Occurrence rate of hot Jupiters orbiting red giant stars

Leiden Observatory, Leiden University, Postbus 9513, 2300 RA, Leiden, The Netherlands
e-mail: temmink@strw.leidenuniv.nl

Received: 3 June 2022
Accepted: 1 December 2022

Abstract

Context. Hot Jupiters form an enigmatic class of object whose formation pathways are not yet clear. Determining their occurrence rates as a function of orbit, planet and stellar mass, and system age can be an important ingredient for understanding how they form. To date, various hot Jupiters have been discovered orbiting red giant stars, and deriving their incidence would be highly interesting.

Aims. In this study our aim is to determine the number of hot Jupiters in a well-defined sample of red giants, estimate their occurrence rate, and compare it with that for A-, F-, and G-type stars.

Methods. A sample of 14474 red giant stars, with estimated radii between 2 and 5 R_⊙, was selected using Gaia to coincide with observations by the NASA TESS mission. Subsequently, the TESS light curves were searched for transits from hot Jupiters. The detection efficiency was determined using injected signals, and the results further corrected for the geometric transit probability to estimate the occurrence rate.

Results. Three previously confirmed hot Jupiters were found in the TESS data, in addition to one other TESS object of interest, and two M-dwarf companions. This results in an occurrence rate of 0.37_−0.09^+0.29%. Due to the still large uncertainties, this cannot be distinguished from that of A-, F-, and G-type stars. We argue that it is unlikely that planet engulfment in expanding red giants plays an important role in this sample.