Fit to the HD 27894 RVs with a model consisting of two planets in circular orbits. Note that in this case the exact 2:1 resonance is not forced, but the two period values are both free parameters of the fit. Left: time series together with the best-fitting two-planet circular model (top, thick solid line) and residuals (bottom). For display purposes the x-axis has been broken between BJD – 2 452 950 and BJD – 2 453 267.5 where there is a large data gap. The thin dashed line in the upper panel represents the best-fitting single Keplerian model for comparison. Right: RV data phase folded with the period of the outer planet after subtraction of the signal of the inner planet (top) and phase folded with the period of the inner planet after subtraction of the signal of the outer planet (bottom).