A5048405918- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astro and Planetary Science
- Astronomical Observations and Instrumentation
- Gamma-ray bursts and supernovae
- Adaptive optics and wavefront sensing
- Astrophysical Phenomena and Observations
- Pulsars and Gravitational Waves Research
- History and Developments in Astronomy
- Social Sciences and Governance
- Solar and Space Plasma Dynamics
- Atmospheric Ozone and Climate
- Healthcare Systems and Practices
- Laser-induced spectroscopy and plasma
- High-pressure geophysics and materials
- Scientific Research and Discoveries
- Spectroscopy and Laser Applications
- Galaxies: Formation, Evolution, Phenomena
- Geophysics and Sensor Technology
- Health Policy Implementation Science
- Calibration and Measurement Techniques
- Atomic and Molecular Physics
- Global Public Health Policies and Epidemiology
- Primary Care and Health Outcomes
Université de Montréal
2016-2025
Inserm
2023
Université Paris-Saclay
2023
Institut Gustave Roussy
2023
Université Laval
1974-2017
Hebrew University of Jerusalem
2016
Institut National de Santé Publique du Québec
2004-2013
The Quebec Population Health Research Network
2012
Cerro Tololo Inter-American Observatory
1997-2010
Laboratory for Atmospheric and Space Physics
2010
In the light of recent significant progress on both observational and theoretical fronts, we review status white dwarf stars as cosmochronometers. These objects represent end products stellar evolution for vast majority and, such, can be used to constrain ages various populations evolved in Galaxy. For example, oldest dwarfs solar neighborhood (the remnants very first generation intermediate‐mass Galactic disk) are still visible used, conjunction with cooling theory, estimate age disk. More...
view Abstract Citations (648) References (66) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Spectroscopic Determination of the Mass Distribution DA White Dwarfs Bergeron, P. ; Saffer, Rex A. Liebert, James Attention is given to mass distribution for a sample 129 white dwarfs based on fitting hydrogen line profiles predictions stellar atmosphere models. The atmospheric parameters determined from spectroscopy are shown be improved accuracy over those...
We present an improved spectroscopic and photometric analysis of hydrogen-line DA white dwarfs from the Sloan Digital Sky Survey Data Release 4 (SDSS DR4) based on model atmospheres that include Stark broadening profiles with non-ideal gas effects. also perform a careful visual inspection all fits high signal-to-noise ratios (S/Ns > 12) atmospheric parameters (Teff log g) for each dwarf. Through comparison temperatures, we report discovery 35 DA+DB/DC double degenerate candidates two...
We have calibrated four major ground-based photometric systems with respect to the Hubble Space Telescope (HST) absolute flux scale, which is defined by Vega and fundamental DA white dwarfs. These include Johnson-Kron-Cousins UBVRI, Strömgren uvby filters, Two Micron All Sky Survey JHKs, Sloan Digital ugriz filters. Synthetic magnitudes are calculated from model dwarf spectra folded through published filter response functions; these in turn absolutely HST scale. Effective zero-magnitude...
Bolometric corrections and color indices on various photometric systems are provided for an extensive grid of hydrogen- helium-rich white dwarf model atmospheres. Absolute visual magnitudes, masses, ages also obtained each from detailed evolutionary cooling sequences appropriate these stars. The results our calculations briefly compared with published observational material. These can easily be extended to any given system.
Spectrophotometric observations at high signal-to-noise ratio were obtained of a complete sample 347 DA white dwarfs from the Palomar Green (PG) Survey. Fits observed Balmer lines to synthetic spectra calculated pure-hydrogen model atmospheres used obtain robust values Teff, log g, masses, radii, and cooling ages. The luminosity function sample, weighted by 1/Vmax, was compared with other determinations. mass distribution is derived, after important corrections for radii in this...
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...
We present improved calculations for the Stark broadening of hydrogen lines in dense plasmas typical white dwarf atmospheres. Our new model is based on unified theory from Vidal, Cooper, & Smith. For first time, we account non-ideal effects a consistent way directly inside line profile calculations. The Hummer Mihalas used to describe due perturbations absorber protons and electrons. use truncation electric microfield distribution quasi-static proton take into fact that high microfields...
We present a detailed analysis of 108 helium-line (DB) white dwarfs based on model atmosphere fits to high signal-to-noise optical spectroscopy. derive mean mass 0.67 Mo for our sample, with dispersion only 0.09 Mo. White also showing hydrogen lines, the DBA stars, comprise 44% and their distribution appears similar that DB stars. As in previous investigation, we find no evidence existence low-mass (M < 0.5 Mo) dwarfs. luminosity function subset identified Palomar-Green survey. show 20% all...
Abstract As they evolve, white dwarfs undergo major changes in surface composition, a phenomenon known as spectral evolution. In particular, some stars enter the cooling sequence with helium atmospheres (type DO) but eventually develop hydrogen DA), most likely through upward diffusion of residual hydrogen. Our empirical knowledge this process remains scarce: fractions that are born rich and experience DO-to-DA transformation poorly constrained. We tackle issue by performing detailed...
A detailed photometric and spectroscopic analysis of cool (Teff ≲ 12,000 K) white dwarf stars is presented. The sample has been drawn from the Yale Parallax Catalog a proper motion survey in southern hemisphere. Optical BVRI infrared JHK photometry, as well spectroscopy at Hα, have secured for 152 dwarfs. discovery seven new DA dwarfs, two DQ one magnetic dwarf, three weak candidates, reported. Our also identifies 19 known or suspected double degenerates. energy distributions, Hα line...
view Abstract Citations (370) References (71) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Atmospheric Parameters of Field Subdwarf B Stars Saffer, Rex A. ; Bergeron, P. Koester, D. Liebert, James High signal-to-noise ratio optical spectrophotometry a sample field subluminous stars drawn largely from the Palomar Green ultraviolet-excess survey is analyzed with new grid model atmospheres and synthetic spectra. The stellar effective temperatures, surface...
Photometric and spectroscopic observations of 110 cool white dwarf stars are presented analyzed with state-of-the-art model atmosphere calculations appropriate for dwarfs pure hydrogen helium, as well mixed H/He compositions. High signal-to-noise spectroscopy reveals the presence Hα in 20 previously classified DC stars, four which magnetic. Cool shown to form a narrow sequence both color-color color-magnitude diagrams, little evidence separation between hydrogen- helium-rich compositions...
view Abstract Citations (314) References (79) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical and Ultraviolet Analyses of ZZ Ceti Stars Study the Atmospheric Convective Efficiency in DA White Dwarfs Bergeron, P. ; Wesemael, F. Lamontagne, R. Fontaine, G. Saffer, A. Allard, N. New high signal-to-noise optical spectrophotometry is presented for 22 stars. The atmospheric parameters (Teff log g) mass are derived each object using new model atmospheres...
view Abstract Citations (194) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS New Model Atmospheres for Very Cool White Dwarfs with Mixed H/He and Pure He Compositions Bergeron, P. ; Saumon, D. Wesemael, F. model atmosphere calculations very cool white dwarfs mixed pure compositions are presented. The hydrogen-rich models incorporate improved cross section of the collision-induced absorption by molecular hydrogen due to collisions H2, H, He....
view Abstract Citations (255) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Whole Earth Telescope Observations of the DBV White Dwarf GD 358 Winget, D. E. ; Nather, R. Clemens, J. C. Provencal, L. Kleinman, S. Bradley, P. A. Claver, F. Dixson, Montgomery, M. H. Hansen, Hine, B. Birch, Candy, Marar, T. K. Seetha, Ashoka, N. Leibowitz, O'Donoghue, Warner, Buckley, Tripe, Vauclair, G. Dolez, Chevreton, Serre, Garrido, Kepler, O. Kanaan,...
We present a detailed analysis of large spectroscopic and photometric sample DZ white dwarfs based on our latest model atmosphere calculations. revise the atmospheric parameters trigonometric parallax Bergeron, Leggett, & Ruiz (12 stars) analyze 147 new discovered in Sloan Digital Sky Survey. The inclusion metals hydrogen calculations leads to different than those derived from pure helium models. Calcium abundances are found range log (Ca/He) = -12 -8. also find that fits coolest objects...
We present improved atmospheric parameters of nearby white dwarfs lying within 20 pc the Sun. The aim current study is to obtain best statistical model least-biased sample dwarf population. A homogeneous analysis local population performed combining detailed spectroscopic and photometric analyses based on atmosphere calculations for various spectral types including DA, DB, DC, DQ, DZ stars. technique applied all stars in our which optical spectra are available. Photometric energy...
Abstract We present a critical review of the determination fundamental parameters white dwarfs discovered by Gaia mission. first reinterpret color–magnitude and color–color diagrams using photometric spectroscopic information contained in Montreal White Dwarf Database (MWDD), combined with synthetic magnitudes calculated from self-consistent set model atmospheres various atmospheric compositions. The same models are then applied to measure so-called technique, which relies on exquisite...
We present a new model atmosphere analysis of the most metal contaminated white dwarf known, DBZ SDSS J073842.56+183509.06. Using high resolution spectroscopic observations taken with Keck and Magellan, we determine precise atmospheric parameters measure abundances 14 elements heavier than helium. also report Spitzer mid-infrared photometric data that are used to better constrain properties debris disk orbiting this star. Our detailed analysis, which combines from 7 different observational...
Gravitational deflection of starlight around the Sun during 1919 total solar eclipse provided measurements that confirmed Einstein's general theory relativity. We have used Hubble Space Telescope to measure analogous process astrometric microlensing caused by a nearby star, white dwarf Stein 2051 B. As B passed closely in front background star's position was deflected. Measurement this at multiple epochs allowed us determine mass -- sixth nearest as 0.675 +/- 0.051 masses. This determination...
We present follow-up spectroscopy of 711 white dwarfs within 100 pc, and a detailed model atmosphere analysis the pc dwarf sample in SDSS footprint. Our spectroscopic is complete for 83% hotter than 6000 K, where atmospheric composition can be constrained reliably. identify 1508 DA with pure hydrogen atmospheres. The mass distribution has an extremely narrow peak at $0.59~M_{\odot}$, reveals shoulder from relatively massive $M=0.7$-$0.9~M_{\odot}$. Comparing this binary population synthesis...
Abstract We present an analysis of 1023 DBZ/DZ(A) and 319 DQ white dwarf stars taken from the Montreal White Dwarf Database. This represents a significant increase over previous comprehensive studies on these types objects. use new trigonometric parallax measurements Gaia second data release, together with photometry Sloan Digital Sky Survey, Pan-STARRS, , or BVRI literature, which allow determination mass for majority objects in our sample. photometric spectroscopic techniques recently...
We present a detailed description of the physical properties our current census white dwarfs within 40 pc Sun, based on an exhaustive spectroscopic survey northern hemisphere candidates from SUPERBLINK proper motion database. Our method for selecting dwarf is combination theoretical color–magnitude relations and reduced diagrams. reported in earlier publication discovery nearly 200 new dwarfs, we here additional 133 among which identify 96 DA, 3 DB, 24 DC, DQ, 7 DZ stars. further 178 that...
The Canada-France Imaging Survey (CFIS) will map the northern high Galactic latitude sky in $u$-band ("CFIS-u", 10,000$\, {\rm deg^2}$) and $r$-band ("CFIS-r", 5,000$\, deg^2}$), enabling a host of stand-alone science investigations, providing some ground-based data necessary for photometric redshift determination Euclid mission. In this first contribution we present component survey, describe observational strategy, discuss highlight results, based on approximately one third final area. We...