Measurements of Physical Parameters of White Dwarfs: A Test of the Mass–Radius Relation

Abstract

We present a detailed spectroscopic and photometric analysis of 219 DA and DB white dwarfs for which trigonometric parallax measurements are available. Our aim is to compare the physical parameters derived from the spectroscopic and photometric techniques, and then to test the theoretical mass-radius relation for white dwarfs using these results. The agreement between spectroscopic and photometric parameters is found to be excellent, especially for effective temperatures, showing that our model atmospheres and fitting procedures provide an accurate, internally consistent analysis. Values of surface gravity and solid angle, obtained respectively from spectroscopy and photometry, are combined with parallax measurements in various ways to study the validity of the mass-radius relation from an empirical point of view. After a thorough examination of our results, we find that 73% and 92% of the white dwarfs are consistent within 1 and 2σ confidence levels, respectively, with the predictions of the mass-radius relation, thus providing strong support to the theory of stellar degeneracy. Our analysis also allows us to identify 15 stars that are better interpreted in terms of unresolved double degenerate binaries. Atmospheric parameters for both components in these binary systems are obtained using a novel approach. We further identify a few white dwarfs that are possibly composed of an iron core rather than a carbon/oxygen core, since they are consistent with Fe-core evolutionary models.

Two new double-lined spectroscopic binary white dwarfs

“…We presented follow-up spectroscopy of four over-luminous white dwarfs identified by Bédard, Bergeron & Fontaine (2017). Two of these, WD 0311−649 and WD 1606+422, are double-lined systems, and we provide orbital periods, mass ratios, component masses, and effective temperatures of each binary based on their spectral line profiles, spectral energy distributions, and radial velocity data.…”

“…This procedure gives 4 km s −1 errors for both lines in the spectrum shown in Figure 2. Bédard, Bergeron & Fontaine (2017) showed that it is possible to constrain the atmospheric parameters (T eff and log g) of both white dwarfs in an unresolved DA+DA binary system by combining spectroscopic, photometric, and astrometric information. More specifically, they developed a deconvolution procedure that involves fitting simultaneously the observed Balmer lines and spectral energy distribution with composite model atmospheres.…”

“…Recently, Bédard, Bergeron & Fontaine (2017) performed a spectroscopic and photometric analysis of 219 white dwarfs with trigonometric parallax measurements available at the time, and identified 15 unresolved double degenerate binary candidates, including several previously known double-lined spectroscopic binaries. Bergeron, et al (2019) presented an updated analysis of these objects based on Gaia Data Release 2 parallaxes, and confirmed the overluminous nature of all but one of these targets, WD1130+189.…”

“…Here we present follow-up spectroscopy of four of these white dwarfs, three of which are confirmed to be binary systems. We present an overview of the over-luminous white dwarf sample from Bédard, Bergeron & Fontaine (2017) and discuss the period and mass distribution of the sample, as well as the fractions of SB2, SB1, and systems that show no significant radial velocity variability.…”

A 1201 s Orbital Period Detached Binary: The First Double Helium Core White Dwarf LISA Verification Binary

“…Our approach is to construct composite binary models by adding two synthetic WD spectra, properly weighted by their respective radii using the astrometric parallax constraint. We then simultaneously fit the spectroscopic Balmer line profiles and the broadband photometric measurements using the Levenberg-Marquardt algorithm (Bédard et al 2017;Kilic et al 2020). We use de-reddened GALEX FUV and NUV (Martin et al 2005), SDSS ugriz (Abolfathi et al 2018), Pan-STARRS grizy (Tonry et al 2012), and UKIDSS Y J photometry (Lawrence et al 2007).…”