Comparison of power spectra measured for the time interval 1997–2008 (red, left) and 2002–2008 (blue, right) to the power spectrum measured in the 1997–2001 data (black), i.e., the time interval used by Smith et al. (2002a). The peaks show a difference in period of 0.32 d and 0.33 d, respectively. Histograms show the peak PSD values for 10 000 realizations of a detrended light curve with residuals with a Gaussian distribution in the indicated period interval (see text for further explanation).