Activity indexes periodograms for star HD 38801. Top panel: post-fit residual data periodogram, the most significant period peak value and power shown in the lower left corner, the horizontal lines indicating the false alarm probability levels of 10% (solid red line), 1% (dashed orange line) and 0.1% (dotted green line). Following panels: periodograms for the activity indexes studied in the paper, respectively bisector, FWHM, Ca II and Hα, the correlation rank r and significance p with the radial velocity residuals shown in each panel’s lower left corner. The residual data periodogram’s most significant period is highlighted by a vertical red dotted line in all the panels, while the stellar rotation period is shown as a blue dotted vertical line.