On the Measurement of Fundamental Parameters of White Dwarfs in the Gaia Era

Abstract

We present a critical review of the determination of fundamental parameters of white dwarfs discovered by the Gaia mission. We first reinterpret color-magnitude and color-color diagrams using photometric and spectroscopic information contained in the Montreal White Dwarf Database (MWDD), combined with synthetic magnitudes calculated from a self-consistent set of model atmospheres with various atmospheric compositions. The same models are then applied to measure the fundamental parameters of white dwarfs using the so-called photometric technique, which relies on the exquisite Gaia trigonometric parallax measurements, and photometric data from Pan-STARRS, SDSS, and Gaia. In particular, we discuss at length the systematic effects induced by these various photometric systems. We then study in great detail the mass distribution as a function of effective temperature for the white dwarfs spectroscopically identified in the MWDD, as well as for the white dwarf candidates discovered by Gaia. We pay particular attention to the assumed atmospheric chemical composition of cool, non-DA stars. We also briefly revisit the validity of the mass-radius relation for white dwarfs, and the recent discovery of the signature of crystallization in the Gaia color-magnitude diagram for DA white dwarfs. We finally present evidence that the core composition of most of these white dwarfs is, in bulk, a mixture of carbon and oxygen, an expected result from stellar evolution theory, but never empirically well established before.

The Canada–France Imaging Survey: Reconstructing the Milky Way Star Formation History from Its White Dwarf Population

“…Within this temperature range, our resulting model produces very few white dwarfs, and those which pass our selection criteria have pure-hydrogen atmospheres. This is consistent with recent results suggesting that the majority of cool white dwarfs have nearly pure-hydrogen atmospheres (Kowalski, & Saumon 2006;Giammichele et al 2012;Limoges et al 2015;Bergeron et al 2019). The addition of mixed H/He atmospheres may allow a few He-dominant white dwarfs to pass the selection criteria by slowing down their cooling at this epoch, however, this effect would be minimal given the scarcity of objects in this region.…”

J-PLUS: photometric calibration of large-area multi-filter surveys with stellar and white dwarf loci

“…We obtain a DA fraction of f DA = 0.85 ± 0.01 and a median gravity of the WD population of log g = 8.01 ± 0.03. This gravity value is similar to previous analysis (see Jiménez-Esteban et al 2018;Gentile Fusillo et al 2019;Tremblay et al 2019;Bergeron et al 2019, and references therein). We were able to constraint these two parameters using instrumental magnitudes in most of the J-PLUS filters thanks to the presence of the DA and DB+DC branches, and to the variation of the locus curvature with the gravity.…”

Carbon-rich (DQ) white dwarfs in the Sloan Digital Sky Survey

“…The DZ, DB, and DC objects were drawn from the samples in Kleinman et al (2013); Kepler et al (2015Kepler et al ( , 2016; Kepler et al (2019), but the parameters were redetermined for this study. A significant fraction of DB white dwarfs is known to contain traces of hydrogen (spectral type DBA), and Bergeron et al (2019) have argued that using pure helium atmospheres for cool DC can lead to artificially higher masses. We have used different grids with [H/He] between −3.0 and −6.0 for the fitting.…”