Frequency spectra of selected BSGs. We show the periodograms calculated at the beginning (cyan) and the end (red) of the pre-whitening process. The vertical lines at the top of each panel point to the different types of identified frequencies: independent (solid), harmonics (dashed), and combinations (dotted). The solid black line corresponds to the best-fit SLF variability model (Eq. (4)) that we adopt for the star. The gray-shaded region indicates the range of frequencies that can be identified as being due to the stellar rotation.