2D periodograms of the Stokes I NC (upper left), BC (lower left), AC (lower right), and Stokes V (upper right) in He I λ5876. The dashed red lines mark a period of 7.4 days (NC and Stokes V), 3.2 days (BC and AC), and 6.6 days (AC). The dashed black contours denote a constant FAP of 3% (except for 15% for the BC). The average profiles (black line) surrounded by their 1σ deviations (light blue) are shown below the periodograms.