2014MNRAS.437.1045S

Kepler-13b is a most intriguing exoplanet system due to the rapid precession rate, exhibiting several exotic phenomena. We analysed Kepler short cadence data up to Quarter 14, with a total time-span of 928d, to reveal changes in transit duration, depth, asymmetry and identify the possible signals of stellar rotation and low-level activity. We investigated long-term variations of transit light curves testing for duration, peak depth and asymmetry. We also performed cluster analysis on Kepler quarters. We computed the autocorrelation function of the out-of-transit light variations. Transit duration, peak depth and asymmetry evolve slowly, due to the slowly drifting transit path through the stellar disc. The detected transit shapes will map the stellar surface on the time-scale of decades. We found a very significant clustering pattern with 3-orbit period. Its source is very probably the rotating stellar surface, in the 5:3 spin-orbit resonance reported in a previous study. The autocorrelation function of the out-of-transit light variations, filtered to 25.4h and harmonics, shows slow variations and a peak around 300-360d period, which could be related to the activity cycle of the host star.