Searching For Transiting Planets Around Halo Stars. II. Constraining the Occurrence Rate of Hot Jupiters

TL;DR

This study uses TESS data to set the most stringent upper limit on hot Jupiter occurrence around metal-poor halo stars, confirming that planet formation is unlikely below certain metallicity levels.

Contribution

It provides the first large-sample constraint on hot Jupiter occurrence rates in metal-poor environments, improving understanding of planet formation limits.

Findings

Upper limit of hot Jupiter occurrence is 0.18% around halo stars.

Results support the metallicity threshold hypothesis for planet formation.

Findings are consistent with previous theoretical predictions.

Abstract

Jovian planet formation has been shown to be strongly correlated with host star metallicity, which is thought to be a proxy for disk solids. Observationally, previous works have indicated that jovian planets preferentially form around stars with solar and super solar metallicities. Given these findings, it is challenging to form planets within metal-poor environments, particularly for hot Jupiters that are thought to form via metallicity-dependent core accretion. Although previous studies have conducted planet searches for hot Jupiters around metal-poor stars, they have been limited due to small sample sizes, which are a result of a lack of high-quality data making hot Jupiter occurrence within the metal-poor regime difficult to constrain until now. We use a large sample of halo stars observed by TESS to constrain the upper limit of hot Jupiter occurrence within the metal-poor regime (-2.0 $\leq$ [Fe/H] $\leq$ -0.6). Placing the most stringent upper limit on hot Jupiter occurrence, we find the mean 1-$\sigma$ upper limit to be 0.18 $\%$ for radii 0.8 -2 R$_{\rm{Jupiter}}$ and periods $0.5- 10$ days. This result is consistent with previous predictions indicating that there exists a certain metallicity below which no planets can form.