Predicting <i>Gaia</i> astrometry’s ability to constrain the populations of circumbinary planets

ABSTRACT The coming data releases of Gaia are expected to result in an upheaval of exoplanet science, in particular for long-period giant planets ($0.2\, {M_{\rm J}}\, \le M\le 25\, {M_{\rm J}}$). One class of exoplanets that Gaia will help investigate is circumbinary planets. Using the current knowledge of the circumbinary exoplanet population and expectations for the Gaia sensitivity, we investigate the impact Gaia will have on our understanding of circumbinary planets. We compare our results to a pre-launch estimate, the main differences arising from a better understanding of the circumbinary planet population, which results in a lower expected yield than previously predicted, though still significant compared to the known population. We make a rough yield estimate, with conservative detection criteria and parameter-space cuts, predicting in the 10–100s of detections in Gaia Data Release 4. More importantly, we show how the yield estimate varies strongly with different assumptions on the injected circumbinary population, showing Gaia’s sensitivity to the mass and orbital period distribution of circumbinary planets. We find that Gaia circumbinary exoplanet detections will be biased towards planets closer to the instability zone surrounding the binary, due to the larger number of binaries on wider orbits and the limited time span of Gaia. We also assess the impact Gaia will have on known circumbinary systems, one being that it may resolve the question of the reliability of the claimed planets orbiting post-common-envelope binaries, with Gaia Data Release 5 being sensitive to between 3 and 11 out of 32 such planet candidates.