BEER analysis of Kepler and CoRoT light curves: IV. Discovery of four new low-mass white dwarf companions in the Kepler data

TL;DR

This paper reports the discovery of four new short-period eclipsing systems with low-mass white dwarf companions in Kepler data, expanding the known population and providing detailed component properties through combined light curve and spectroscopic analysis.

Contribution

It introduces four newly identified dA+WD binary systems with detailed characterization, including their masses, radii, and orbital parameters, extending the known sample to older, cooler systems.

Findings

Four new short-period eclipsing dA+WD binaries discovered.

White dwarf radii are among the smallest known for such systems.

Some systems show evidence of past mass transfer and eccentricity.

Abstract

We report the discovery of four short-period eclipsing systems in the Kepler light curves, consisting of an A-star primary and a low-mass white dwarf (WD) secondary (dA+WD) - KIC 4169521, KOI-3818, KIC 2851474, and KIC 9285587. The systems show BEaming, Ellipsoidal and Reflection (BEER) phase modulations together with primary and secondary eclipses. These add to the 6 Kepler and 18 WASP short-period eclipsing dA+WD binaries that were previously known. The light curves, together with follow-up spectroscopic observations, allow us to derive the masses, radii, and effective temperatures of the two components of the four systems. The orbital periods, of 1.17-3.82 days, and WD masses, of 0.19-0.22 Msun, are similar to those of the previously known systems. The WD radii of KOI-3818, KIC 2851474, and KIC 9285587 are 0.026, 0.035, and 0.026 Rsun, respectively, the smallest WD radii derived so far for short-period eclipsing dA+WD binaries. These three binaries extend the previously known population to older systems with cooler and smaller WD secondaries. KOI-3818 displays evidence for a fast-rotating primary and a minute but significant eccentricity of ~0.0015. These features are probably the outcome of the mass-transfer process.