Fourier power spectra of the 2009 (left) and 2010 (right) time series of the secondary’s He i λ 4471 line. The top panels of each row show the full 2D periodograms (between 0 and 2 d^-1), whilst the second and third panels illustrate the mean periodogram over the emission humps, respectively before and after prewhitening (see text). The spectral window is shown in the lower panel.