Magnetic activity, differential rotation, and dynamo action in the pulsating F9IV star KIC 5955122

Abstract

We present photometric spot modeling of the nearly four-year long light-curve of the Kepler target KIC 5955122 in terms of persisting dark circular surface features. With a Bayesian technique, we produced a plausible surface map that shows dozens of small spots. After some artifacts are removed, the residuals are at ± 0.16'mmag. The shortest rotational period found is P = 16.4 ± 0.2 days. The equator-to-pole extrapolated differential rotation is 0.25 ± 0.02 rad/d. The spots are roughly half as bright as the unperturbed stellar photosphere. Spot latitudes are restricted to the zone ±60° latitude. There is no indication for any near-pole spots. In addition, the p-mode pulsations enabled us to determine the evolutionary status of the star, the extension of the convective zone, and its radius and mass. We discuss the possibility that the clear signature of active regions in the light curve of the F9IV star KIC 5955122 is produced by a flux-transport dynamo action at the base of the convection zone. In particular, we argue that this star has evolved from an active to a quiet status during the Q0-Q16 period of observation, and we predict, according to our dynamo model, that the characteristic activity cycle is of the order of the solar one.