HIP 21850 periodograms. Shown from top to bottom: RVs, model residuals, FWHM, BIS, and the window function. The FAP lines are included for 0.1, 1, and 10% and are plotted as dashed red, dotted purple, and dotted blue lines, respectively. The circles show the periods with the greatest power, coloured by FAP region. The coloured regions correspond to $P_1={2539}_{-3.1}^{+0.8}$ d (green) and $P_2={11320}_{-940}^{+490}$ (orange).