Fourier frequency spectra of the combined data of OGLE-BLAP-001 at three steps of pre-whitening. For the original data (top panels), after subtracting the dominant term f₁ and its strongest harmonic, 2f₁ (middle panels), and after subtracting all seven detected 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 downward tics.