Upper panel: full CoRoT light curve of CoRoT-33. The gray points represent the median-normalized raw data points after a 5-point width median filtering. We only used data points with flag “0” for this curve. The red line is a convolution of the raw light curve with a Savitzky-Golay filter that enhances the light-curve variations. Middle panel: Lomb-Scargle periodogram of the light curve of CoRoT-33. The horizontal dashed line denotes the 0.01% false-alarm probability (Scargle 1982). The vertical red line marks the rotation period of the star. Lower panel: autocorrelation function (ACF) of light curve, following the subtraction of the best fitting transit model. The red dashed line marks the peak corresponding to the rotation period of CoRoT-33 (see Sect. 3.5).