A Search for Substellar Companions around A-type Stars: Pulsation Timing Detection of Eight Brown Dwarf Candidates and a Possible Habitable-zone Planet

Abstract

Substellar companions are most often studied around solar-like or smaller stars, as the rapid rotation and variability of massive stars impede detection using traditional methods. An alternative technique, pulsation timing, uses photometry to measure light-travel-time variations—the time integral of the radial velocity signal—providing orbital constraints with strong sensitivity to intermediate-period companions. We analyze the pulsation timing variations of 16,440 δ Scuti pulsators from the Transiting Exoplanet Survey Satellite (TESS), with the goal of identifying substellar companions. We report the discovery of one candidate planet, HD 156295 b, and eight candidate brown dwarfs by fitting orbital models to the pulsation timing variations, which are consistent with the constraints from Hipparcos–Gaia astrometric acceleration, when available. We infer a mass of 6.3 ± 1.1 MJ for the planet, which is in agreement with the 2σ upper limit of 10.5 MJ derived from Hipparcos–Gaia accelerations. If confirmed, HD 156295 would be the hottest star to host a habitable-zone planet. Given this candidate, we infer an occurrence rate of η=0.10−0.08+0.21 for 5–10 Jupiter mass planets with periods between 1900 and 2600 days around A-type stars. If the system is instead a false positive, we infer the 1σ and 2σ upper limits on the occurrence rate to be 19% and 39%, respectively. Astrometric follow-up could confirm and further characterize the planet candidate. At least two of our candidate brown dwarf systems represent useful targets for follow-up with direct imaging.