TOI-7169 b: A Hot Jupiter Transiting a Metal-Poor Star

TL;DR

This paper reports the discovery of TOI-7169 b, a hot Jupiter orbiting a very old, metal-poor star, providing new insights into planet formation in low-metallicity environments.

Contribution

It presents the first detailed characterization of a giant planet around one of the most metal-poor, oldest stars known, expanding understanding of planet formation in such environments.

Findings

TOI-7169 b has a radius of 1.475 R_Jup and a mass of 0.41 M_Jup.

The host star is approximately 12.3 billion years old and has a metallicity of [Fe/H] = -0.72.

The planet is highly inflated with a low density of 0.159 g/cm^3.

Abstract

Most known planets are found around metal-rich host stars, which has made it difficult to determine whether a lower metallicity limit for planet formation exists and how the properties of planets born in low-metallicity environments may differ from those with metal-rich origins. We present the discovery and characterization of TOI-7169 b (TIC 372048733 b), a hot Jupiter that is orbiting a spectroscopically-confirmed metal-poor ([Fe/H] = -0.72 +/- 0.05) host star. Based on photometry from TESS and follow-up ground-based imaging, we measure an orbital period of 3.4373125 d and a planetary radius of 1.475 +/- 0.029 R_Jup. We use TRES spectroscopy to determine a mass for TOI-7169 b of 0.41 +/- 0.14 M_Jup. The planet is therefore inflated, with a low density of 0.159 +0.055/-0.054 g/cm^3. We also characterize the host star, showing that TOI-7169 is ancient (12.3 +/- 0.6 Gyr) and alpha-enhanced ([alpha/Fe] ~ 0.3), but with a Galactocentric orbit that is confined to the thin disk. TOI-7169 is perhaps the oldest and most metal-poor star currently known to host a transiting giant planet. Future transmission spectroscopy probing the atmosphere of TOI-7169 b may provide insight into the effect of metallicity on the physical properties of giant planets.