Periodograms of the raw (top plot), filtered (middle plot) and residual (bottom plot) LBL RVs of IRAS 04125+2902. The cyan vertical dashed lines trace the derived P_rot and known orbital period P_b of IRAS 04125+2902 b, whereas the horizontal dashed lines indicate the 1 per cent and 0.1 per cent false alarm probabilities in the periodograms of our RV data. The orange curve depicts the periodogram of the window function.