Top two panels: seven-year-long ASAS dataset and its Fourier amplitude spectrum resulting in a rotational period of 36.27 days. The two “satellite peaks” in the amplitude spectrum are the sidebands of the one-year observational window function. Bottom two panels: data “cleaned” of the rotational period, and its amplitude spectrum. Apart from the remaining signals near the 36 day periods, half periods also show up significantly due to the non-sinusoidal light curves in the second half of the dataset.