Lomb-Scargle periodograms (LSPs; amplitude in per cent of the mean brightness versus frequency in μHz) for each data set constructed from the TESS observation of TIC 441725813 (from top to bottom, respectively). The grey horizontal line indicates our conservative threshold of 5.2 times the median noise level (see text). The upper panel in each diagram displays all signals extracted above 5.2 times S/N. The curve plotted upside-down is the reconstruction of the LSPs based on all extracted frequencies. The lower panels show the residual left after extracting all the significant frequencies.