Magnetic Activity and Possible Anti-solar Differential Rotation in Two RS CVn–type Eclipsing Binaries

Abstract

Using Kepler photometry and LAMOST spectroscopy, we present the first combined photometric and spectroscopic investigations for two Kepler eclipsing binaries: KIC 8893936 and KIC 10014830. Precise absolute physical parameters are derived from simultaneous modelling of light curves and radial-velocity curves. Evolutionary stage of both components and clear signatures of intense magnetic activity, including prominent chromospheric characteristic emission lines in the spectra, persistent non-eclipse luminosity modulations and superflares in the photometry, implies they are two typical RS CVn-type binaries with two giant components. By modelling the long-baseline, continuous Kepler light curves spanning nearly four years, we find that the long-term intrinsic light variations can be adequately described within the adopted two-spot modelling framework. The fitted spot longitudes exhibit systematic prograde migration in the binary reference frame. Under the assumption that this migration is caused by surface differential rotation, the inferred effective surface shear is consistent with the possibility of weak anti-solar differential rotation in both systems.