Fourier frequency spectra of ZGP-BLAP-08 combined data at three steps of pre-whitening: for the original data (top panels), after subtracting the dominant term f₁ and its two strongest harmonics (middle panels), and after subtracting all 12 terms (bottom panels). The left panels show spectra in the range of 0–250 d⁻¹ and the right panels, zoomed parts of the frequency spectra close to the dominant term f₁. The middle right panel shows the location of f₂ and f₃ and their nearest daily aliases, marked with tics.