On the follow-up efforts of long-period transiting planet candidates detected with Gaia astrometry

TL;DR

This paper explores how Gaia astrometry, combined with ground-based observations, can improve the detection and characterization of long-period transiting cold Jupiters, reducing transit search windows and enabling follow-up studies.

Contribution

It develops a framework for combining Gaia astrometry with radial-velocity data to accurately predict transit times of cold giant planets, enhancing follow-up observation efficiency.

Findings

Gaia can predict transit centers within a few months for most cases.

Combined data analysis reduces transit search windows to about two weeks.

Follow-up requires moderate observing time, making it feasible for many candidates.

Abstract

The class of transiting cold Jupiters, orbiting at $\gtrsim0.5-1.0$ au, is to-date underpopulated. Probing their atmospheric composition and physical characteristics is particularly valuable, as it allows for direct comparisons with the Solar System giant planets. We investigate some aspects of the synergy between Gaia astrometry and other ground-based and space-borne programs for detection and characterization of such companions. We carry out numerical simulations of Gaia observations of systems with one cold transiting gas giant, using Jovian planets around a sample of nearby low-mass stars as proxies. Using state-of-the-art orbit fitting tools, we gauge the potential of Gaia astrometry to predict the time of transit centre $T_c$ for the purpose of follow-up observations to verify that the companions are indeed transiting. Typical uncertainties on $T_c$ will be on the order of a few months, reduced to several weeks for high astrometric signal-to-noise ratios and periods shorter than $\sim3$ yr. We develop a framework for the combined analysis of Gaia astrometry and radial-velocity data from representative ground-based campaigns and show that combined orbital fits would allow to significantly reduce the transit windows to be searched for, down to about $\pm2$ weeks ($2-\sigma$ level) in the most favourable cases. These results are achievable with a moderate investment of observing time ($\sim0.5$ nights per candidate, $\sim50$ nights for the top 100 candidates), reinforcing the notion that Gaia astrometric detections of potentially transiting cold giant planets, starting with Data Release 4, will constitute a valuable sample worthy of synergistic follow-up efforts with a variety of techniques.