The Impact of Observing Cadence and Undetected Companions on the Accuracy of Planet Mass Measurements from Radial Velocity Monitoring

Abstract We conduct experiments on both real and synthetic radial velocity (RV) data to quantify the impact that observing cadence, the number of RV observations, and undetected companions all have on the accuracy of small planet mass measurements. We run resampling experiments on four systems with small transiting planets and substantial public data from the High Resolution Echelle Spectrometer in order to explore how degrading observing cadence and the number of RVs affects the planets’ mass measurement relative to a baseline value. From these experiments, we recommend that observers obtain 2–3 RVs per orbit of the innermost planet and acquire at minimum 40 RVs. Following these guidelines, we then conduct simulations using synthetic RVs to explore the impact of undetected companions and untreated red noise on the masses of planets with known orbits. While undetected companions generally do not bias the masses of known planets, in some cases, when coupled with an inadequate observing baseline, they can cause the mass of an inner transiting planet to be systematically overestimated on average.