Secular Acceleration as a Deterministic Long-term Trend in Precision Exoplanet Radial-velocity Time Series

Slow linear or even curved trends can sometimes be detected in long-baseline radial velocity (RV) curves. One such trend is due to a purely geometric effect: the proper motion of the target which causes a continuously variable line of sight to a moving star. The effect can be parametrized by Gaia proper motion and parallax data. This RV-drift is characterized via v ˙ sec = 2.298 × 1 0 − 5 μ α * 2 + μ δ 2 ϖ m s − 1 yr − 1 , where the proper motions and parallax are in milliarcsecond (mas) yr −1 and mas, respectively. The accumulated trend can reach or exceed meter-per-second levels over several years for nearby high-proper-motion targets. This contribution should be reported in precise RV analyses and is relevant for future multi-year ground-based RV follow-up of PLATO targets, as well as being potentially important for planetary systems hosting Earth- and SuperEarth-like planets in the habitable zones of Solar-like stars.