Synthetic data and their analysis. (a) Synthetic data contain the periods P₁ and P_long. (b) Residuals (observed minus computed). (c) Histogram of the residuals. (d) GLS periodogram of the residuals, showing a significant peak at P₂. (e) Full GLS periodogram, the peak at P_long is present for both the observational and the synthetic data. (f) Zoom onto the orbital frequency range. The peak at P₁ is reproduced by the synthetic data, but besides that, the periodograms differ substantially between observational and synthetic data.