Occurrence rate of hot Jupiters orbiting red giant stars

TL;DR

This study estimates the occurrence rate of Hot Jupiters around red giant stars using TESS data, finding a rate similar to that around other star types, which informs theories of planetary formation and evolution.

Contribution

It provides the first occurrence rate estimate of Hot Jupiters around red giants based on a large Gaia-selected sample and TESS observations, including detection efficiency correction.

Findings

Occurrence rate of Hot Jupiters around red giants is approximately 0.37%.

Detected three confirmed Hot Jupiters and one TESS Object of Interest.

Results suggest similar Hot Jupiter occurrence rates across different stellar types.

Abstract

Hot Jupiters form an enigmatic class of object with yet unclear formation pathways. Determination of their occurrence rates as function 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. In this study we aim 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. A sample of 14474 red giant stars, with estimated radii between 2 and 5 $R_\odot$, 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. 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 $0.37^{+0.29}_{-0.09}$%. Due to the yet 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 yet an important role in this sample.