Discovery of Two New Thermally Bloated Low-Mass White Dwarfs Among the Kepler Binaries

TL;DR

This paper reports the discovery of two new thermally bloated low-mass white dwarfs in Kepler eclipsing binaries, providing detailed measurements and evolutionary insights, and suggesting the presence of a third body in one system.

Contribution

It presents the identification and characterization of two new low-mass white dwarfs with detailed mass, radius, and temperature measurements, and offers independent theoretical mass estimates based on evolutionary models.

Findings

White dwarfs have large thermal bloating factors, up to 14 times their cold degenerate radius.

Precise mass measurements: 0.197 +/- 0.005 Msun and 0.266 +/- 0.035 Msun.

Evidence for a third body with an 8-14 year orbital period in KIC 9164561.

Abstract

We report the discovery of two new low-mass, thermally bloated, hot white dwarfs among the Kepler sample of eclipsing binaries. These are KIC 9164561 and KIC 10727668 with orbital periods of 1.2670 and 2.3058 days, respectively. The current primary in both systems is an A star of about 2 Msun. This brings the number of similar binaries among the Kepler sample to six, and the two new systems have the shortest orbital periods among them. The white dwarf in KIC 9164561 has the largest thermal bloating, compared to its cold degenerate radius, of about a factor of 14. We utilize RV measurements of the A star in KIC 9164561 to determine the white dwarf mass rather accurately: 0.197 +/- 0.005 Msun. The mass of the white dwarf in KIC 10727668 is based on the Doppler boosting signal in the Kepler photometry, and is less accurately determined to be 0.266 +/- 0.035 Msun. Based on the inferred radii and effective temperatures of these two white dwarfs we are able to make an independent theoretical estimate of their masses to within ~0.01 Msun based on evolutionary models of their cooling history after they lose their hydrogen-rich envelopes. We also present evidence that there is a third body in the KIC 9164561 system with an orbital period of 8-14 years.