A Mass-accreting Gamma Doradus Pulsator with a Synchronized Core in Kepler Eclipsing Binary KIC 7385478

Abstract

The short-period (P $\approx1.7$ d), Algol-type eclipsing binary KIC 7385478 consists of an F-type primary star ($M_1 \approx 1.71M_{\odot}$) and an evolved K-type secondary ($M_2 \approx 0.37M_{\odot}$) (Ozdarcan \& Ali Dal 2017). We study the variability of the {\it Kepler} light curve and attribute many frequency peaks in the Fourier spectrum to the spot modulation. These frequencies are in the form of orbital harmonics and are highly variable in amplitude. They are most likely from the mass-accreting primary star. In addition, we identify a series prograde dipole g-modes from the primary star which show a quasi-linear period spacing pattern and are very stable in amplitude. The period spacing pattern reveals an asymptotic period spacing value in agreement with fundamental parameters of the primary star and also implies that the near-convective-core rotation rate is almost the same as the orbital period. Thus both the surface and the core of this Gamma Dor pulsator have synchronized with the binary orbit. We find that a lower stellar mass $\approx 1.50 M_{\odot}$ and higher effective temperature are needed in order to be compatible with the asteroseismic constraints from single star evolutionary models.