Illustration of the four PCs vectors obtained by the PCA on the LBL RVs of HD20794. Even if the periodograms indicate a power excess around 32 days (left panels), the systematics is in fact related to a comb-like structure (see also Fig. B.2) that is fixed in the terrestrial rest-frame. This is illustrated by plotting the PCA components as a function of the BERV (right panels). This comb-like structure, that is fixed in the laboratory rest-frame, then moves relatively to the stellar rest-frame with a 1-year periodicity due to the own Earth’s revolution.