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

TL;DR

This study analyzes 219 white dwarfs using spectroscopic and photometric data to empirically test the theoretical mass-radius relation, confirming its validity for most stars and identifying potential binary systems and unusual core compositions.

Contribution

It provides a comprehensive empirical validation of the white dwarf mass-radius relation using combined spectroscopic, photometric, and parallax data, and introduces a new method for analyzing unresolved binaries.

Findings

73% of white dwarfs are consistent with the mass-radius relation within 1σ

92% are consistent within 2σ, supporting stellar degeneracy theory

Identified 15 potential unresolved double degenerate binaries

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 2$\sigma$ 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.