The impact of observing cadence and undetected companions on the accuracy of planet mass measurements from radial velocity monitoring

TL;DR

This study investigates how observing cadence, number of radial velocity observations, and undetected companions influence the accuracy of small planet mass measurements, providing practical guidelines for observational strategies.

Contribution

It offers new empirical guidelines on RV observation cadence and number, and explores the effects of undetected companions and red noise on mass estimates.

Findings

2-3 RVs per orbit recommended for accuracy

Minimum of 40 RVs needed for reliable measurements

Undetected companions can bias mass estimates under certain conditions

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 HIRES 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 inner-most 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.