Exoplanet mass estimation for a sample of targets for the Ariel mission

Abstract

Ariel’s ambitious goal to survey a quarter of known exoplanets will transform our knowledge of planetary atmospheres. Masses measured directly with the radial velocity technique are essential for well determined planetary bulk properties. Radial velocity masses will provide important checks of masses derived from atmospheric fits or alternatively can be treated as a fixed input parameter to reduce possible degeneracies in atmospheric retrievals. We quantify the impact of stellar activity on planet mass recovery for the Ariel mission sample using Sun-like spot models scaled for active stars combined with other noise sources. Planets with necessarily well-determined ephemerides will be selected for characterisation with Ariel. With this prior requirement, we simulate the derived planet mass precision as a function of the number of observations for a prospective sample of Ariel targets. We find that quadrature sampling can significantly reduce the time commitment required for follow-up RVs, and is most effective when the planetary RV signature is larger than the RV noise. For a typical radial velocity instrument operating on a 4 m class telescope and achieving 1 m s−1 precision, between ~17% and ~ 37% of the time commitment is spent on the 7% of planets with mass Mp < 10 M⊕. In many low activity cases, the time required is limited by asteroseismic and photon noise. For low mass or faint systems, we can recover masses with the same precision up to ~3 times more quickly with an instrumental precision of ~10 cm s−1.

The Ariel Target List: The Impact of TESS and the Potential for Characterising Multiple Planets Within a System

“…Several studies have explored the time need to provide radial velocity measurements necessary to constrain planet masses for Ariel (e.g. Barnes & Haswell 2021;Demangeon et al submitted) and the ongoing work of radial velocity teams, both within the Ariel consortium and outside of it (e.g. Lillo-Box et al 2020;Chontos et al 2021;Nielsen et al 2020;Kaye et al 2021;Van Eylen et al 2021), are ensuring that the best targets for atmospheric characterisation are followed-up.…”

The Ariel Target List: The Impact of TESS and the Potential for Characterizing Multiple Planets within a System

“…Accurately knowing the planet's mass is also useful, particularly for smaller or cloudier worlds (Batalha et al 2019;Changeat et al 2020b). Several studies have explored the time needed to provide the radial velocity measurements necessary to constrain planet masses for Ariel (e.g., Barnes & Haswell 2021;Demangeon et al 2022), and the ongoing work of the radial velocity teams, both within the Ariel consortium and outside of it (e.g., Lillo-Box et al 2020;Nielsen et al 2020;Chontos et al 2021;Kaye et al 2021;Van Eylen et al 2021), is ensuring that the best targets for atmospheric characterization are followed up. Nevertheless, it may not be Figure 14.…”