Panel a) power spectrum of the original light curve of 2000 June 7/9, after removal of the eclipses and variations on timescales longer than ≈15^m. Panel b) power spectrum of the randomized light curve with the highest peak in 10 000 trials. Panel c) power spectrum of the randomized light curve with the largest contrast between the highest and the second highest peak. Panel d) power spectrum of the original light curve of 2000 May 24/25. See text for details.