GLS periodograms of RVs (blue) and activity indicators (red) of HN Peg: (a) SONG RVs, (b) SONG RVs after fitting a sinusoid with a period of 5.1 days, (c) SONG Hα indicator, and (d) SONG Hα indicator after fitting a sinusoid with P = 420 days. Vertical green and orange lines represent the star’s rotation period and the first harmonic of the rotation with their 1-day alias, respectively. Horizontal dashed lines show the theoretical FAP levels of 10%, 1%, and 0.1% for each panel.