Left panel: distribution of cycle periods P_{cyc, var} derived from all time series R_var which satisfied our selection criterion FAP < 5%. The black distribution shows all cases where random permutations of time series R_var yielded a higher peak in the Lomb-Scargle periodogram than the original time series in less than 5% of all cases. The red curve shows the results from a Monte Carlo experiment where the analysis was performed on random permutations of each R_var time series for the whole sample. Error bars are based on the Monte Carlo simulations and show one standard deviation. Right panel: distribution of P_{cyc, rot}, the cycle period determined from variations in the determined rotation periods P_rot, satisfying the selection criterion of FAP < 5%. Again the black histogram shows the cycle period distribution of the 5% strongest periodicity data, and the red curve shows the period distribution obtained from the Monte Carlo experiments.