A5008655726- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astro and Planetary Science
- Gamma-ray bursts and supernovae
- Astronomical Observations and Instrumentation
- Pulsars and Gravitational Waves Research
- Geophysics and Gravity Measurements
- Astrophysical Phenomena and Observations
- Adaptive optics and wavefront sensing
- Dark Matter and Cosmic Phenomena
- History and Developments in Astronomy
- High-pressure geophysics and materials
- Solar and Space Plasma Dynamics
- Advanced Frequency and Time Standards
- Space Exploration and Technology
- Geophysics and Sensor Technology
- Galaxies: Formation, Evolution, Phenomena
- Geological and Geophysical Studies
- Cosmology and Gravitation Theories
- Geomagnetism and Paleomagnetism Studies
- Scientific Research and Discoveries
- Impact of Light on Environment and Health
- Remote Sensing in Agriculture
- Astronomical and nuclear sciences
Universidade Federal do Rio Grande do Sul
2016-2025
The University of Texas at Austin
1980-2009
University of Göttingen
2009
Universidade Federal do Rio Grande
2006
Laboratório Nacional de Astrofísica
2003
Cerro Tololo Inter-American Observatory
1993-2003
National Council for Scientific and Technological Development
1998
Association of Universities For Research In Astronomy
1997
Université de Montréal
1991
Ames Research Center
1991
view Abstract Citations (453) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS An Independent Method for Determining the Age of Universe Winget, D. E. ; Hansen, C. J. Liebert, James van Horn, H. M. Fontaine, G. Nather, R. Kepler, S. O. Lamb, Q. The observed number white dwarfs in a given volume space increases monotonically with decreasing luminosity, as expected from cooling rate considerations. However, their drops abruptly at luminosity log...
We present a new catalog of spectroscopically confirmed white dwarf stars from the Sloan Digital Sky Survey (SDSS) Data Release 7 spectroscopic catalog. find 20,407 spectra, representing 19,712 stars, and provide atmospheric model fits to 14,120 DA 1011 DB spectra 12,843 923 respectively. These numbers represent more than factor two increase in total number previous SDSS catalogs based on DR4 data. Our distribution subtypes varies due our conservative, manual classifications each star...
Galactic history is written in the white dwarf stars. Their surface properties hint at interiors composed of matter under extreme conditions. In forty years since their discovery, pulsating stars have moved from side-show curiosities to center stage as important tools for unraveling deep mysteries Universe. Innovative observational techniques and theoretical modeling breathed life into precision asteroseismology. We are just learning use this powerful tool, confronting models with observed...
We report the discovery of 9 089 new spectroscopically confirmed white dwarfs and subdwarfs in Sloan Digital Sky Survey Data Release 10. obtain Teff, log g mass for hydrogen atmosphere dwarf stars (DAs) helium (DBs), estimate calcium/helium abundances with metallic lines (DZs) carbon/helium carbon dominated spectra DQs. found 1 central star a planetary nebula, 2 oxygen on dwarfs, 71 DQs, 42 hot DO/PG1159s, 171 dwarf+main sequence binaries, 206 magnetic DAHs, 327 continuum DCs, 397 metal...
view Abstract Citations (332) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Asteroseismology of the DOV Star PG 1159-035 with Whole Earth Telescope Winget, D. E. ; Nather, R. Clemens, J. C. Provencal, Kleinman, S. Bradley, P. A. Wood, M. Claver, F. Frueh, L. Grauer, Hine, B. Hansen, Fontaine, G. Achilleos, N. Wickramasinghe, T. Marar, K. Seetha, Ashoka, O'Donoghue, Warner, Kurtz, W. Buckley, Brickhill, Vauclair, Dolez, Chevreton, Barstow,...
We determined masses for the 7167 DA and 507 DB white dwarf stars classified as single non-magnetic in Data Release 4 of Sloan Digital Sky Survey (SDSS). obtained revised Teff log g determinations most massive by fitting SDSS optical spectra with a synthetic grid derived from model atmospheres extending to g= 10.0. also calculate radii evolutionary models create volume-corrected mass distributions our samples. The mean brighter than 19 hotter Teff= 12 000 K is . For 150 DBs 16 K, we find It...
To obtain better statistics on the occurrence of magnetism among white dwarfs, we searched spectra hydrogen atmosphere dwarf stars (DAs) in Data Release 7 Sloan Digital Sky Survey (SDSS) for Zeeman splittings and estimated magnetic fields. We found 521 DAs with detectable splittings, fields range from around 1 to 733 MG, which amounts 4 per cent all observed. As SDSS have low signal-to-noise ratios, carefully investigated by simulations theoretical how reliable our detection field was.
ABSTRACT White dwarfs carry information on the structure and evolution of Galaxy, especially through their luminosity function initial-to-final mass relation. Very cool white provide insight into early ages each population. Examining spectra all stars with 3σ proper motion in Sloan Digital Sky Survey Data Release 14, we report classification for 20 088 spectroscopically confirmed dwarfs, plus 415 hot subdwarfs, 311 cataclysmic variables. We obtain Teff, log g, hydrogen atmosphere dwarf...
ZZ Ceti stars form the most numerous group of degenerate variable stars. They are otherwise normal DA (H-rich atmospheres) white dwarfs that exhibit pulsations. Here, we present an asteroseismological analysis for 44 bright based on a new set fully evolutionary dwarf models characterized by detailed chemical profiles from centre to surface. One our targets is archetypal star G117$-$B15A, which obtain model with effective temperature and surface gravity in excellent agreement spectroscopy....
We employ a state-of-the-art asteroseismological model of G117-B15A, the archetype H-rich atmosphere (DA) white dwarf pulsators (also known as DAV or ZZ Ceti variables), and use most recently measured value rate period change for dominant mode this pulsating star to derive new constraint on mass axion, still conjectural non-barionic particle considered candidate dark matter Universe. Assuming that G117-B15A is truly represented by our model, in particular, associated pulsation g-mode trapped...
We present a spectroscopic survey of 230 white dwarf candidates within 40 pc the Sun from William Herschel Telescope and Gran Telescopio Canarias. All were selected $\textit{Gaia}$ Data Release 2 (DR2) in almost all cases had no prior classifications. find total 191 confirmed dwarfs 39 main-sequence star contaminants. The majority stellar remnants sample are relatively cool ($\langle T_{\rm eff} \rangle$ = 6200 K), showing either hydrogen Balmer lines or featureless spectrum, corresponding...
We report the discovery of 74 new pulsating DA white dwarf stars, or ZZ Cetis, from data obtained by Transiting Exoplanet Survey Satellite (TESS) mission, Sectors 1 to 39, corresponding first 3 cycles. This includes objects Southern Hemisphere (Sectors 1-13 and 27-39) Northern 14-26), observed with 120 s- 20 s-cadence. Our sample likely 13 low-mass one extremely candidate, considering mass determinations fitting Gaia magnitudes parallax. In addition, we present follow-up time series...
We present the first volume-limited sample of spectroscopically confirmed hot subluminous stars out to 500 pc, defined using accurate parallax measurements from Gaia space mission data release 3 (DR3). The comprises a total 397 members, with 305 (~77%) identified as subdwarf stars, including 83 newly discovered systems. Of these, we observe that 178 (~58%) are hydrogen-rich sdBs, 65 sdOBs (~21%), 32 sdOs (~11%), and 30 He-sdO/Bs (~10%). Among them, 48 (~16%) exhibit an infrared excess in...
The white dwarfs are promising laboratories for the study of cosmochronology and stellar evolution. Through observations pulsating dwarfs, we can measure their internal structures compositions, critical to understanding post main sequence evolution, along with cooling rates, allowing us calibrate ages directly. most important set dwarf variables oldest pulsators, cool DAVs, which have not previously been explored through asteroseismology due complexity instability. a time-series photometry...
We present 35 new pulsating DA (hydrogen atmosphere) white dwarf stars discovered from the Sloan Digital Sky Survey (SDSS) and Hamburg Quasar (HQS). have acquired high-speed time series photometry of preselected dwarfs with a prime focus CCD photometer on 2.1 m telescope at McDonald Observatory over 15 months. selected these basis prior photometric spectroscopic observations by SDSS HQS. For homogeneous sample, we achieve success rate 80% for finding variables detection threshold 0.1%-0.3%....
We present a theoretical study on the metallicity dependence of initial-to-final mass relation and its influence white dwarf age determinations. compute grid evolutionary sequences from main sequence to ∼3000 K cooling curve, passing through all intermediate stages. During thermally pulsing asymptotic giant branch no third dredge-up episodes are considered thus photospheric C/O ratio is below unity for with metallicities larger than Z = 0.0001. consider initial 0.0001 0.04, accounting...
We explore the evolution of hydrogen-rich and hydrogen-deficient white dwarf stars with masses between 1.012 1.307 Msun, initial metallicity Z=0.02. These sequences are result main sequence 8.8 11.8 Msun. The simulations were performed MESA, starting at zero-age sequence, through thermally pulsing mass-loss phases, ending dwarfs cooling sequence. present reliable chemical profiles for whole mass range considered, covering different expected central compositions, i.e. C/O, O/Ne Ne/O/Mg, its...
We present the first phase in our ongoing work to use Sloan Digital Sky Survey (SDSS) data create separate white dwarf (WD) luminosity functions (LFs) for two or more different mass ranges. In this paper, we determine completeness of SDSS spectroscopic WD sample by comparing a proper-motion selected WDs from imaging with large catalog spectroscopically determined WDs. derive selection probability as function single color (g − i) and apparent magnitude (g) that covers range −1.0 < g i 0.2 15...
We present full evolutionary calculations appropriate for the study of hot hydrogen-deficent DO white dwarfs, PG 1159 stars, and DB dwarfs. White dwarf sequences are computed a wide range stellar masses helium envelopes on basis complete treatment history progenitors including core hydrogen burning phases, thermally-pulsing AGB phase, born-again episode that is responsible deficiency. also provide colors magnitudes new $T_{\rm eff} < 40 000$ K, where NLTE effects not dominant. These an...
Pulsating white dwarfs with hydrogen-rich atmospheres, also known as DAV stars, can be used astrophysical laboratories to constrain the properties of fundamental particles like axions. Comparing measured cooling rates these stars expected values from theoretical models allows us search for sources additional due emission weakly interacting particles. In this paper, we present an independent inference mass axion using recent determination evolutionary rate R548, class prototype. We employ a...
We employ an asteroseismic model of L19-2, a relatively massive ($M_{\star} \sim 0.75 M_{\sun}$) and hot ($T_{\rm eff} 12\,100$ K) pulsating DA (H-rich atmosphere) white dwarf star (DAV or ZZ Ceti variable), use the observed values temporal rates period change its dominant pulsation modes ($\Pi 113$ s $\Pi 192$ s), to derive new constraint on mass axion, hypothetical non-barionic particle considered as possible component dark matter Universe. If employed is accurate representation then our...
Context. Among the spectroscopically identified white dwarfs, a fraction smaller than 2% have spectra dominated by carbon lines, mainly molecular C 2 , but also group I and II lines. These are together called DQ dwarfs. Aims. We want to derive atmospheric parameters T eff log g abundances for large sample of these stars discuss implications their spectral evolution. Methods. Sloan Digital Sky Survey ugriz photometry were used, with Gaia Data Release parallaxes G band photometry. fitted...
Context. ZZ Ceti stars are pulsating white dwarfs with a carbon-oxygen core build up during the helium burning and thermally pulsing Asymptotic Giant Branch phases. Through interpretation of their pulsation periods by means asteroseismology, details about origin evolution can be inferred. The whole spectrum exhibited strongly depends on inner chemical structure. At present, there several processes affecting profiles that still not accurately determined.