Activity of the Young Star with an Exoplanet Kepler-1627

Abstract

Based on data from the Kepler Space Telescope archive, we have studied the photometric variability of the young solar analog Kepler-1627, a G8V-type star with a planet of 3.777 Earth radii in size and an orbital period ${\sim}$7.2 days. Kepler-1627 is a member of the $\delta$ Lyr cluster with an age of 38 Myr and is currently the system with the youngest planet with a precise age detected by the Kepler primary mission. We have found the stellar rotation period $P=2.606\pm 0.020$ days, the differential stellar rotation parameter $\Delta\Omega=0.066\pm 0.011$ rad day${}^{-1}$, and the photometric variability amplitude as well as estimated the spottedness parameter of Kepler-1627 by a standard technique, which lies in the range 1.1–6.5${\%}$ of the stellar surface area. In absolute measure the spot area on the surface of Kepler-1627 exceeds the maximum spot area on the Sun and varies from 11 700 to 68 200 m.s.h., with the mean value being 34 560 m.s.h. We suggest that during the interval of its observations the spot area on the stellar surface had cyclic variations similar to the Rieger periodicity on the Sun. High flare activity (88 flares with an energy $\log E$ in the range from 33.41 to 35.25 have been recorded) and spot activity have been detected in the star. Possible manifestations of the cyclicity in the flaring activity of Kepler-1627 are considered. We have found the chromospheric activity indices $\log R^{\prime}_{HK}(T_{\rm eff})$ for Kepler-1627, which independently suggest that the object is young.