An astrometric search for planets in debris disk systems

Debris disks are likely created and sculpted by planetary bodies in the orbital space they share. The properties of these disks, including mass, orbital extent, and morphology, can be indicators of their planetary shepherds. Recently, T. D. Pearce and collaborators placed limits on the masses and orbits of hypothetical planets around 178 stars with debris disks. Here, we consider 176 of these stars, all objects that have astrometric data in the Gaia Data Release 3 archive, to assess planet detection from astrometry. Our analysis begins with a set of stellar hosts of known exoplanets, selected to have parallax, apparent magnitude, and color similar to the 176 debris disk systems. We confirm that Gaia’s ruwe parameter, a measure of the quality of astrometric fitting to a linear drift model, is sensitive to the presence of massive companions, even planetary ones. We also train a machine-learning model with a range of planet host properties from Gaia, considering more detailed astrometric data beyond ruwe that might indicate orbital motion. In addition, the model incorporates Gaia photometry to inform how brightness and stellar type affect detectability, with the risk that selection bias in the training set may affect reliability. Guided by ruwe and predictions of the machine-learning model, we identify stars with debris disks that may host as-yet-undiscovered planets. Overall, the model predictions, ruwe, and the mass limits from debris disk morphology do not show strong trends. Nonetheless, our top candidates with high ruwe and high planethood probability from the machine learning model will be compelling subjects for time‑series analyses with Gaia Data Release 4.