Predicting Gaia 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 ($0.2 {\rm M_{J}} \leq M\leq25 {\rm M_{J}}$). One class of exoplanets which Gaia will help investigate is circumbinary planets. Using the current knowledge of the circumbinary exoplanet population as well as 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 result 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 10s - 100s of detections in Gaia DR4. 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 timespan of Gaia. We also assess the impact Gaia will have on known circumbinary systems, one being that it may resolve the question of reliability of the claimed planets orbiting post-common-envelope binaries, with Gaia DR5 being sensitive to between 3 and 11 out of 32 such planet candidates.

Figures (14)

• Figure 1: Distributions of parameters for the synthetic population of binary stars which will be used for simulation for Gaia yield of circumbinary planets. Orbital period distribution shows the full simulated sample in the background while specifying the range that is actually considered for potential circumbinary planet hosts.
• Figure 2: Planet mass and scaled orbital period distributions used in circumbinary planet injections to test Gaia yield. There are four different scaled period distributions used (top), and three different mass distributions used (bottom). The middle distribution (in black) in each case is our fiducial one, it is kept the same when varying the other parameter.
• Figure 3: Distributions of the binary orbital periods around which circumbinary planets are expected to be detected in Setup 1 (the fiducial setup see Table \ref{['tab:GaiaYieldSetup']}). Top for DR4 and bottom for DR5, the other distributions are those restricted to binaries with $P_{\rm bin}<50\,{\rm days}$.
• Figure 4: Distributions of detected planet masses of Gaia circumbinary planets in the Setups 1, 2, and 3 (top, middle, and bottom). The other distributions are those restricted to binaries with $P_{\rm bin}<50\,{\rm days}$.
• Figure 5: Distributions of planet's scaled orbital period for predicted Gaia circumbinary planet detections in the Setups 1, 4, 5, and 6 (top-left,top-right,bottom-left,bottom-right). The other distributions are those restricted to binaries with $P_{\rm bin}<50\,{\rm days}$.