Examples for single-component fits to the RV data of a pair of 2:1-RCO planets. Thick solid lines represent the input data which are shown for amplitude ratios and 2/1 (from left to right) and values of the phase shift Δφ = 0° (upper row of panels) and 90° (lower row of panels). Thin solid lines depict the best-fitting Keplerian orbits with P = 1 (not discernible in the leftmost panels because of their very good match to the thick solid line). Dotted lines indicate best-fitting circular orbits (sine waves) with P = 1. Dashed lines stand for best-fitting circular orbits with P = 0.5. Note that the best-fitting Keplerian orbits with P = 0.5 are identical to the circular orbits with the same period, since the eccentricity vanishes for all fits. Plots for phase shifts of 180° and 270° can be obtained by flipping the 0° and the 90° plots, respectively, around the horizontal axis and then shifting them by 0.5 in phase.