Spectroscopy vs. Photometry periodograms. Upper panel: Lomb–Scargle periodogram of the mean intensity profile presented in Fig. 1 (red line). Middle panel: periodogram of the light curve since 1990 as retrived from the AAVSO database (blue line). Lower panel: periodogram of the light curve (orange line) from AAVSO when the dates correspond to the TBL observations. In every panel, the green line marks the associated window function. The 400 d and the 200 d periods are marked by the black dashed lines.