P. Bergeron

Université du Québec à Montréal, Montréal, Quebec, Canada

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Publications (261)867.53 Total impact

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    A Gianninas · P Bergeron · M T Ruiz
  • M. -M. Limoges · P. Bergeron · S. Lépine
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    ABSTRACT: We present a detailed description of the physical properties of our current census of white dwarfs within 40 pc of the Sun, based on an exhaustive spectroscopic survey of northern hemisphere candidates from the SUPERBLINK proper motion database. Our method for selecting white dwarf candidates is based on a combination of theoretical color-magnitude relations and reduced proper motion diagrams. We reported in an earlier publication the discovery of nearly 200 new white dwarfs, and we present here the discovery of an additional 133 new white dwarfs, among which we identify 96 DA, 3 DB, 24 DC, 3 DQ, and 7 DZ stars. We further identify 178 white dwarfs that lie within 40 pc of the Sun, representing a 40% increase of the current census, which now includes 492 objects. We estimate the completeness of our survey at between 66 and 78%, allowing for uncertainties in the distance estimates. We also perform a homogeneous model atmosphere analysis of this 40 pc sample and find a large fraction of massive white dwarfs, indicating that we are successfully recovering the more massive, and less luminous objects often missed in other surveys. We also show that the 40 pc sample is dominated by cool and old white dwarfs, which populate the faint end of the luminosity function, although trigonometric parallaxes will be needed to shape this part of the luminosity function more accurately. Finally, we identify 4 probable members of the 20 pc sample, 4 suspected double degenerate binaries, and we also report the discovery of two new ZZ Ceti pulsators.
    The Astrophysical Journal Supplement Series 05/2015; 219(2). DOI:10.1088/0067-0049/219/2/19 · 14.14 Impact Factor
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    ABSTRACT: We present parallax observations and a detailed model atmosphere analysis of 54 cool and ultracool ($T_{\rm eff}$ < 4000 K) white dwarfs (WDs) in the solar neighborhood. For the first time, a large number of cool and ultracool WDs have distance and tangential velocities measurements available. Our targets have distances ranging from 21 pc to >100 pc, and include five stars within 30 pc. Contrary to expectations, all but two of them have tangential velocities smaller than 150 km s$^{-1}$ thus suggesting Galactic disk membership. The oldest WDs in this sample have WD cooling ages of 10 Gyr, providing a firm lower limit to the age of the thick disk population. Many of our targets have uncharacteristically large radii, indicating that they are low mass WDs. It appears that we have detected the brighter population of cool and ultracool WDs near the Sun. The fainter population of ultracool CO-core WDs remain to be discovered in large numbers. The Large Synoptic Survey Telescope should find these elusive, more massive ultracool WDs in the solar neighborhood.
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    ABSTRACT: We present parallax observations and a detailed model atmosphere analysis of 54 cool and ultracool (T eff < 4000 K) white dwarfs (WDs) in the solar neighborhood. For the first time, a large number of cool and ultracool WDs have distance and tangential velocities measurements available. Our targets have distances ranging from 21 pc to > 100 pc, and include five stars within 30 pc. Contrary to expectations, all but two of them have tangential velocities smaller than 150 km s −1 thus suggesting Galactic disk membership. The oldest WDs in this sample have WD cooling ages of 10 Gyr, providing a firm lower limit to the age of the thick disk population. Many of our targets have uncharacteristically large radii, indicating that they are low mass WDs. It appears that we have detected the brighter population of cool and ultracool WDs near the Sun. The fainter population of ultracool CO-core WDs remain to be discovered in large numbers. The Large Synoptic Survey Telescope should find these elusive, more massive ultracool WDs in the solar neighborhood.
    Monthly Notices of the Royal Astronomical Society 03/2015; 000(4):1-2015. DOI:10.1093/mnras/stv545 · 5.23 Impact Factor
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    ABSTRACT: We present high-speed photometric observations of ZZ Ceti white dwarf candidates drawn from the spectroscopic survey of bright DA stars from the Villanova White Dwarf Catalog by Gianninas et al., and from the recent spectroscopic survey of white dwarfs within 40 parsecs of the Sun by Limoges et al. We report the discovery of six new ZZ Ceti pulsators from these surveys, and several photometrically constant DA white dwarfs, which we then use to refine the location of the ZZ Ceti instability strip.
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    ABSTRACT: We use Hubble Space Telescope (HST) to reach the end of the white dwarf (WD) cooling sequence (CS) in the solar-metallicity open cluster NGC 6819. Our photometry and completeness tests show a sharp drop in the number of WDs along the CS at magnitudes fainter than mF606W = 26.050 ± 0.075. This implies an age of 2.25 ± 0.20 Gyr, consistent with the age of 2.25 ± 0.30 Gyr obtained from fits to the main-sequence turn-off. The use of different WD cooling models and initial–final-mass relations have a minor impact the WD age estimate, at the level of ∼0.1 Gyr. As an important by-product of this investigation we also release, in electronic format, both the catalogue of all the detected sources and the atlases of the region (in two filters). Indeed, this patch of sky studied by HST (of size ∼70 arcmin2) is entirely within the main Kepler-mission field, so the high-resolution images and deep catalogues will be particularly useful.
    Monthly Notices of the Royal Astronomical Society 01/2015; 448(2). DOI:10.1093/mnras/stv069 · 5.23 Impact Factor
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    C. Genest-Beaulieu · P. Bergeron
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    ABSTRACT: We present a comparative analysis of atmospheric parameters obtained with the so-called photometric and spectroscopic techniques. Photometric and spectroscopic data for 1360 DA white dwarfs from the Sloan Digital Sky Survey (SDSS) are used, as well as spectroscopic data from the Villanova White Dwarf Catalog. We first test the calibration of the ugriz photometric system by using model atmosphere fits to observed data. Our photometric analysis indicates that the ugriz photometry appears well calibrated when the SDSS to AB_95 zeropoint corrections are applied. The spectroscopic analysis of the same data set reveals that the so-called high-log g problem can be solved by applying published correction functions that take into account 3D hydrodynamical effects. However, a comparison between the SDSS and the White Dwarf Catalog spectra also suggests that the SDSS spectra still suffer from a small calibration problem. We then compare the atmospheric parameters obtained from both fitting techniques and show that the photometric temperatures are systematically lower than those obtained from spectroscopic data. This systematic offset may be linked to the hydrogen line profiles used in the model atmospheres. We finally present the results of an analysis aimed at measuring surface gravities using photometric data only.
    The Astrophysical Journal 10/2014; 796(2). DOI:10.1088/0004-637X/796/2/128 · 6.28 Impact Factor
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    ABSTRACT: We present a detailed spectroscopic analysis of 61 low mass white dwarfs and provide precise atmospheric parameters, masses, and updated binary system parameters based on our new model atmosphere grids and the most recent evolutionary model calculations. For the first time, we measure systematic abundances of He, Ca and Mg for metal-rich extremely low mass white dwarfs and examine the distribution of these abundances as a function of effective temperature and mass. Based on our preliminary results, we discuss the possibility that shell flashes may be responsible for the presence of the observed He and metals. We compare stellar radii derived from our spectroscopic analysis to model-independent measurements and find good agreement except for those white dwarfs with Teff < 10,000 K. We also calculate the expected gravitational wave strain for each system and discuss their significance to the eLISA space-borne gravitational wave observatory. Finally, we provide an update on the instability strip of extremely low mass white dwarf pulsators.
    The Astrophysical Journal 08/2014; 794(1). DOI:10.1088/0004-637X/794/1/35 · 6.28 Impact Factor
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    ABSTRACT: We have identified eight to ten new cool white dwarfs from the Large Area Survey (LAS) Data Release 9 of the United Kingdom InfraRed Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS). The data set was paired with the Sloan Digital Sky Survey (SDSS) to obtain proper motions and a broad ugrizYJHK wavelength coverage. Optical spectroscopic observations were secured at Gemini Observatory and confirm the degenerate status for eight of our targets. The final sample includes two additional white dwarf candidates with no spectroscopic observations. We rely on improved 1D model atmospheres and new multi-dimensional simulations with CO5BOLD to review the stellar parameters of the published LAS white dwarf sample along with our additional discoveries. Most of the new objects possess very cool atmospheres with effective temperatures below 5000 K, including two pure-hydrogen remnants with a cooling age between 8.5 and 9.0 Gyr, and tangential velocities in the range 40 km/s < vtan < 60 km/s. They are likely thick disk 10-11 Gyr-old objects. In addition we find a resolved double degenerate system with vtan ~ 155 km/s and a cooling age between 3.0 and 5.0 Gyr. These white dwarfs could be disk remnants with a very high velocity or former halo G stars. We also compare the LAS sample with earlier studies of very cool degenerates and observe a similar deficit of helium-dominated atmospheres in the range 5000 < Teff (K) < 6000. We review the possible explanations for the spectral evolution from helium-dominated towards hydrogen-rich atmospheres at low temperatures.
    The Astrophysical Journal 05/2014; 788(2). DOI:10.1088/0004-637X/788/2/103 · 6.28 Impact Factor
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    ABSTRACT: We first present a brief description of the six distinct families of pulsating white dwarfs that are now known. These are all opacity-driven pulsators showing low- to mid-order, low-degree gravity modes. We then discuss some recent highlights that have come up in the field of white dwarf asteroseismology.
    Proceedings of the International Astronomical Union 01/2014; 9(S301). DOI:10.1017/S1743921313014440
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    ABSTRACT: We have applied our empirical-PSF-based photometric techniques on a large number of calibration-related WFC3/UVIS UV-B exposures of the core of {\omega} Cen, and found a well-defined split in the right part of the white-dwarf cooling sequence (WDCS). The redder sequence is more populated by a factor of ~2. We can explain the separation of the two sequences and their number ratio in terms of the He-normal and He-rich subpopulations that had been previously identified along the cluster main sequence. The blue WDCS is populated by the evolved stars of the He-normal component (~0.55 Msun CO-core DA objects) while the red WDCS hosts the end-products of the He-rich population (~0.46 Msun objects, ~10% CO-core and ~90% He-core WDs). The He-core WDs correspond to He-rich stars that missed the central He-ignition, and we estimate their fraction by analyzing the population ratios along the cluster horizontal branch.
    The Astrophysical Journal Letters 05/2013; 769(2). DOI:10.1088/2041-8205/769/2/L32 · 5.60 Impact Factor
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    M. -M. Limoges · S. Lepine · P. Bergeron
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    ABSTRACT: We present the preliminary results of a survey aimed at significantly increasing the range and completeness of the local census of spectroscopically confirmed white dwarfs. The current census of nearby white dwarfs is reasonably complete only to about 20 parsecs of the Sun, a volume that includes around 130 white dwarfs, a sample too small for detailed statistical analyses. This census is largely based on follow-up investigations of stars with very large proper motions. We describe here the basis of a method that will lead to a catalog of white dwarfs within 40 parsecs of the Sun and north of the celestial equator, thus increasing by a factor of 8 the extent of the northern sky census. White dwarf candidates are identified from the SUPERBLINK proper motion database, allowing us to investigate stars down to a proper motion limit mu>40 mas yr-1, while minimizing the kinematic bias for nearby objects. The selection criteria and distance estimates are based on a combination of color-magnitude and reduced proper motion diagrams. Our follow-up spectroscopic observation campaign has so far uncovered 193 new white dwarfs, among which we identify 127 DA (including 9 DA+dM and 4 magnetic), 1 DB, 56 DC, 3 DQ, and 6 DZ stars. We perform a spectroscopic analysis on a subsample of 84 DAs, and provide their atmospheric parameters. In particular, we identify 11 new white dwarfs with spectroscopic distances within 25 pc of the Sun, including 5 candidates to the D<20 pc subset.
    The Astronomical Journal 03/2013; 145(5). DOI:10.1088/0004-6256/145/5/136 · 4.05 Impact Factor
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    ABSTRACT: We present extensive calculations of linear and non-linear limb-darkening coefficients as well as complete intensity profiles appropriate for modeling the light-curves of eclipsing white dwarfs. We compute limb-darkening coefficients in the Johnson-Kron-Cousins UBVRI photometric system as well as the Large Synoptic Survey Telescope (LSST) ugrizy system using the most up-to-date model atmospheres available. In all, we provide the coefficients for seven different limb-darkening laws. We describe the variations of these coefficients as a function of the atmospheric parameters, including the effects of convection at low effective temperatures. Finally, we discuss the importance of having readily available limb-darkening coefficients in the context of present and future photometric surveys like the LSST, Palomar Transient Factory, and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS). The LSST, for example, may find ~10^5 eclipsing white dwarfs. The limb-darkening calculations presented here will be an essential part of the detailed analysis of all of these systems.
    The Astrophysical Journal 01/2013; 766(1). DOI:10.1088/0004-637X/766/1/3 · 6.28 Impact Factor
  • P. Bergeron · P. Dufour · N. Giammichele
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    ABSTRACT: We recently published a detailed model atmosphere, spectroscopic, and photometric analysis of nearby white dwarf candidates within a distance of 20 pc from the Sun. During the course of this study, we encountered some intriguing results that remained unexplained and unpublished. We discuss here some of these results.
    01/2013;
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    ABSTRACT: White dwarf stars cool as they age, hence they can be used as chronometers for various stellar systems. Their value as clocks depends critically on how well we understand the physics of cooling. In this contribution we outline how to derive an empirical cooling sequence and then compare it with a standard white dwarf cooling model. Some differences are noted suggesting that there is still missing physics in the models. A more detailed version of this communication can be found in Goldsbury et al. (2012).
    01/2013;
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    ABSTRACT: White dwarf stars with a surface composition completely dominated by carbon and oxygen, the so-called Hot DQs, are found to be magnetic in an extremely high proportion. Here we present new high-resolution spectroscopic observations with the VLT and try to determine whether all Hot DQs could be magnetic at some level. We also discuss further the idea that most, if not all, white dwarfs showing either C I or C II atomic absorption lines in the optical may form a continuous sequence of massive white dwarf stars.
    01/2013;
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    ABSTRACT: Here, we report on the white dwarf catalog built from the SDSS DR7 (Cat. II/294). We have applied automated techniques supplemented by complete, consistent human identifications of each candidate white dwarf spectrum. We make use of the latest SDSS reductions and white dwarf model atmosphere improvements in our spectral fits, providing logg and Teff determinations for each identified clean DA and DB where we use the word "clean" to identify spectra that show only features of non-magnetic, nonmixed, DA or DB stars. Our catalog includes all white dwarf stars from the earlier Kleinman et al. (2004, Cat. J/ApJ/607/426) and Eisenstein et al. (2006, Cat. J/ApJS/167/40) catalogs, although occasionally with different identifications. (1 data file).
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    ABSTRACT: We present a new catalog of spectroscopically-confirmed white dwarf stars from the Sloan Digital Sky Survey Data Release 7 spectroscopic catalog. We find 20,407 white dwarf spectra, representing 19,712 stars, and provide atmospheric model fits to 14,120 DA and 1011 DB white dwarf spectra from 12,843 and 923 stars, respectively. These numbers represent a more than factor of two increase in the total number of white dwarf stars from the previous SDSS white dwarf catalog based on DR4 data. Our distribution of subtypes varies from previous catalogs due to our more conservative, manual classifications of each star in our catalog, supplementing our automatic fits. In particular, we find a large number of magnetic white dwarf stars whose small Zeeman splittings mimic increased Stark broadening that would otherwise result in an overestimated log(g) if fit as a non-magnetic white dwarf. We calculate mean DA and DB masses for our clean, non-magnetic sample and find the DB mean mass is statistically larger than that for the DAs.
    The Astrophysical Journal Supplement Series 12/2012; 204(1). DOI:10.1088/0067-0049/204/1/5 · 14.14 Impact Factor
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    ABSTRACT: We present accurate trigonometric parallaxes for 20 new members of the 25 pc white dwarf sample as part of the DENSE project (Discovery and Evalution of Nearby Stellar Embers
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    ABSTRACT: We explore the physics of crystallization in the deep interiors of white dwarf stars using the color-magnitude diagram and luminosity function constructed from proper motion cleaned Hubble Space Telescope photometry of the globular cluster NGC 6397. We demonstrate that the data are consistent with the theory of crystallization of the ions in the interior of white dwarf stars and provide the first empirical evidence that the phase transition is first order: latent heat is released in the process of crystallization as predicted by van Horn (1968). We outline how this data can be used to observationally constrain the value of Γ ≡ ECoulomb/Ethermal near the onset of crystallization, the central carbon/oxygen abundance, and the importance of phase separation. Subject headings: white dwarfs — dense matter — equation of state

Publication Stats

5k Citations
867.53 Total Impact Points

Institutions

  • 1993–2015
    • Université du Québec à Montréal
      • Department of Music
      Montréal, Quebec, Canada
  • 1984–2015
    • Université de Montréal
      • Department of Physics
      Montréal, Quebec, Canada
  • 2013
    • National Institute of Astrophysics
      Roma, Latium, Italy
  • 2011
    • University of California, San Diego
      • Center for Astrophysics and Space Sciences (CASS)
      San Diego, California, United States
  • 1995–2011
    • Space Telescope Science Institute
      Baltimore, Maryland, United States
  • 2008
    • Georgia State University
      • Department of Physics and Astronomy
      Atlanta, Georgia, United States
  • 2007
    • Victoria University of Wellington
      • School of Chemical and Physical Sciences
      Wellington, Wellington, New Zealand
    • Polytechnic University of Catalonia
      • Department of Applied Physics (FA)
      Barcino, Catalonia, Spain
  • 1994
    • The University of Arizona
      • Department of Astronomy
      Tucson, Arizona, United States
  • 1992–1993
    • University of Santiago, Chile
      • Departamento de Economía
      CiudadSantiago, Santiago Metropolitan, Chile