold enough to be subject to Jeans instability. However, while the equilibrium temperature and chemical state of interstellar gas are well correlated, the timescale required to reach chemical equilibrium is much longer than that required to reach thermal equilibrium, and both timescales are metallicity-dependent. Here I show that the difference in timescales implies that, at metallicities below a few percent of the solar value, well shielded gas will reach low temperatures and proceed to star formation before the bulk of it is able to convert from atomic to molecular. As a result, at extremely low metallicities, star formation will occur in a cold atomic phase of the ISM rather than a molecular phase. I calculate the observable consequences of this result for star formation in low-metallicity galaxies, and I discuss how some current numerical models for H2-regulated star formation may need to be modified.

Krumholz, Mark R.



Star Formation at z ~ 1  

NASA Astrophysics Data System (ADS)

We propose using FLAMINGOS in MOS mode to obtain near-infrared spectra of ~ 200 GOODS galaxies at z ~ 1, using the 4-m telescope on Kitt Peak. This will, for the first time, provide a sample of sufficient size to allow for a statistically sound analysis of the star formation rate at z ~ 1; a crucial epoch in the star formation history of the Universe. Several controversial issues will be addressed using this dataset. H(alpha), used routinely as a local star formation indicator, will be directly measured in order to determine the global star formation rate at z ~ 1, where many conflicting results exist. Star formation rates derived from the H(alpha) emission will also be used to calibrate star formation derived from existing MIPS 24 (mu) m data, equivalent at z ~ 1 to 12 (mu) m rest frame emission, which is caused by PAHs and warm, small-grain thermal continuum. Finally, star formation estimates from the most commonly used indicators, namely H(alpha), [OII], radio, UV and PAH features, will be compared and assessed. Line ratios from features in the FLAMINGOS near-IR and recently obtained Keck optical spectra will allow for the quantification of extinction and metallicity.

MacDonald, Emily; Dickinson, Mark; Mobasher, Bahram; Allen, Paul; Papovich, Casey



Validation of GOMOS vertical profiles using the stratospheric balloon-borne AMON and SALOMON UV-Visible spectrometers  

Microsoft Academic Search

The stratospheric balloon-borne UV-visible spectrometers AMON and SALOMON, which uses stars and Moon as light source, respectively, were involved in the validation of the UV-visible spectrometer GOMOS onboard ENVISAT, which uses also stars as light source. A low spectral resolution UV-visible spectrometer, AMON-RA, is also implanted in the AMON gondola, for the validation of the GOMOS algorithm dedicated to the

J. B. Renard; M. Chartier; G. Berthet; C. Robert; T. Lemaire; F. Pepe; M. George; M. Pirre



Chemical abundances in an UV-selected sample of galaxies  

Microsoft Academic Search

We discuss the chemical properties of a sample of UV-selected\\u000aintermediate-redshift (0 < z < 0.4) galaxies in the context of their physical\\u000anature and star formation history. This work represents an extension of our\\u000aprevious studies (Treyer et al. 1998; Sullivan et al. 2000, 2001) on\\u000aUV-selected galaxies. We revisit the optical spectra of these galaxies and\\u000aperform further

Thierry Contini; Marie A. Treyer; Mark Sullivan; Richard S. Ellis



Massive star formation in galaxies with excess ultraviolet emission  

NASA Astrophysics Data System (ADS)

From an analysis of almost 2000 Galaxy Evolution Explorer images of galaxies with morphological types ranging from E to Sab, we have found a significant subset (28 per cent) that show ultraviolet (UV) emission outside R25. We have obtained H? imaging of 10 such galaxies, and found that their star formation rates are similar in the UV and in H?, with values ranging from a few tenths to a few M? yr-1. Probably because our sample selection is biased towards star-forming galaxies, these rates are comparable to those found in disc galaxies, although the star formation rates of the elliptical galaxies in our sample are well below 1 M? yr-1. We confirm that the extended UV emission in our sample is caused by massive star formation in outer spiral arms and/or outer (pseudo) rings, rather than by alternative mechanisms such as the UV upturn.

Erroz-Ferrer, Santiago; Knapen, Johan H.; Mohd Noh Velastín, Elena A. N.; Ryon, Jenna E.; Hagen, Lea M. Z.



Single Particle Damage Events in Candidate Star Camera Sensors.  

National Technical Information Service (NTIS)

Si charge coupled devices (CCDs) are currently the preeminent detector in star cameras as well as in the near ultraviolet (uv) to visible wavelength region for astronomical observations in space and in earth-observing space missions. Unfortunately, the pe...

P. Marshall C. Marshall E. Polidan A. Wacyznski S. Johnson



Symbiotic Stars  

NASA Astrophysics Data System (ADS)

During the production of the Henry Draper Catalog, Wilhemina Fleming identified several M-type stars with unusually strong hydrogen emission lines. Paul Merrill obtained higher quality spectra of these `stars with combination spectra' and found intense emission from He II or [O III] and [Ne III] in addition to H I. All of these stars varied by 0.5-1 mag on a timescale of several years. A few syst...

Kenyon, S.; Murdin, P.



Sea Stars  

NSDL National Science Digital Library

At first glance, starfish, more properly called sea stars, arenât doing much of anything. In this video, Jonathanâs investigations reveal a slow-motion predator that hunts and attacks its prey. Traveling the world, Jonathan investigates sea stars from the tropics to the Antarctic and uses time-lapse photography to reveal an amazing complexity to the world of the sea star. Please see the accompanying study guide for educational objectives and discussion points.

Productions, Jonathan B.



Lucky Star  

NSDL National Science Digital Library

Watch this video from Cyberchase and then play the Lucky Star game! The Lucky Star game show the will ask you math-related questions and give you four possible answers to choose from. Your goal is to answer the questions correctly and score as many points as you can. You can score points during two different rounds: the pick-a-star round and the lightning round. During the pick-a-star round you have as much time as you want to answer the questions. During the lightning round you have to think fast in order to earn the points. Good luck!



Comparing Ultraviolet and H alpha Star Formation Rates  

Microsoft Academic Search

We have used a sample of 43 star-forming galaxies imaged in the\\u000afar-ultraviolet (FUV) by the UIT supplemented with 33 galaxies observed by\\u000aFAUST, to explore the consistency of UV and H alpha derived star formation\\u000arates (SFRs). We find, even before correction for dust, that UV and H alpha\\u000aSFRs are quantitatively consistent for low-luminosity galaxies, and that higher

Eric F. Bell; Robert C. Kennicutt Jr.



all-S,S-dioxygenated star oligothiophenes.  


Star-shaped oligothiophenes are promising materials for applications in the organic electronics field. For the first time, a range of star-oligothiophenes was oxidized to the corresponding all-S,S-dioxides by using the HOF·CH(3)CN complex. These materials exhibit considerable thermal stability and red-shift absorptions in the UV/vis relative to the parent compounds. PMID:21755931

Potash, Shay; Rozen, Shlomo




Microsoft Academic Search

We use our ultraviolet (UV) atlas of premain-sequence stars constructed from all useful, short- wavelength, low-resolution spectra in the International Ultraviolet Explorer (IUE) satellite Final Archive to analyze the short-wavelength UV properties of 49 T Tauri stars (TTSs). We compare the line and continuum —uxes in these TTSs with each other and with previously published parameters of these systems, including



An IUE Atlas of Pre-Main-Sequence Stars. II. Far-Ultraviolet Accretion Diagnostics in T Tauri Stars  

Microsoft Academic Search

We use our ultraviolet (UV) atlas of pre-main-sequence stars constructed from all useful, short-wavelength, low-resolution spectra in the International Ultraviolet Explorer (IUE) satellite Final Archive to analyze the short-wavelength UV properties of 49 T Tauri stars (TTSs). We compare the line and continuum fluxes in these TTSs with each other and with previously published parameters of these systems, including rotation

Christopher M. Johns-Krull; Jeff A. Valenti; Jeffrey L. Linsky



NGC 4656UV: A UV-selected Tidal Dwarf Galaxy Candidate  

NASA Astrophysics Data System (ADS)

We report the discovery of a UV-bright tidal dwarf galaxy (TDG) candidate in the NGC 4631/4656 galaxy group, which we designate NGC 4656UV. Using survey and archival data spanning from 1.4 GHz to the ultraviolet, we investigate the gas kinematics and stellar properties of this system. The H I morphologies of NGC 4656UV and its parent galaxy NGC 4656 are extremely disturbed, with significant amounts of counterrotating and extraplanar gas. From UV-FIR photometry, computed using a new method to correct for surface gradients on faint objects, we find that NGC 4656UV has no significant dust opacity and a blue spectral energy distribution. We compute a star formation rate of 0.027 M ? yr-1 from the far-ultraviolet flux and measure a total H I mass of 3.8 × 108 M ? for the object. Evolutionary synthesis modeling indicates that NGC 4656UV is a low-metallicity system whose only major burst of star formation occurred within the last ~260-290 Myr. The age of the stellar population is consistent with a rough timescale for a recent tidal interaction between NGC 4656 and NGC 4631, although we discuss the true nature of the object—whether it is tidal or pre-existing in origin—in the context of its metallicity being a factor of 10 lower than its parent galaxy. We estimate that NGC 4656UV is either marginally bound or unbound. If bound, it contains relatively low amounts of dark matter. The abundance of archival data allows for a deeper investigation into this dynamic system than is currently possible for most TDG candidates. Based in part on observations made with the NASA Galaxy Evolution Explorer. GALEX is operated for NASA by the California Institute of Technology under NASA contract NAS5-98034.

Schechtman-Rook, Andrew; Hess, Kelley M.



Star Images, Star Performances (College Course File).  

ERIC Educational Resources Information Center

|Describes a course that focuses attention on the position of the actor, especially the star actor, in cinematic and television signification. Divides the course into three sections: "The Star System,""Stars as Images," and "Star Performance." (RS)|

Butler, Jeremy G.



Compact Stars  

NASA Astrophysics Data System (ADS)

Neutron stars are the smallest denses stars known, with densities some 1014 times that of the Earth. They rotate with periods of fractions of a second, and their magnetic fields drive intense interstellar dynamos, lighting up entire nebulae. This text discusses the physics of these extreme objects. It includes the needed background in classical general relativity in nuclear and particle physics.

Glendenning, Norman K.


Rogue Star  

NSDL National Science Digital Library

This program calculates and depicts the effects of a rogue star coming through our solar system. Users adjust the date, the rogue star's mass, approach distance in astronomical units (AU) and flyby speed to run an animation of what would happen to the planets under the specified conditions.

Hamilton, Douglas


The Mass of the Subdwarf B Star in HD 185510  

Microsoft Academic Search

HD 185510 is an RS CVn star with a K0 III-IV primary and an orbital period of 21 days. The secondary was discovered to be a hot subdwarf B star with IUE. The system also shows eclipses, secondary eclipse being total in the far UV. We propose here to determine the velocity amplitude of the secondary orbit, K2, from high

Theodore Simon



Grids of synthetic spectra for H-poor central stars of planetary nebulae (CSPNe)  

NASA Astrophysics Data System (ADS)

We present comprehensive grids of model spectra from far-UV to IR, covering the parameter space of [WC] (Keller et al. 2011) and PG1159 stars. Models are calculated with the CMFGEN code, accounting for non-LTE, line blanketing, wind, clumping, and including ions previously neglected. The grids are available at We used them to analyse UV and far-UV spectra of NGC6905's and NGC5189's central stars.

Keller, Graziela R.; Bianchi, Luciana; Herald, James E.; Maciel, Walter J.



UV LED Space Qualification  

NASA Astrophysics Data System (ADS)

Electric charges induced by cosmic rays tend to accumulate on the free floating proof mass at the core of a drag-free satellite. The Lorentz force will affect stationarity of the proof mass. Generation of photoelectrons via ultraviolet (UV) light is an effective method of charge management. Previous missions have relied on mercury lamps as a UV light source. We have proposed the use of UV LEDs as a source for UV light generation, because they have significantly lower mass and power requirements. Since 2005, we have conducted systematic UV LED power and spectral lifetime tests. The UV LED has now been operated more than 16,668 hours (as of submission of this abstract) without significant power decay. At the 10,000 hour mark, the UV LED spectral shift was measured to be approximately 1 nm towards shorter wavelengths. To fully simulate the space environment, we have initiated another UV LED lifetime test in 1E-7 torr vacuum chamber starting in January 2008. Thus far the UV LED output has been stable without noticeable degradation. We have conducted a large dose radiation test using an accelerator source for 59.0 64.8 MeV proton generation. For proton flux from 10E10 to 2E12 protons per square centimeter, there was no significant power drop and spectral shift for UV LED light output, This level of radiation test exceeded 100 years of radiation dose at deep space LISA orbits. The combination of the successful tests in power lifetime, spectral stability, and radiation hardness have proven that UV LED should be the primary choice for the charge management system for LISA and other high precision space flights.

Buchman, Saps; Sun, K.; Leindecker, N.; Higuchi, S.; Byer, R.; Goebel, J.



Catalog of Visual Extinction Obtained from UV Color Excesses  

NASA Astrophysics Data System (ADS)

Large collection of visual extinction A(V) and R_V equiv A_V/E(B-V) parameters for 1013 OB type stars is presented. The A(V) and R_V values were obtained from UV extinction curves. A comparison of obtained values with those obtained by Cardelli and Clayton (1991) from the near IR photometry is also discussed.

Gnacinski, P.; Sikorski, J.



UV Extinction and IR Emission in Diffuse H2 Regions.  

National Technical Information Service (NTIS)

During this period, much work was spent in an attempt to use theoretical UV line indices as a basis for spectral calibration of the program stars. Five line indices are shown as functions of effective temperature and log g, calculated with the spectral sy...

P. A. Aannestad



UV Spectral Synthesis of Sirius A  

NASA Astrophysics Data System (ADS)

UV Spectral Synthesis of Sirius A We report the first results from a study of the fundamental physical properties of the A1 V star Sirius A. Using archival spectrophotometric data from the Hubble Space Telescope's STIS spectrograph, we have produced a synthetic UV spectrum of the star. The data were obtained at medium resolution with the G160M, G200M, and G270M gratings (FWHM 15 km/s) and cover the wavelength range 1265-3200 Angstroms. The synthetic spectrum was constructed using Kurucz's ATLAS9 LTE stellar atmospheric models and Hubeny's SYNSPEC spectral synthesis program and is a function of the star's effective temperature, surface gravity, microturbulence velocity, rotational velocity, radial velocity, and chemical composition. A chi2-minimization program was used to find the values of these parameters which produce the best match of the synthetic spectrum with the observed spectrum. In addition to determining the stellar properties, this program can illuminate - and help rectify - deficiencies in the spectral line database used to construct the synthetic spectra. In this poster, we illustrate the first results from this program, including the quality of the match between the observed and computed spectra and the elemental abundance profile of Sirius A, including CNO, the light metals (e.g., Si and Al), and the Fe group.

McClain, Timothy; Fitzpatrick, E.



UV-tanning Pathway  

Center for Biologics Evaluation and Research (CBER)

Text Version... Keratinocyte. Melanin. Y. UV radiation. p53. D'Orazio et al. Nature 2006. Cui et al. ... Keratinocyte. Melanin. Y. UV radiation. p53. D'Orazio et al. Nature 2006 ... More results from


Searching for Star Formation in the Smith Cloud  

NASA Astrophysics Data System (ADS)

Recent discoveries of star formation in regions previously thought impossible implies new criteria for where stars can form. The Smith Cloud, a high velocity cloud (HVC) primarily comprised of neutral hydrogen located 12 kpc away in the halo of the Milky Way, meets these criteria by having a large reservoir of gas and the tidal pull of the Milky Way as a mechanism for perturbing the gas. We obtained GALEX NUV magnitudes for stars in the field of the Smith Cloud. These sources were matched with WISE and 2MASS catalogs to obtain infrared magnitudes. We determined the expected colors of young stars in these wavelength bands using synthetic spectral libraries. By comparing the observed UV and IR colors of stars to the expected colors of young stars, while also comparing star positions to existing 21cm data, we aim to isolate possible recent star formation in the Smith Cloud.

Baker, Ashley; Stark, D.; Kannappan, S.



UV observations of the galaxy cluster Abell 1795 with the optical monitor on XMM-Newton  

Microsoft Academic Search

We present the results of an analysis of broad band UV observations of the central regions of Abell 1795 observed with the optical monitor on XMM-Newton. As have been found with other UV observations of the central regions of clusters of galaxies, we find evidence for star formation. However, we also find evidence for absorption in the cD galaxy on

J. P. D. Mittaz; J. S. Kaastra; T. Tamura; A. C. Fabian; R. F. Mushotzky; J. R. Peterson; Y. Ikebe; D. H. Lumb; F. Paerels; G. Stewart; S. Trudolyubov



Models of H2 Fluorescence in the UV spectrum of the CTTS TW Hya  

Microsoft Academic Search

Strong UV emission lines produced in accretion shocks of classical T Tauri stars significantly affect the chemistry of the circumstellar disks. The surface layers of the disk close to the star are analgous to a photo-dissociation region, only controlled by line rather than continuum emission. A broad Ly-alpha emission line incident on surface layers of the disk photoexcites the warm

Gregory J. Herczeg; Brian E. Wood; Jeffrey L. Linsky; J. A. Valenti; C. M. Johns-Krull



An investigation of warm carbon stars  

NASA Astrophysics Data System (ADS)

Warm carbon stars were investigated with narrow band photometric systems designed to measure band strengths of NH, CN, CH, and C2, an index of the C12/C13 ratio, and the color temperature. It is shown from molecular indices for R, CH, CH like, and barium stars as compared to G and K giants that the barium stars have slightly higher C/O ratios than normal field giants and, though they are N-enriched with respect to the sun, they generally are not as N enriched as the field giants. A comparison of the photometry with model atmospheres shows the energy distribution of the R stars in the near IR, but are underblanketed in the UV. It is found that the R stars have nitrogen abundances somewhat lower than those of the giants.

Yorka, S. B.


Stars equilibrium  

NSDL National Science Digital Library

What causes the fusion reaction in a star's core? This activity page, part of an interactive laboratory series for grades 8-12, introduces students to processes inside a star. Students read about the equilibrium process in a star, in which outward gas pressure equals inward gravitational pressure. Then, an interactive lab activity offers students the opportunity to predict temperature, pressure, and gravity changes that occur during equilibrium. The chemical reactions of the fusion process are presented, and more specific detailed reactions are available in a pop-up box. Student practice quizzes about the equilibrium process and pressure and gravity interactions inside the star are included, as are answers. Copyright 2005 Eisenhower National Clearinghouse

University of Utah. Astrophysics Science Project Integrating Research and Education (ASPIRE)



Stratification and isotope separation in CP stars  

Microsoft Academic Search

We investigate the elemental and isotopic stratification in the atmospheres of selected chemically peculiar (CP) stars of the upper main sequence. Reconfiguration of the UV-Visual Echelle Spectrograph in 2004 has made it possible to examine all three lines of the CaII infrared (IR) triplet. Much of the material analysed was obtained in 2008. We support the claim of Ryabchikova, Kochukhov

C. R. Cowley; S. Hubrig; J. F. González




SciTech Connect

We present the results of GALEX observations of 17 cool core (CC) clusters of galaxies. We show that GALEX is easily capable of detecting star formation in brightest cluster galaxies (BCGs) out to z {>=} 0.45 and 50-100 kpc. In most of the CC clusters studied, we find significant UV luminosity excesses and colors that strongly suggest recent and/or current star formation. The BCGs are found to have blue UV colors in the center which become increasingly redder with radius, indicating that the UV signature of star formation is most easily detected in the central regions. Our findings show good agreement between UV star formation rates and estimates based on H{alpha} observations. IR observations coupled with our data indicate moderate-to-high dust attenuation. Comparisons between our UV results and the X-ray properties of our sample suggest clear correlations between UV excess, cluster entropy, and central cooling time, confirming that star formation is directly and incontrovertibly related to the cooling gas.

Hicks, A. K.; Donahue, M. [Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824-2320 (United States); Mushotzky, R., E-mail:, E-mail: donahue@pa.msu.ed, E-mail: richard@astro.umd.ed [Goddard Space Flight Center, Code 662, Greenbelt, MD, 20771 (United States)



UnISIS: Laser Guide Star and Natural Guide Star Adaptive Optics System  

Microsoft Academic Search

UnISIS (University of Illinois Seeing Improvement System) is a versatile adaptive optics system mounted on a large optics bench at the coudé focus of the Mount Wilson 2.5-m telescope. It was designed to have both laser guide star (LGS) and natural guide star (NGS) adaptive optics capabilities. The LGS side of the system relies on a pulsed UV laser with

Laird A. Thompson; Scott W. Teare; Yao-Heng Xiong; Richard M. Castle; Abhijit Chakraborty; Robert A. Gruendl; Robert W. Leach



Revisiting binary stars in population synthesis models  

NASA Astrophysics Data System (ADS)

We report results of a population synthesis model that follows the evolution of single and binary stars. In this model, we include the two He white dwarfs merger channel, suggested by Han et al., for the formation of extreme horizontal branch (EHB) stars. The physical parameters of the resulting EHB stars are derived from the Bag of Stellar Tracks and Isochrones data base by Pietrinferni et al., and are thus realistic and observationally supported. The predictions of this model are in good agreement with traditional population synthesis models, except when the spectrum of the stellar population is dominated by binary stars or their products, e.g., EHB stars in the ultraviolet (UV) of early-type galaxies (ETGs). We reproduce successfully the observed colour-magnitude diagram and spectral energy distribution of the metal-rich open cluster NGC 6791. The stellar population in this cluster may be archetypal of the stellar population in ETGs that show the UV excess phenomenon. Our models should be appropriate to study the UV upturn in ETGs.

Hernández-Pérez, Fabiola; Bruzual, Gustavo



Activity on young stars.  

NASA Astrophysics Data System (ADS)

Simultaneous photometry and spectroscopy were made of 6 young stars during two observing periods mainly to study short-term variability on time-scales from minutes to a few hours. The material includes two classical T Tauri stars (CTTS): SY Ori and VW Cha; three T Tauri stars with weak emission line spectra (WTTS): San 1, SZ Cha and ADA 481 and one post-T Tauri candidate: HD 70309B. Both UBV and Stroemgren photometry was made. In the visible spectral region we resolved rapid fluctuations - events - with total amplitudes of about 5% (0.05 magnitudes). In the ultraviolet, the corresponding limit of detection was usually <=10%. On the basis of totally about 100 hours of monitoring we conclude that the normal state of these stars is that they are completely constant in brightness or that they vary only slowly with small amplitudes over several hours. Only a few percent of the time, on the average, is a given star caught at brightness changes >=0.2mag. during one night. No event reached a total amplitude of >=0.3mag. VW Cha is the most active star, but no events were seen on SY Ori and HD 70309B. This confirms earlier indications that powerful "flaring" on T Tauri stars is not frequent. We make a detailed study of all events and find two types of slow events, usually with d(U or u)/dt<=0.1mag/hour. One is caused by changes in the continuous emission (the veiling) superimposed on the stellar photospheric spectrum and operates mainly on VW Cha. These events have nothing to do with stellar surface flares of the type observed on flare stars and we suggest that they originate from inhomogeneous mass accretion from a circumstellar disk to the stellar surface. The time-scales support models with magnetically controlled accretion along the stellar dipole field to rings or spots at the stellar surface. The other type of event appears to originate from relatively rapid changes in the opacity of circumstellar dust in the line-of-sight to the star. This effect dominates on SZ Cha, a WTTS surrounded by a substantial dust reservoir. Also for the rapid events we distinguish two types. On two WTTS we detected a few flare-like events produced by a sudden increase in emission in the Balmer continuum and the Balmer lines and no detectable change of the continuum long-ward of the Balmer jump. With only UBV photometry the Balmer flares could erronously been interpreted as very hot blackbody radiators. We suggest that these events are genuine surface flares with total energies of 10^33^ to 10^34^erg, and discuss the implication of energy supply. On ADA 481 we detected 2 flare-like events in white light. If these are due to the ignition of a source of blackbody radiation, the inferred temperature of the flare is low compared to what is normally observed for flare stars. Even though the events are rare and have small total amplitudes in UV, they are extremely powerful, with the same total energies as the largest flares seen on flare stars. The flare stars may show much larger changes in UV, but the difference comes from the lower contrast of the flares on the TTS. If all TTS have surface magnetic activity similar to the flare stars, only the radii being larger, then we conclude that the frequency distribution of the flare-like events on WTTS are similar to flare stars in the field, but much higher than for the dwarfs in the Pleiades. No flare-like event was seen on the CTTS and we discuss possible implications. For the long-term changes (over days) we conclude that very dark spots on the rotating surfaces of SY Ori and San 1 dominates, while VW Cha varies because of variable veiling, but with an uncertain period. For SZ Cha variable circumstellar extinction operates, also in phase with the hydrogen line absorption. The situation for ADA 481 is still unclear. HD 70309B did not vary.

Gahm, G. F.; Loden, K.; Gullbring, E.; Hartstein, D.



Neutron Stars and Quark Stars  

NASA Astrophysics Data System (ADS)

The tremendous densities reached in the centers of neutron stars provide a high pressure environment in which exciting particles processes are likely compete with each other and novel phases of matter may exist. The particle processes range from the generation of hyperons, to quark deconfinement, to the formation of kaon condensates and H-matter. Another striking possibility concerns the formation of absolutely stable strange quark matter. In the latter event all neutron stars could in fact be strange (quark matter) stars, which would be largely composed of pure quark matter possibly enveloped in a thin nuclear crust made up ordinary hadronic matter. This paper gives an overview of the properties of both classes of stars.

Weber, Fridolin



Abundances in Hot Evolved Stars  

NASA Astrophysics Data System (ADS)

The hydrogen-deficiency in extremely hot post-AGB stars of spectral class PG1159 is probably caused by a (very) late helium-shell flash or a AGB final thermal pulse that consumes the hydrogen envelope, exposing the usually-hidden intershell region. Thus, the photospheric element abundances of these stars allow us to draw conclusions about details of nuclear burning and mixing processes in the precursor AGB stars. We compare predicted element abundances to those determined by quantitative spectral analyses performed with advanced non-LTE model atmospheres. A good qualitative and quantitative agreement is found for many species (He, C, N, O, Ne, F, Si, Ar) but discrepancies for others (P, S, Fe) point at shortcomings in stellar evolution models for AGB stars. Almost all of the chemical trace elements in these hot stars can only be identified in the UV spectral range. The Far Ultraviolet Spectroscopic Explorer and the Hubble Space Telescope played a crucial role for this research.

Werner, Klaus; Rauch, Thomas; Kruk, Jeffrey W.



Panchromatic Hubble Andromeda Treasury (PHAT): Tests of UV Flux-Based SFR Estimates  

NASA Astrophysics Data System (ADS)

Ultraviolet (UV) flux is often used to trace and quantify recent star formation in nearby and distant galaxies. With new observations of resolved stars in the disk of M31 from the Panchromatic Hubble Andromeda Treasury (PHAT), we are able to test the validity of estimating ages and masses of stellar populations based on integrated UV flux. We use a maximum likelihood color-magnitude diagram fitting method (Dolphin, 2002), optimized to fit the main sequence, with the PHAT optical photometry to measure recent (within the last ~200 Myr) star formation histories and extinctions for 33 UV-bright regions in a 7.4 kpc2 area. With these results, we draw comparisons with single-age characterizations of these regions derived from integrated NUV and FUV GALEX flux by Kang et al. (2009). This study is the beginning of our effort to investigate all UV-bright regions within the entire PHAT survey area.

Simones, Jacob; Weisz, D. R.; Skillman, E. D.; Dalcanton, J.; Dolphin, A. E.; Williams, B. F.; PHAT Team



Detection of Ongoing, Low-Level Star Formation in Nearby Ellipticals  

NASA Astrophysics Data System (ADS)

Small amounts of star formation in early-type galaxies are suggested by several results: surprisingly young ages from optical line index dating, cooling X-ray gas, and mid-IR dust emission. Low levels of star formation have previously been difficult to detect, but using UV imaging from the Hubble Space Telescope's Wide Field Camera 3 (WFC3), we have identified individual young stars and star clusters in four nearby ellipticals by their UV colors and magnitudes. Ongoing, low-level star formation is detected in all four galaxies, including three ellipticals that have previously exhibited potential signposts of star forming conditions (NGC 4636, NGC 4697, and NGC 4374), and our "control” galaxy, the typical "red and dead" elliptical NGC 3379. The detected current star formation rates in our closest targets, where the census of young stars and clusters is reasonably complete, are between 3E-5 and 8E-5 M?/yr.

Ford, Alyson; Bregman, J. N.



UVS Technology Issues  

Microsoft Academic Search

\\u000a The aspirational capability objectives for UVS in the air, land and maritime environments articulated by several national\\u000a roadmap documents (e.g. [202] [205] [206] [267] [268] [278] [281]) may effectively be expressed as: 2008-10 conduct of ISR\\u000a missions; 2015-2020 autonomous patrol; and, 2025-2030 strike capability and combat missions. This implies a need for persistent\\u000a UVS autonomy in complex dynamic military environments

Anthony Finn; Steve Scheding


CETI. Metaphor and universal language  

Microsoft Academic Search

Are we alone in the Universe or are we but one of many advanced technical civilizations? Assuming that we are not alone and wished to make contact with our galactic neighbours how could we do so? When humans communicate, meaning comes from written and verbal language embedded in metaphor. However, the public nature of metaphoric language reduces the personal essence

Eric James Blown; John Kirkland; Jan McPherson; Bill Anderson



The Blueing Effect in Massive Young Stars  

NASA Astrophysics Data System (ADS)

The remarkable photometric effect known as "blueing" or "color-reversal", in which when the star fades the color index (B-V) becomes bluer instead of redder, as predicted for normal main sequence stars, has been found to be present in several massive pre-main sequence or Herbig Ae/Be stars (HAEBE). This obscuration of the central source in many cases of up to 3 magnitudes, due to probably large thick clouds orbiting in the outer parts of the circumstellar disks, gives us the opportunity of obtaining the spectral signature of bipolar flows, winds normal to the disk, and of the incident scattering. No general consensus exits in the explanation of this phenomenon, which occurs mostly in objects later than A0 and possible edgeon systems. Two case studies, UX Ori and HD 45677, are discussed here, which led us to propose that the blueing effect is the signature of the accretion and bipolar winds in these stars. Therefore, in this proposal we would like to observe a larger sample of massive PMS stars at deep minima in order to properly assess the UV signature of the blueing effect. Our current interpretation of this phenomenon is radically different from the explanations derived from optical photometry. Up to now, the blueing effect has only be observed and interpreted using optical photometry; our goal is to describe this phenomenon in term of UV continuum and emission fluxes in a larger sample of HAEBE stars.

Perez, Mario R.


Massive star-formation regions in the Magellanic Clouds  

SciTech Connect

Optical and UV spectroscopy of stars from six compact, luminous groups or clusters in the SMC and LMC is presented. The groups are characterized by high concentrations of nebulosity or starlight confined to areas smaller than 30 arcsec on a side, in which some stars can be resolved. The spectra and fluxes are used to derive luminosities and effective temperatures for the stars. Spectroscopic and stellar wind properties are also noted. It is found that the stars are all of O and B-type, with low extinction. The stars generally have little or no sign of stellar winds, and often have spectral peculiarities, such as weak lines or mixed spectral indicators. Most spectra have strong, broad Ly-alpha absorption, and some have broad Ca II absorption. The stars are placed on the H-R diagram, and it is argued that some of them are massive stars in pre-main-sequence stages of their evolution. 8 references.

Hutchings, J.B.; Thompson, I.B.



Starbursts and Star Clusters in the Ultraviolet  

NASA Astrophysics Data System (ADS)

We present ultraviolet (UV) images of nine starburst galaxies obtained with the Hubble Space Telescope using the Faint Object Camera. The galaxies range in morphology from blue compact dwarfs to ultraluminous merging far-infrared galaxies. Our data combined with new and archival UV spectroscopy and far-infrared fluxes allow us to dissect the anatomy of starbursts in terms of the distributions of stars, star clusters, and dust. The overall morphology of starbursts is highly irregular, even after excluding compact sources (clusters and resolved stars). The irregularity is seen both in the isophotes and the surface brightness profiles. In most cases the latter cannot be characterized by either exponential or R^0.25^ profiles. Most (7/9) starbursts are found to have similar intrinsic effective surface brightnesses, suggesting that a negative feedback mechanism is setting an upper limit to the star formation rate per unit area. Assuming a continuous star formation rate and a Salpeter [ApJ, 121,161(1955)] IMF slope, this surface brightness corresponds to an areal star formation rate of 0.7 M_sun_ kpc^-2^ yr^-1^ in stars in the mass range of 5-100 M_sun_. All starbursts in our sample contaIn UV bright star clusters indicating that cluster formation is an important mode of star formation in starbursts. On average about 20% of the UV luminosity comes from these clusters. The clusters with M_220_ <- 14 mag, or super star clusters (SSC) are preferentially found at the very heart of starbursts; over 90% of the SSCs are found where the underlying surface brightness is within 1.5 mag arcsec^-2^ of its peak value. The size of the SSCs in the nearest host galaxies are consistent with those of Galactic globular clusters. Our size estimates of more distant SSCs are likely to be contaminated by neighboring clusters and the underlying peaked high surface brightness background. The luminosity function of SSCs is well represented by a power law [?(L) is proportional to Lalpha^] with a slope ? ~ -2. We find a strong correlation between the far-infrared excess and the UV spectral slope for our sample and other starbursts with archival data. The correlation is in the sense that as the UV color becomes redder, more far-infrared flux is observed relative to the UV flux. The correlation is well modeled by a geometry where much of their dust is in a foreground screen near to the starburst, but not by a geometry of well-mixed stars and dust. Some starbursts have noticeable dust lanes, or completely obscured ionizing sources, indicating that the foreground screen is not uniform but must have some patchiness. Nevertheless, the reddened UV colors observed even in these cases indicates that the foreground screen has a high covering factor and can account for a significant fraction of the far-infrared flux.

Meurer, G. R.; Heckman, T. M.; Leitherer, C.; Kinney, A.; Robert, C.; Garnett, D. R.



Chameleon stars  

SciTech Connect

We consider a gravitating spherically symmetric configuration consisting of a scalar field nonminimally coupled to ordinary matter in the form of a perfect fluid. For this system we find static, regular, asymptotically flat solutions for both relativistic and nonrelativistic cases. It is shown that the presence of the nonminimal interaction leads to substantial changes both in the radial matter distribution of the star and in the star's total mass. A simple stability test indicates that, for the choice of parameters used in the paper, the solutions are unstable.

Dzhunushaliev, Vladimir [Institute for Basic Research, Eurasian National University, Astana, 010008 (Kazakhstan); Institute of Physicotechnical Problems and Material Science of the NAS of the Kyrgyz Republic, 265 a, Chui Street, Bishkek, 720071 (Kyrgyzstan); Folomeev, Vladimir [Institute of Physicotechnical Problems and Material Science of the NAS of the Kyrgyz Republic, 265 a, Chui Street, Bishkek, 720071 (Kyrgyzstan); Singleton, Douglas [Institute for Basic Research, Eurasian National University, Astana, 010008 (Kazakhstan); Physics Department, CSU Fresno, Fresno, California 93740-8031 (United States)



The Galaxy Evolution Explorer (GALEX) Surveys of the UV Sky  

NASA Astrophysics Data System (ADS)

The Galaxy Evolution Explorer (GALEX), a NASA Small Explorer UV survey mission, is in its sixth year of science operations. We have completed the Baseline Mission surveys and begun the Extended Mission program. We have continued a popular Guest Investigator (GI) Program. We are delivering our fifth GALEX Data Release (GR5). We have accelerated our data release schedule to once per year. The GALEX Extended Mission has four overarching goals: 1) Extend the UV/SFR calibration to low mass, low metallicity, and transitional galaxies; 2) Relate star formation history to environment, mass, halo mass and assembly history, and star formation regime, and measure star formation history in the low mass universe; 3) Determine the drivers of SF history by linking SF history to halo mass and assembly history, environment, AGN and their evolution, and the Intergalactic medium; 4) Extend the exploration of the UV universe into the dynamic and ultra-low surface brightness UV sky. These objectives are highly complementary to NASA's HST/COS and WFC3 goals, and all three instruments will benefit greatly from contemporaneous operation. The GALEX Primary and Extended Mission surveys will also complement PanSTARRS-1, SDSS-3, Fermi, Herschel, WISE, Warm Spitzer, UKIDSS, and other ground and space-based survey programs.

Martin, Christopher D.; GALEX Science Team



Variable Stars  

NASA Astrophysics Data System (ADS)

It is a tradition to observe variable stars using small telescopes; actually, variable stars are the favorites of small telescopes. What it is needed is those telescopes to be well-equipped (to get good observations), and to be supplied with users (to be productive). The first can be easily achieved; the second, related to the poor job prospects, seems more difficult. Keeping in mind that there is no any Observatory, that could cover the whole sky and that an astronomical event can not be repeated, each individual observation, is very valuable. Especially that of variable stars, where the variability of their luminosity can be caused by many reasons, intrinsic or extrinsic. What is missing -from at least some of the small telescopes spread in whole Europe- is better organization. This means that, besides either some research projects of personal interest, or(/and) students training, some others -being parts of international programs- could also be carried out, focusing to specific objects and goals. The work carried out in the field of variable stars with the use of small telescopes in some European countries, will be presented.

Rovithis-Livaniou, Helen


Brittle Star  

USGS Multimedia Gallery

A tiny brittle star (the central disc is smaller than a dime) clings to the branches of a soft coral in a sample bucket brought into the shipboard laboratory from a submersible dive. This creature makes its home on the deep, dark ocean floor. ...



Star quality.  


Around 150 wards are participating in the voluntary Star Wards scheme to provide mental health inpatients with more activities with therapeutic value. Suggested activities range from a library, to horse riding Internet access and comedy. Service users are particularly keen to have more exercise, which can be a challenge in inpatient settings. PMID:17970387

Dent, Emma




SciTech Connect

Compared to starburst galaxies, normal star-forming galaxies have been shown to display a much larger dispersion of the dust attenuation at fixed reddening through studies of the IRX-beta diagram (the IR/UV ratio 'IRX' versus the UV color 'beta'). To investigate the causes of this larger dispersion and attempt to isolate second parameters, we have used GALEX UV, ground-based optical, and Spitzer infrared imaging of eight nearby galaxies, and examined the properties of individual UV and 24 mum selected star-forming regions. We concentrated on star-forming regions, in order to isolate simpler star formation histories than those that characterize whole galaxies. We find that (1) the dispersion is not correlated with the mean age of the stellar populations; (2) a range of dust geometries and dust extinction curves are the most likely causes for the observed dispersion in the IRX-beta diagram, (3) together with some potential dilution of the most recent star-forming population by older unrelated bursts, at least in the case of star-forming regions within galaxies; and (4) we also recover some general characteristics of the regions, including a tight positive correlation between the amount of dust attenuation and the metal content. Although generalizing our results to whole galaxies may not be immediate, the possibility of a range of dust extinction laws and geometries should be accounted for in the latter systems as well.

Boquien, M.; Calzetti, D.; Hong, S. [University of Massachusetts, Department of Astronomy, LGRT-B 619E, Amherst, MA 01003 (United States); Kennicutt, R. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom); Dale, D. [Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States); Engelbracht, C.; Portouw, J. [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Gordon, K. D. [STScI, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Lee, J. C., E-mail: boquien@astro.umass.ed [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)



Environmental UV photobiology  

SciTech Connect

This book looks at the global depletion of stratospheric ozone and the consequences of the predicted increases of solar ultraviolet radiation. The introductory chapter deals with a characterization of solar UV-B and how radiation in this waveband can be influenced by ozone reduction in different locations. Two chapters deal with some technical aspects of measuring and simulating solar UV-B radiation. Seven chapters deal with the adverse effects of various aspects of human health that are anticipated in response to a change in level of solar UV-B, four dealing specifically with skin cancer. Two chapters address the basic aspects of ultraviolet photobiology, and finally the book addresses the implications of ozone reduction for aquatic ecosystems and for terrestrial plants.

Young, A.R.; Bjoern, L.O.; Moan, J.; Nultsch, W. [eds.



Electron stars for holographic metallic criticality  

SciTech Connect

We refer to the ground state of a gravitating, charged ideal fluid of fermions held at a finite chemical potential as an ''electron star.'' In a holographic setting, electron stars are candidate gravity duals for strongly interacting finite fermion density systems. We show how electron stars develop an emergent Lifshitz scaling at low energies. This IR scaling region is a consequence of the two-way interaction between emergent quantum critical bosonic modes and the finite density of fermions. By integrating from the IR region to an asymptotically AdS{sub 4} spacetime, we compute basic properties of the electron stars, including their electrical conductivity. We emphasize the challenge of connecting UV and IR physics in strongly interacting finite density systems.

Hartnoll, Sean A.; Tavanfar, Alireza [Center for the Fundamental Laws of Nature, Harvard University, Cambridge, Massachusetts 02138 (United States)



UV extinction and IR emission in diffuse H2 regions  

NASA Astrophysics Data System (ADS)

During this period, much work was spent in an attempt to use theoretical UV line indices as a basis for spectral calibration of the program stars. Five line indices are shown as functions of effective temperature and log g, calculated with the spectral synthesis programs of Kurucz. Open stars and circles are observed values from Fanelli et al., using the spectral class-effective temperature calibration of Schmidt-Kaler. We conclude that these line indices may be used to determine an effective stellar temperature, but with uncertainties of approximately a few thousand degrees. Also, for the hotter stars, theoretical line opacities are systematically low compared to observations. We have also found that Kurucz's new models appear to represent hot stars very well, even at far-UV wavelengths. This is shown in an example where two spectra of mu Col (spectral class 09.5 V) are compared to a synthetic spectrum for Teff = 33,000 K, log g = 4.0. Also shown (uppermost curve) is an empirical estimate of the intrinsic flux distribution for 09.5 V stars from Papaj, Wegner, and Krelowski.

Aannestad, Per A.


Star Formation in Brightest Cluster Galaxies  

NASA Astrophysics Data System (ADS)

We present Spitzer and GALEX spectral energy distributions (SEDs) for a sample of brightest cluster galaxies (BCGs). The BCG sample was selected from the Chandra archive, to have uniformly and well-measured X-ray cluster gas profiles for temperature, density, and entropy (Cavagnolo et al. 2009). The galaxy SEDs include data from GALEX [124 galaxies] , 2MASS [202 galaxies], and Spitzer IRAC [108 galaxies] and MIPS [83 galaxies]. These spectral energy distributions are fit to Siebenmorgen and Krügel (2006) starburst galaxy models in the IR and Groves et al. (2008) star formation models which span the IR through the UV, as well as an SED for an old stellar population. This sample provides a good baseline for the colors to expect from a quiescent BCG, since this sample includes BCGs that do not inhabit cool core clusters. We confirm the trend for BCGs in systems with low central hot gas entropy to have UV and mid-IR emission in excess over that expected from a quiescent BCG. We compare the star formation signatures in the BCGs with those from star-forming and starburst galaxies and find that their IR/UV ratios are similar to other star-forming galaxies, while their FUV-NUV colors might be somewhat bluer.

Hoffer, Aaron Scott; Donahue, M.; Hicks, A.; Barthelemy, R.



Wf/pc Cycle 1 Calibration: UV GRISM Test  

NASA Astrophysics Data System (ADS)

This program obtains UV grism (G200L) exposures on each PC detector of the standard star A+81D266. These observations must be obtained immediately following a WF/PC decontamination to be useful. There observations will: 1) Validate the modified exposure times used in the SMS based UV flood proposal (Dec 1991). 2) Aid in the determination of the success of the flash decontamination relative to a high temp decon. 3) Assess the absence of contamination on the external WF/PC optical (pickoff mirror and plug).

MacKenty, John



Star Formation Triggering Mechanisms in Dwarf Galaxies: The Far-Ultraviolet, H-alpha, and HI Morphology of Holmberg II  

Microsoft Academic Search

Far-UV (FUV), H-alpha, and HI observations of dwarf galaxy Holmberg II are used to trace the interaction between sites of massive star formation and the neutral and ionized components of the surrounding ISM. The data emphasize the importance of local conditions in regulating star formation from evidence such as massive stars inside ionized shells, compact HII regions surrounding aging clusters,

S. G. Stewart; M. N. Fanelli; G. G. Byrd; J. K. Hill; D. J. Westpfahl; K. P. Cheng; R. W. O'Connell; M. S. Roberts; S. G. Neff; A. M. Smith; T. P. Stecher



IUE observations of the exciting stars of giant H II regions in M33 - Supermassive stars?  

NASA Astrophysics Data System (ADS)

International Ultraviolet Explorer ultraviolet spectrometry is presented for seven bright starlike objects located in large H II regions in M33. Six of these have UV spectra very similar to R136a, the alleged supermassive star in the center of the 30 Dor nebula in the LMC. The UV line spectra suggest temperatures of 40,000-45,000 K. These temperatures, in combination with the observed UV flux, demonstrate that these objects produce essentially all the ionizing photons necessary to power their H II regions. Bolometric magnitudes are conservatively estimated at -12 to -14. Whatever its nature, R136a is shown to be the dominant source of ionization for 30 Dor. The possibility that such objects are supermassive stars is discussed. It is also found that the ultraviolet extinction curve in M33 resembles that of the LMC rather than the Galaxy.

Massey, P.; Hutchings, J. B.



Stars : the end of a star  

NSDL National Science Digital Library

What happens during the death of a star? This activity page, part of an interactive laboratory series for grades 8-12, introduces students to the final processes of stars. Here students read about low-mass, medium-mass, and massive stars. Low-mass stars produce white dwarfs. A pop-up window describes how white dwarfs form. Medium-mass stars produce neutron stars and supernova. Pop-up information explains the supernova process. Massive stars undergo carbon burning. An interactive lab activity presents students the opportunity to predict temperature, pressure, and gravity changes that occur during carbon fusion. In a final lab activity, students compare initial star size with the type of death that occurs. Activity questions about star death are provided for each star size and are recordable and printable. Copyright 2005 Eisenhower National Clearinghouse

University of Utah. Astrophysics Science Project Integrating Research and Education (ASPIRE)



Are You UV Safe?  

ERIC Educational Resources Information Center

|Students may be slathered with SPF 30 sunscreen all summer at the beach or pool, but what do they know about ultraviolet (UV) light radiation and absorption? The authors of this article found the perfect opportunity to help students find out the science behind this important health precaution, when they developed a series of practical strategies…

Capobianco, Brenda; Thiel, Elizabeth Andrew



Silicon carbide UV photodiodes  

Microsoft Academic Search

SiC photodiodes were fabricated using 6 H single-crystal wafers. These devices have excellent UV responsivity characteristics and very low dark current even at elevated temperatures. The reproducibility is excellent and the characteristics agree with theoretical calculations for different device designs. The advantages of these diodes are that they will operate at high temperatures and are responsive between 200 and 400

D. M. Brown; E. T. Downey; M. Ghezzo; J. W. Kretchmer; R. J. Saia; Y. S. Liu; J. A. Edmond; G. Gati; J. M. Pimbley; W. E. Schneider



The True Nature of Bursting Star Formation  

NASA Astrophysics Data System (ADS)

The rate of star formation (SFR) is a fundamental parameter shaping the evolution of a galaxy. In the extreme environments of starburst galaxies, the elevated levels of star formation can have a dramatic impact on the chemical composition and dynamics of the galaxy, on the future star formation within the galaxy, and potentially drive enriched material into the intergalactic medium surrounding the galaxy. While starbursts are a very important phenomenon with many aspects still not well understood, there has been no GALEX survey dedicated to the study of the nearest starburst galaxies. Starburst dwarf galaxies are ultimately an ultraviolet (UV) phenomenon due to their low dust content and as such warrant a legacy project of deep observations with GALEX that will produce a homogeneous archive. We propose a comprehensive comparison of the SFRs and spatial structure in twenty nearby, spatially resolved starburst galaxies derived from new and existing GALEX observations. Our sample of nearby starbursts is composed of galaxies for which we have reconstructed star formation histories (SFHs) from resolved stars using archival Hubble Space Telescope (HST) observations. The spatial structure, the SFRs, and the temporally resolved SFHs will allow us to understand the true nature of starbursts in dwarf galaxies for the first time. We will be able to determine how the bursts propagate within a galaxy, whether they are causally connected or of a more stochastic nature, and if starbursts are indeed ``self-quenching. Further, we will be able to probe the timescales of star formation responsible for the UV emission while considering the spatial migration of a starburst. Finally, the UV data will be coupled with Spitzer 24 micron and HST data sets to populate a new public archive of multi-wavelength observations of great use to a large community of researchers. Our proposed work will build our understanding of how galaxies change over time, one of NASA's strategic goals.

Skillman, Evan


Death Star  

NSDL National Science Digital Library

Death Star, a program from the PBS NOVA series, probes the deep mysteries of gamma-ray bursts, the most powerful celestial explosions since the Big Bang. A description of what would happen to Earth if a gamma-ray burst occurred in our own galaxy, a celestial glossary, and a virtual tour of the electromagnetic spectrum are included. Additional websites and published works about space topics are given, and the accompanying video is available to order.


Symbiotic Stars  

NASA Astrophysics Data System (ADS)

Symbiotic stars are interacting binary systems composed of a white dwarf (WD) accreting at high rate from a cool giant companion, which frequently fills its Roche lobe. The WD usually is extremely hot and luminous, and able to ionize a sizeable fraction of the cool giant wind, because it is believed the WD undergoes stable hydrogen nuclear burning on its surface of the material accreted from the companion. This leads to consider symbiotic stars as good candidates for the yet-to-be-identified progenitors of type Ia supernovae. Symbiotic stars display the simultaneous presence of many different types of variability, induced by the cool giant, the accreting WD, the circumstellar dust and ionized gas, with time scales ranging from seconds to decades. The long orbital periods (typically a couple of years) and complex outburst patterns, lasting from a few years to a century, make observations from professionals almost impossible to carry out, and open great opportunities to amateur astronomers to contribute fundamental data to science.

Munari, U.



Exceptional Stars  

NASA Astrophysics Data System (ADS)

As part of our Interdisciplinary Scientist effort (PI, Kulkarni) for the Space Interferometry Mission (SIM) we proposed an investigation with SIM of a number of exceptional stars. With SIM we plan to observe dozens of nearby white dwarfs and search for planets surviving the evolution away from the main sequence as well as (newly formed) planets formed in the circumbinary disks of post-AGB binaries or as a result of white dwarf mergers. We propose to measure the proper motion of a sample of X-ray binaries and Be star binaries with the view of understanding the originof high latitude objects and inferring natal kicks and pre-supernova orbits. We plan to observe several compact object binaries to determine the mass of the compact star. Of particular importance is the proposed observation of SS 433 (for which we propose to use the spectrometer on SIM to measure the proper motion of the emission line clumps embedded in the relativistic jets). Separately we are investigating the issue of frame tie between SIM and the ecliptic frame (by observing binary millisecond pulsars with SIM; the position of these objects is very well determined by pulsar timing) and the degree to which highly precise visibility amplitude measurements can be inverted to infer binary parameters.

Kulkarni, S. R.; Hansen, B.; van Kerkwijk, M.; Phinney, E. S.



First-Ever Census of Variable Mira-Type Stars in Galaxy Outside the Local Group  

NASA Astrophysics Data System (ADS)

First-Ever Census of Variable Mira-Type Stars in Galaxy Outsidethe Local Group Summary An international team led by ESO astronomer Marina Rejkuba [1] has discovered more than 1000 luminous red variable stars in the nearby elliptical galaxy Centaurus A (NGC 5128) . Brightness changes and periods of these stars were measured accurately and reveal that they are mostly cool long-period variable stars of the so-called "Mira-type" . The observed variability is caused by stellar pulsation. This is the first time a detailed census of variable stars has been accomplished for a galaxy outside the Local Group of Galaxies (of which the Milky Way galaxy in which we live is a member). It also opens an entirely new window towards the detailed study of stellar content and evolution of giant elliptical galaxies . These massive objects are presumed to play a major role in the gravitational assembly of galaxy clusters in the Universe (especially during the early phases). This unprecedented research project is based on near-infrared observations obtained over more than three years with the ISAAC multi-mode instrument at the 8.2-m VLT ANTU telescope at the ESO Paranal Observatory . PR Photo 14a/03 : Colour image of the peculiar galaxy Centaurus A . PR Photo 14b/03 : Location of the fields in Centaurus A, now studied. PR Photo 14c/03 : "Field 1" in Centaurus A (visual light; FORS1). PR Photo 14d/03 : "Field 2" in Centaurus A (visual light; FORS1). PR Photo 14e/03 : "Field 1" in Centaurus A (near-infrared; ISAAC). PR Photo 14f/03 : "Field 2" in Centaurus A (near-infrared; ISAAC). PR Photo 14g/03 : Light variation of six variable stars in Centaurus A PR Photo 14h/03 : Light variation of stars in Centaurus A (Animated GIF) PR Photo 14i/03 : Light curves of four variable stars in Centaurus A. Mira-type variable stars Among the stars that are visible in the sky to the unaided eye, roughly one out of three hundred (0.3%) displays brightness variations and is referred to by astronomers as a "variable star". The percentage is much higher among large, cool stars ("red giants") - in fact, almost all luminous stars of that type are variable. Such stars are known as Mira-variables ; the name comes from the most prominent member of this class, Omicron Ceti in the constellation Cetus (The Whale), also known as "Stella Mira" (The Wonderful Star). Its brightness changes with a period of 332 days and it is about 1500 times brighter at maximum (visible magnitude 2 and one of the fifty brightest stars in the sky) than at minimum (magnitude 10 and only visible in small telescopes) [2]. Stars like Omicron Ceti are nearing the end of their life. They are very large and have sizes from a few hundred to about a thousand times that of the Sun. The brightness variation is due to pulsations during which the star's temperature and size change dramatically. In the following evolutionary phase, Mira-variables will shed their outer layers into surrounding space and become visible as planetary nebulae with a hot and compact star (a "white dwarf") at the middle of a nebula of gas and dust (cf. the "Dumbbell Nebula" - ESO PR Photo 38a-b/98 ). Several thousand Mira-type stars are currently known in the Milky Way galaxy and a few hundred have been found in other nearby galaxies, including the Magellanic Clouds. The peculiar galaxy Centaurus A ESO PR Photo 14a/03 ESO PR Photo 14a/03 [Preview - JPEG: 400 x 451 pix - 53k [Normal - JPEG: 800 x 903 pix - 528k] [Hi-Res - JPEG: 3612 x 4075 pix - 8.4M] ESO PR Photo 14b/03 ESO PR Photo 14b/03 [Preview - JPEG: 570 x 400 pix - 52k [Normal - JPEG: 1140 x 800 pix - 392k] ESO PR Photo 14c/03 ESO PR Photo 14c/03 [Preview - JPEG: 400 x 451 pix - 61k [Normal - JPEG: 800 x 903 pix - 768k] ESO PR Photo 14d/03 ESO PR Photo 14d/03 [Preview - JPEG: 400 x 451 pix - 56k [Normal - JPEG: 800 x 903 pix - 760k] Captions : PR Photo 14a/03 is a colour composite photo of the peculiar galaxy Centaurus A (NGC 5128) , obtained with the Wide-Field Imager (WFI) cam



The AP stars  

Microsoft Academic Search

Ap stars are stars with peculiar characteristics which made it difficult to assign them to the stellar types of the conventional classification scheme. Ap stars are frequently observed. Up to 10% Ap stars are found in the case of the concerned spectral types. Attention is given to the spectroscopic properties of the Ap stars, aspects of stellar spectrum and stellar

H. Muthsam



Star formation in disks  

Microsoft Academic Search

It is noted that the principal characteristics of the stellar populations in galaxies depend on the history of star formation and the initial mass spectrum with which the stars are formed. Whereas there have been a number of attempts to model the history of star formation in galaxies using various quasi-theoretical descriptions of star formation, star formation remains poorly understood

R. B. Larson



UV disinfection of water: the need for UV reactor validation  

Microsoft Academic Search

Disinfection by ultraviolet light (UV) has received wide endorsement as an important contribution to the multiple barrier approach for protection of public health. UV can be used both to disinfect wastewater discharged to the environment, and to disinfect that water when it is picked up again for human consumption. UV readily blocks infectivity by such chlorine-resistant pathogens as Cryptosporidium parvum,

Y. A. Lawryshyn; B. Cairns


Solar-blind UV region and UV detector development objectives  

Microsoft Academic Search

The vulnerability of aircraft to missile attacks is briefly sketched. Aircraft and helicopter defensive electronic self- protection systems against missile attacks including passive and active radar and IR countermeasures are summarized. Radar and IR missile threat warnings are outlined. The development of UV missile threat warning is recounted. UV missile warning coverage is defined. UV missile plume photon emission is

Peter Schreiber; Tuoc Dang; Thad Pickenpaugh; Gary Smith; Paul Gehred; Cole Litton



UV radiometry issues for UV stabilization of photoresist  

Microsoft Academic Search

The use of intense, broadband, ultraviolet (UV) radiation in the stabilization of photoresist requires stable UV sources and sensors, as well as suitable calibration procedures. We have constructed and measured the stability of a new UV transfer source standard with a spectrum that is identical to that of a commercially available photostabilizer. This device is particularly useful in calibrating the

Jianou Shi; Steven P. Grindle; Sharine Chen; Greg Owen; Linda J. Insalaco; Christopher L. Cromer; Lori Goldner



Far-UV spectroscopic atlas of B stars (Smith, 2010)  

Microsoft Academic Search

Data reprocessings of IUE and STIS echelle spectra were completed in 1997 and 2006, respectively. The FUSE data were reprocessed with CalFUSE version 3.2 (Dixon et al., 2007PASP..119..527D) during 2007-2008. These spectra were ingested into the MAST archive, and we retrieved them from this facility. (4 data files).

M. A. Smith



Far-UV spectroscopic atlas of B stars (Smith, 2010)  

NASA Astrophysics Data System (ADS)

Data reprocessings of IUE and STIS echelle spectra were completed in 1997 and 2006, respectively. The FUSE data were reprocessed with CalFUSE version 3.2 (Dixon et al., 2007PASP..119..527D) during 2007-2008. These spectra were ingested into the MAST archive, and we retrieved them from this facility. (4 data files).

Smith, M. A.



IR and UV star formation in ACCEPT BCGs (Hoffer+, 2012)  

NASA Astrophysics Data System (ADS)

The original galaxy cluster sample is from the Archive of Chandra Cluster Entropy Profile Tables (ACCEPT) database (Cavagnolo et al. 2009, Cat. J/ApJS/182/12), which includes 239 galaxy clusters. We used the 2MASS archive and previous literature to determine the locations of the BCGs in these galaxy clusters (Table 2). Table 2 also gives the GALEX object identifiers for each BCG detected and the Astronomical Observing Request (AOR) numbers from the Spitzer archive observations. (6 data files).

Hoffer, A. S.; Donahue, M.; Hicks, A.; Barthelemy, R. S.



UV Radiation Climatology and Trends  

Microsoft Academic Search

The global distribution of erythemally weighted UV radiation and its seasonal changes are compared with the corresponding trends due to changing atmospheric composition. Because of the success of the Montreal Protocol, the trends in UV radiation have been relatively small outside the regions directly affected by the Antarctic ozone Hole. We do not expect further large increases in UV radiation

Richard L. McKenzie


UVS is rare in seabirds  

Microsoft Academic Search

Ultraviolet-sensitive vision (UVS), believed to have evolved from an ancestral state of violet-sensitive vision (VS), is widespread among terrestrial birds, where it is thought to play a role in orientation, foraging, and sexual selection. Less is known, however, about the distribution and significance of UVS in seabirds. To date UVS has been definitively demonstrated only in two families (Laridae and

Gabriel E. Machovsky Capuska; Leon Huynen; David Lambert; David Raubenheimer



SBC UV Contamination Check  

NASA Astrophysics Data System (ADS)

ACS/SBC throughput in the far-UV will be monitored during the bright earth avoidance period through use of two non-BEA visits, each of one orbit separated by one week allowing observations of NGC 6681. A waiver for two non-BEA orbits during BEA was previously granted. Exposures will be taken in PR110L, F115LP, F125LP, F140LP, F150LP and F165LP as in recent UV Monitor program observations. These results will be one of the activities determining if the BEA can be ended. A third visit just after BEA ends will repeat the above monitoring and include one orbit with F122M. ON HOLD visits 4 and 5 would substitute for 1 and 2 if SM4 is delayed.;

Gilliland, Ronald



Star clusters in the Whirlpool Galaxy  

NASA Astrophysics Data System (ADS)

This thesis presents the results of observational studies of the star cluster population in the interacting spiral galaxy M51, also known as the Whirlpool galaxy. Observations taken by the Hubble Space Telescope in the optical and the near-UV are used to determine fundamental properties of the star clusters, such as their ages, masses, radii and their spatial distribution. We study how these properties are related and how they depend on different environmental conditions in the galaxy, such as galactocentric radius and the distance from the spiral arms. By comparing the properties of the young star clusters to the properties of the giant molecular clouds from which they form, we study the process of star formation indirectly. We determine the radius distribution of 1284 young star clusters, which is different compared to the radius distribution of the giant molecular clouds. This suggests that during the formation of star clusters their radii change in a non-uniform way. The majority of the youngest star clusters are found in the spiral arms and these clusters are slightly more compact compared to older star clusters in the interarm regions. We discover a peculiar, fuzzy object with a projected position close to the nucleus of M51. After considering different scenarios for this object, we conclude that this object is most likely a fuzzy star cluster in front of the disc, with an age of 1.4 Gyr. The spatial distribution of the young star clusters is analysed using two-point autocorrelation functions. From this we find that the positions of the star clusters show a hierarchy with a fractal dimension similar to that of the turbulent interstellar medium in other galaxies, suggesting that star formation is hierarchical with a universal fractal dimension. Exploiting different multi-wavelength datasets we compare the positions of current star formation sites and recently formed star clusters younger than 10 Myr. A quantitative comparison between star and cluster formation is used to study the rapid dispersion, also called infant mortality, of young star clusters. Both star and cluster formation peak in the spiral arms and in the centre of the galaxy, but also at a galactocentric radius of 2.5 and 5 kpc, which is likely caused by the presence of the 4:1 resonance and the corotation radius, respectively. We derive the star cluster formation efficiency, which is the fraction of star formation that takes place in the star clusters we observe. We correct this fraction for selection effects by use of the cluster initial mass function, which we derive from our new data. We conclude that 20% of the star formation takes place in the form of star clusters. The remaining 80% takes place in a dispersed way, suggesting that the infant mortality can be as high as 80% and occuring on timescales of less than 10 Myr.

Scheepmaker, R. A.




SciTech Connect

We have assembled a sample of high spatial resolution far-UV (Hubble Space Telescope Advanced Camera for Surveys/Solar Blind Channel) and H{alpha} (Maryland-Magellan Tunable Filter) imaging for 15 cool core galaxy clusters. These data provide a detailed view of the thin, extended filaments in the cores of these clusters. Based on the ratio of the far-UV to H{alpha} luminosity, the UV spectral energy distribution, and the far-UV and H{alpha} morphology, we conclude that the warm, ionized gas in the cluster cores is photoionized by massive, young stars in all but a few (A1991, A2052, A2580) systems. We show that the extended filaments, when considered separately, appear to be star forming in the majority of cases, while the nuclei tend to have slightly lower far-UV luminosity for a given H{alpha} luminosity, suggesting a harder ionization source or higher extinction. We observe a slight offset in the UV/H{alpha} ratio from the expected value for continuous star formation which can be modeled by assuming intrinsic extinction by modest amounts of dust (E(B - V) {approx} 0.2) or a top-heavy initial mass function in the extended filaments. The measured star formation rates vary from {approx}0.05 M{sub sun} yr{sup -1} in the nuclei of non-cooling systems, consistent with passive, red ellipticals, to {approx}5 M{sub sun} yr{sup -1} in systems with complex, extended, optical filaments. Comparing the estimates of the star formation rate based on UV, H{alpha}, and infrared luminosities to the spectroscopically determined X-ray cooling rate suggests a star formation efficiency of 14{sup +18}{sub -8}%. This value represents the time-averaged fraction, by mass, of gas cooling out of the intracluster medium, which turns into stars and agrees well with the global fraction of baryons in stars required by simulations to reproduce the stellar mass function for galaxies. This result provides a new constraint on the efficiency of star formation in accreting systems.

McDonald, Michael; Veilleux, Sylvain; Mushotzky, Richard; Reynolds, Christopher [Department of Astronomy, University of Maryland, College Park, MD 20742 (United States); Rupke, David S. N., E-mail:, E-mail: [Department of Physics, Rhodes College, Memphis, TN 38112 (United States)



BEA UV Contamination Monitor  

NASA Astrophysics Data System (ADS)

The observations consist of imaging and spectroscopy with ACS/SBC of the scaled OB association NGC 604 in M33 prior to SM4. Data will be obtained with the F122M, F150LP, F165LP filters and the PR130L prism. The observations will allow any UV contamination to be monitored by comparing these data with identical observations to be obtaining during the BEA phase of SMOV4.;

Smith, Linda



UV curable materials development  

SciTech Connect

Adhesives, coatings, and inks were selected for evaluation based on literature search and possible production applications. A differential photocalorimeter was used to measure degree of cure and allow prediction of optimum processing conditions. UV cure equipment were characterized and the ability to size equipment to specific materials cure needs established. Adhesion tests procedures were developed for the adhesives and solvent resistance testing procedures developed for the coatings and inks.

Parker, B.G.



UV Induced Insulator Flashover  

Microsoft Academic Search

Insulators are critical components in high-energy, pulsed power systems. It is known that the vacuum surface of the insulator will flashover when illuminated by ultraviolet (UV) radiation depending on the insulator material, insulator cone angle, applied voltage and insulator short-history. A testbed comprised of an excimer laser (KrF, 248 nm, ~2 MW\\/cm2, 30 ns FWHM,), a vacuum chamber (low 1.0E-6

J. B. Javedani; T. L. Houck; B. T. Kelly; D. A. Lahowe; M. D. Shirk; D. A. Goerz



Beryllium and Boron abundances in population II stars  

NASA Astrophysics Data System (ADS)

The scientific focus of this program was to undertake UV spectroscopic abundance analyses of extremely metal poor stars with attention to determining abundances of light elements such as beryllium and boron. The abundances are likely to reflect primordial abundances within the early galaxy and help to constrain models for early galactic nucleosynthesis. The general metal abundances of these stars are also important for understanding stellar evolution.



Binary Stars behind the Vela Super Nova Remnant  

NASA Astrophysics Data System (ADS)

Spectroscopic observations of a pair of double stars behind the Vela SNR, in the UV provide information on the variations of the intersteallar medium composition, spatially and because these stars have been observed earlier by GHRS the data will also provide a measure of temporal variations. The Vela SNR is close and movement of the ISM infront perpendicular to the sightline is easily seen. Observations of interstellar lines and line ratios will give information on shock scale lengths and grain destruction.

Danks, Anthony




SciTech Connect

In star-forming galaxies, dust plays a significant role in shaping the ultraviolet (UV) through infrared (IR) spectrum. Dust attenuates the radiation from stars, and re-radiates the energy through equilibrium and non-equilibrium emission. Polycyclic aromatic hydrocarbons (PAHs), graphite, and silicates contribute to different features in the spectral energy distribution; however, they are all highly opaque in the same spectral region-the UV. Compared to old stellar populations, young populations release a higher fraction of their total luminosity in the UV, making them a good source of the energetic UV photons that can power dust emission. However, given their relative abundance, the question of whether young or old stellar populations provide most of these photons that power the IR emission is an interesting question. Using three samples of galaxies observed with the Spitzer Space Telescope and our dusty radiative transfer model, we find that young stellar populations (on the order of 100 million years old) dominate the dust heating in star-forming galaxies, and old stellar populations (13 billion years old) generally contribute less than 20% of the far-IR luminosity.

Law, Ka-Hei [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Gordon, Karl D. [STScI, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Misselt, K. A., E-mail:, E-mail:, E-mail: [Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 (United States)



Bursting dwarf galaxies from the far-UV and deep surveys  

Microsoft Academic Search

The far-ultraviolet (UV) counts and the deep optical spectroscopic surveys have revealed an unexpected number of very blue galaxies (vBG). Using constraints from the UV and optical, we apply the galaxy evolution model PEGASE (Fioc & Rocca-Volmerange 1997, hereafter FRV) to describe this population with a cycling star formation. When added to normally evolving galaxy populations, vBG are able to

Michel Fioc; Brigitte Rocca-Volmerange



UV Radiation and the Skin  

PubMed Central

UV radiation (UV) is classified as a “complete carcinogen” because it is both a mutagen and a non-specific damaging agent and has properties of both a tumor initiator and a tumor promoter. In environmental abundance, UV is the most important modifiable risk factor for skin cancer and many other environmentally-influenced skin disorders. However, UV also benefits human health by mediating natural synthesis of vitamin D and endorphins in the skin, therefore UV has complex and mixed effects on human health. Nonetheless, excessive exposure to UV carries profound health risks, including atrophy, pigmentary changes, wrinkling and malignancy. UV is epidemiologically and molecularly linked to the three most common types of skin cancer, basal cell carcinoma, squamous cell carcinoma and malignant melanoma, which together affect more than a million Americans annually. Genetic factors also influence risk of UV-mediated skin disease. Polymorphisms of the melanocortin 1 receptor (MC1R) gene, in particular, correlate with fairness of skin, UV sensitivity, and enhanced cancer risk. We are interested in developing UV-protective approaches based on a detailed understanding of molecular events that occur after UV exposure, focusing particularly on epidermal melanization and the role of the MC1R in genome maintenance.

D'Orazio, John; Jarrett, Stuart; Amaro-Ortiz, Alexandra; Scott, Timothy



UV matters in shoaling decisions  

PubMed Central

Shoaling behaviour in fish is influenced by numerous factors, such as familiarity, kinship, group size and shoal composition. Grouping decisions are based on both olfactory and visual cues. The visual system of many vertebrates is extended into the ultraviolet (UV) wave range as in three-spined sticklebacks (Gasterosteus aculeatus, L.). We investigated whether the presence or absence of UV wavelengths has an influence on shoaling behaviour in this species. Reproductively non-active three-spined sticklebacks were given the choice between two shoals, equal in numbers of individuals, which could be seen either through a UV-transmitting [UV(+)] or a UV-blocking [UV(?)] filter. Test fish preferred to join the shoal seen under UV(+) conditions. Due to differences in quantal flux between the UV(+) and UV(?) filters used, control experiments with neutral-density optical filters were performed in order to clarify the role of luminance. Here, test fish spent significantly more time near shoals that were seen in a darker environment, suggesting a potential trade-off between UV radiation and lower brightness during shoal choice. To our knowledge, these results demonstrate for the first time that shoaling decisions are influenced by UV wavelengths.

Modarressie, Ricarda; Rick, Ingolf P; Bakker, Theo C.M



UV-B induced morphogenesis  

PubMed Central

Low levels of ultraviolet (UV)-radiation alter the morphology of plants. UV-B exposure can lead to shorter petioles and shorter, narrower and/or thicker leaf blades. The resulting decrease in leaf area has been associated with inhibitory UV-B effects on biomass accumulation. In Arabidopsis, UV-B effects on leaf area have variously been attributed to altered cell division, cell expansion or combinations of these two processes. A dedicated UV-B sensory system, crosstalk between flavonoids and auxins, endoreduplication and generic Stress Induced Morphogenic Responses (SIMR) have all been proposed to contribute to the UV-B phenotype. Here, we propose that UV-mediated morphogenesis, rather than being controlled by a single regulatory pathway, is controlled by a regulatory blur involving multiple compensatory molecular and physiological feedback interactions.

Jansen, Marcel A.K.; Coffey, Aoife M.; Prinsen, Els



The FIREBall fiber-fed UV spectrograph  

NASA Astrophysics Data System (ADS)

FIREBall (Faint Intergalactic Redshifted Emission Balloon) had a successful first engineering flight in July of 2007 from Palestine, Texas. Here we detail the design and construction of the spectrograph. FIREBall consists of a 1m telescope coupled to a fiber-fed ultraviolet spectrograph flown on a short duration balloon. The spectrograph is designed to map hydrogen and metal line emission from the intergalactic medium at several redshifts below z=1, exploiting a small window in atmospheric oxygen absorption at balloon altitudes. The instrument is a wide-field IFU fed by almost 400 fibers. The Offner mount spectrograph is designed to be sensitive in the 195-215nm window accessible at our altitudes of 35-40km. We are able to observe Ly?, as well as OVI and CIV doublets, from 0.3 < z < 0.9. Observations of UV bright B stars and background measurements allow characterization of throughput for the entire system and will inform future flights.

Tuttle, Sarah E.; Schiminovich, David; Milliard, Bruno; Grange, Robert; Martin, D. Christopher; Rahman, Shahinur; Deharveng, Jean-Michel; McLean, Ryan; Tajiri, Gordon; Matuszewski, M.



Hubble Space Telescope Fine Guidance Sensor Parallaxes of Galactic RR Lyrae Stars  

Microsoft Academic Search

We present new absolute trigonometric parallaxes and proper motions for seven Pop II variable stars: the five RR Lyr stars; RZ Cep, XZ Cyg, SU Dra, RR Lyr, UV Oct; and two W Vir Pop II Cepheids; VY Pyx and kappa Pav. We obtain these results with astrometric data from Fine Guidance Sensor 1r, a white-light interferometer on Hubble Space

G. Fritz Benedict; B. E. McArthur



A Model for the Ae-Star with Detected Magnetic Field HD190073  

Microsoft Academic Search

An MHD model has been built for the A2 IIIe star HD 190073 in order to account for the following observational facts. (i) The star has a magnetic field. (ii) It has an expanding chromosphere. (iii) Shell lines of single ionized metals display large expansion velocities. (iv) The continuum spectrum displays an important IR excess. (v) The UV continuum spectrum

M. Cuttela; A. E. Ringuelet



Pagb Stars in Elliptical and Bulge-Dominated Nearby Galaxies -- Cycle 4 Carryover  

NASA Astrophysics Data System (ADS)

We propose to search for the stellar population which produces the far ultraviolet rising branch from 1200-1800 A in the spectral energy distributions of early-type galaxies. One of the most likely sources of this hot emission are evolved post-asymptotic giant branch (PAGB) stars. We estimate that the brightest PAGB stars at the distance of M31 can be unambiguously detected using the far-UV imaging capabilities of HST+FOC. The possible presence of other kinds of hot stellar components that could contribute flux to the rising branch (e.g. young stars, accreting white dwarf stars in binaries) can also be detected in these images, as they will be intrinsically brighter than PAGB stars, but less numerous. If the source of this far -UV flux is PAGB stars, their absolute magnitudes in galaxies of different mean metallicities are critical tests of current theories of PAGB evolution.

Bertola, Francesco



UV immobilized phospholipid bilayers  

SciTech Connect

Dinitrophenyl phosphotidylethanolamine-containing bilayers have been immobilized on carbon-shadowed support films by UV irradiation of the first monolayer transferred to the support film. The immobilized bilayer is capable of allowing bound protein (anti-DNP antibody) to organize into 2-D arrays in the presence of organic solvents such as acetonitrile and dilute concentrations of detergents such as beta-octyl glucoside. The ability of the bilayers to remain attached to supports under various conditions that include organic solvents and detergents as well as divalent ions is of potential interest in the study of protein crystallization and particularly in the study of membrane proteins.

Uzgiris, E.E.



Holographic UV laser microsurgery  

PubMed Central

Abstract We use a spatial light modulator (SLM) to diffract a single UV laser pulse to ablate multiple points on a Drosophila embryo. This system dynamically generates a phase hologram for ablating a user-defined pattern fast enough to be used with living, and thus moving, tissue. We demonstrate the ability of this single-pulse multi-point system to perform two experiments that are very difficult for conventional microsurgery—isolating single cells in vivo and measuring fast retractions from large incisions.

Jayasinghe, Aroshan K; Rohner, Jason; Hutson, M Shane



Doppler Tomography of Massive Compact Binary Stars in Multiple Star Systems  

NASA Astrophysics Data System (ADS)

I present a study of IUE spectra for three O stars in multiple star systems. These spectra were first subjected to cross-correlation analysis to find their radial velocity curves and hence their orbital elements. I then used Doppler tomographic methods to separate the individual component spectra in order to find their MK types, projected rotational velocities, and UV flux ratios, and to search for evidence of unusual abundances. Using the properties derived from the reconstructed spectra, the component stars were placed on the Hertzsprung-Russell diagram and compared to the evolutionary tracks predicted by Schaller et al. (1992), Maeder & Meynet (2001), and Heger & Langer (2001). These three O stars, ? Ori A, HD 206267, and HD 215835, are all triple star systems in which at least one component is an O star. All three consist of a massive close binary star with a more distant tertiary component recently discovered through speckle interferometry. I examined these systems to try to detect and correct for the effects of the previously unknown third light in their spectra. In the case of ? Ori A, the masses of both components of its close binary were determined, and both components are highly overluminous for their spectroscopically-determined masses. This is probably a result of the close binary having undergone one or more episodes of Roche lobe overflow.

Harvin, J. A.



Intrinsic Energy Distributions in Spectra of Early Type Stars  

NASA Astrophysics Data System (ADS)

The intrinsic energy distributions in the spectra of stars hotter than B5 are derived from the TD-1 data samples as mean distributions, averaged for some spectral types over more than 100 stars. The `peculiarities' resulting from incorrect classifications or errors in recording the data have been detected and excluded from the samples. The new set of intrinsic (B-V)0 colours, differing slightly from the existing ones is proposed. The derived spectrophotometric standards are apparently free of reddening effects in visual and far-UV segments of their spectra. The set of stars proposed as natural standards is also included.

Papaj, J.; Wegner, W.; Krelowski, J.



The UV-metallicity Characteristics Of UCDs, GCs And dEs In The Fornax Cluster  

NASA Astrophysics Data System (ADS)

The remarkable variation of UV-optical ratios in elliptical galaxies suggests that the observed "UV-excess" may be uniquely sensitive to their star formation histories and chemical enrichment. While the stellar evolutionary phase responsible for creating this "excess" is fairly well understood (He-rich, hot-HB stars), the UV emission of an integrated stellar population and its dependence on global characteristics such as metallicity is far more complex. Because they are mostly simple stellar populations with small dispersion in age and abundance, globular clusters (GCs) have been considered good calibrators for understanding these global characteristics. The GCs of M87 appear to follow a far-UV-metallicity relation (FUV - Mg_2) similar to Milky Way GCs, but distinct from that observed for ellipticals.Ultra-compact dwarf galaxies (UCDs) may provide an alternative, more luminous calibrator of the UV-excess in early-type galaxies. Near- and far-UV GALEX imaging provides tantalising hints that at least some UCDs exhibit a "UV-excess" comparable to the UV-luminous GCs in M87. I will present the FUV - Mg_2 relation for Fornax Cluster UCDs from GALEX imaging and our Magellan/IMACS spectroscopy, and compare them with NGC1399 GCs and cluster dE,Ns. By combining GALEX imaging with our optical g,r,i imaging, I will also show that the UV-optical properties of Fornax UCDs and NGC1399 GCs, provide an efficient tool for discriminating between new candidates and foreground stars in ground based images.

Karick, Arna; Gregg, M.



Fluorescent UV-Curable Resists for UV Nanoimprint Lithography  

Microsoft Academic Search

We developed fluorescent UV-curable resists for UV nanoimprint lithography to readily detect residual layer thickness and analyze its profile in addition to pattern defects by fluorescence microscopy. A fluorescent dye of rhodamine 6G, 2-[6-(ethylamino)-3-(ethylimino)-2,7-dimethyl-3H-xanthen-9-yl]benzoic acid ethyl ester tetrafluoroborate 5a, showed sufficient durability of photobleaching in solution toward UV-light exposure at >350 nm in the absence and presence of a radical

Kei Kobayashi; Nobuji Sakai; Shinji Matsui; Masaru Nakagawa



Lifestyles of the Stars.  

ERIC Educational Resources Information Center

|Some general information on stars is provided in this National Aeronautics and Space Administration pamphlet. Topic areas briefly discussed are: (1) the birth of a star; (2) main sequence stars; (3) red giants; (4) white dwarfs; (5) neutron stars; (6) supernovae; (7) pulsars; and (8) black holes. (JN)|

National Aeronautics and Space Administration, Cocoa Beach, FL. John F. Kennedy Space Center.


Theories of star formation  

Microsoft Academic Search

A well defined theory of star formation does not yet exist. A serious deficiency therefore remains in current theories of the structure and evolution of stars. Since stars must be forming at the present phase of Galactic evolution, it is pertinent to investigate what conditions favour star formation. Observational evidence for the pre-main sequence phase of stellar evolution is entirely

D. McNally



Extragalactic Star Clusters: the Resolved Star Approach  

NASA Astrophysics Data System (ADS)

The physical processes leading to the dissolution of star clusters is a topic barely studied and still not understood. We started a pilot project to develop a new approach to directly detect and study the properties of stellar clusters while they are being destroyed. Our technique currently under development makes use of the exceptional spatial resolution and sensitivity of the ACS camera onboard HST to resolve individual stars in nearby galaxies. PSF stellar photometry and color-magnitude diagrams allows us to separate the most massive stars (more likely to be in clusters) from the star field background. While applying the method to the normal spiral galaxy NGC1313, we found that the method of studying star clusters through resolved stars in nearby galaxies is even more powerful than we first expected. The stellar maps obtained for NGC1313 show that a large fraction of early B-type stars contained in the galaxy are already part of the star field background rather that being in star clusters. Such stars live for 5 to 25 Myr. Since most stars form in clusters, the presence of such massive stars in the field means that they must have left their birthplace very rapidly. It also means that the processes involved in the dissolution of the clusters are extremely efficient. The only plausible explanation for so many young stars to be in the field background is the infant mortality of star clusters. We will present the latest results on the two galaxies NGC 1313 and IC 2475 and discuss the potential of the new approach for studying extragalactic stellar clusters.

Pellerin, Anne; Meyer, M. J.; Jason, H.; Calzetti, D.



Testing the THINGS Star Formation Law in Nearby Galaxies  

NASA Astrophysics Data System (ADS)

The star formation law (SFL) is an essential tool for understanding galaxy evolution. However, the star formation process is not well understood and the broadly used Schmidt-Kennicutt SFL is based on a biased sample of bright nearby spirals. Here we derive a star formation recipe based on the THINGS SFL of Leroy et. al (2008) and Bigiel et al.(2009), which can predict the star formation rate using the rotation curve and stellar mass profile as an input. We use optical and radio rotation curves combined with optical broad band images of HI selected galaxies to make predicted star formation profiles using this prescription which are then compared to our UV and H-alpha images from the SINGG and SUNGG surveys. We look at how the predictions compare to the observations in the two different tracers especially in the outer disks which were not accounted for when the THINGS SFL was derived.

Meurer, Gerhardt R.; Zheng, Z.; Zwaan, M.; Knezek, P.



Stochastic Star Formation in Low Mass Galaxies: A case study of DDO 210  

NASA Astrophysics Data System (ADS)

To address the longstanding question of whether dwarf galaxies have bursty star formation histories requires a large sample of dwarf galaxies and an accurate tracer of star formation. Here we explore the utility of using two common tracers, H-alpha and the ultraviolet (UV). H-alpha and UV photons are primarily produced by massive stars, so stochastic effects come into play when the star formation rate (SFR) is so low that the upper mass end of the initial mass function (IMF) is not fully populated. We use Monte-Carlo simulations to explore these effects at a range of SFRs for a standard Chabrier IMF. We do not impose the restriction that stars form primarily in low mass clusters as explored by Kroupa and Weidner. Here we simply consider Poisson fluctuations in the number of massive stars when star formation occurs at a constant low rate. We find that above SFRs of 0.001 Msun/yr both the far-UV and H-alpha are reliable tracers of SFR. Below this value both indicators begin to show deviations, with H-alpha being more strongly affected. We explore the implications of these findings for the 11 Mpc H-alpha UV Galaxy Survey (11HUGS), a GALEX Legacy program designed to characterize the star formation properties of a local volume-limited sample. We highlight the dwarf galaxy DDO 210, which has a UV luminosity of 270 L_sun, but no nebular H-alpha emission. While we cannot rule out a truncated star formation history for this galaxy, our simulations demonstrate that this H-alpha deficient galaxy could be forming stars at a constant rate of 0.0001 Msun/yr.

Tremonti, Christina A.; Lee, J. C.; van Zee, L.; Kennicutt, R. C.; Gil de Paz, A.; Sakai, S.; Funes, J.; Akiyama, S.



The Evolution of Low Mass Stars in Close Binary Systems  

Microsoft Academic Search

We report on our extensive investigation of the evolution of low mass stars in close binary systems with white dwarfs. Cataclysmic variables (CVs), which are the most numerous UV and X-ray sources in the Galaxy, and Type Ia supernovae, which are standard candles for cosmology, are believed to be the end products of these close binary systems, but little is

N. M. Silvestri; S. L. Hawley; P. Szkody; J. J. Bochanski; A. A. West; O. J. Fraser; K. R. Covey; M. A. Wolfe; K. M. Vanlandingham; L. C. Dang



Modelling the light variability of the Ap star ? Ursae Majoris  

Microsoft Academic Search

Aims: We simulate the light variability of the Ap star ? UMa using the observed surface distributions of Fe, Cr, Ca, Mn, Mg, Sr, and Ti obtained with the help of the Doppler imaging technique. Methods: Using all photometric data available, we specified light variations of ? UMa modulated by its rotation from far UV to IR. We employed the

D. Shulyak; J. Krticka; Z. Mikulásek; O. Kochukhov; T. Lüftinger



Star Formation Signatures in Optically Quiescent Early-type Galaxies  

Microsoft Academic Search

In recent years, an argument has been made that a high fraction of early-type galaxies (ETGs) in the local universe experience low levels (lsim1 M sun yr-1) of star formation (SF) that causes strong excess in UV flux, yet leaves the optical colors red. Many of these studies were based on Galaxy Evolution Explorer imaging of Sloan Digital Sky Survey

Samir Salim; R. Michael Rich



Tomographic Separation of Composite Spectra. The Components of Plaskett's Star.  

National Technical Information Service (NTIS)

The UV photospheric lines of Plaskett's Star (HD 47129), a 14.4 day period, double lined O-type spectroscopic binary were analyzed. Archival data from IUE (17 spectra well distributed in orbital phase) were analyzed with several techniques. A cross correl...

W. G. Bagnuolo D. R. Gies M. S. Wiggs




SciTech Connect

The carbon Mira UV Aur (photometric period 394 days) and its companion present several interesting spectroscopic issues. The late B-type companion, at a separation of 3.''36, is seen through at least two shells expanding from the C9-type primary, as evidenced by a series of narrow, displaced absorption features at the D{sub 1,2} lines of Na I. The (projected) expansion velocity of the fastest shell is about 116 km s{sup -1}, much larger than the typical outflow velocity of about 15 km s{sup -1} seen in C-type giants, but reminiscent of the velocities observed in the envelope of another C-type Mira, V Hya. Emission lines of H, Ca II, and Na I are present in UV Aur A; its Balmer emission lines are heavily mutilated by overlying C-type absorptions (much as is seen in Me-type Miras), so they must be formed at a lower level. UV Aur B offers the opportunity to test a speculation that the carriers of the diffuse interstellar bands (DIBs), believed to be a family of carbon-containing polyatomic molecules, may be formed in cool, carbon-rich stars. Moderately strong DIBs are indeed present in the spectrum of UV Aur B at about the same strength and velocity seen in nearby (in the sky) B-type stars. But the essential question is, are DIBs present in the outflow from UV Aur A, at the velocities of the Na I shell components? The answer is no, at least at the level permitted by the signal-to-noise ratio of these Keck/HIRES spectrograms.

Herbig, G. H. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States)



Habitable Niches In Single and Binary Star Systems  

NASA Astrophysics Data System (ADS)

We investigate habitable niches, defined as locations with optimum conditions for complex life to exist. The recent discovery of planets in several binaries motivates this study to examine favorable habitability circumstances in both single and binary star systems. Stellar evolution calculations are used to model time dependent stellar luminosity, UV flux, photo-synthetic flux and atmospheric water photolysis. Tidal interactions such as synchronization timescales, heat generation, and forcing frequency are also investigated. An Earth-analogue planet in the habitable zone of a 0.8 solar mass star is well suited for complex life. Several high quality niches are available to planets in habitable zones of binaries. For example, orbiting a pair of twin stars each 0.75 solar masses with a binary period of ten days will provide ample photo-synthetic radiation without an overdose of UV radiation, and tidal effects mimicking the Earth-Moon. A solar like star with a close red dwarf companion, like the recently discovered Kepler 47, provides a high quality niche because both stars are relatively long lived and the habitable zone has abundant photo-synthetic light while avoiding harmful UV light. A similar niche exists with a sun like star, which in turn is orbited by a distant red dwarf, providing a roughly annual enhanced red photo-synthetic flux. Also, moons orbiting Jupiter mass planets may exist within habitable zones of both single and binary stars. Such moons might be synchronized to the planet rather than the star. Due to the abundance of binary systems and the presence of high quality niches; binaries may harbor a significant fraction of inhabited planets within the universe. The present study allows for selection of the best habitability follow up targets for large telescopes.

Clark, Joni; Mason, P. A.



Herschel's Star Gages  

NSDL National Science Digital Library

The EJS Herschel's Star Gages Model illustrates William Herschel's methods of "star gages" by which he attempted to map out the shape of our galaxy in 1785. Herschel's star gages (sic) relied on two important assumptions: that Herschel's telescope (his "large 20 foot" with an 18.5 inch aperture) could see to the ends of the galaxy, and that within the galactic system stars are distributed uniformly. If the first assumption holds then the stars seen in the telescope all lie within a conical region of space with the apex at the telescope and the base at the edge of the galaxy. If the second assumption holds then the number of stars seen in the telescope is proportional to the volume of this cone. Since the volume of the cone is proportional to the cube of its height, the distance to the galactic edge in any direction is proportional to the cube root of the number of stars seen in that direction. This simulation allows the user to use Herschel's method of star gages to map out the shape of an artificial "star system" for which Herschel's assumptions are valid. One window shows the view through a telescope, with a slider to change the telescopes direction (around a single fixed axis). Another window shows a 3D view of the star system, showing either all of the stars in the system or only those stars visible through the telescope. A third window shows a plot of the star gages. Plotting star gages for many different directions maps out a cross-section of the star system. An optional slider allows the user to decrease the distance to at which stars are no longer visible, and a menu allows the user to select a star system in which the stars are not distributed uniformly. These options let the user explore how violations of Herschel's two fundamental assumptions invalidate his star gage method.

Timberlake, Todd



Symbiotic stars in X-rays  

NASA Astrophysics Data System (ADS)

Until recently, symbiotic binary systems in which a white dwarf accretes from a red giant were thought to be mainly a soft X-ray population. Here we describe the detection with the X-ray Telescope (XRT) on the Swift satellite of nine white dwarf symbiotics that were not previously known to be X-ray sources and one that had previously been detected as a supersoft X-ray source. The nine new X-ray detections were the result of a survey of 41 symbiotic stars, and they increase the number of symbiotic stars known to be X-ray sources by approximately 30%. The Swift/XRT telescope detected all of the new X-ray sources at energies greater than 2 keV. Their X-ray spectra are consistent with thermal emission and fall naturally into three distinct groups. The first group contains those sources with a single, highly absorbed hard component that we identify as probably coming from an accretion-disk boundary layer. The second group is composed of those sources with a single, soft X-ray spectral component that probably originates in a region where low-velocity shocks produce X-ray emission, i.e., a colliding-wind region. The third group consists of those sources with both hard and soft X-ray spectral components. We also find that unlike in the optical, where rapid, stochastic brightness variations from the accretion disk typically are not seen, detectable UV flickering is a common property of symbiotic stars. Supporting our physical interpretation of the two X-ray spectral components, simultaneous Swift UV photometry shows that symbiotic stars with harder X-ray emission tend to have stronger UV flickering, which is usually associated with accretion through a disk. To place these new observations in the context of previous work on X-ray emission from symbiotic stars, we modified and extended the ?/?/? classification scheme for symbiotic-star X-ray spectra that was introduced by Muerset et al. based upon observations with the ROSAT satellite, to include a new ? classification for sources with hard X-ray emission from the innermost accretion region. Because we have identified the elusive accretion component in the emission from a sample of symbiotic stars, our results have implications for the understanding of wind-fed mass transfer in wide binaries, and the accretion rate in one class of candidate progenitors of type Ia supernovae. Tables 1 and 3 are available in electronic form at

Luna, G. J. M.; Sokoloski, J. L.; Mukai, K.; Nelson, T.



UV-Luminosity Function to z 3 with the UKIDSS UDS Survey  

NASA Astrophysics Data System (ADS)

The star formation history is a key-element to understand galaxy evolution and formation. Recent studies have shown that the star-formation rate peaks at redshift z=1-3 and then decline to its local value. The physical processes responsible for the sudden quenching of star-formation are still unknown. In order to better understand the origin of these effects, we propose in this study to use the UV-luminosity as an indicator of the Star-formation rate. We take advantage of our deep NIR/optical data from the UKIDSS-UDS/SXDS survey and our very deep CFHT U-band data to compute the luminosity function of galaxies at z=1-3. Fitting the Schechter parameters to integrate luminosity density to explore the evolution of the Star-formation rate.

Lo, C.-M.; Foucaud, S.; Grützbauch, R.; Hartley, W.; Simpson, C.; Almaini, O.



Mapping H_2 Emission Around T Tauri Stars  

NASA Astrophysics Data System (ADS)

We will study the distribution of circumstellar dust and molecular {H_2} gas around six classical T Tauri stars {cTTS}. We will probe both the near circumstellar environment {the accretion disk} as well as the environment further out where strong winds from these stars may be interacting with remnants of the cloud material from which they formed. The primary goal is to map the distribution of the molecular gas around cTTS. All our proposed targets show UV fluorescent H_2 emission {Johns-Krull et al. 1997; Valenti et al. 1997}, and are therefore expected to show IR molecular hydrogen emission. These images will reveal what fraction of the H_2 emission is produced in the warm circumstellar disks surrounding young these stars. The morphology of the extended emission will constrain collimation processes that focus the outflows from these stars. Combined with our UV data, these observations will allow us to test the thermal+fluorescent excitation model of molecular hydrogen {Black & van Dishoeck 1987}. These data, combined with future HST UV imaging and long-slit spectroscopy {STIS and ground-based IR} will provide very tight constraints on the physical conditions and excitation mechanisms present in the gaseous circumstellar environments of these stars.

Johns-Krull, Christopher



Star Formation in Galaxies  

NASA Astrophysics Data System (ADS)

The process of star formation is at the core of the evolutionary cycle of galaxies, as newborn stars produce new chemical elements, dust, and light. The energetic output delivered first by stellar winds and then by supernovae a few Myr after a star formation episode may also directly impact on the evolution of galaxies and their interstellar medium (ISM), as well as having an effect on the intergalactic medium (IGM), through feedback and outflows.This chapter concerns star formation on galactic scales. First, the galactic processes that may affect large-scale star formation are presented. Second, the various methods to measure star formation rates are discussed (star formation tracers, timescales, calibrations, limits). Finally, the observational status concerning star formation in galaxies (its relation to other quantities and its evolution) is presented. The Schmidt Law (star formation rate-gas relationship) is amply discussed.

Boissier, Samuel


Phase Resolved UV Spectroscopy of the Peculiar Binary V Sge  

NASA Astrophysics Data System (ADS)

The close binary system V Sge is an extremely unusual object. It is thought to be related to cataclysmic variables or low mass X-ray binaries, though it is not clear if the compact accreting star is a white dwarf, neutron star or black hole. The light curve of V Sge shows deep primary and shallow secondary eclipses, while the optical spectra have shown that it is undergoing rapid mass loss in a wind. V Sge may represent a short--lived stage in the evolution of interacting binaries that has otherwise not been observed. It has faded significantly in the last 30 years. Optical spectroscopy and UV studies with IUE have led to contradictory conclusions for the model of the system. This problem is probably due to the low spectral resolution of the time-resolved IUE spectra. We will use the GHRS on HST to obtain high time-resolution, high spectral-resolution UV spectroscopy. With the G160M grating in WSCAN mode we will observe the the CIV 1549Angstrom doublet to investigate the mass loss and the HeII 1641Angstrom line to relate this to the behaviour of the underlying system. We will use the changes in the line profiles throughout the orbit and through the primary and secondary eclipses to determine the origin of the UV light and the structure of the system.

Wood, Janet



Mapping the Dark Matter From UV Light at High Redshift: An Empirical Approach to Understand Galaxy Statistics  

SciTech Connect

We present a simple formalism to interpret the observations of two galaxy statistics, the UV luminosity function (LF) and two-point correlation functions for star-forming galaxies at z {approx} 4, 5 and 6 in the context of {Lambda}CDM cosmology. Both statistics are the result of how star formation takes place in dark matter halos, and thus are used to constrain how UV light depends on halo properties, in particular halo mass. The two physical quantities we explore are the star formation duty cycle, and the range of UV luminosity that a halo of mass M can have (mean and variance). The former directly addresses the typical duration of star formation activity in halos while the latter addresses the averaged star formation history and regularity of gas inflow into these systems. In the context of this formalism, we explore various physical models consistent with all the available observational data, and find the following: (1) the typical duration of star formation observed in the data is {approx}< 0.4 Gyr (1{sigma}), (2) the inferred scaling law between the observed L{sub UV} and halo mass M from the observed faint-end slope of the luminosity functions is roughly linear out to M {approx} 10{sup 11.5} - 10{sup 12} h{sup -1} M{sub {circle_dot}} at all redshifts probed in this work, and (3) the observed L{sub UV} for a fixed halo mass M decreases with time, implying that the star formation efficiency (after dust extinction) is higher at earlier times. We explore several different physical scenarios relating star formation to halo mass, but find that these scenarios are indistinguishable due to the limited range of halo mass probed by our data. In order to discriminate between different scenarios, we discuss the possibility of using the bright-faint galaxy cross-correlation functions and more robust determination of luminosity-dependent galaxy bias for future surveys.

Lee, Kyoung-Soo; /Yale Ctr. Astron. Astrophys.; Giavalisco, Mauro; /Massachusetts U., Amherst; Conroy, Charlie; /Princeton U. Observ.; Wechsler, Risa H; /KIPAC, Menlo Park; Ferguson, Henry C.; Somerville, Rachel S.; /Baltimore, Space Telescope Sci.; Dickinson, Mark E.; /NOAO, Tucson; Urry, Claudia M.; /Yale Ctr. Astron. Astrophys.



The Symmetry of Nearby Spiral Galaxies in Galex UV & Halpha Images  

Microsoft Academic Search

In order to find the relationship between the spatial distribution of star forming regions and physical parameters of spiral galaxies, we are studying the rotational symmetry of several hundred nearby spiral galaxies observed by GALEX (Galaxy Evolution Explorer) in the UV and as part of the Carnegie Halpha imaging survey. We have deprojected the galaxy images and computed the degree

Y. H. Joe; B. F. Madore; A. Gil de Paz; S. Boissier; Y.-W. Lee; J. Rhee; S.-C. Rey



Future Far-UV Studies of Hot White Dwarfs  

NASA Astrophysics Data System (ADS)

We are beginning to understand the evolution of the hot white dwarfs, but even with telescopes such as IUE and HST, we have still only observed a modest number of the most interesting objects with the spectral resolution and signal-to-noise required. This is in part arises from the intense competition for HST time, against both optical and IR observations as well as other far-UV bids. A key requirement of any new far-UV telescope is sufficient sensitivity to observe most of the ~100 or so brightest hot white dwarfs at high spectral resolution. A spectral resolving power of at least 30,000 is required for studies of white dwarfs. First it is necessary to detect and resolve photospheric, circumstellar and interstellar absorption features. Interstellar/circumstellar features may have several components that can only be separated in velocity space. For example, it is interesting to note that IUE was unable to resolve the photospheric and circumstellar CIV components of G191-B2B, discovered by the HST STIS instrument, leading to a serious overestimate of the carbon abundance in this star. There may be similar components in other stars observed only by IUE. In those stars that have highly stratified atmospheres, the detailed shape of the absorption lines is sensitive to the atmospheric structure. High-resolution observations of the line shapes can provide us with a direct probe of atmospheric structure.

Barstow, M. A.


Red Leak Characterization for the WFPC2 UV Filters  

NASA Astrophysics Data System (ADS)

We characterize the red leaks for all eight WFPC2 UV filters (F122M, F160BW, F170W, F185W, F218W, F250W, F300W, and F336W). We crossed each UV filter with three broad band optical filters (F450W, F606W, and F814W) in order to isolate different spectral regions in the red leak. We observed 15 Mon, an O7Ve-type star, using five different pointings to position the star at different locations on three WFPC2 chips (PC1, WF2, and WF3) to study possible filter inhomogeneities. We also observed g Gem, a K4III-type star, with WF3 as a follow-up to further study selected filters. Our results for F160BW, F170W, F300W, and F336W show good agreement (within 20%) between the observed off-band count rates and those predicted by SYNPHOT. Filters F185W, F218W, and F255W showed significant discrepancies between the observed and predicted values (20% to 250%); we derived new throughput curves for these filters, and delivered them to CDBS. The F122M filter shows evidence for a long-term throughput decline and will require additional studies beyond the scope of this report.

Lim, P. L.; Chiaberge, M.; Biretta, J.; di Nino, D.



III-Nitride UV Devices  

NASA Astrophysics Data System (ADS)

The need for efficient, compact and robust solid-state UV optical sources and sensors had stimulated the development of optical devices based on III-nitride material system. Rapid progress in material growth, device fabrication and packaging enabled demonstration of high efficiency visible-blind and solar-blind photodetectors, deep-UV light-emitting diodes with emission from 400 to 250 nm, and UV laser diodes with operation wavelengths ranging from 340 to 350 nm. Applications of these UV optical devices include flame sensing; fluorescence-based biochemical sensing; covert communications; air, water and food purification and disinfection; and biomedical instrumentation. This paper provides a review of recent advances in the development of UV optical devices. Performance of state-of-the-art devices as well as future prospects and challenges are discussed.

Asif Khan, M.; Shatalov, M.; Maruska, H. P.; Wang, H. M.; Kuokstis, E.



Estrogenic activity of UV filter mixtures  

Microsoft Academic Search

UV-absorbing chemicals (UV filters) are widely used for protection against UV radiation in sunscreens and in a variety of cosmetic products and materials. Depending on the breadth and factor of UV protection, they are added as single compounds or as a combination thereof. Some UV filters have estrogenic activity, but their activity and interactions in mixtures are largely unknown. In

Petra Y.. Kunz; Karl. Fent



Photometry of XX Cam, UV Cas, and SU Tau in the optical and infrared ranges  

SciTech Connect

The results of UBVRJHK photometry of three stars of the R CrB type, XX Cam, UV Cas, and SU Tau, at maximum light are presented. The observed energy distribution in the spectrum of XX Cam corresponds to the spectral class G3 I and no infrared emission excess is detected. The energy distribution in the spectrum of UV Cas, with allowance for interstellar absorption, corresponds to the spectral class F7 I and an emission excess in the infrared region is absent. The question of the affiliation of XX Cam and UV Cas to the R CrB type is discussed. The energy distribution in the spectrum of SU Tau, with allowance for interstellar absorption, corresponds to the spectral class F8 I. An infrared excess is detected, comprising approx.60% of the star's emission in the K band. This excess is interpreted as the emission of a circumstellar dust shell with a temperature of < or =900 /sup 0/K.

Shenavrin, V.I.



Pursuing Local Group blue massive stars with WSO-ISSIS  

NASA Astrophysics Data System (ADS)

The Local Group galaxies enable us to study the impact of metallicity on the structure and evolution of massive stars through spectroscopic analyses. However, color-based target selection for spectroscopy (in absence of known spectral types), though relatively successful, usually produces lists dominated by B-type modest-mass stars. We have developed a friends of friends code to find OB associations in Local Group galaxies (Garcia et al. in Astron. Astrophys. 502:1015, 2009; Bull. Soc. R. Sci. Liege 80:381, 2011a). The interpretation of the association's color-magnitude diagrams (CMDs) and the automatic determination of evolutionary masses for the members, allow a more insightful choice of candidates for spectroscopy and to spot out potential advanced evolutionary stages (Garcia et al. in Astron. Astrophys. 523:A23, 2010). We show our results on the dwarf irregular IC 1613 as illustration of the potential of the method. Because of its large field of view and high spatial resolution at ultraviolet (UV) wavelengths, ISSIS at the WSO is a powerful discovery machine of resolved blue massive stars in nearby galaxies. Our code can be easily modified to choose candidate OB stars based on ISSIS magnitudes on the UV, where hot young massive stars are intrinsically brighter and their color degeneracy is broken. The combination of our algorithm and ISSIS's panchromatic photometry can readily produce a list of the most massive stars of the Local Group.

Garcia, Miriam



[Ozone decline and UV increase].  


The following results have been obtained from long-term observations on the ozone layer and UV at the Meteorological Observatory Hohenpeigenberg:The seasonally varying decline of the ozone layer determines the maximum exposure to UV. Since ozone decline shows the highest rates in the spring months the UV exposure has most strongly increased in this time of the year. This is especially important because in spring the human skin is not adapted to UV exposure. Weather changes from day to day can induce rapid ozone reductions in spring about -30% which in turn is followed by an increase in UV of about 40%. Clouds, especially the transparent cirrus clouds (high clouds consisting of ice particles) have increased in frequency during spring and fall while a decrease is observed in summer. This change in cloudiness reduces the daily UV dose in spring and fall while it is enhanced in summer. With increasing height above sea level UV rises by roughly 10% per 1000 m (rule of thumb). Snow reflects the UV-radiation by up to 80% enhancing the UV-doses at relevant conditions. Strong volcano eruptions destroy ozone in the stratosphere additionally during 1-2 years after the eruption. Therafter the ozone layer recovers. In April 1993, after the eruption of Mt. Pinatubo (1991), the UV burden was still 40% higher than average. Miniholes and streamers can appear unexpected on a short-time scale and cross over Central Europe within 1-2 days, thus enhancing UV irradiation. The human skin reacts to UV exposure depending on the type of skin. The campaign "Sonne(n) mit Verstand" of the Bavarian Ministries for Environment, for Health and for Education informs about the danger of UV radiation (see The German Weather Service informs the public on present developments of the ozone layer and relevant topics byits ozone bulletin, which is also available via internet under ( PMID:14770335

Winkler, P; Trepte, S



UV spectrum of Enceladus  

NASA Astrophysics Data System (ADS)

We present a far ultraviolet (FUV) spectrum of Saturn's moon Enceladus from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST). We have put upper limits on emission from C, N, and O lines in Enceladus' atmosphere and column densities for the C lines assuming solar resonance scattering. We find these upper limits to be relatively low—on the order of tens to thousands of Rayleighs and with C column densities on the order of 108-1015 cm-2, depending on the assumed source size. We also present a segment of a reflectance spectrum in the FUV from ˜1900-2130 Å. This region was sensitive to the different ice mixtures in the model spectra reported by Hendrix et al. (Hendrix, A.R., Hansen, C.J., Holsclaw, G.M. [2010]. Icarus, 206, 608). We find the spectrum brightens quickly longward of ˜1900 Å, constraining the absorption band observed by Hendrix et al. from ˜170 to 190 nm. We find our data is consistent with the suggestion of Hendrix et al. of the presence of ammonia ice (or ammonia hydrate) to darken that region, and also possibly tholins to darken the mid-UV, as reported by Verbiscer et al. (Verbiscer, A.J., French, R.G., McGhee, C.A. [2005]. Icarus, 173, 66).

Zastrow, Mark; Clarke, John T.; Hendrix, Amanda R.; Noll, Keith S.



Diffuse UV Background  

NASA Astrophysics Data System (ADS)

We propose a LEGACY project, with the aim of characterizing the diffuse ultraviolet background radiation. In order to achieve maximum impact, we propose to observe exclusively targets for which we already have in hand Voyager diffuse - background spectra (shortward of Lyman alpha). Our Voyager spectroscopy will allow powerful insight into the interpretation and meaning of the deep GALEX images longward of Lyman alpha that we propose (here) to obtain. There is good evidence that a substantial portion of the diffuse UV background at moderate and high Galactic latitudes is exotic in its origin - that is, that the radiation is not simply diffuse galactic light plus the integrated light of distant galaxies. We propose to find clues to the nature and physical origin of the diffuse ultraviolet background radiation in as comprehensive a manner as can be accomplished using GALEX. But in the course of carrying out the proposed work, we will also be creating a permanent GALEX archive of well-chosen deep images that are supported by spectroscopy - images valuable for a wide range of purposes beyond those that we propose. To speed this broader use, we waive all data rights.

Henry, Richard


Astronomy: A Star Party  

NSDL National Science Digital Library

This lesson is designed to teach students about the functions of a telescope, the daylight uses of a telescope, the parts of the telescope, and to identify and view certain stars and planets during a star party at night.


Quark core stars, quark stars and strange stars  

SciTech Connect

A recent one flavor quark matter equation of state is generalized to several flavors. It is shown that quarks undergo a first order phase transition. In addition, this equation of state depends on just one parameter in the two flavor case, two parameters in the three flavor case, and these parameters are constrained by phenomenology. This equation of state is then applied to the hadron-quark transition in neutron stars and the determination of quark star stability, the investigation of strange matter stability and possible strange star existence. 43 refs., 6 figs.

Grassi, F.




SciTech Connect

Binarity is believed to dramatically affect the history and geometry of mass loss in asymptotic giant branch (AGB) and post-AGB stars, but observational evidence of binarity is sorely lacking. As part of a project to look for hot binary companions to cool AGB stars using the Galaxy Evolution Explorer archive, we have discovered a late-M star, Y Gem, to be a source of strong and variable UV emission. Y Gem is a prime example of the success of our technique of UV imaging of AGB stars in order to search for binary companions. Y Gem's large and variable UV flux makes it one of the most prominent examples of a late-AGB star with a mass accreting binary companion. The UV emission is most likely due to emission associated with accretion activity and a disk around a main-sequence companion star. The physical mechanism generating the UV emission is extremely energetic, with an integrated luminosity of a few x L{sub sun} at its peak. We also find weak CO J = 2-1 emission from Y Gem with a very narrow line profile (FWHM of 3.4 km s{sup -1}). Such a narrow line is unlikely to arise in an outflow and is consistent with emission from an orbiting, molecular reservoir of radius 300 AU. Y Gem may be the progenitor of the class of post-AGB stars which are binaries and possess disks but no outflows.

Sahai, Raghvendra [Jet Propulsion Laboratory, MS 183-900, California Institute of Technology, Pasadena, CA 91109 (United States); Neill, James D. [California Institute of Technology, 1200 E. California Blvd. MC278-17, Pasadena, CA 91125 (United States); Gil de Paz, Armando [Dpto. de Astrofisica, Universidad Complutense de Madrid, E-28040 Madrid (Spain); Sanchez Contreras, Carmen [Astrobiology Center (CSIC-INTA), ESAC campus, E-28691 Villanueva de la Canada, Madrid (Spain)




SciTech Connect

We examine the global properties of the stellar and H I components of 229 low H I mass dwarf galaxies extracted from the ALFALFA survey, including a complete sample of 176 galaxies with H I masses <10{sup 7.7} M{sub Sun} and H I line widths <80 km s{sup -1}. Sloan Digital Sky Survey (SDSS) data are combined with photometric properties derived from Galaxy Evolution Explorer to derive stellar masses (M{sub *}) and star formation rates (SFRs) by fitting their UV-optical spectral energy distributions (SEDs). In optical images, many of the ALFALFA dwarfs are faint and of low surface brightness; only 56% of those within the SDSS footprint have a counterpart in the SDSS spectroscopic survey. A large fraction of the dwarfs have high specific star formation rates (SSFRs), and estimates of their SFRs and M{sub *} obtained by SED fitting are systematically smaller than ones derived via standard formulae assuming a constant SFR. The increased dispersion of the SSFR distribution at M{sub *} {approx}< 10{sup 8} M{sub Sun} is driven by a set of dwarf galaxies that have low gas fractions and SSFRs; some of these are dE/dSphs in the Virgo Cluster. The imposition of an upper H I mass limit yields the selection of a sample with lower gas fractions for their M{sub *} than found for the overall ALFALFA population. Many of the ALFALFA dwarfs, particularly the Virgo members, have H I depletion timescales shorter than a Hubble time. An examination of the dwarf galaxies within the full ALFALFA population in the context of global star formation (SF) laws is consistent with the general assumptions that gas-rich galaxies have lower SF efficiencies than do optically selected populations and that H I disks are more extended than stellar ones.

Huang Shan; Haynes, Martha P.; Giovanelli, Riccardo [Center for Radiophysics and Space Research, Space Sciences Building, Cornell University, Ithaca, NY 14853 (United States); Brinchmann, Jarle [Sterrewacht Leiden, Leiden University, NL-2300 RA Leiden (Netherlands); Stierwalt, Sabrina [Spitzer Science Center, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125 (United States); Neff, Susan G., E-mail:, E-mail:, E-mail:, E-mail:, E-mail:, E-mail: [NASA GSFC, Code 665, Observational Cosmology Lab, Greenbelt, MD 20771 (United States)



Star formation in irregular galaxies  

Microsoft Academic Search

The problems associated with star formation in irregular galaxies are outlined. The basic model of star formation is reviewed. Global star formation rates, feedback processes, the physical conditions of the interstellar medium which affect star formation, and the internal structures of star-forming regions in irregular galaxies are discussed. In addition, star formation in the amorphous irregular galaxies described by Sandage

D. A. Hunter; J. S. Gallagher III



QCD in Neutron Stars and Strange Stars  

SciTech Connect

This paper provides an overview of the possible role of Quantum Chromo Dynamics (QCD) for neutron stars and strange stars. The fundamental degrees of freedom of QCD are quarks, which may exist as unconfined (color superconducting) particles in the cores of neutron stars. There is also the theoretical possibility that a significantly large number of up, down, and strange quarks may settle down in a new state of matter known as strange quark matter, which, by hypothesis, could be more stable than even the most stable atomic nucleus, {sup 56}Fe. In the latter case new classes of self-bound, color superconducting objects, ranging from strange quark nuggets to strange quark stars, should exist. The properties of such objects will be reviewed along with the possible existence of deconfined quarks in neutron stars. Implications for observational astrophysics are pointed out.

Weber, Fridolin [Department of Physics, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-1233 (United States); Negreiros, Rodrigo [FIAS, Goethe University, Ruth Moufang Str 1, 60438 Frankfurt (Germany)



Managing the star performer.  


Our culture seems to be endlessly fascinated with its stars in entertainment, athletics, politics, and business, and holds fast to the idea that extraordinary talent accounts for an individual's extraordinary performance. At first glance, managing a star performer in your medical practice may seem like it would be an easy task. However, there's much more to managing a star performer than many practice managers realize. The concern is how to keep the star performer happy and functioning at a high level without detriment to the rest of the medical practice team. This article offers tips for practice managers who manage star performers. It explores ways to keep the star performer motivated, while at the same time helping the star performer to meld into the existing medical practice team. This article suggests strategies for redefining the star performer's role, for holding the star performer accountable for his or her behavior, and for coaching the star performer. Finally, this article offers practical tips for keeping the star performer during trying times, for identifying and cultivating new star performers, and for managing medical practice prima donnas. PMID:23767124

Hills, Laura


Superbursts from Strange Stars  

Microsoft Academic Search

Recent models of carbon ignition on accreting neutron stars predict superburst ignition depths that are an order of magnitude larger than those observed. We explore a possible solution to this problem, that the compact stars in low-mass X-ray binaries that have shown superbursts are in fact strange stars with a crust of normal matter. We calculate the properties of superbursts

Dany Page; Andrew Cumming



Dark Stars: D\\\\  

Microsoft Academic Search

The first phase of stellar evolution in the history of the universe may be Dark Stars, powered by dark matter heating rather than by fusion. Weakly interacting massive particles, which are their own antiparticles, can annihilate and provide an important heat source for the first stars in the universe. This and the previous contribution present the story of Dark Stars.

Douglas Spolyar; Katherine Freese; Paolo Gondolo; Anthony Aguirre; Peter Bodenheimer; Jeremy A. Sellwood; Naoki Yoshida



Dark Stars: Begynnelsen  

Microsoft Academic Search

The first phase of stellar evolution in the history of the universe may be Dark Stars, powered by dark matter heating rather than by fusion. Weakly interacting massive particles, which are their own antiparticles, can annihilate and provide an important heat source for the first stars in the universe. This and the following contribution present the story of Dark Stars.

Paolo Gondolo; Katherine Freese; Douglas Spolyar; Anthony Aguirre; Peter Bodenheimer; Jeremy A. Sellwood; Naoki Yoshida



The Neutron Star Census  

Microsoft Academic Search

The paucity of old isolated accreting neutron stars in ROSAT observations is used to derive a lower limit on the mean velocity of neutron stars at birth. The secular evolution of the population is simulated following the paths of a statistical sample of stars for different values of the initial kick velocity, drawn from an isotropic Gaussian distribution with mean

S. B. Popov; M. Colpi; A. Treves; R. Turolla; V. M. Lipunov; M. E. Prokhorov



Star Formation in Galaxies  

Microsoft Academic Search

Star formation on a galactic scale is regulated by the self-gravity of the gas, as shown by the Jeans-length spacing of giant cloud complexes along spiral arms and the sensitivity of the star formation rate to the gravitational stability parameter Q. Simple models based on this scenario reproduce the general properties of galactic star formation in both normal and starburst

B. G. Elmegreen



Theory of Star Formation  

Microsoft Academic Search

We review current understanding of star formation, outlining an overall theoretical framework and the observations that motivate it. A conception of star formation has emerged in which turbulence plays a dual role, both creating overdensities to initiate gravitational contraction or collapse, and countering the effects of gravity in these overdense regions. The key dynamical processes involved in star formation---turbulence, magnetic

Christopher F. McKee; Eve C. Ostriker



Analyzing Star Trails  

NSDL National Science Digital Library

In this activity, students examine a photograph of the night sky and answer questions about their observations. The picture, taken by a high school student in upstate New York, offers insight into the Earth's rotation, apparent star motion, the location of Polaris (the North Star), circumpolar constellations, and pointer stars.

Kluge, Steve


Star Trail Photography  

NSDL National Science Digital Library

This web page contains information about taking photographs of star trails, which illustrate the rotation of the Earth. The site provides techniques to take successful star trail photos, including a technique using a series of short exposures and assembling them with computer software. Techniques for including foreground images of ground objects are given. Examples of star trail photos are provided.

Peiker, E. J.



Eclipsing Binary Stars  

NSDL National Science Digital Library

Eclipsing Binary Stars model simulates the detection of eclipsing binary stars. In this method, the light curve from the combination of the two stars, and how it changes over time due to each star transiting (or being occulted or eclipsing the other), is observed and then analyzed. In this simulation each star orbits the other in circular motion via Kepler's third law.  When one star passes in front of the other (transits), it blocks part of the starlight of the other star. This decrease in starlight is shown on the graph.  In the simulation the binary star system is shown as seen from Earth (edge on view) and from overhead, but magnified greatly, and with the star sizes not shown to the scale of the orbit. The mass, radius, and temperature of each star can be changed. The simulation uses either simple 3D or Java 3D (if installed) to render the view the stars. If Java 3D is not installed, the simulation defaults to simple 3D using Java. The Eclipsing Binary Stars model was created using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_astronomy_eclipsing_binaries.jar file will run the program if Java is installed.

Belloni, Mario



Possible Sources of UV Radiation in Elliptical Galaxies  

NASA Astrophysics Data System (ADS)

We have compiled a sample of 519 nearby (z < 0.13) elliptical galaxies, selected by matching the Galaxy Evolution Explorer (GALEX) Medium Imaging Survey (MIS) with the Sloan Digital Sky Survey (SDSS) Fourth Data Release (DR4). Our galaxies are bright, with r < 16.8 and have FUV (far ultraviolet) an NUV (near ultraviolet) emission. We build a UV Color Magnitude Relation (CMR) using GALEX and SDSS photometric bands, and analyze the evolution of this CMR for these galaxies using stellar population synthesis models. We find that these galaxies may have suffered a small amount of recent residual star formation (1-2% of the galaxy mass). Extreme Horizontal Branch (EHB) stars can explain galaxies with 4 < NUV-r < 5.4.

Hernández, F. C.; Bruzual, G.



Cool stars, stellar systems, and the sun; Proceedings of the 6th Cambridge Workshop, Seattle, WA, Sept. 18-21, 1989  

SciTech Connect

The present conference on cool stars, stellar systems, and the sun encompasses stellar chromospheres and coronae, binary stars, the stellar evolution of contracting stars and red giants, stellar evolution abundances of the elements, mass loss and envelopes, and stellar pulsation. Specific issues addressed include theories regarding the acoustic and magnetic heating of stellar chromospheres and coronae, stellar granulation, wave heating in magnetic flux tubes, observations of the solar Ca-II lines, longitudinal-transverse magnetic tube waves in the solar atmosphere, radio emission from rapidly rotating cool giant stars, and spot temperatures and area coverages on active dwarf stars. Also addressed are the optical and UV spectra of RS-CVn stars, emission lines from T-Tauri stars, the spectroscopy of HR1614 group stars, red giants in external galaxies, the rotation of evolved stars, the transition from red giant to planetary nebula, and radiative transfer in the dynamic atmospheres of variable stars.

Wallerstein, G.; (Washington, University, Seattle)



The Galaxy Evolution Explorer (GALEX): A New View of the UV Universe  

NASA Astrophysics Data System (ADS)

The Galaxy Evolution Explorer (GALEX) has surveyed the ultraviolet sky for almost nine years. GALEX surveys have supported numerous galaxy evolution investigations: calibrating UV as a star formation rate tracer, using wide and deep surveys to measure star formation history, studying the evolution of dust extinction and metallicity, selecting and analyzing galaxies in transitory states, finding local analogs to Lyman Break Galaxies, probing and time-dating star formation in a wide variety of physical regimes, and probing star formation properties in low mass, low density settings. Archival data will support more complex investigations such as relating star formation history and galaxy evolution paths to the properties of dark matter halos and their assembly history, and beginning to relate the evolution of galaxies to that of black holes and the intergalactic medium. Over and above GALEX's study of galaxy evolution the surveys have: found all UV bright QSOs at low and high redshift, discovering tidal capture flares from inactive black holes, discovering shock breakout flashes from distant supernovae, selecting a sample of galaxies for Baryon Acoustic Oscillation surveys, and in our own Milky Way, discovering and diagnosing spectacular new stellar wind nebulae from aging, mass- losing stars.

Wyder, Ted; Martin, Christopher



The Giants Stars HE 0107-5240 and HE 0557-4840 and New Searches for Metal-Poor Stars  

NASA Astrophysics Data System (ADS)

We report on a new determination of the iron abundance of HE 0107-5240, based on the detection of two Fe II lines in an UV spectrum of the star, which yields [Fe/H] = -5.7. Another interesting metal-poor star recently discovered with Hamburg/ESO Survey (HES) is HE 0557-4840. With [Fe/H] = -4.8, it is the first star located in the ``gap'' in the metallicity distribution function of the galactic halo, in metallicity between the two stars known at [Fe/H]>-4.0. HE 0557-4840 is carbon-enhanced (i.e., [C/Fe] = +1.7). The abundance ratios of the heavier elements are similar to those seen in the majority of the metal-poor stars at [Fe/H]>-4.0. We also describe two upcoming wide-angle surveys which will be used for searches for metal-poor stars: The Southern Sky Survey (SSS), and a stellar survey to be conducted with the Chinese LAMOST telescope. These efforts are expected to increase the number of known extremely metal-poor stars, including stars below [Fe/H] = -5.0, by about two orders of magnitude.

Christlieb, Norbert; Korn, Andreas J.; Eriksson, Kjell; Bessell, Michael S.; Norris, John E.; Keller, Stefan C.; Zhao, Yongheng; Zhang, Haotong; Beers, Timothy C.



UV-LED photopolymerised monoliths.  


For the first time photopolymerisation of polymer monoliths has been realised with UV-light emitting diodes (LEDs) as light source and demonstrated with polymethacrylate monoliths created in fused silica capillaries and plastic chips. PMID:18575635

Abele, Silvija; Nie, Fu-Qiang; Foret, Frantisek; Paull, Brett; Macka, Mirek



Star Formation Rate at z = 0.2 derived from H_alpha luminosities: constraint on the reddening  

Microsoft Academic Search

We discuss the relative merits of using UV and H_alpha as star formation\\u000aindicators from galaxy surveys. In particular, comparing UV and H_alpha in the\\u000aCFRS gives a limit of a factor 2.5 for the UV(2800 Angs.) flux extinction from\\u000adust, using the conversion factors of Madau et al. 1998 (Salpeter IMF, 0.1-125\\u000asolar mass). Our strong correlation between B

Laurence Tresse; Steve J. Maddox



Star Formation Rate at Z = 0.2 derived from H alpha luminosities: constraint on the reddening  

Microsoft Academic Search

We discuss the relative merits of using UV and H_alpha as star formation indicators from galaxy surveys. In particular, comparing UV and H_alpha in the CFRS gives a limit of a factor 2.5 for the UV(2800 Angs.) flux extinction from dust, using the conversion factors of Madau et al. 1998 (Salpeter IMF, 0.1-125 solar mass). Our strong correlation between B

L. Tresse; S. J. Maddox




SciTech Connect

Galaxy Evolution Explorer observations of IC 3418, a low surface brightness galaxy in the Virgo Cluster, revealed a striking 17 kpc UV tail of bright knots and diffuse emission. H{alpha} imaging confirms that star formation is ongoing in the tail. IC 3418 was likely recently ram pressure stripped on its first pass through Virgo. We suggest that star formation is occurring in molecular clouds that formed in IC 3418's turbulent stripped wake. Tides and ram pressure stripping (RPS) of molecular clouds are both disfavored as tail formation mechanisms. The tail is similar to the few other observed star-forming tails, all of which likely formed during RPS. The tails' morphologies reflect the forces present during their formation and can be used to test for dynamical coupling between molecular and diffuse gas, thereby probing the origin of the star-forming molecular gas.

Hester, Janice A.; Neill, James D.; Wyder, Ted K.; Martin, D. Christopher [California Institute of Technology, Pasadena, CA 91125 (United States); Seibert, Mark; Madore, Barry F. [Observatories of the Carnegie Institute of Washington, Pasadena, CA 91101 (United States); Gil de Paz, Armando [Dpto. de Astrofisica, Universidad Computense de Madrid, Madrid 28040 (Spain); Schiminovich, David [Department of Astronomy, Columbia University, New York, NY 10027 (United States); Rich, R. Michael, E-mail: jhester@srl.caltech.ed [Department of Physics and Astronomy, Division of Astronomy and Astrophysics, University of California, Los Angeles, CA 90095 (United States)



Star formation in the Eagle Nebula and NGC 6611  

NASA Astrophysics Data System (ADS)

M16, also known as the Eagle Nebula, is a prime example for the study of star formation under the hostile environment created by massive O-stars. A rich young stellar population (NGC6611) has been identified. The well-known elephant trunks are striking examples of the massive star feedback into the parent molecular cloud. The detection of several water maser sources as well as embedded IR objects points at current star formation. I will present an overview of our recent observations that aim at characterising not only the young pre-main-sequence (PMS) and their disc, but also the still embedded population. We have discovered a rich population of low-mass PMS stars concentrated around the massive stars and the first results show that the IMF in NGC6611 is consistent with the IMF in less extreme star forming regions. I am using VLT/ VIMOS spectroscopy to determine reddening, effective temperature and gravity for a sample of ~260 cluster candidates to test the validity of the photometric techniques. We have been awarded HST observations to extend the optical and near-IR survey down to brown dwarfs and planetary mass objects. Recent theoretical developments propose that the density in the molecular cloud and/or the UV radiation from O-stars may play an role in shaping the low-mass IMF, with the signs of such influence enhanced in the brown-dwarf regime. Our HST observations will help disentangle these two effects on the IMF. We have also conducted a deep survey of the central area of NGC 6611 in L-band to determine the fraction of low-mass stars with circumstellar discs. The K-L colours indicate that 58% of objects retain their circumstellar discs, implying that the O-stars might not significantly hasten disc dissipation. We are complementing our data on NGC6611 with Spitzer/IRAC data for the outer regions where crowding is less severe, allowing us to investigate disc properties like inner disc temperature and geometry. Star formation is still ongoing in the denser regions of the nebula. We are using VLT/VISIR imaging to identify young stars embedded in dense cores and clumps, and map the emission from the dust and ionised gas across these structures. This will allow us to assess the eroding effect of the NGC6611 massive stars on the molecular cloud and on star formation occurring within. massive stars on the molecular cloud and on star formation occurring within. Star formation is still ongoing in the denser regions of the nebula. I will be using VLT/VISIR imaging to identify young stars still embedded in dense cores and clumps, and map the emission from the dust and ionised gas across these structures. This will allow us to assess the eroding effect of the NGC6611 massive stars on the molecular cloud and on star formation occurring within. imply that the O-stars have little influence in hastening disc dissipation. We are complementing our data on NGC 6611 with Spitzer/IRAC data for the outer regions where crowding is less severe. This also allows us to investigate disc properties (e.g., inner disc temperature and geometry). Star formation is still ongoing in the denser regions of the nebula. I will be using VLT/VISIR imaging to identify young stars still embedded in dense cores and clumps, and map the emission from the dust and ionised gas across these structures. This will allow us to assess the eroding effect of the NGC6611 massive stars on the molecular cloud and on star formation occurring within.

Oliveira, J. M.; Jeffries, R. D.; van Loon, J. Th


Evolution of variable stars  

SciTech Connect

Throughout the domain of the H R diagram lie groupings of stars whose luminosity varies with time. These variable stars can be classified based on their observed properties into distinct types such as ..beta.. Cephei stars, delta Cephei stars, and Miras, as well as many other categories. The underlying mechanism for the variability is generally felt to be due to four different causes: geometric effects, rotation, eruptive processes, and pulsation. In this review the focus will be on pulsation variables and how the theory of stellar evolution can be used to explain how the various regions of variability on the H R diagram are populated. To this end a generalized discussion of the evolutionary behavior of a massive star, an intermediate mass star, and a low mass star will be presented. 19 refs., 1 fig., 1 tab.

Becker, S.A.



Stars main sequence  

NSDL National Science Digital Library

What happens during most of a star's life? This activity page, part of an interactive laboratory series for grades 8-12, introduces students to the main sequence phase of a star's existence. This phase is where a star lives out the majority of its life. In an interactive lab activity, students predict the length of the main sequence for four different stars. The predictions can be printed for later evaluation. Students view diagrams that compare the size and color of stars to human lives, and equilibrium within a star is stressed. Finally, students choose between two hypotheses about the length of life of a star. Students write a one- to three-sentence explanation for their hypotheses. The correct answer is provided. Copyright 2005 Eisenhower National Clearinghouse

University of Utah. Astrophysics Science Project Integrating Research and Education (ASPIRE)



Star Formation Triggering Mechanisms in Dwarf Galaxies: The Far-Ultraviolet, H-alpha, and HI Morphology of Holmberg II  

Microsoft Academic Search

Far-UV (FUV), H-alpha, and HI observations of dwarf galaxy Holmberg II are\\u000aused to trace the interaction between sites of massive star formation and the\\u000aneutral and ionized components of the surrounding ISM. The data emphasize the\\u000aimportance of local conditions in regulating star formation from evidence such\\u000aas massive stars inside ionized shells, compact HII regions surrounding aging\\u000aclusters,

Susan G. Stewart; Michael N. Fanelli; Gene G. Byrd; Jesse K. Hill; David J. Westpfahl; K. P. Cheng; R. W. O'Connell; M. S. Roberts; S. G. Neff; A. M. Smith; T. P. Stecher



Rotation-Activity-Age Relations of Sun-like Stars: In Search of the Much Coveted Solar Twin  

Microsoft Academic Search

We present the current results of our ongoing investigation of the coronal (X-ray; Einstein\\/ROSAT), transition region (FUV; IUE\\/FUSE), and chromospheric (FUV-UV; IUE) emissions of single solar-type stars. By considering only main-sequence stars in a restricted range of spectral types ranging from F8 V to G8 V and stars with measured rotation periods, we have focused on the role of rotation

R. T. Hamilton; E. F. Guinan; L. E. DeWarf



The Effects of Episodic Star Formation on the FUV-NUV Colors of Star Forming Regions in Outer Disks  

NASA Astrophysics Data System (ADS)

We run stellar population synthesis models to examine the effects of a recently episodic star formation history (SFH) on UV and H? colors of star forming regions. Specifically, the SFHs we use are an episodic sampling of an exponentially declining star formation rate (SFR; ? model) and are intended to simulate the SFHs in the outer disks of spiral galaxies. To enable comparison between our models and observational studies of star forming regions in outer disks, we include in our models sensitivity limits that are based on recent deep UV and H? observations in the literature. We find significant dispersion in the FUV-NUV colors of simulated star forming regions with frequencies of star formation episodes of 1 × 10–8 to 4 × 10–9 yr–1. The dispersion in UV colors is similar to that found in the outer disk of nearby spiral galaxies. As expected, we also find large variations in L_{H_{\\alpha }}/L_{FUV}. We interpret our models within the context of inside-out disk growth, and find that a radially increasing ? and decreasing metallicity with an increasing radius will only produce modest FUV-NUV color gradients, which are significantly smaller than what is found for some nearby spiral galaxies. However, including moderate extinction gradients with our models can better match the observations with steeper UV color gradients. We estimate that the SFR at which the number of stars emitting FUV light becomes stochastic is ~2 × 10–6 M ? yr–1, which is substantially lower than the SFR of many star forming regions in outer disks. Therefore, we conclude that stochasticity in the upper end of the initial mass function is not likely to be the dominant cause of dispersion in the FUV-NUV colors of star forming regions in outer disks. Finally, we note that if outer disks have had an episodic SFH similar to that used in this study, this should be taken into account when estimating gas depletion timescales and modeling chemical evolution of spiral galaxies.

Barnes, Kate L.; van Zee, Liese; Dowell, Jayce D.



Diffuse Interstellar Bands in Lines of Sight toward Cool Stars  

NASA Astrophysics Data System (ADS)

We plan to investigate one of the most important open questions regarding the diffuse interstellar bands (DIBs), using the KPNO coude feed telescope and its moderade-resolution camera (Camera 5). The issue at hand is whether or not the DIBs require high far-UV flux levels to form efficiently. Nearly all of the existing data on the DIBs are based on spectroscopic measurements toward O and B stars, which have local H II regions where ample UV photon fluxes are present. But despite existing studies which show no dependence of DIB behavior on stellar spectral type, and other studies which which show a weakness of the DIBs in nebulous regions excited by far-UV flux, there remains some question about whether or not the DIB carriers require significant UV flux. This question is especially timely in view of a recent DIBs formation model in which a two-photon process in H_2 molecules is thought to form the DIBs (this model requires a very high far-UV photon flux and therefore will be vitiated if the DIBs are found to form in sightlines toward cool stars). Our proposed observations require six nights on the coude feed telescope, using Camera 5 to obtain a spectral resolving power of (lambda)/(Delta)$(lambda) 20,000 and S/N levels >=50, in the spectra of a number of F5 and G5 stars identified as being at least moderately reddened. Unreddened comparison stars will be observed as well, to ensure that we have removed stellar photospheric line contamination.

Snow, Theodore P.



VUV-UV absorption spectroscopy of DNA and UV screens suggests strategies for UV resistance during evolution and space travel  

Microsoft Academic Search

Early life on Earth had to cope with harsh conditions, including full spectrum solar UV. Since DNA absorbs in the highly energetic UV-C and VUV, solar irradiation was likely an obstacle to the expansion of life on Earth, until biological mechanisms evolved to cope with UV liability (including the biosynthesis of UV screens) and ozone (derived from oxygen produced by

Andreja Zalar; David Tepfer; Søren V. Hoffmann; Albert Kollmann; Sydney Leach



NuSTAR Observations of Bright AGNs  

NASA Astrophysics Data System (ADS)

The dramatically improved signal-to-noise provided by NuSTAR up to ~80 keV allows a qualitative change in our understanding of the X-ray emission of Active Galactic Nuclei (AGNs). Despite intensive investigation for over 30 years, during which the 0.1-10 keV spectra and variability of AGNs have been mapped out in detail, we do not know the origin of the X-ray source in AGNs. The "standard model" of supermassive black hole, accretion disk and relativistic jet does not predict an X-ray source in a straightforward way. It is usually assumed that the X-rays were UV photons from the accretion disk that have been Compton up-scattered in a "hot corona", but the temperature, optical depth and geometry of this corona are unknown - if it exists. NuSTAR enables the measurement of the high energy cut-off of the X-ray spectrum, and so the corona temperature, to be measured precisely for the first time, and tests the relativistic Fe-K line and Compton reflection models. If this model is correct then, with Suzaku and XMM-Newton, NuSTAR can measure black hole spins to high accuracy. We outline the NuSTAR GTO program on bright, unobscured, AGNs including simultaneous observations with Suzaku and XMM-Newton, and show early data.

Elvis, Martin; Ballantyne, D. R.; Blandford, R. D.; Boggs, S.; Boydstun, K.; Brenneman, L.; Cappi, M.; Christensen, F.; Craig, W.; Fabian, A.; Fuerst, F.; Guainazzi, M.; Hailey, C. J.; Harrison, F.; Madejski, G. M.; Marinucci, A.; Matt, G.; Nandra, K.; Reynolds, C. S.; Stern, D.; Walton, D.; Zhang, W.; NuSTAR Team



HST-STIS abundances in the uranium-rich very metal-poor star CS 31082-001  

NASA Astrophysics Data System (ADS)

The abundance derivation of heavy r-elements may provide a better understanding of the r-process, and the determination of several reference r-elements should allow a better determination of the star's age. The spatial ultraviolet (UV) region presents a large number of lines of heavy elements, and in some cases such as Bi, Pt, Au, detectable lines are only available in the UV. The extreme “r-process star” CS 31082-001 ([Fe/H] = -2.9) was observed in the spatial UV in order to determine abundances of the heavy elements, using STIS on board HST.

Barbuy, B.; Spite, M.; Hill, V.; Primas, F.; Plez, B.; Cayrel, R.; Sneden, C.; Spite, F.; Beers, T. C.; Andersen, J.; Nordström, B.; Bonifacio, P.; François, P.; Molaro, P.; Siqueira-Mello, C.



Modelling the spectral energy distribution of spiral galaxies from the UV to FIR/Submm  

NASA Astrophysics Data System (ADS)

We present new calculations of the attenuation of stellar light and dust emission from spiral galaxies. We use geometries for stars and dust which can reproduce the entire spectral energy distribution from the ultraviolet (UV) to the Far-infrared (FIR)/submillimeter (submm) and can also account for the surface brightness distribution in both the optical/Near-infrared (NIR) and FIR/submm. The calculations are based on the model of Popescu et al. (2000), which incorporates a dustless stellar bulge, a disk of old stars with associated diffuse dust, a thin disk of young stars with associated diffuse dust, and a clumpy dust component associated with star-forming regions in the thin disk.

Popescu, Cristina C.; Tuffs, Richard J.



Massive stars, disks, and clustered star formation  

NASA Astrophysics Data System (ADS)

The formation of an isolated massive star is inherently more complex than the relatively well-understood collapse of an isolated, low-mass star. The dense, clustered environment where massive stars are predominantly found further complicates the picture, and suggests that interactions with other stars may play an important role in the early life of these objects. In this thesis we present the results of numerical hydrodynamic experiments investigating interactions between a massive protostar and its lower-mass cluster siblings. We explore the impact of these interactions on the orientation of disks and outflows, which are potentially observable indications of encounters during the formation of a star. We show that these encounters efficiently form eccentric binary systems, and in clusters similar to Orion they occur frequently enough to contribute to the high multiplicity of massive stars. We suggest that the massive protostar in Cepheus A is currently undergoing a series of interactions, and present simulations tailored to that system. We also apply the numerical techniques used in the massive star investigations to a much lower-mass regime, the formation of planetary systems around Solar- mass stars. We perform a small number of illustrative planet-planet scattering experiments, which have been used to explain the eccentricity distribution of extrasolar planets. We add the complication of a remnant gas disk, and show that this feature has the potential to stabilize the system against strong encounters between planets. We present preliminary simulations of Bondi-Hoyle accretion onto a protoplanetary disk, and consider the impact of the flow on the disk properties as well as the impact of the disk on the accretion flow.

Moeckel, Nickolas Barry


Observations of a WO star in the LMC  

NASA Astrophysics Data System (ADS)

Oxygen sequence Wolf-Rayet stars (WO-type) represent the final, brief phase in the evolution of the most massive stars prior to a SN explosion. Their properties are truly extreme - temperatures are in excess of 100,000K, mass-loss rates typically one solar mass per 100,000 years, with the fastest winds of any `normal' star (approx 4,500 km/s!). However, of the known 300+ WR stars in the Galaxy and Magellanic Clouds, only five are of WO-type, characterised by extremely broad high excitation oxygen and carbon emission lines in their UV and optical spectra, with mammoth OVI 3811-34A emission, reaching 10 times the local continuum. Of these, solely Sanduleak 2 (= Brey 93) in the LMC is lightly reddened and single. FUSE observations will reveal a strong OVI 1032-1038A P Cygni profile, plus weaker oxygen, carbon and sulphur features. We will carry out a quantitative analysis of Sand 2 (WO3) to help address the exact evolutionary status of WO stars. FUSE data - specifically OVI (1032-1038, 1123), CIV (948, 1108) OIV (922) and SVI (939) will be combined with UV HST/FOS and optical ground-based observations plus state-of-the-art model atmosphere synthesis to allow improved atmospheric elemental abundances (He, C, O), mass-loss rate and wind velocity determinations.

Crowther, Paul A., , Dr


IUE and Einstein survey of late-type giant and supergiant stars and the dividing line  

SciTech Connect

Results are presented on an IUE UV survey of 255 late-type G, K, and M stars, complementing the Maggio et al. (1990) Einstein X-ray survey of 380 late-type stars. The large data sample of X-ray and UV detections make it possible to examine the activity relationship between the X-ray and the UV emissions. The results confirm previous finding of a trend involving a steeply-dropping upper envelope of the transition region line fluxes, f(line)/f(V), as the dividing line is approached. This suggests that a sharp decrease in maximum activity accompanies the advancing spectral type, with the dividing line corresponding to this steep gradient region. The results confirm the rotation-activity connection for stars in this region of the H-R diagram. 67 refs.

Haisch, B.M.; Bookbinder, J.A.; Maggio, A.; Vaiana, G.S.; Bennett, J.O. (Lockheed Research Laboratories, Palo Alto, CA (USA) Smithsonian Astrophysical Observatory, Cambridge, MA (USA) Osservatorio Astronomico, Palermo (Italy) Colorado Univ., Boulder (USA))



Numerical Simulations of Self-Regulated, Star Forming Galactic Disks  

NASA Astrophysics Data System (ADS)

While star formation feedback models have been used in the study of galaxy formation, the effects of these processes on the global structure of disks have received less attention. We have adapted Hydra, the adaptive particle-particle, particle-mesh with smoothed particle hydrodynamics code by Couchman et al., to include heating processes deriving from star formation in order to study the effects of this heating on the structure of the disk and on the star formation itself. These processes include mechanical heating from strong stellar winds and supernovae, as well as heating due to photoelectric removal of electrons from grains by UV flux from young OB stars. Mechanisms of this type can be implemented in a simple way within the Hydra code, allowing us to study the density and temperature profiles of the gas, the balance among the multiple thermal phases generated in the disk, and the kinematics of the disk. Preliminary results from numerical simulations of star-forming gas disks of late type spirals are presented. Self-regulating effects of star formation on the global structure of the disk are discussed. We describe and compare the results of different star formation criteria and discuss the effects of particle resolution. This study was funded, in part, by a grant from the George Washington Carver Charitable Trust.

Smith, D. C.; Struck, C.



Circumnuclear Rings: Probes of Star Formation and Galaxy Dynamics  

NASA Astrophysics Data System (ADS)

We propose to image the dense molecular gas associated with the star-forming circumnuclear ring (CNR) in the prototypical barred ringed galaxy NGC 1433, building on our successful observations of NGC 7552 in 2005. Our primary science goals include (1) comparing the locations of dense gas clouds with young UV-bright star clusters; (2) looking for an HCN enhancement relative to HCO+ in the nucleus, as has been reported in other Seyferts; and (3) deriving an inner rotation curve to test resonance ring theory. We request observations in H75 and H168 to produce a high-resolution image of the circumnuclear gas.

Wong, Tony; Dahlem, Michael; Ryder, Stuart; Kohno, Kotaro; Buta, Ron



Measuring UV radiation on inclined surfaces  

Microsoft Academic Search

In general measurements of UV-radiation are related to horizontal surfaces, as e.g. also done for the internationally standardized and applied UV-index. In order to get more information on biologically relevant UV-exposure, there is a need for quantitative data of radiation fluxes on tilted surfaces. UV exposure of the human skin is one of the most essential issues in UV research,

Andreas Oppenrieder; Peter Hoeppe; Peter Koepke; Jochen Reuder; Meinhard Seefeldner; Dieter Rabus



UV monitoring of sugars during wine making  

Microsoft Academic Search

A UV\\/UV system for the spectrophotometric determination of sugars during wine production is described. The methodology is based on the formation of a UV-absorbing byproduct produced by the photodegradation of sugars. Under the given experimental conditions, the influence of increasing the amount of acids and alcohol is negligible. The measurement by UV\\/UV is compared with FTIR as reference method and

B. Roig; O. Thomas



Star Show Classroom Activity  

NSDL National Science Digital Library

In this lesson from Math Machines, the class will "plan and conduct a simulated astronomical observing session to photgraph a variety of star types." The instructor will set up several "stars" around the classroom, and students will then set up a telescope location and estimate the altitude and azimuth to photograph each star. A participant handout (including worksheet) and facilitator notes are made available for download in DOC file format. Links to calculator programs are also included.

Thomas, Fred



Dark Stars: D\\\\\\  

Microsoft Academic Search

The first phase of stellar evolution in the history of the universe may be\\u000aDark Stars, powered by dark matter heating rather than by fusion. Weakly\\u000ainteracting massive particles, which are their own antiparticles, can\\u000aannihilate and provide an important heat source for the first stars in the\\u000auniverse. This and the previous contribution present the story of Dark Stars.

Douglas Spolyar; Katherine Freese; Paolo Gondolo; Anthony Aguirre; Peter Bodenheimer; Jeremy A. Sellwood; Naoki Yoshida



The Neutron Stars Census  

Microsoft Academic Search

The paucity of old isolated accreting neutron stars in ROSAT observations is\\u000aused to derive a lower limit on the mean velocity of neutron stars at birth.\\u000aThe secular evolution of the population is simulated following the paths of a\\u000astatistical sample of stars for different values of the initial kick velocity,\\u000adrawn from an isotropic Gaussian distribution with mean

S. B. Popov; M. Colpi; A. Treves; R. Turolla; V. M. Lipunov; M. E. Prokhorov



Impulsively Triggered Star Formation  

Microsoft Academic Search

I review several different modes of impulsively triggered star formation, starting with star formation in turbulent molecular\\u000a clouds, and exploring the origin of the clump mass function and the scaling relations between clump mass, radius and internal\\u000a velocity dispersion. This leads to the identification of a critical ram pres-sure for triggering rapid star formation, and\\u000a a reappraisal of the minimum

A. P. Whitworth



Preliminary Map Star Catalog  

NASA Astrophysics Data System (ADS)

As part of an ongoing study, the Allegheny Observatory is in the process of measuring high precision, (1 milliarcsec), parallaxes and proper motions for approximately 900 stars selected at random in the northern sky. The spectral type of these stars is also being determined from UBVRI, uvby, H-Beta, and DDO photometry. This catalog represents a unique and complete statistical set of data for 900 stars of visual magnitude 6-12. A preliminary catalog will be presented.

Persinger, T.; Gatewood, G.; Castelaz, M.



Our Super Star  

NSDL National Science Digital Library

Our star, the Sun, is an ordinary star. It is not particularly special compared to other stars in the universe; however, it is crucially important to us. As the massive energy source at the center of our solar system, the Sun is responsible for Earth's climate, weather, and life. In this lesson, students use observations, activities, and videos to learn basic facts about the Sun. Students also model the mechanics of day and night and use solar energy to make a tasty treat.

Foundation, Wgbh E.



Star Trek Generations  

NSDL National Science Digital Library

Paramount Pictures and Viacom Online have developed a World Wide Web site to herald the upcoming motion picture Star Trek Generations. The site offers a galaxy of unique Star Trek elements for downloading, including pictures, sounds and a preview of the movie, in addition to behind-the-scenes information. Make sure to give Paramount "Your Input"- all respondents will receive a digital version of the Star Trek Generations movie poster


Interpreting the observed UV continuum slopes of high-redshift galaxies  

NASA Astrophysics Data System (ADS)

The observed UV continuum slope of star-forming galaxies is strongly affected by the presence of dust. Its observation is then a potentially valuable diagnostic of dust attenuation, particularly at high redshift where other diagnostics are currently inaccessible. Interpreting the observed UV continuum slope in the context of dust attenuation is often achieved assuming the empirically calibrated Meurer et al. relation. Implicit in this relation is the assumption of an intrinsic UV continuum slope (? = -2.23). However, results from numerical simulations suggest that the intrinsic UV continuum slopes of high-redshift star-forming galaxies are bluer than this, and moreover vary with redshift. Using values of the intrinsic slope predicted by numerical models of galaxy formation combined with a Calzetti et al. reddening law we infer UV attenuations (A1500) 0.35-0.5 mag (AV: 0.14 - 0.2 mag assuming Calzetti et al. reddening law) greater than simply assuming the Meurer relation. This has significant implications for the inferred amount of dust attenuation at very high (z ? 7) redshift given current observational constraints on ?, combined with the Meurer relation, suggesting dust attenuation to be virtually zero in all but the most luminous systems.

Wilkins, Stephen M.; Bunker, Andrew; Coulton, William; Croft, Rupert; Matteo, Tiziana Di; Khandai, Nishikanta; Feng, Yu



The Slow Death (Or Rebirth?) of Extended Star Formation in z ~ 0.1 Green Valley Early-type Galaxies  

NASA Astrophysics Data System (ADS)

UV observations in the local universe have uncovered a population of early-type galaxies with UV flux consistent with low-level recent or ongoing star formation. Understanding the origin of such star formation remains an open issue. We present resolved UV-optical photometry of a sample of 19 Sloan Digital Sky Survey (SDSS) early-type galaxies at z ~ 0.1 drawn from the sample originally selected by Salim & Rich to lie in the bluer part of the green valley in the UV-optical color-magnitude diagram as measured by the Galaxy Evolution Explorer (GALEX). Utilizing high-resolution Hubble Space Telescope (HST) far-UV imaging provides unique insight into the distribution of UV light in these galaxies, which we call "extended star-forming early-type galaxies" (ESF-ETGs) because of extended UV emission that is indicative of recent star formation. The UV-optical color profiles of all ESF-ETGs show red centers and blue outer parts. Their outer colors require the existence of a significant underlying population of older stars in the UV-bright regions. An analysis of stacked SDSS spectra reveals weak LINER-like emission in their centers. Using a cross-matched SDSS DR7/GALEX GR6 catalog, we search for other green valley galaxies with similar properties to these ESF-ETGs and estimate that ?13% of dust-corrected green valley galaxies of similar stellar mass and UV-optical color are likely ESF-candidates, i.e., ESF-ETGs are not rare. Our results are consistent with star formation that is gradually declining in existing disks, i.e., the ESF-ETGs are evolving onto the red sequence for the first time, or with rejuvenated star formation due to accreted gas in older disks provided that the gas does not disrupt the structure of the galaxy and the resulting star formation is not too recent and bursty. ESF-ETGs may typify an important subpopulation of galaxies that can linger in the green valley for up to several Gyrs, based on their resemblance to nearby gas-rich green valley galaxies with low-level ongoing star formation.

Fang, Jerome J.; Faber, S. M.; Salim, Samir; Graves, Genevieve J.; Rich, R. Michael



Delta Scuti stars: Theory  

SciTech Connect

The purpose of asteroseismology is not only to derive the internal structure of individual stars from their observed oscillation frequencies, but also to test and extend one`s understanding of the physics of matter under the extremes of temperature, density, and pressure found in stellar interiors. In this review, the author hopes to point out what one can learn about the Sun by studying {delta} Scuti stars, as well as what one can learn about stars more massive or evolved than the Sun. He discusses some of the difficulties in theoretical approaches to asteroseismology for {delta} Scuti stars, using FG Vir, {delta} Scuti, and CD-24{degree} 7599 as examples.

Guzik, J.A.



GALEX Ultraviolet Lightcurves of M-Dwarf Flare Stars  

NASA Astrophysics Data System (ADS)

We present several high time-resolution (0.1 s) lightcurves of bright, short-duration (< 1000 s) flare events recorded at ultraviolet wavelengths (1350 - 2750 A) during the first 18 months of observations by the NASA Galaxy Evolution Explorer (GALEX). These outbursts originate on nearby M-dwarf (dMe) flare stars, and can result in a brightening of over 5 UV magnitudes in a period of less than 200 seconds. We compare and contrast pre and post flare behavior in order to derive meaningful parameters that can be used as a general diagnostic tool of the complex emission structure often exhibited by these outbursts. Finally, we show plots of SDSS (g - r) and GALEX UV magnitudes that can be used to identify previously unknown active dM stars. GALEX is a NASA Small Explorer. We gratefully acknowledge NASA's support for construction, operation, and science analysis for the GALEX mission.

Wheatley, J. M.; Welsh, B. Y.; Browne, S. E.; Robinson, R. D.; Seibert, M.; Rich, R. M.; GALEX Science Team



Global Star Formation Revisited  

NASA Astrophysics Data System (ADS)

A general treatment of disk star formation is developed from a dissipative multiphase model, with the dominant dissipation due to cloud collisions. The Schmidt-Kennicutt (SK) law emerges naturally for star-forming disks and starbursts. We predict that there should be an inverse correlation between Tully-Fisher law and SK law residuals. The model is extended to include a multiphase treatment of supernova feedback that leads to a turbulent pressure-regulated generalization of the star formation law and is applicable to gas-rich starbursts. Enhanced pressure, as expected in merger-induced star formation, enhances star formation efficiency. An upper limit is derived for the disk star formation rate in starbursts that depends on the ratio of global ISM to cloud pressures. We extend these considerations to the case where the interstellar gas pressure in the inner galaxy is dominated by outflows from a central active galactic nucleus (AGN). During massive spheroid formation, AGN-driven winds trigger star formation, resulting in enhanced supernova feedback and outflows. The outflows are comparable to the AGN-boosted star formation rate and saturate in the super-Eddington limit. Downsizing of both SMBH and spheroids is a consequence of AGN-driven positive feedback. Bondi accretion feeds the central black hole with a specific accretion rate that is proportional to the black hole mass. AGN-enhanced star formation is mediated by turbulent pressure and relates spheroid star formation rate to black hole accretion rate. The relation between black hole mass and spheroid velocity dispersion has a coefficient (Salpeter time to gas consumption time ratio) that provides an arrow of time. Highly efficient, AGN-boosted star formation can occur at high redshift.

Silk, Joseph; Norman, Colin



A Massive Runaway Star from 30 Doradus  

NASA Astrophysics Data System (ADS)

We present the first ultraviolet (UV) and multi-epoch optical spectroscopy of 30 Dor 016, a massive O2-type star on the periphery of 30 Doradus in the Large Magellanic Cloud. The UV data were obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope as part of the Servicing Mission Observatory Verification program after Servicing Mission 4, and reveal #016 to have one of the fastest stellar winds known. From analysis of the C IV ??1548-51 doublet we find a terminal velocity, v ? = 3450 ± 50 km s-1. Optical spectroscopy is from the VLT-FLAMES Tarantula Survey, from which we rule out a massive companion (with 2 days < P < 1 yr) to a confidence of 98%. The radial velocity of #016 is offset from the systemic value by -85 km s-1, suggesting that the star has traveled the 120 pc from the core of 30 Doradus as a runaway, ejected via dynamical interactions. Based on observations obtained at the European Southern Observatory Very Large Telescope in program 184.D-0222 and with the NASA/ESA Hubble Space Telescope in program 11484, 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.

Evans, C. J.; Walborn, N. R.; Crowther, P. A.; Hénault-Brunet, V.; Massa, D.; Taylor, W. D.; Howarth, I. D.; Sana, H.; Lennon, D. J.; van Loon, J. Th.



A Study of Interstellar Ultraviolet Extinction in OB Associations and Star Forming Regions  

NASA Astrophysics Data System (ADS)

The authors studied the interstellar UV extinction towards 115 stars, selected from the IUE data bank. The complete catalogue, including extinction data for the whole sample as well as the reduction procedure and error analysis, is in preparation (Aiello et al., 1986). Here the authors present the results referring to two regions (Carina and Ophiuchus Complexes) where the interstellar medium is disturbed by the effects of recent and ongoing star formation. For comparison purposes, the extinction towards Cas OB6 is also reported.

Aiello, S.; Barsella, B.; Chlewicki, G.; Greenberg, J. M.; Patriarchi, P.; Perinotto, M.


Long-term chromospheric activity of non-eclipsing RS CVn-type stars  

Microsoft Academic Search

Context. The IUE database provides a large number of UV high and\\u000alow-resolution spectra of RS CVn-type stars from 1978 to 1996. In particular,\\u000amany of these stars were monitored continuously during several seasons by IUE.\\u000aAims. Our main purpose is to study the short and long-term chromospheric\\u000aactivity of the RS CVn systems most observed by IUE: HD 22468

Andrea P. Buccino; Pablo J. D. Mauas



Long-term chromospheric activity of non-eclipsing RS CVn-type stars  

Microsoft Academic Search

Context: The IUE database provides several UV high and low-resolution spectra of RS CVn-type stars from 1978 to 1996. In particular, many of these stars were monitored continuously during several seasons by IUE. Aims: Our main purpose is to study the short and long-term chromospheric activity of the RS CVn systems most observed by IUE: HD 22 468 (V711 Tau,

A. P. Buccino; P. J. D. Mauas



UV photobiochemistry under space conditions  

NASA Astrophysics Data System (ADS)

The response of spores of Bacillus subtilis, cells of Deinococcus radiodurans and conidia of Aspergillus ochraceus to actual and simulated space conditions (UV in combination with long-term exposure to extremely dry conditions, including vacuum) has been studied: The following effects have been analyzed: decrease of viability, occurrence of DNA double strand breaks, formation of DNA-protein cross-links and DNA-DNA cross-links. All organisms show an increased sensitivity to UV light in extreme dryness (dry argon or vacuum) compared to an irradiation in aqueous suspension. The UV irradiation leads in all cases to a variety of DNA lesions. Very conspicuous is the occurrence of double strand breaks. Most of these double strand breaks are produced by incomplete repair of other lesions, especially base damages. The increase in DNA lesions can be correlated to the loss in viability. The specific response of the chromosomal DNA to UV irradiation in extreme dryness, however, varies from species to species and depends on the state of dehydration. The formation of DNA double strand breaks and DNA-protein cross-links prevails in the case of B. subtilis spores. In cells of Deinococcus radiodurans DNA-DNA cross-links often predominate, in conidia of Aspergillus ochraceus double strand breaks. The results obtained by direct exposure to space conditions (EURECA mission and D2 mission) largely agree with the laboratory data.

Dose, K.; Bieger-Dose, A.; Dillmann, R.; Gill, M.; Kerz, O.; Klein, A.; Stridde, C.


Systematic Organic UV Photoelectron Spectroscopy  

Microsoft Academic Search

Photoelectron spectroscopy (PES) provides valuable information on the ionization energies of atoms and molecules. The ionization energy (IE) is given by the relation.hv = IE + Twhere hv is t h e energy of the radiation and T i s the kinetic energy of the electron. The IEs are directly related to the orbital energies (Koopmans' theorem). By employing UV

C. N. R. Rao; P. K. Basu; M. S. Hegde



Melanoma and lifetime UV radiation  

Microsoft Academic Search

ObjectiveBecause most risk factors for melanoma are immutable constitutional factors such as skin type, it is important to more fully understand the relationship between melanoma risk and sun exposure, one of the few modifiable risk factors for the disease. The goal of this case–control study was to quantify the risks of melanoma associated with UV exposure at different periods of

Cam C. Solomon; Emily White; Alan R. Kristal; Thomas Vaughan



A high-resolution spectral atlas of carbon stars  

Microsoft Academic Search

We present a spectral atlas of six bright carbon stars (U Hya, TX Psc, RZ Peg, V Oph, Y CVn, and UV Cam) observed with the Hamilton Echelle Spectrograph at coude using the 3 m telescope at Lick Observatory. These data are of high resolution (0.13 A at 6100 A) and high signal-to-noise. The spectral range spans from 5080 to

Cecilia Barnbaum



Rapid Formation of Super-Earths around M Dwarf Stars  

Microsoft Academic Search

While the recent microlensing discoveries of super-Earths orbiting two M\\u000adwarf stars have been taken as support for the core accretion mechanism of\\u000agiant planet formation, we show here that these planets could also have been\\u000aformed by the competing mechanism of disk instability, coupled with\\u000aphotoevaporative loss of their gaseous envelopes by a strong external source of\\u000aUV radiation,

Alan P. Boss



HST Observations of the Chromosphere of a Carbon Star  

Microsoft Academic Search

Ultraviolet spectra from the first Hubble Space Telescope observations of a carbon star are presented, as well as line identifications and an initial analysis of the velocity structure of the emitting region. Two spectra of UU Aur (HD 46687, type N3; C5,3) have been obtained. In the lower-resolution FOS spectrum (2310 -- 3275 Angstroms), UV emission lines of Mg I,

L. M. Ensman; H. R. Johnson; K. G. Carpenter; R. D. Robinson; D. Luttermoser



The Components of the HD 206267 A Triple Star System  

Microsoft Academic Search

We present double-lined spectroscopic orbital elements for the central binary in the massive multiple star, HD 206267 based on fits of cross-correlation functions of the 36 IUE high dispersion UV spectra available. These elements give masses for the primary and secondary components of m1 sin 3 i = 28.0 M&sun; ± 1.8 and m2 sin 3 i = 15.3 M&sun;

J. A. Harvin; D. R. Gies; L. R. Penny



Observing Double Stars  

NASA Astrophysics Data System (ADS)

Double stars have been systematically observed since William Herschel initiated his program in 1779. In 1803 he reported that, to his surprise, many of the systems he had been observing for a quarter century were gravitationally bound binary stars. In 1830 the first binary orbital solution was obtained, leading eventually to the determination of stellar masses. Double star observations have been a prolific field, with observations and discoveries - often made by students and amateurs - routinely published in a number of specialized journals such as the Journal of Double Star Observations. All published double star observations from Herschel's to the present have been incorporated in the Washington Double Star Catalog. In addition to reviewing the history of visual double stars, we discuss four observational technologies and illustrate these with our own observational results from both California and Hawaii on telescopes ranging from small SCTs to the 2-meter Faulkes Telescope North on Haleakala. Two of these technologies are visual observations aimed primarily at published "hands-on" student science education, and CCD observations of both bright and very faint doubles. The other two are recent technologies that have launched a double star renaissance. These are lucky imaging and speckle interferometry, both of which can use electron-multiplying CCD cameras to allow short (30 ms or less) exposures that are read out at high speed with very low noise. Analysis of thousands of high speed exposures allows normal seeing limitations to be overcome so very close doubles can be accurately measured.

Genet, Russell M.; Fulton, B. J.; Bianco, Federica B.; Martinez, John; Baxter, John; Brewer, Mark; Carro, Joseph; Collins, Sarah; Estrada, Chris; Johnson, Jolyon; Salam, Akash; Wallen, Vera; Warren, Naomi; Smith, Thomas C.; Armstrong, James D.; McGaughey, Steve; Pye, John; Mohanan, Kakkala; Church, Rebecca



Close triple star systems  

Microsoft Academic Search

Triple-star systems, especially those in which one star has very small mass, are examined. Observations that provide information about the physical nature of close systems, in particular, changes of the period of orbital revolution, are discussed. It is shown that the detection and study of these changes is best obtained by observations of the precise times of light minima in

F. B. Wood



Hyperons in neutron stars  

SciTech Connect

Generalized beta equilibrium involving nucleons, hyperons, and isobars is examined for neutron star matter. The hyperons produce a considerable softening of the equation of state. It is shown that the observed masses of neutron stars can be used to settle a recent controversy concerning the nuclear compressibility. Compressibilities less than 200 MeV are incompatible with observed masses. 7 refs., 9 figs.

Glendenning, N.K.



Carbon star effective temperatures  

Microsoft Academic Search

Possible methods for measuring the effective temperatures of individual carbon stars are discussed. Since calibrations of broad or narrow-band photometric colors is impractical at present, empirical corrections to narrow band color temperatures is the only valid procedure. The effective temperature of the star TW Oph is estimated, based on preliminary reduction of the occultation and associated photometry

S. T. Ridgway; G. H. Jacoby; R. R. Joyce; D. C. Wells



The Violent Neutron Star  

NASA Astrophysics Data System (ADS)

Neutron stars enable us to study both the highest densities and the highest magnetic fields in the known Universe. In this article I review what can be learned about such fundamental physics using magnetar bursts. Both the instability mechanisms that trigger the bursts, and the subsequent dynamical and radiative response of the star, can be used to explore stellar and magnetospheric structure and composition.

Watts, A. L.



Quarkonium at STAR.  

National Technical Information Service (NTIS)

The STAR detector is capable of reconstruction the J/(psi) meson in its dielectron decay channel, along with continuum dielectrons from heavy quark decay. The limitation is not instrumental--the ability of the STAR detector to identify electrons--rather, ...

T. J. LeCompte



Stars for Navigation  

NASA Astrophysics Data System (ADS)

During World War II, stars were important navigation aids for pilots flying long night patrols. Several aspects of navigation by stars are discussed from personal experience by the author who flew Catalina aircraft over the ocean and North Africa during this period. This paper is based on a talk given to the Southland Astronomical Society.

Neave, Tom



Party with the Stars.  

ERIC Educational Resources Information Center

|Describes a Star Party which involves comparing the different colors of the stars, demonstrating how astronomers measure the sky with degrees, determining the cardinal direction, discussing numerous stories that ancient civilizations gave to constellations, exercising science process skills, and using science instruments. (JRH)|

Blaine, Lloyd



Build Your Own Star  

NSDL National Science Digital Library

This SEED website from Schlumberger provides a simulation of the life-cycle of a star. The user chooses the initial mass and "metal" (non-hydrogen/helium) content, and the site shows how the star evolves and ultimately how it dies. The site also explains "the most famous graph in astronomy," the H-R diagram.



Why Observe Double Stars?  

NASA Astrophysics Data System (ADS)

Like many branches of astronomy, the observation of double stars can be appreciated 5 at several levels. For those who enjoy the night sky, double stars offer some of 6 the most attractive sights around and they are particularly good in small telescopes 7 where the colours are much more obvious.

Argyle, Bob; Argyle, R. W.


Observing Variable Stars  

NASA Astrophysics Data System (ADS)

Observing variable stars is one of the major contributions amateur astronomers make to science. There are 36,000 variable stars listed in the General Catalogue of Variable Stars, so it is clearly impossible for the limited number of professional observatories to target even the majority of them. That's where amateur astronomers come in - thousands of them turning their telescopes to the sky every night. Variable star observing is the most popular of "real science" activities for amateurs, and Gerry Good's book provides everything needed. The first part of the book provides a highly detailed account of the various classes of variable star, with examples, illustrations and physical descriptions. The second section covers practical aspects of observing, everything from preparation and planning, through observing techniques, to data management and reduction.

Good, Gerry A.


A complete census of massive star formation in M31 and M33: The relation between star formation and ISM properties  

Microsoft Academic Search

We utilize GALEX FUV and NUV observations (Thilker et al. 2004), WSRT and VLA HI mosaics, published CO data, plus Spitzer (MIPS) and ISO imagery of M31 and M33 to measure the spatial distribution of extinction-corrected star formation rate (SFR) and gas surface density. The powerful combination of UV and IR datasets allows us to firmly constrain the SFR over

D. A. Thilker; L. Bianchi; R. Braun; K. Gordon; G. Rieke; O. Krause; C. Engelbracht; D. Hines; J. Hinz; K. Misselt; P. Perez-Gonzalez; K. Su; E. Young; W. Latter; D. Levine; S. Stolovy; A. Noriega-Crespo; M. Werner; J. Mould; P. Barmby; S. Willner



UV and optical spectrum variability of T Tau and RY Tau  

NASA Astrophysics Data System (ADS)

In this report we have presented results of spectral observations of classical T Tauri type stars T Tau and RY Tau. Observational dates were obtained from following sources: spectrograms of the UV range from the IUE archive data, and spectrograms of the visual range obtained in the 2 m telescope of ShAO of the NAS of Azerbaijan (Ismailov et al. 2010). For both of stars on the Scargle method we have searched a periodicity of variations in equivalent widths of emission lines in the optical and UV ranges. In the RY Tau firstly was detected the periodic variability in MgII ?2800 Å emission doublet intensities with a period of 23 days. The observed period had also revealed with the equivalent widths and displacements of components of H? and H+H? and K CaII emission.

Ismailov, N. Z.; Quliyev, N. Kh.; Khalilov, O. V.; Adigezalzade, H. N.



Far Ultraviolet Observations of Hot-Star Winds  

NASA Astrophysics Data System (ADS)

P Cygni profiles were first detected in the ultraviolet resonance lines of luminous OB stars during sounding rocket flights more than 30 years ago. Since then, there have been spectacular advances in our understanding of the mechanism responsible for driving hot-star winds (which is momentum transfer from the stellar radiation field to the wind material by scattering in line transitions) and the astrophysical consequences of the resultant mass loss (which include altering the evolutionary track of the star and depositing energy, momentum, and chemically enriched material into the interstellar medium). Although a wealth of spectroscopic information has been returned by UV and far-UV satellite observatories, and sophisticated model atmosphere programs have been developed to interpret these data, several fundamental challenges to our understanding still remain. These include: (a) accurate empirical determinations of mass-loss rates from the P Cygni profiles of resonance lines; (b) detailed knowledge of the processes that determine the ionization balance in the wind; and (c) the nature of the variability exhibited by hot-star winds. This review will emphasize the diagnostic leverage that can be applied to these problems by spectroscopic observations in the far-UV. The Far Ultraviolet Spectroscopic Explorer (FUSE) satellite will have greater spectral resolution and sensitivity and/or a longer operational lifetime than other FUV missions, and consequently rapid progress in solving these problems is expected. Thus, on the near horizon lies the tantalizing prospect of using hot-star winds as quantitative tools to probe young stellar populations in a variety of astronomical settings.

Fullerton, A. W.



The star formation rate distribution function of the local Universe  

NASA Astrophysics Data System (ADS)

We present total infrared (IR) and ultraviolet (UV) luminosity functions derived from large representative samples of galaxies at z˜ 0, selected at IR and UV wavelengths from the Imperial IRAS Faint Source Catalogue redshift data base (IIFSCz) catalogue, and the GALEX All-Sky Imaging Survey (AIS), respectively. We augment these with deep Spitzer and GALEX imaging of galaxies in the 11 Mpc Local Volume Legacy (LVL) Survey, allowing us to extend these luminosity functions to lower luminosities (˜106 L?), and providing good constraints on the slope of the luminosity function at the extreme faint end for the first time. Using conventional star formation prescriptions, we generate from our data the star formation rate (SFR) distribution function for the local Universe. We find that it has a Schechter form, the faint-end slope has a constant value (to the limits of our data) of ?=-1.51 ± 0.08 and the ‘characteristic’ SFR ?* is 9.2 M? yr-1. We also show the distribution function of the SFR volume density; we then use this to calculate a value for the total SFR volume density at z˜ 0 of 0.025 ± 0.0016 M? yr-1 Mpc-3, of which ˜20 per cent is occurring in starbursts. Decomposing the total star formation by infrared luminosity, it can be seen that 9 ± 1 per cent is due to LIRGs, and 0.7 ± 0.2 per cent is occurring in ULIRGs. By comparing UV and IR emission for galaxies in our sample, we also calculate the fraction of star formation occurring in dust-obscured environments, and examine the distribution of dusty star formation: we find a very shallow slope at the highly extincted end, which may be attributable to line-of-sight orientation effects as well as conventional internal extinction.

Bothwell, M. S.; Kenicutt, R. C.; Johnson, B. D.; Wu, Y.; Lee, J. C.; Dale, D.; Engelbracht, C.; Calzetti, D.; Skillman, E.




SciTech Connect

We compare multi-wavelength star formation rate (SFR) indicators out to z {approx} 3 in the GOODS-South field. Our analysis uniquely combines U to 8 {mu}m photometry from FIREWORKS, MIPS 24 {mu}m and PACS 70, 100, and 160 {mu}m photometry from the PEP, and H{alpha} spectroscopy from the SINS survey. We describe a set of conversions that lead to a continuity across SFR indicators. A luminosity-independent conversion from 24 {mu}m to total infrared luminosity yields estimates of L{sub IR} that are in the median consistent with the L{sub IR} derived from PACS photometry, albeit with significant scatter. Dust correction methods perform well at low-to-intermediate levels of star formation. They fail to recover the total amount of star formation in systems with large SFR{sub IR}/SFR{sub UV} ratios, typically occuring at the highest SFRs (SFR{sub UV+IR} {approx}> 100 M{sub sun} yr{sup -1}) and redshifts (z {approx}> 2.5) probed. Finally, we confirm that H{alpha}-based SFRs at 1.5 < z < 2.6 are consistent with SFR{sub SED} and SFR{sub UV+IR} provided extra attenuation toward H II regions is taken into account (A{sub V,neb} = A{sub V,continuum}/0.44). With the cross-calibrated SFR indicators in hand, we perform a consistency check on the star formation histories inferred from spectral energy distribution (SED) modeling. We compare the observed SFR-M relations and mass functions at a range of redshifts to equivalents that are computed by evolving lower redshift galaxies backward in time. We find evidence for underestimated stellar ages when no stringent constraints on formation epoch are applied in SED modeling. We demonstrate how resolved SED modeling, or alternatively deep UV data, may help to overcome this bias. The age bias is most severe for galaxies with young stellar populations and reduces toward older systems. Finally, our analysis suggests that SFHs typically vary on timescales that are long (at least several 100 Myr) compared to the galaxies' dynamical time.

Wuyts, Stijn; Foerster Schreiber, Natascha M.; Lutz, Dieter; Nordon, Raanan; Berta, Stefano; Genzel, Reinhard; Magnelli, Benjamin; Poglitsch, Albrecht [Max-Planck-Institut fuer extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching (Germany); Altieri, Bruno [Herschel Science Centre, ESAC, Villanueva de la Canada, 28691 Madrid (Spain); Andreani, Paola [ESO, Karl-Schwarzschild-Str. 2, D-85748 Garching (Germany); Aussel, Herve; Daddi, Emanuele; Elbaz, David [Laboratoire AIM, CEA/DSM-CNRS-Universite Paris Diderot, IRFU/Service d'Astrophysique, Bat.709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex (France); Bongiovanni, Angel; Cepa, Jordi; Garcia, Ana Perez [Instituto de Astrofisica de Canarias, 38205 La Laguna (Spain); Cimatti, Andrea [Departamento di Astronomia, Universita di Bologna, via Ranzani 1, 40127 Bologna (Italy); Koekemoer, Anton M. [Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States); Maiolino, Roberto [INAF, Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone (Italy); McGrath, Elizabeth J. [University of California Observatories/Lick Observatory, University of California, Santa Cruz, CA 95064 (United States)



The Massive Star Content of Circumnuclear Star Clusters in M83  

NASA Astrophysics Data System (ADS)

The circumnuclear starburst of M83 (NGC 5236), the nearest such example (4.6 Mpc), constitutes an ideal site for studying the massive star IMF at high metallicity (12+log[O/H]=9.1±0.2, Bresolin & Kennicutt 2002). We analyzed archival HST/STIS FUV imaging and spectroscopy of 13 circumnuclear star clusters in M83. We compared the observed spectra with two types of single stellar population (SSP) models; semi-empirical models, which are based on an empirical library of Galactic O and B stars observed with IUE (Robert et al. 1993), and theoretical models, which are based on a new theoretical UV library of hot massive stars described in Leitherer et al. (2010) and computed with WM-Basic (Pauldrach et al. 2001). The models were generated with Starburst99 (Leitherer & Chen 2009). We derived the reddenings, the ages, and the masses of the clusters from model fits to the FUV spectroscopy, as well as from optical HST/WFC3 photometry.

Wofford, A.; Chandar, R.; Leitherer, C.



Computational Star Formation (IAU S270)  

NASA Astrophysics Data System (ADS)

1. Historical introduction; 2. Individual star formation: observations; 3. Low-mass star formation: observations; 4. Individual star formation: theory; 5. Formation of clusters: observations; 6. Formation of clusters: theory; 7. Numerical methods: MHD; 8. Numerical methods: radiative dynamics; 9. Local star formation processes; 10. Star formation feedback; 11. Star formation on galactic scales; 12. Special purpose hardware; 13. Computational methods; 14. Radiation diagnostics of star formation; 15. Large scale star formation; 16. Cosmological star formation; 17. Computational star formation: Summary; Index.

Alves, João.; Elmegreen, Bruce G.; Girart, Josep M.; Trimble, Virginia



The Number of Supernovae From Primordial Stars in the Universe  

SciTech Connect

Recent simulations of the formation of the first luminous objects in the universe predict isolated very massive stars to form in dark matter halos with virial temperatures large enough to allow significant amounts of molecular hydrogen to form. We construct a semi-analytic model based on the Press-Schechter formalism and calibrate the minimum halos mass that may form a primordial star with the results from extensive adaptive mesh refinement simulations. The model also includes star formation in objects with virial temperatures in excess of ten thousand Kelvin. The free parameters are tuned to match the optical depth measurements by the WMAP satellite. The models explicitly includes the negative feedback of the destruction of molecular hydrogen by a soft UV background which is computed self-consistently. We predict high redshift supernova rates as one of the most promising tools to test the current scenario of primordial star formation. The supernova rate from primordial stars peaks at redshifts {approx}20. Using an analytic model for the luminosities of pair-instability supernovae we predict observable magnitudes and discuss possible observational strategies. Such supernovae would release enough metals corresponding to a uniform enrichment to a few hundred thousands of solar metalicity. If some of these stars produce gamma ray bursts our rates will be directly applicable to understanding the anticipated results from the SWIFT satellite. This study highlights the great potential for the James Webb space telescope in probing cosmic structure at redshifts greater than 20.

Wise, J



Dark stars: Implications and constraints from cosmic reionization and extragalactic background radiation  

SciTech Connect

Dark stars powered by dark matter annihilation have been proposed as the first luminous sources in the Universe. These stars are believed to form in the central dark matter cusp of low-mass minihalos. Recent calculations indicate stellar masses up to {approx}1000M{sub {center_dot}} and/or have very long lifetimes. The UV photons from these objects could therefore contribute significantly to cosmic reionization. Here we show that such dark star models would require a somewhat artificial reionization history, based on a double-reionization phase and a late star burst near redshift z{approx}6, in order to fulfill the WMAP (Wilkinson Microwave Anisotropy Probe) constraint on the optical depth as well as the Gunn-Peterson constraint at z{approx}6. This suggests that, if dark stars were common in the early universe, then models are preferred which predict a number of UV photons similar to conventional Pop. III stars. This excludes 800M{sub {center_dot}} dark stars that enter a main-sequence phase and other models that lead to a strong increase in the number of UV photons. We also derive constraints for massive as well as light dark matter candidates from the observed x-ray, gamma-ray, and neutrino background, considering dark matter profiles which have been steepened during the formation of dark stars. This increases the clumping factor at high redshift and gives rise to a higher dark matter annihilation rate in the early universe. We furthermore estimate the potential contribution from the annihilation products in the remnants of dark stars, which may provide a promising path to constrain such models further, but which is currently still uncertain.

Schleicher, Dominik R. G.; Banerjee, Robi; Klessen, Ralf S. [Institute of Theoretical Astrophysics/ZAH, Albert-Ueberle-Str. 2, D-69120 Heidelberg (Germany)



Tunable UV source for UV fluorescence remote sensing  

SciTech Connect

Efficient generation of ultraviolet radiation tunable over the 240--410 nm range has been achieved in a system suitable for ultraviolet (uv) fluorescence remote sensing. Light from an Optical Parametric Oscillator/Amplifier turning in the 0.7--2.1 {mu}m range is mixed with the second or third harmonic from a Nd:YAG laser, to obtain up to 30 mJ of broadly tunable output in the ultraviolet.

Mead, R.D.; Lowenthal, D.D. [Aculight Corp., Bellevue, WA (United States); Raymond, T.D.; Alford, W.J.; Smith, A.V.; Johnson, M.S. [Sandia National Labs., Albuquerque, NM (United States)



Dissociation of the benzene molecule by UV and soft X-rays in circumstellar environment  

Microsoft Academic Search

Benzene molecules, present in the proto-planetary nebula CRL 618, are ionized\\u000aand dissociated by UV and X-ray photons originated from the hot central star\\u000aand by its fast wind. Ionic species and free radicals produced by these\\u000aprocesses can lead to the formation of new organic molecules. The aim of this\\u000awork is to study the photoionization and photodissociation processes

H. M. Boechat-Roberty; R. Neves; S. Pilling; A. F. Lago; G. G. B. de Souza



Far-UV and deep surveys: bursting dwarfs versus normal galaxies  

Microsoft Academic Search

Galaxy counts from bright ultraviolet (UV) and deep optical spectroscopic surveys have revealed an unexpectedly large number of very blue galaxies (vBG). The colors and luminosities of these objects indicate that they are dwarf galaxies undergoing bursts of star formation. We use a galaxy evolution model (\\\\textsc{pégase}, Fioc & Rocca-Volmerange 1997, hereafter FRV) to describe this population as galaxies undergoing

Michel Fioc; Brigitte Rocca-Volmerange



UV Filters for Lighting of Plants.  

National Technical Information Service (NTIS)

The wavelength dependent interaction of biological systems with radiation is commonly described by appropriate action spectra. Particularly effective plant responses are obtained for ultraviolet (UV) radiation. Excess shortwave UV-B radiation will induce ...

T. Doehring M. Koefferlein S. Thiel H. K. Seidlitz H. D. Payer



Near UV Observation of HAT-P-16b  

NASA Astrophysics Data System (ADS)

We observed the primary transit of the hot Jupiter HAT-P-16b in the near-UV photometric band on December 29, 2012 in an attempt to detect its magnetic field. Vidotto, Jardine & Helling (2011) postulate that the magnetic field of HAT-P-16b can be constrained if its near-UV light curve shows an early ingress compared to its optical light curve, while its egress remains unswayed. Predicted magnetic fields of Jupiter-like planets should range between 8 G (Reiners & Christensen 2010) and 40 G (Sanchez-Lavega 2004). However, we derived an upper limit of the magnetic field strength of HAT-P-16b to range between 0.0082 and 0.82 G (for a 1--100 G magnetic field strength range for the host star, HAT-P-16). Using these magnetic field values and an assumed B* of 100 G, the Vidotto, Jardine & Helling (2011) method predicts a timing difference of 19--38 mins. We did not detect an early ingress in our night of observing when using a cadence of 45 seconds and an average photometric precision of 2.25 mmag. We present the first near-UV light curve of HAT-P-16b and find a near-UV planetary radius of 1.242+-0.056 (R_Jup) which is consistent with its near-IR radius of R=1.289+-0.066 (R_Jup) (Buchhave 2010). We developed an automated reduction pipeline and a modeling package to process our data. The modeling package utilizes the Levenberg-Marquardt minimization algorithm to find a least-squares best fit and a differential evolution Markov Chain Monte Carlo to find the best fit to the light curve, and uses both the residual permutation (rosary bead) method and time-averaging method (Pont 2006) to constrain the red noise in both fitting methods.

Pearson, Kyle; Turner, J.



Infrared and Ultraviolet Star Formation in Brightest Cluster Galaxies in the ACCEPT Sample  

NASA Astrophysics Data System (ADS)

We present infrared (IR) and ultraviolet (UV) photometry for a sample of brightest cluster galaxies (BCGs). The BCGs are from a heterogeneous but uniformly characterized sample, the Archive of Chandra Cluster Entropy Profile Tables (ACCEPT), of X-ray galaxy clusters from the Chandra X-ray telescope archive with published gas temperature, density, and entropy profiles. We use archival Galaxy Evolution Explorer (GALEX), Spitzer Space Telescope, and Two Micron All Sky Survey (2MASS) observations to assemble spectral energy distributions (SEDs) and colors for BCGs. We find that while the SEDs of some BCGs follow the expectation of red, dust-free old stellar populations, many exhibit signatures of recent star formation in the form of excess UV or mid-IR emission, or both. We establish a mean near-UV (NUV) to 2MASS K color of 6.59 ± 0.34 for quiescent BCGs. We use this mean color to quantify the UV excess associated with star formation in the active BCGs. We use both fits to a template of an evolved stellar population and library of starburst models and mid-IR star formation relations to estimate the obscured star formation rates (SFRs). We show that many of the BCGs in X-ray clusters with low central gas entropy exhibit enhanced UV (38%) and mid-IR emission (43%) from 8 to 160 ?m, above that expected from an old stellar population. These excesses are consistent with ongoing star formation activity in the BCG, star formation that appears to be enabled by the presence of high-density, X-ray-emitting intergalactic gas in the core of the cluster of galaxies. This hot, X-ray-emitting gas may provide the enhanced ambient pressure and some of the fuel to trigger star formation. This result is consistent with previous works that showed that BCGs in clusters with low central gas entropies host H? emission-line nebulae and radio sources, while clusters with high central gas entropy exhibit none of these features. GALEX UV and Spitzer mid-IR measurements combined provide a complete picture of unobscured and obscured star formation occurring in these systems. We present IR and UV photometry and estimated equivalent continuous SFRs for a sample of BCGs.

Hoffer, Aaron S.; Donahue, Megan; Hicks, Amalia; Barthelemy, R. S.



Diagnostics of the ISM in star formation regions  

NASA Astrophysics Data System (ADS)

Line emissions of high- and low-density molecular tracers serve as powerful diagnostic tools for the ISM in both Galactic and extragalactic star formation environments. The emission line strengths and line ratios may be interpreted using detailed modeling of both the dominant physics and the chemistry of the molecular constituents. Observed molecular line ratios will thus reveal the signatures of dominant UV, X-ray, and CR radiation fields and of mechanical heating and feedback from the star formation process. In addition, certain line ratios reflect the physical and chemical changes resulting from the time-evolution of a star formation region. In this paper, we present results of Galactic sources and extragalactic starbursts covering a large range of FIR luminosities and illustrate the similarities between the diagnostics of these environments.

Baan, Willem A.; Loenen, Edo; Lian, Xiaoli



The Use of Virtual Observatory Databases in Binary Star Research  

NASA Astrophysics Data System (ADS)

The rapidly-accumulating archives of ground-based and spacecraft data worldwide that are being linked together through the International Virtual Observatory Alliance (IVOA) provide the binary star community with unparalleled opportunities for research. The main databases that are available to the astronomical community through the IVOA are discussed. Data from long-lasting spacecraft missions such as IUE are especially valuable for studying long-term variability. Some examples of current research on close binary stars that is being carried through with UV spectra from the IUE archive are presented. Included are the search for O-subdwarf companions to bright Be stars and some results from an ongoing investigation of the Double Periodic Variable phenomenon in Algol binaries.

Peters, Geraldine J.



Colour indices of selected OB stars (Krelowski+, 2012)  

NASA Astrophysics Data System (ADS)

Tables contain V magnitudes and colour indices: (B-V), (U-V), (1500-V), (1800-V), (2200-V), (3300-V), (J-V), (H-V) and (K-V) of selected stars of spectral types: O9V, B0V, B1V, B1Ve, B2V and B3V. Spectral type of each star is according to SIMBAD. The stars are identified with their HD/BD numbers or names. The used photometry was taken from: U,B,V (in the Johnson System) from SIMBAD magnitudes at 5 ANS passbands (15, 18, 22, 25, 33) from Wesselius et al. (1982, Cat. II/97) J, H, K from IR 2MASS Catalog (Kleinmann et al., 1994Ap&SS.217...11K). (6 data files).

Krelowski, J.; Strobel, A.



Interstellar extinction curves of OB stars (Wegner 2002)  

NASA Astrophysics Data System (ADS)

The paper presents a collection of 436 extinction curves covering the whole available range of wavelengths from satellite UV to near-IR. The data were taken from the ANS photometric catalogue (Cat. ) and from the compilations of IR photometric measurements. The data curves have been obtained with the aid of "artificial standards" Papaj et al. (1993A&A...273..575P) and Wegner (1994MNRAS.270..229W, 1995, Interstellar Absorption Structures in the Direction of Nearby OB stars, Wyd. Uczelniane WSP, Bydgoszcz, p. 1-383). The visual magnitudes and spectral classifications of O and B type stars with EB-V>=0.05 were taken from the SIMBAD database. The curves are given in the form of plots and tables E{lambda}-V/EB-V versus 1/{lambda}. The observed variety of extinction laws among slightly reddened stars is apparently due to the various physical parameters of interstellar clouds. (3 data files).

Wegner, W.




SciTech Connect

We present Hubble Space Telescope/Advanced Camera for Surveys ultraviolet photometry of three quiescent black hole X-ray transients, X-ray Nova Muscae 1991 (GU Mus), GRO J0422+32 (V518 Per), and X-ray Nova Vel 1993 (MM Vel), and one neutron star system, Aql X-1. These are the first quiescent UV detections of these objects. All are detected at a much higher level than expected from their companion stars alone and are significant detections of the accretion flow. Three of the four UV excesses can be characterized by a blackbody of temperature 5000-13, 000 K, hotter than expected for the quiescent outer disk. A good fit could not be found for MM Vel. The source of the blackbody-like emission is most likely a heated region of the inner disk. Contrary to initial indications from spectroscopy, there does not appear to be a systematic difference in the UV luminosity or spectral shape between black holes and neutron star systems. However, combining our new data with earlier spectroscopy and published X-ray luminosities, there is a significant difference in the X-ray to UV flux ratios, with the neutron stars exhibiting L{sub X}/L{sub UV} about 10 times higher than the black hole systems. This is consistent with earlier comparisons based on estimating non-stellar optical light, but since both bandpasses we use are expected to be dominated by accretion light, we present a cleaner comparison. This suggests that the difference in X-ray luminosities cannot simply reflect differences in quiescent accretion rates and so the UV/X-ray ratio is a more robust discriminator between the black hole and neutron star populations than the comparison of X-ray luminosities alone.

Hynes, R. I. [Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 (United States); Robinson, E. L., E-mail:, E-mail: [Department of Astronomy, University of Texas at Austin, 1 University Station C1400, Austin, TX 78712 (United States)



The Far-infrared, UV, and Molecular Gas Relation in Galaxies up to z = 2.5  

NASA Astrophysics Data System (ADS)

We use the infrared excess (IRX) FIR/UV luminosity ratio to study the relation between the effective UV attenuation (A IRX) and the UV spectral slope (?) in a sample of 450 1 < z < 2.5 galaxies. The FIR data are from very deep Herschel observations in the GOODS fields that allow us to detect galaxies with star formation rates (SFRs) typical of galaxies with log(M *) > 9.3. Thus, we are able to study galaxies on and even below the main SFR-stellar mass relation (main sequence). We find that main-sequence galaxies form a tight sequence in the IRX-? plane, which has a flatter slope than commonly used relations. This slope favors a Small-Magellanic-Cloud-like UV extinction curve, though the interpretation is model dependent. The scatter in the A IRX-? plane correlates with the position of the galaxies in the SFR-M * plane. Using a smaller sample of galaxies with CO gas masses, we study the relation between the UV attenuation and the molecular gas content. We find a very tight relation between the scatter in the IRX-? plane and the specific attenuation SA , a quantity that represents the attenuation contributed by the molecular gas mass per young star. SA is sensitive to both the geometrical arrangement of stars and dust and to the compactness of the star-forming regions. We use this empirical relation to derive a method for estimating molecular gas masses using only widely available integrated rest-frame UV and FIR photometry. The method produces gas masses with an accuracy between 0.12 and 0.16 dex in samples of normal galaxies between z ~ 0 and z ~ 1.5. Major mergers and submillimeter galaxies follow a different SA relation.

Nordon, R.; Lutz, D.; Saintonge, A.; Berta, S.; Wuyts, S.; Förster Schreiber, N. M.; Genzel, R.; Magnelli, B.; Poglitsch, A.; Popesso, P.; Rosario, D.; Sturm, E.; Tacconi, L. J.



Hubble Space Telescope Spectroscopy of the Carbon Star TX PISCIUM  

NASA Astrophysics Data System (ADS)

Ultraviolet spectra obtained with the Hubble Space Telescope of the carbon star TX Piscium (HR 9004) are presented, along with analysis providing information on its outer atmosphere, including flow and turbulent velocities, line formation mechanisms, and variations with time. Both thermal (collisionally excited) and fluorescent emission from the chromosphere of the star appear to be formed near the stellar rest velocity, i.e., in a region below that in which the stellar wind is accelerated. Absorption self-reversals in the Mg II emission confirm the presence of an outflowing stellar wind at a mean velocity of about 9--10 km s-1. Circumstellar absorption features (Mn I and Fe I) overlying the Mg II emission indicate a cool shell expanding at about 5--6 km s-1 relative to the photosphere. The widths (FWHM) of various emission lines indicate that the chromospheric turbulence is at least 16 km s-1, but that it may increase with altitude to as much as 34 km s-1. Three hours of integration on the C II] lines are examined for any signs of variability that might indicate the presence of shocks, but no statistically significant variations are seen. A previous identification (in spectra of UU Aur) of an emission line at 2807 Angstroms, seen only in spectra of carbon stars, as belonging to Fe I multiplet UV45 pumped by the C II] line at 2325 Angstroms is confirmed by the discovery of an absorption feature corresponding exactly to the wavelength of the pumped transition (Fe I UV13) near 2325 Angstroms. Lines from Fe II UV165, previously seen in solar off-limb spectra and in Goddard High-Resolution Spectrograph spectra of alpha Tau, are clearly present. The normally much stronger Fe II UV32, 62, and 63 multiplets are seen but are weaker relative to both the UV165 lines and the intercombination lines of C II] and Si II] than in alpha Tau. The weakness of these Fe II lines is indicated both by their absolute flux levels and by their narrow, single-peaked profiles, which are in sharp contrast to the broad, double-peaked profiles seen in oxygen-rich cool giant and supergiant stars. The weakness of the Fe II lines and the presence of the Fe I 2807 Angstroms line suggest that the ionization fraction of iron (Fe II/Fe I) is significantly lower in the outer atmospheres of carbon stars. Fluxes in emission lines of Fe II and Mg II are >=2--3 times lower than in a 1984 IUE spectrum of TX Psc, confirming that the latter was obtained at an epoch of unusual UV brightness for the star. The Mg II profiles are heavily mutilated by overlying absorption, even more so than in 1984. The TX Psc profiles are very similar to those seen in the carbon star TW Hor but are dramatically different than those in another carbon star, UU Aur, whose lines show violet wing emission out to much shorter wavelengths than in the other two stars.

Carpenter, Kenneth G.; Robinson, Richard D.; Johnson, Hollis R.; Eriksson, Kjell; Gustafsson, Bengt; Pijpers, Frank P.; Querci, Francois; Querci, Monique



Star Formation in LITTLE THINGS: HI Line Profile Analysis of Nearby Dwarfs  

NASA Astrophysics Data System (ADS)

Dwarf galaxies are unique laboratories for studying the process of star formation in metal-poor environments. The comprehensive data of the LITTLE THINGS project provide an excellent tool to probe the relation between star formation and the interstellar media of these systems. By analyzing HI velocity dispersions for Gaussian (and modified Gaussian) profiles, we can separate the cold neutral medium (CNM) and warm neutral medium (WNM) phases of the ISM. From that, we can determine which areas and conditions are more favorable for star formation. Comparison with data from other wavelengths such as H-alpha, UV, and FIR will test the predictions of the HI line profile analysis.

Cigan, Phil; Young, L.; Hunter, D.



Evaporating very small grains as tracers of the UV radiation field in photo-dissociation regions  

NASA Astrophysics Data System (ADS)

Context. In photo-dissociation regions (PDRs), polycyclic aromatic hydrocarbons (PAHs) may be produced by evaporation of very small grains (VSGs) by the impinging UV radiation field from a nearby star. Aims: We quantitatively investigate the transition zone between evaporating VSGs (eVSGs) and PAHs in several PDRs. Methods: We studied the relative contribution of PAHs and eVSGs to the mid-IR emission in a wide range of excitation conditions. We fitted the observed mid-IR emission of PDRs by using a set of template band emission spectra of PAHs, eVSGs, and gas lines. The fitting tool PAHTAT (PAH Toulouse Astronomical Templates) is made available to the community as an IDL routine. From the results of the fit, we derived the fraction of carbon feVSG locked in eVSGs and compared it to the intensity of the local UV radiation field. Results: We show a clear decrease of feVSG with increasing intensity of the local UV radiation field, which supports the scenario of photo-destruction of eVSGs. Conversely, this dependence can be used to quantify the intensity of the UV radiation field for different PDRs, including unresolved ones. Conclusions: PAHTAT can be used to trace the intensity of the local UV radiation field in regions where eVSGs evaporate, which correspond to relatively dense (nH = [100,105] cm-3) and UV irradiated PDRs (G0 = [100,5 × 104] ) where H2 emits in rotational lines.

Pilleri, P.; Montillaud, J.; Berné, O.; Joblin, C.



Extraction and analysis of diffuse UV radiation from GALEX observations  

NASA Astrophysics Data System (ADS)

Using the GALEX observations available over the web, we are probing diffuse UV background radiation in FUV and NUV. Each GALEX field consist of stars, galaxies and diffuse UV radiations like airglow, zodiacal light (especially in NUV), star light scattered from interstellar dust, etc. In this poster we describe our method to extract the diffuse UV background and its components from the GALEX fields and the preliminary results we have derived from correlation studies, using four nearby Deep Imaging Survey (DIS) targets (DR1 - DIS 8-11). Even though all the 4 DIS targets are observed from the neighbouring regions, the correlation studies show different results i.e., there is a strong correlation between FUV and NUV as well as between FUV(NUV) and IR in the DIS 8 region, suggesting that except for the non-zero intercept values (600 and 1050 photons /cm2/s/sr/ in FUV and NUV), what we are seeing in the field is star light scattered from interstellar dust. In DIS 9 region, there is absolutely no correlation in either case, suggesting that there is no dust scattered radiation, but ofcourse this region is almost free from dust. In DIS 10 and 11 regions, both the correlations are week compared to DIS 8. But in all the 4 regions (and many other GALEX DIS locations), there is a strong level of non-zero intercept in FUV and NUV, (for e.g., in DIS 9 region, 950 PU in FUV and 1350 PU in NUV), which cannot be attributed to dust scattered starlight. For these amount in FUV, (in NUV almost half of this is zodiacal light), we do not have proper explanations at this point of time,! However comparing FUV and NUV correlation plots with IR (note that FUV and NUV plots are not following the same pattern), the apparent reduction of NUV intensity with increase in the amount of dust seems to point to an extragalactic contribution in the regions. So some part of the unexplained radiation could be attributed to this.

Sujatha, N. V.; Murthy, Jayant; Henry, R. C.


Bistable UV pigment in the lamprey pineal  

Microsoft Academic Search

Lower vertebrates can detect UV light with the pineal complex independently of eyes. Electrophysiological studies, together with chromophore extraction analysis, have suggested that the underlying pigment in the lamprey pineal exhibits a bistable nature, that is, reversible photoreaction by UV and visible light, which is never achieved by known UV pigments. Here we addressed the molecular identification of the pineal

Mitsumasa Koyanagi; Emi Kawano; Yoshimi Kinugawa; Tadashi Oishi; Yoshinori Shichida; Satoshi Tamotsu; Akihisa Terakita



UV disinfection in a model distribution system  

Microsoft Academic Search

Two model distribution systems were operated in parallel to investigate the impact of UV disinfection on water distribution system biofilms and microbial community composition. One system received an influent irradiated with UV light, whereas the control received the same influent with no treatment. The biofilm in the UV system, as compared to the control, was more responsive (i.e., had a

Nicki Pozos; Kate Scow; Stefan Wuertz; Jeannie Darby



Solar UV-Protective Properties of Textiles  

Microsoft Academic Search

Skin cancer is increasing worldwide, and exposure to ultraviolet (UV) radiation is thought to be the most important risk factor [1, 2]. Outdoor professionals and people practising outdoor sports are considerably exposed to solar UV radiation [3]. We have reported high personal UV exposure in cycling professionals up to about 17 MED\\/day [4]. Obviously, adequate protection is mandatory. Here, a

Matthias Moehrle; Claus Garbe



Scope on the Skies: Star light, star bright  

NSDL National Science Digital Library

In astronomy, the brightness of a star is described in terms of a star's magnitude. Stellar magnitude is expressed two different ways, using the terms apparent magnitude and absolute magnitude . For both magnitudes, the numbering scale is the same, with negative numbers being brighter stars and positive numbers being dimmer stars. This month's column sheds light on the stars and how astronomers measure distances to these celestial objects.

Riddle, Bob



Clustering properties of BzK-selected galaxies in GOODS-N: environmental quenching and triggering of star formation at z ~ 2  

Microsoft Academic Search

Using a sample of $\\\\textit{BzK}$-selected galaxies at $z \\\\sim 2$ identified from the CFHT\\/WIRCAM near-infrared survey of GOODS-North, we discuss the relation between star formation rate (SFR), specific star formation rate (SSFR), and stellar mass (\\\\sm), and the clustering of galaxies as a function of these parameters. For star-forming galaxies (\\\\textit{sBzK}s), the UV-based SFR, corrected for extinction, scales with the

Lihwai Lin; Mark Dickinson; Hung-Yu Jian; A. I. Merson; C. M. Baugh; Douglas Scott; Sebastien Foucaud; Wei-Hao Wang; Chi-Hung Yan; Hao-Jing Yan; Yi-Wen Cheng; Yicheng Guo; John Helly; Franz Kirsten; David C. Koo; Claudia del P. Lagos; Nicole Meger; Alexandra Pope; Luc Simard; Norman A. Grogin; Hugo Messias; Shiang-Yu Wang



The Constellations and their Stars  

NSDL National Science Digital Library

This website is a tutorial on constellations and the stars in them. It offers an alphabetical and monthly listing of the constellations. It also provides a listing of stars, messier objects, and a list of the brightest stars in the sky. The user can also use the website's interactive star chart, Milky Way photos, or helpful links.

Dolan, Chris



Infrared studies of star formation  

Microsoft Academic Search

Infrared observations at wavelengths of a few microns to 1 mm are reviewed which pertain to the problem of star formation. The data considered include observations of large gas and dust clouds within which stars may be forming and detailed studies of individual objects within these clouds. Stages of star formation are outlined, the IR luminosity of forming stars is

M. W. Werner; E. E. Becklin; G. Neugebauer



Lithium in stars with exoplanets  

Microsoft Academic Search

Our recent study of solar-type stars from the HARPS GTO sample provides highly accurate information with regard to Lithium abundances in stars with and without detected planets (Israelian et al. 2009). When the Li abundances of planet bearing stars are compared with the ``single'' stars, we find an excess of Li depletion in planet hosts with effective temperatures in the

Garik Israelian



Visual Binary Star Observations  

NASA Astrophysics Data System (ADS)

A special mathematics course (MAT298AC) was offered in the fall 2010 and spring 2011 semesters at the Estrella Mountain Community College (EMCC), providing students the opportunity to gain real-world experience through observations, applied mathematics and research techniques. The students and instructor in MAT298AC chose to pursue visual binary star observations with the goal of contributing to the scientific knowledge base. Visual observations of selected binary stars were obtained by utilizing EMCC campus astronomical equipment. Data collected includes the separation of potential binary stars and their position angle.

Darling, Kodiak; Diaz, Kristy; Lucas, Arriz; Santo, Travis; Walker, Douglas



Transcriptional profiling of summer wheat, grown under different realistic UV-B irradiation regimes.  


There is limited information on the impact of present-day ultraviolet-B (UV-B) radiation on a reprogramming of gene expression in crops. Summer wheat was cultivated in controlled environmental facilities under simulated realistic climatic conditions. We investigated the effect of different regimes of UV-B radiation on summer wheat (Triticum aestivum L.) cultivars Nandu, Star and Turbo. Until recently, these were most important in Bavaria. Different cultivars of crops often show great differences in their sensitivity towards UV-B radiation. To identify genes that might be involved in UV-B defence mechanisms, we first analyzed selected genes known to be involved in plant defence mechanisms. RNA gel blot analysis of RNA isolated from the flag leaf of 84-day-old plants showed differences in transcript levels among the cultivars. Flag leaves are known to be important for grain development, which was completed at 84 days post-anthesis. Catalase 2 (Cat2) transcripts were elevated by increased UV irradiation in all cultivars with highest levels in cv. Nandu. Pathogenesis-related protein 1 (PR1) transcripts were elevated only in cv. Star. A minor influence on transcripts for phenylalanine ammonia-lyase (PAL) was observed in all three cultivars. This indicates different levels of acclimation to UV-B radiation in the wheat cultivars studied. To analyze these responses in more detail, UV-B-exposed flag leaves of 84-day-old wheat (cv. Nandu) were pooled to isolate cDNAs of induced genes by suppression-subtractive hybridization (SSH). Among the initially isolated cDNA clones, 13 were verified by RNA gel blot analysis showing an up-regulation at elevated levels of UV-B radiation. Functional classification revealed genes encoding proteins associated with protein assembly, chaperonins, programmed cell death and signal transduction. We also studied growth, flowering time, ear development and yield as more typical agricultural parameters. Plant growth of young plants was reduced at increased UV-B radiation. Flowering and ear development were delayed concomitantly, whereas total grain weight was not influenced at any of the UV-B irradiation regimes. PMID:16893592

Zinser, Christian; Seidlitz, Harald K; Welzl, Gerhard; Sandermann, Heinrich; Heller, Werner; Ernst, Dieter; Rau, Werner




SciTech Connect

We present ultraviolet-integrated and azimuthally averaged surface photometric properties of a sample of 44 dwarf irregular (dIm), blue compact dwarf, and Sm galaxies measured from archival near-ultraviolet (NUV) and far-ultraviolet (FUV) images obtained with the Galaxy Evolution Explorer (GALEX). We compare the UV to H{alpha} and V-band properties and convert FUV, H{alpha}, and V-band luminosities into star formation rates (SFRs). We also model the star formation history from colors and compare the integrated SFRs and SFR profiles with radius for these methods. In most galaxies, the UV photometry extends beyond H{alpha} in radius, providing a better measure of the star formation activity in the outer disks. The H{alpha} appears to be lacking in the outer disk because of faintness in low-density gas. The FUV and V-band profiles are continuous with radius, although they sometimes have a kink from a double exponential disk. There is no obvious difference in star formation properties between the inner and outer disks. No disk edges have been observed, even to stellar surface densities as low as 0.1 M {sub sun} pc{sup -2} and SFRs as low as 10{sup -4} M {sub sun} yr{sup -1} kpc{sup -2}. Galaxies with low H I to luminosity ratios have relatively low FUV compared to V-band emission in the outer parts, suggesting a cessation of star formation there. Galaxies with relatively high H I apparently have fluctuating star formation with a gigayear timescale.

Hunter, Deidre A.; Ludka, Bonnie C. [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Elmegreen, Bruce G. [IBM T. J. Watson Research Center, P.O. Box 218, Yorktown Heights, NY 10598 (United States)], E-mail:, E-mail:, E-mail:



Research on UV scattering communication  

NASA Astrophysics Data System (ADS)

Ultraviolet (UV) scattering communication is a broadcast communication mode of information transmission by particles in the atmosphere scattering effect on the blind band ultraviolet light, there are many advantages such as unaffected by electromagnetic radiation, good confidentiality, non-line-of sight communication. This type communication mainly used in a short distance, secure communication, which was superior to no line communication in aspect of anti-jamming and secrecy. Firstly the military requirement of UV scattering communication is analyzed in this paper, The development trend is introduced, then the composition and working principle of ultraviolet scattering communication system are also discussed, The key influential factors of UV communication system path transmission loss effects on parameters such as receiver, transmitter and received beam divergence angle, pitch angle and the communication distance were analyzed. Attenuation was quantitatively simulated under different atmospheres, communication patterns and structure parameters. The results show that: transmission distance increases with increasing beam divergence angle and decreasing field angle. And the received view angle of influence on the communication distance is far greater than the emission beam divergence angle; transmission distance increases with increasing beam divergence angle and decreasing field and field angle effects on communication distance is greater than beam divergence angle.

Dong, Ke-yan; Lou, Yan; Ding, Ying; Wang, Shuo; Wang, Hongliang; Jiang, Hui-lin



XI UV Laser Trigger System  

SciTech Connect

The X1 accelerator project at Sandia National Laboratory/New Mexico utilizes SF6 insulated, multi-stage, UV laser triggered gas switches. A 265 nm UV laser system was designed and built to generate eight simultaneous output pulses of 10 mJ each with a 13 nsec pulse width. A 1061 nm solid-state Nd:Cr:GSGG laser was frequency quadrupled using a two-stage doubling process. The 1061 nm fundamental laser energy was frequency doubled with a KTP crystal to 530 nm, achieving 65% conversion efficiency. The 530 nm output was frequency doubled with KD*P crystal to 265 nm, achieving conversion efficiency of 31%. The 265 nm beam pulse was split into eight parallel channels with a system of partially reflecting mirrors. Low timing jitter and stable energy output were achieved. The entire optical system was packaged into a rugged, o-ring sealed, aluminum structure 10''x19''x2.75''. The size of the electronics was 12''x8''x8''. Subsequent accelerator system requirements dictated a redesign of the triggering system for an output beam with less angular divergence. An unstable, crossed porro prism resonator was designed and incorporated into the system. The beam divergence of the redesigned system was successfully decreased to 0.97 mrad in the UV. The resulting frequency doubling efficiencies were 55% to 530 nm and 25% to 265 nm. The optical output remained at 10 mJ in each channel with an 11 nsec pulse width.

Brickeen, B.K.; Morelli, G.L.; Paiva, R.A.; Powell, C.A.; Sundvold, P.D.



VUV-UV absorption spectroscopy of DNA and UV screens suggests strategies for UV resistance during evolution and space travel  

NASA Astrophysics Data System (ADS)

Early life on Earth had to cope with harsh conditions, including full spectrum solar UV. Since DNA absorbs in the highly energetic UV-C and VUV, solar irradiation was likely an obstacle to the expansion of life on Earth, until biological mechanisms evolved to cope with UV liability (including the biosynthesis of UV screens) and ozone (derived from oxygen produced by photosynthesis) accumulated in the stratosphere. In an effort to better understand the UV liability of DNA, we used synchrotron light to measure VUV-UV absorption spectra (125-340 nm) for DNA and its components (oligonucleotides and mononucleotides). We also measured VUV-UV absorption spectra for potential and known UV screens, including amino acids, proteins, amines (including polyamines), scytonemin, mycosporine-like amino acids, ?- carotene, melanin and flavonoids. Among these, flavonoids seem remarkably suited to protecting DNA in the VUV-UV. Flavonoids accumulate in seed coats, where they confer resistance to monochromatic UV (254 nm) and polychromatic UV (200-400 nm). We discuss these findings in relation to the origin and evolution of life and its potential dispersal through space.

Zalar, Andreja; Tepfer, David; Hoffmann, Søren V.; Kollmann, Albert; Leach, Sydney




SciTech Connect

In recent years, an argument has been made that a high fraction of early-type galaxies (ETGs) in the local universe experience low levels ({approx_lt}1 M {sub sun} yr{sup -1}) of star formation (SF) that causes strong excess in UV flux, yet leaves the optical colors red. Many of these studies were based on Galaxy Evolution Explorer imaging of Sloan Digital Sky Survey (SDSS) galaxies (z {approx} 0.1), and were thus limited by its 5'' FWHM. Poor UV resolution left other possibilities for UV excess open, such as the old populations or an active galactic nucleus (AGN). Here, we study high-resolution far-ultraviolet HST/ACS images of optically quiescent early-type galaxies with strong UV excess. The new images show that three-quarters of these moderately massive ({approx}5 x 10{sup 10} M {sub sun}) ETGs shows clear evidence of extended SF, usually in form of wide or concentric UV rings, and in some cases, striking spiral arms. SDSS spectra probably miss these features due to small fiber size. UV-excess ETGs have on average less dust and larger UV sizes (D > 40 kpc) than other green-valley galaxies, which argues for an external origin for the gas that is driving the SF. Thus, most of these galaxies appear 'rejuvenated' (e.g., through minor gas-rich mergers or intergalactic medium accretion). For a smaller subset of the sample, the declining SF (from the original internal gas) cannot be ruled out. SF is rare in very massive early-types (M {sub *} > 10{sup 11} M {sub sun}), a possible consequence of AGN feedback. In addition to extended UV emission, many galaxies show a compact central source, which may be a weak, optically inconspicuous AGN.

Salim, Samir [Department of Astronomy, Indiana University, Bloomington, IN 47404 (United States); Rich, R. Michael, E-mail: salims@indiana.ed [Department of Physics and Astronomy, University of California, Los Angeles, CA 90095 (United States)



Possible Nova among Hyades stars  

NASA Astrophysics Data System (ADS)

A new(?) very red 6th mag star was discovered among the stars of the Hyades from images obtained on 2012 October 22 04:28 EDT (10:28 UT). The coordinates of the star are RA,Dec (J2000.0): 04:23:29, +17:58:29 (+/-10"). This position is 2.23 arcmin south of the star GSC 1268-1045; and although this faint (13th mag) star does not appear on the discovery images, it is not believed to be the new star. Follow-up observations, especially spectroscopy are very desirable to confirm the presence and nature of the new star.

Shelton, Ian



Study of Implosion in Wire Arrays with UV interferometry and Faraday Rotation Diagnostics  

NASA Astrophysics Data System (ADS)

The implosion stage in wire arrays was studied with UV interferometry and Faraday rotation diagnostics at the wavelength of 266 nm implemented at the 1 MA Zebra pulsed power generator at UNR. Al cylindrical, star, and planar wire arrays were investigated. UV interferometry allows direct study of electron plasma density > 10^20 cm-3. Measurement of higher density is limited by spatial resolution, plasma motion, and plasma opacity at 266 nm. The density of the non-imploded plasma was measured at different times during the implosion stage. The first results from the UV Faraday rotation diagnostics are presented. Comparison of Faraday images with shadowgrams and interferograms allow measurement of current in the imploding plasma and non-imploded material in wire arrays.

Anderson, Austin; Papp, Daniel; Altemara, Sara; Ivanov, Vladimir



Lithium abundances of 21 solar-type stars near the Sun  

NASA Astrophysics Data System (ADS)

We present high-resolution spectroscopic observations for a sample of 21 young, solar-type stars near the Sun recently discovered in the X-ray wavelength range during the ROSAT all-sky survey. Based on these observations, we derive the lithium (Li) abundances of these 21 sample stars. Using the lithium abundances and the X-ray luminosity, we investigated the relationship between the Li abundances and the X-ray activity. We found a clear correlation between the lithium abundances and the X-ray luminosity: as the X-ray luminosity became stronger, the lithium abundance decreases in our sample stars. Our sample results provide further evidence that a correlation appears to exist between Li abundances, X-ray activity and age for a large number of solar-type stars. The results also confirm the presence of very active young stars close to the Sun, in agreement with recent findings from UV and X-ray surveys.

Xing, Li-Feng; Zhao, Shuang-Yi; Zhang, Xiao-Dong



Interstellar Ultraviolet Extinction Towards the Nitrogen Sequence Wolf-Rayet Stars  

NASA Astrophysics Data System (ADS)

With the archive IUE spectra of WR stars collected by Niedzielski and Rochowicz (1994) we obtain the UV extinction curve for WN stars. Using the two-color diagram method we can reach the goal almost independently, assuming only similar (b-v)_0 for all single galactic WN stars, what is discussed on the basis of latest results. The resulting extinction curve differs strongly shortwards of the 2200 bump from that of Seaton (1979) and is virtually identical to that of Krelowski and Papaj (1992). Assuming the power law shape of WN continua we obtain a new value of (b-v)_0=-0.22 for single WN stars and present E_{b-v} for 34 galactic WN stars.

Niedzielski, Andrzej



Variable star data online  

NASA Astrophysics Data System (ADS)

Roger Pickard, Andy Wilson and Gary Poyner describe the online database of the British Astronomical Association Variable Star Section, a treasure trove of observations stretching back nearly 125 years.

Pickard, Roger; Wilson, Andy; Poyner, Gary



Detector limitations, STAR.  

National Technical Information Service (NTIS)

Every detector has limitations in terms of solid angle, particular technologies chosen, cracks due to mechanical structure, etc. If all of the presently planned parts of STAR (Solenoidal Tracker At RHIC) were in place, these factors would not seriously li...

D. G. Underwood



Cosmions and stars  

SciTech Connect

Hypothetical particles such as the heavy neutrino, the photino, or the sneutrino/emdash/generically called cosmions/emdash/may solve the so called missing mass problem. If they exist, the cosmions may close the Universe. In addition to their gravitational effect on cosmological scales, the cosmions may also be captured by stars and concentrate in their cores. Since cosmions are able to transport heat outside stellar cores much more efficiently than photons, they may seriously affect the thermodynamics of the inner layer of stars. We have done an exact calculation of the accretion rate of cosmions by main sequence stars and we have studied the suppression of their central convection. We concluded that central convection inside stars between 0.3 Msub solar and 1 Msub solar is broken in the presence of cosmions. 6 refs., 2 figs.

Salati, P.



Structure of Neutron Stars.  

National Technical Information Service (NTIS)

Structure of neutron stars consisting of a cold and catalyzed superdense matter were investigated by integrating the equations for hydrostatic equilibrium based on the General Relativity theory. The equations of state were obtained with the help of semiem...

C. K. Cheong



Inside a Star . . .  

ERIC Educational Resources Information Center

|Describes classroom activities to understand the evolution of elements as it occurs in the stars. Activities can be undertaken in groups. Explicit instructions and background materials are included. (PS)|

Akerman, Jane; Wentzel, Donat G.



A UV-B-specific signaling component orchestrates plant UV protection  

Microsoft Academic Search

UV-B radiation in sunlight has diverse effects on humans, animals, plants, and microorganisms. UV-B can cause damage to molecules and cells, and consequently organisms need to protect against and repair UV damage to survive in sunlight. In plants, low nondamaging levels of UV-B stimulate transcription of genes involved in UV-protective responses. However, remarkably little is known about the underlying mechanisms

Bobby A. Brown; Catherine Cloix; Guang Huai Jiang; Eirini Kaiserli; Pawel Herzyk; Daniel J. Kliebenstein; Gareth I. Jenkins



Diurnal changes in epidermal UV transmittance of plants in naturally high UV environments.  


Studies were conducted on three herbaceous plant species growing in naturally high solar UV environments in the subalpine of Mauna Kea, Hawaii, USA, to determine if diurnal changes in epidermal UV transmittance (T(UV)) occur in these species, and to test whether manipulation of the solar radiation regime could alter these diurnal patterns. Additional field studies were conducted at Logan, Utah, USA, to determine if solar UV was causing diurnal T(UV) changes and to evaluate the relationship between diurnal changes in T(UV) and UV-absorbing pigments. Under clear skies, T(UV), as measured with a UV-A-pulse amplitude modulation fluorometer for leaves of Verbascum thapsus and Oenothera stricta growing in native soils and Vicia faba growing in pots, was highest at predawn and sunset and lowest at midday. These patterns in T(UV) closely tracked diurnal changes in solar radiation and were the result of correlated changes in fluorescence induced by UV-A and blue radiation but not photochemical efficiency (F(v)/F(m)) or initial fluorescence yield (F(o)). The magnitude of the midday reduction in T(UV) was greater for young leaves than for older leaves of Verbascum. Imposition of artificial shade eliminated the diurnal changes in T(UV) in Verbascum, but reduction in solar UV had no effect on diurnal T(UV) changes in Vicia. In Vicia, the diurnal changes in T(UV) occurred without detectable changes in the concentration of whole-leaf UV-absorbing compounds. Results suggest that plants actively control diurnal changes in UV shielding, and these changes occur in response to signals other than solar UV; however, the underlying mechanisms responsible for rapid changes in T(UV) remain unclear. PMID:18346077

Barnes, Paul W; Flint, Stephan D; Slusser, James R; Gao, Wei; Ryel, Ronald J



The Bibliographical Star Index  

NASA Astrophysics Data System (ADS)

The Bibliographical Star Index (BSI) is a bibliographical survey of astrophysical papers on stars that were published in 12 journals from 1950 to 1972 or have been published in about 40 journals since 1972. Difficulties that prevented complete coverage of the stellar literature are discussed, along with limitations of and errors in the BSI. The contents of the BSI for the period from 1950 to 1978 are summarized, and the availability of the index is briefly noted.

Ochsenbein, F.


SSE: Single Star Evolution  

NASA Astrophysics Data System (ADS)

SSE is a rapid single-star evolution (SSE) code; these analytical formulae cover all phases of evolution from the zero-age main-sequence up to and including remnant phases. It is valid for masses in the range 0.1-100 Msun and metallicity can be varied. The SSE package contains a prescription for mass loss by stellar winds. It also follows the evolution of rotational angular momentum for the star.

Hurley, Jarrod R.; Pols, Onno R.; Tout, Christopher A.



What Drives Star Formation?  

Microsoft Academic Search

Current theoretical models for what drives star formation (especially low-mass star formation) are: (1) magnetic support of self-gravitating clouds with ambipolar diffusion removing support in cores and triggering collapse, and (2) compressible turbulence forming self-gravitating clumps that collapse as soon as the turbulent cascade produces insufficient turbulent support. A crucial observational difference between the two models is the mass to

R. M. Crutcher



Reaching for the STARs  

Microsoft Academic Search

\\u000a The prototype STAR (Signal Transduction and Activation of RNA) protein is Sam68, the Src-associated substrate during mitosis of 68 kDa. Sam68, like all other STAR proteins, belongs to the large class of heteronuclear ribonucleoprotein particle K (hnRNP\\u000a K) homology (KH) domain family of RNA-binding proteins. The KH domain is an evolutionarily conserved RNA binding domain that\\u000a consists of 70–100 amino

Stéphane Richard


Physics and Star Trek  

NSDL National Science Digital Library

Created and maintained by physicist Jason Hinson, the Physics and Star Trek Web site investigates faster than light travel and subspace physics. Each topic is presented as a mix of factual information along with speculation on the author's part on how these phenomena could or could not work. Although the site consists of much text and few graphics, which may turn away some potential readers, the interesting subject will definitely appeal to hard core Star Trek or physics junkies.



Comparison Of UV And H-alpha SFR Indicators At Intermediate Redshift: Extraction Of H-alpha Fluxes From Near-IR Narrowband Imaging  

Microsoft Academic Search

We present preliminary results of an on-going study of the systematics between two commonly used star formation rate (SFR) indicators, UV and H-alpha emission at z 0.8. This poster reports on the measurement of emission-line fluxes from new H-alpha near-IR narrowband imaging in the Extended Groth Strip (EGS), while a companion poster describes the extraction of UV fluxes from ultra-deep

Andrew R. Esselman; J. Lee; S. Salim; R. Finn; D. Dale



Galaxy and mass assembly (GAMA): dust obscuration in galaxies and their recent star formation histories  

Microsoft Academic Search

We present self-consistent star formation rates derived through pan-spectral analysis of galaxies drawn from the Galaxy and Mass Assembly (GAMA) survey. We determine the most appropriate form of dust obscuration correction via application of a range of extinction laws drawn from the literature as applied to Halpha, [O II] and UV luminosities. These corrections are applied to a sample of

D. B. Wijesinghe; A. M. Hopkins; R. Sharp; M. Gunawardhana; S. Brough; E. M. Sadler; S. Driver; I. Baldry; S. Bamford; J. Liske; J. Loveday; P. Norberg; J. Peacock; C. C. Popescu; R. J. Tuffs; J. Bland-Hawthorn; E. Cameron; S. Croom; C. Frenk; D. Hill; D. H. Jones; E. van Kampen; L. Kelvin; K. Kuijken; B. Madore; B. Nichol; H. Parkinson; K. A. Pimbblet; M. Prescott; A. S. G. Robotham; M. Seibert; E. Simmat; W. Sutherland; E. Taylor; D. Thomas



Star forming galaxies at z ~ 2 in the GOODS\\/HDF-N  

Microsoft Academic Search

Galaxies at z ~ 2 are a relatively unexplored population, lying between the well-studied epoch of Lyman break galaxies (LBGs, z ~ 3) and the bounds of traditional magnitude-limited redshift surveys (z ~ 1). The UV-optimized LRIS-B spectrograph is opening this redshift range for systematic study. Galaxies at z ~ 2 are an important key to understanding high redshift star

Mark Dickinson; David Elbaz; Ranga-Ram Chary; Bahram Mobasher; Mauro Giavalisco; Daniel Stern



IR/UV and UV/UV double-resonance study of guaiacol and eugenol dimers  

NASA Astrophysics Data System (ADS)

Guaiacol (2-methoxyphenol) and eugenol (4-allyl-2-methoxyphenol) molecules are biologically active phenol derivatives with an intramolecular -OH...OCH3 hydrogen bond (H bond). Pulsed supersonic expansions of mixtures of either of the two molecules with He yield weakly bound homodimers as well as other higher-order complexes. A number of complementary and powerful laser spectroscopic techniques, including UV-UV and IR-UV double resonances, have been employed to interrogate the species formed in the expansion in order to get information on their structures and spectroscopic properties. The interpretation of the spectra of eugenol dimer is complex and required a previous investigation on a similar but simpler molecule both to gain insight into the possible structures and support the conclusions. Guaiacol (2-methoxyphenol) has been used for that purpose. The combination of the broad laser study combined with ab initio calculations at the Becke 3 Lee-Yang-Parr/6-31+G(d) level has provided the isomer structures, the potential-energy wells, and shed light on the inter- and intramolecular interactions involved. Guaiacol homodimer has been shown to have a single isomer whereas eugenol dimer has at least two. The comparison between the computed geometries of the dimers, their respective energies, and the vibrational normal modes permits the identification of the spectra.

Longarte, Asier; Redondo, Carolina; Fernández, José A.; Castaño, Fernando



Post-AGB Stars  

NASA Astrophysics Data System (ADS)

In this contribution, a review is presented on the ample data obtained on post-AGB stars, both on the central stars and their circumstellar material. The fast evolutionary phase is characterized by a rapid change in the properties of the objects, but the variety is so large that there is yet no clear consensus on how the detailed studies of individual objects are linked together by evolutionary channels. The absence of strong molecular veiling in the photospheres of the central stars, together with a spread in intrinsic metallicity make post-AGB stars very useful in constraining AGB chemical evolutionary models. We discuss the surprisingly wide variety of chemical signatures observed. The onset in the creation process of the panoply of structures and shapes observed in planetary nebulae occurs during the short post-AGB evolution, but the physical nature of the processes involved is still badly understood. In the rapidly growing field of circumstellar mineralogy, post-AGB stars have their story to tell and also the molecular envelope changes significantly due to dilution and hardening of the stellar radiation. The real-time evolution of some objects suffering a late thermal flash is reviewed and their possible link to other hydrogen-deficient objects is discussed. Any review on stellar evolution has a section on binaries and this contribution is no exception because binaries make up a significant fraction of the post-AGB stars known to date.

van Winckel, Hans


The Star*s Family - an Update  

NASA Astrophysics Data System (ADS)

We shall present the current situation of the Star*s Family, a growing collection of products: directories, dictionaries, databases, data sets, and so on. The directories gather together all practical data available on organizations involved in astronomy, space sciences and related fields, while the dictionaries concern abbreviations, acronyms, contractions and symbols encountered in the same fields. The databases correspond both to the dictionaries and directories. They are currently accessible on line at the European Southern Observatory (ESO) through Starcat and at the European Space Agency (ESA) through ESIS. Their implementation is presently carried out at Strasbourg astronomical Data Center (CDS). Other agreements are currently being negociated. Practical information on the availability of all products can be obtained from the author (telefax: +33-88491255).

Heck, Andre



Physiological responses of Scenedesmus quadricauda (Chlorophyceae) to UV-A and UV-C light.  


Despite intensive research focused on the effects of UV-B, deeper metabolic responses to UV-A and UV-C are still scarce. Besides, especially microalgal species had to develop efficient protective features in comparison with tissue structure of vascular plants. We exposed axenic cultures of Scenedesmus quadricauda (Chlorophyceae) to UV-A (366 nm) and UV-C (254 nm) light over 1 h. Both wavelengths stimulated increase in soluble proteins, superoxide radical and hydrogen peroxide, but had a nonsignificant effect on cell viability. Within 17 detected free amino acids, five (including proline) increased in response to UV-A while only aspartic acid and histidine increased in UV-C treatment. Total soluble phenols and flavonoids were influenced neither by UV-A nor by UV-C while selected flavonols (quercetin and kaempferol) decreased in UV-A and were not detected in UV-C treatment. Benzoic acid derivatives increased preferentially after UV-A illumination (vanillic acid and vanillin) while cinnamic derivatives (caffeic, chlorogenic and p-coumaric acids) decreased in both UV-A and UV-C. It is concluded that UV light stimulated oxidative stress while exposure time was not sufficient to stimulate larger changes in phenolic metabolites. Present findings in the context of available data and with emphasis on phenolics in algae are discussed. PMID:20202162

Kovácik, Jozef; Klejdus, Borivoj; Backor, Martin



Performance results from in-flight commissioning of the Juno Ultraviolet Spectrograph (Juno-UVS)  

NASA Astrophysics Data System (ADS)

We present a description of the Juno ultraviolet spectrograph (Juno-UVS) and results from its in-flight commissioning performed between December 5th and 13th 2011 and its first periodic maintenance between October 10th and 12th 2012. Juno-UVS is a modest power (9.0 W) ultraviolet spectrograph based on the Alice instruments now in flight aboard the European Space Agency's Rosetta spacecraft, NASA's New Horizons spacecraft, and the LAMP instrument aboard NASA's Lunar Reconnaissance Orbiter. However, unlike the other Alice spectrographs, Juno-UVS sits aboard a spin stabilized spacecraft. The Juno-UVS scan mirror allows for pointing of the slit approximately +/-30° from the spacecraft spin plane. This ability gives Juno-UVS access to half the sky at any given spacecraft orientation. The planned 2 rpm spin rate for the primary mission results in integration times per 0.2° spatial resolution element per spin of only ~17 ms. Thus, for calibration purposes, data were retrieved from many spins and then remapped and co-added to build up exposure times on bright stars to measure the effective area, spatial resolution, scan mirror pointing positions, etc. The primary job of Juno-UVS will be to characterize Jupiter's UV auroral emissions and relate them to in-situ particle measurements. The ability to point the slit will make operations more flexible, allowing Juno-UVS to observe the atmospheric footprints of magnetic field lines through which Juno flies, giving a direct connection between energetic particle measurements on the spacecraft and the far-ultraviolet emissions produced by Jupiter's atmosphere in response to those particles.

Greathouse, T. K.; Gladstone, G. R.; Davis, M. W.; Slater, D. C.; Versteeg, M. H.; Persson, K. B.; Walther, B. C.; Winters, G. S.; Persyn, S. C.; Eterno, J. S.



A fast star image extraction algorithm for autonomous star sensors  

NASA Astrophysics Data System (ADS)

Star sensors have been developed to acquire accurate orientation information in recent decades superior to other attitude measuring instruments. A star camera takes photos of the night sky to obtain star maps. An important step to acquire attitude knowledge is to compare the features of the observed stars in the maps with those of the cataloged stars using star identification algorithms. To calculate centroids of the star images before this step, they are required to be extracted from the star maps in advance. However, some large or ultra large imaging detectors are applied to acquire star maps for star sensors with the development of electronic imaging devices. Therefore, star image extraction occupies more and more portions of the whole attitude measurement period of time. It is required to shorten star image extraction time in order to achieve higher response rate. In this paper, a novel star image extraction algorithm is proposed which fulfill the tasks efficiently. By scanning star map, the pixels brighter than the gray threshold are found and their coordinates and brightness are stored in a cross-linked list. Data of these pixels are linked by pointers, while other pixels are neglected. Therefore, region growing algorithm can be used by choosing the first element in the list as a starting seed. New seeds are founded if the neighboring pixels are brighter than the threshold, and the last seed is deleted from the list. Next search continues until no neighboring pixels are in the list. At that time, one star image is extracted, and its centroid is calculated. Likely, other star images may be extracted, and then the examined seeds are deleted which are never considered again. A new star image search always begins from the first element for avoiding unnecessary scanning. The experiments have proved that for a 1024×1024 star map, the image extraction takes nearly 16 milliseconds. When CMOS APS is utilized to transfer image data, the real-time extraction can be almost achieved.

Zhu, Xifang; Wu, Feng; Xu, Qingquan



Spitzer Observations of Star Formation in the Extreme Outer Disk of M83 (NGC5236)  

NASA Astrophysics Data System (ADS)

Spitzer Infrared Array Camera (IRAC) observations of two fields in the extended UV disk (XUV-disk) of M83 have been recently obtained, ~3 R HII away from the center of the galaxy (R HII = 6.6 kpc). Galaxy Evolution Explorer (GALEX) UV images have shown the two fields to host in situ recent star formation. The IRAC images are used in conjunction with GALEX data and new H I imaging from The H I Nearby Galaxy Survey (THINGS) to constrain stellar masses and ages of the UV clumps in the fields, and to relate the local recent star formation to the reservoir of available gas. Multi-wavelength photometry in the UV and mid-IR (MIR) bands of 136 UV clumps (spatial resolution >220 pc) identified in the two target fields, together with model fitting of the stellar UV-MIR spectral energy distributions (SEDs), suggests that the clumps cover a range of ages between a few Myr and >1 Gyr with a median value around <=100 Myr, and have masses in the range 103-3 × 106 M sun, with a peak {\\sim} 10^{4.7}M_{\\bigodot }. The range of observed ages, for which only a small fraction of the mass in stars appears to have formed in the past ~10 Myr, agrees with the dearth of H? emission observed in these outer fields. At the location of our IRAC fields, the H I map shows localized enhancement and clumping of atomic gas. A comparison of the observed star formation with the gas reservoir shows that the UV clumps follow the Schmidt-Kennicutt scaling law of star formation, and that star formation is occurring in regions with gas densities at approximately (within a factor of a few) the critical density value derived according to the Toomre Q gravitational stability criterion. The significant 8 ?m excess in several of the clumps (16% of the total by number accounting for ~67% of the 8 ?m flux) provides evidence for the existence of dust in these remote fields, in agreement with results for other galaxies. Furthermore, we observe a relatively small excess of emission at 4.5 ?m in the clumps (14% ± 6% by flux), which suggests contribution from hot small grains (~1000 K), as already observed in other galaxies. From our data, the outer regions of the M83 galaxy disk show evidence of a time-extended star-formation history over lsim1 Gyr, and of a moderately chemically-evolved interstellar medium, in agreement with recent findings on the metallicity of the outer H II regions of M83.

Dong, Hui; Calzetti, Daniela; Regan, Michael; Thilker, David; Bianchi, Luciana; Meurer, Gerhardt R.; Walter, Fabian



The Nature of the UV/Optical Emission of the Ultraluminous X-Ray Source in Holmberg II  

NASA Astrophysics Data System (ADS)

We report on UV and X-ray spectroscopy and broadband optical observations of the ultraluminous X-ray source in Holmberg II. Fitting various stellar spectral models to the combined, non-simultaneous data set, we find that normal metallicity stellar spectra are ruled out by the data, while low-metallicity, Z = 0.1 Z ?, late O-star spectra provide marginally acceptable fits, if we allow for the fact that X-ray ionization from the compact object may reduce or eliminate UV absorption/emission lines from the stellar wind. By contrast, an irradiated disk model fits both UV and optical data with ?2/dof = 175.9/178, and matches the nebular extinction with a reddening of E(B - V) = 0.05+0.05 - 0.04. These results suggest that the UV/optical flux of Holmberg II X-1 may be dominated by X-ray irradiated disk emission.

Tao, Lian; Kaaret, Philip; Feng, Hua; Grisé, Fabien