Detection and Characterisation of Giant Planets with Gaia Astrometry

TL;DR

Gaia astrometry, combined with radial velocity data, enables the detection and characterization of exoplanets and brown dwarfs, with future Gaia data releases promising even more precise orbital parameter constraints.

Contribution

This study demonstrates how Gaia DR3 data can be used with Bayesian inference to constrain exoplanet properties and predicts the impact of upcoming Gaia data releases on exoplanet detection.

Findings

HD 66141 b may be a brown dwarf with a maximum mass of 23.9 M_J.

Combining Gaia astrometry with radial velocity data allows independent measurement of mass and inclination.

Future Gaia epoch astrometry will significantly improve orbital parameter constraints.

Abstract

Astrometric observations with Gaia are expected to play a valuable role in future exoplanet surveys. With current data from Gaia's third data release (DR3), we are sensitive to periods from less than 1 year to more than 4 years but, unlike radial velocity are not as restricted by the orbital inclination of a potential planet. The presence and potential properties of a companion affect the primary's renormalised unit weight error (RUWE) making this a valuable quantity in the search for exoplanets. Using this value and the fitted astrometric tracks from Gaia, we use Bayesian inference to constrain the mass and orbital parameters of companions in known systems. Combining this with radial velocity measurements, we show it is possible to independently measure mass and inclination and suggest HD 66141 b is a possible brown dwarf with maximum mass 23.9$^{+7.2}_{-6.4}$ M$_{\mathrm{J}}$. We show how this method may be applied to directly imaged planets in the future, using $\beta$-Pictoris c as an example but note that the host star is bright and active, making it difficult to draw clear conclusions. We show how the next Gaia data release, which will include epoch astrometry, will allow us to accurately constrain orbital parameters from astrometric data alone, revolutionising future searches for exoplanets. Combining predicted observational limits on planet mass with theoretical distributions, we estimate the probability that a star with a given RUWE will host a detectable planet, which will be highly valuable in planning future surveys.