KIC 5359678: a detached eclipsing binary with starspots

We study the detached eclipsing binary, KIC 5359678, with starspot modulation using the high-quality Kepler photometry and LAMOST spectroscopy. The PHOEBE model, optimal for this binary, reveals that this system is a circular detached binary, composed of two F-type main-sequence stars. The masses and radii of the primary and the secondary are M₁ = 1.31 ± 0.05 M_⊙, R₁ = 1.52 ± 0.04 R_⊙, M₂ = 1.12 ± 0.04 M_⊙, and R₂ = 1.05 ± 0.06 R_⊙, respectively. The age of this binary is estimated to be about 2 Gyr, a value much longer than the synchronization time-scale of 17.8 Myr. The residuals of light curves show quasi-sinusoidal signals, which could be induced by starspots. We apply autocorrelation function analysis on the out-of-eclipse residuals and find that the spot with rotational period close to the orbital period, while, the decay time-scale of starspots is longer than that on the single stars with the same temperature, period range, and rms scatter. A two-starspot model is adopted to fit the signals with two-dip pattern, whose result shows that the longitude decreases with time.