Testing the white dwarf mass-radius relation and comparing optical and far-UV spectroscopic results with Gaia DR2, HST and FUSE

TL;DR

This study tests the white dwarf mass-radius relation using Gaia parallax data combined with UV and optical spectroscopy, confirming theoretical models and highlighting the main sources of measurement uncertainty.

Contribution

It integrates Gaia DR2 parallaxes with space-based UV and optical spectra to evaluate the white dwarf mass-radius relation, addressing previous distance measurement limitations.

Findings

Results support the theoretical mass-radius relation.

Balmer and Lyman line spectroscopic results are consistent with updated broadening tables.

Uncertainty in log g dominates the error budget in mass-radius calculations.

Abstract

Observational tests of the white dwarf mass-radius relationship have always been limited by the uncertainty in the available distance measurements. Most studies have focused on Balmer line spectroscopy because these spectra can be obtained from ground based observatories, while the Lyman lines are only accessible to space based UV telescopes. We present results using parallax data from Gaia DR2 combined with space based spectroscopy from HST and FUSE covering the Balmer and Lyman lines. We find that our sample supports the theoretical relation, although there is at least one star which is shown to be inconsistent. Comparison of results between Balmer and Lyman line spectra shows they are in agreement when the latest broadening tables are used. We also assess the factors which contribute to the error in the mass-radius calculations and confirm the findings of other studies which show that the spread in results for targets where multiple spectra are available is larger than the statistical error. The uncertainty in the spectroscopically derived log g parameter is now the main source of error rather than the parallax. Finally, we present new results for the radius and spectroscopic mass of Sirius B which agree with the dynamical mass and mass-radius relation within 1 sigma.