Two new R CMa-type eclipsing binaries containing a possible low-mass Helium white dwarf precursor: KIC 7368103 and KIC 8823397

Abstract

We report the discovery of two new R CMa-type eclipsing binaries, each consisting of a possible low-mass Helium white dwarf precursor. Based on the Kepler long-cadence photometry and the radial-velocity measurements given by Matson et al., we determined comprehensive photometric solutions and physical parameters of two binaries KIC 7368103 and KIC 8823397. Light-curve modelling reveals that they are both short-period detached system with very low mass ratios q ≃ 0.1. The derived physical parameters show that the two binary systems consist of an extremely low-mass (≃0.2 M|$\odot$|), oversized (>1 R|$\odot$|), and overluminous secondary component, accompanied by a less-evolved early A-type primary star. We therefore introduce KIC 7368103 and KIC 8823397 as two new R CMa-type binaries, which are probably evolving into EL CVn stars. After subtracting the synthetic eclipsing curve from the de-trended Kepler data, we carried out a preliminary frequency analysis of their light-curve residuals. KIC 7368103 was found to pulsate in 35 independent frequencies in the range from 14 to 31 d−1, which could be due to the intrinsic pulsations of the δ Sct-type primary star. However, no significant frequencies above the confidence level were detected in the binary KIC 8823397.