Mean of the Lomb-Scargle periodograms per bin of the season of 2008. From top to bottom: mean Fourier spectra of the original data set, and after prewhitening of 3 and 14 frequencies, respectively. The red solid lines mark the highest peak in each periodogram, while the red dashed lines mark the respective one-day aliases. Highest peaks are f₁ = 7.3764 d^-1 (upper panel) and f₃ = 5.0481 d^-1 (center panel). The inset in the upper panel displays the spectral window for the 2008 data set.