Lomb–Scargle periodogram of the 100 photo-center displacement series of Betelgeuse. Each blue line corresponds to a Lomb–Scargle periodogram of one photo-center displacement. The black line is the average of the 100 periodograms. The red dashed lines represent the 400 and 200 d period, respectively. The green line is the window function. The black horizontal line marks the 1σ confidence level.