Searching for GEMS: TOI-5688 A b, a low-density giant orbiting a high-metallicity early M-dwarf

TL;DR

This paper reports the discovery and characterization of a low-density, high-metallicity giant exoplanet orbiting an early M-dwarf, using TESS data and ground-based follow-up, highlighting its formation in a binary system.

Contribution

First detection of a low-density giant planet around a high-metallicity M-dwarf within a wide binary system, combining TESS, ground-based, and radial velocity data for detailed analysis.

Findings

Planet has a mass of 124±24 M⊕ and radius of 10.4±0.7 R⊕.

Host star is a metal-rich M2V star with [Fe/H] = 0.47±0.16.

System includes a wide-separation M4V binary companion.

Abstract

We present the discovery of a low-density planet orbiting the high-metallicity early M-dwarf TOI-5688 A b. This planet was characterized as part of the search for transiting giant planets ($R \gtrsim8$ M${}_\oplus$) through the Searching for GEMS (Giant Exoplanets around M-dwarf Stars) survey. The planet was discovered with the Transiting Exoplanet Survey Satellite (TESS), and characterized with ground-based transits from Red Buttes Observatory (RBO), the Table Mountain Observatory of Pomona College, and radial velocity (RV) measurements with the Habitable-Zone Planet Finder (HPF) on the 10 m Hobby Eberly Telescope (HET) and NEID on the WIYN 3.5 m telescope. From the joint fit of transit and RV data, we measure a planetary mass and radius of $124\pm24$ M$_\oplus$ ($0.39\pm0.07$ M${}_J$) and $10.4\pm0.7$ R$_\oplus$ ($0.92\pm0.06$ R${}_J$) respectively. The spectroscopic and photometric analysis of the host star TOI-5688 A shows that it is a metal-rich ([Fe/H] $ = 0.47\pm0.16$ dex) M2V star, favoring the core-accretion formation pathway as the likely formation scenario for this planet. Additionally, Gaia astrometry suggests the presence of a wide-separation binary companion, TOI-5688 B, which has a projected separation of $\sim5"$ (1110 AU) and is an M4V, making TOI-5688 A b part of the growing number of GEMS in wide-separation binary systems.