Journal ArticleSearching for GEMS: TOI-5688 A b, a Low-density Giant Orbiting a High-metallicity Early M-dwarf*Reji, Varghese (ORCID:000900067298619X); Kanodia, Shubham (ORCID:0000000184014300); Ninan, Joe P (ORCID:0000000187205612); Cañas, Caleb I (ORCID:0000000348350619); Libby-Roberts, Jessica (ORCID:0000000229907613); Lin, Andrea_S J (ORCID:0000000290826337); Gupta, Arvind F (ORCID:0000000254639980); Swaby, Tera N (ORCID:000000025817202X); Larsen, Alexander (ORCID:0000000224018411); Kobulnicky, Henry A (ORCID:0000000244754176); Choi, Philip I; Evans, Nez; Santomenna, Sage (ORCID:0000000286238268); Winnick, Isabelle; Yu, Larry; Alvarado-Montes, Jaime A (ORCID:0000000303539741); Bender, Chad F (ORCID:0000000343847220); Bernabó, Lia Marta (ORCID:0000000280351032); Blake, Cullen H (ORCID:0000000260961749); Cochran, William D (ORCID:0000000196623496); Diddams, Scott A (ORCID:0000000221440764); Halverson, Samuel (ORCID:0000000313129391); Han, Te (ORCID:0000000271277643); Hearty, Fred (ORCID:0000000216643102); Logsdon, Sarah E (ORCID:0000000296329382); Mahadevan, Suvrath (ORCID:0000000195967983); McElwain, Michael W; Monson, Andrew (ORCID:0000000200482586); Robertson, Paul (ORCID:0000000301499678); Ojha, Devendra K (ORCID:0000000193123816); Roy, Arpita (ORCID:0000000181275775); Schwab, Christian (ORCID:000000024046987X); Stefansson, Gudmundur (ORCID:0000000174095688); Wright, Jason (ORCID:0000000161605888)<title>Abstract</title> <p>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 (<italic>R</italic> ≳ 8<italic>R</italic><sub>⊕</sub>) through the Searching for Giant Exoplanets around M-dwarf Stars (GEMS) survey. The planet was discovered with the Transiting Exoplanet Survey Satellite, and characterized with ground-based transits from Red Buttes Observatory, the Table Mountain Observatory of Pomona College, and radial velocity (RV) measurements with the Habitable-Zone Planet Finder on the 10 m Hobby Eberly Telescope 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 ± 24<italic>M</italic><sub>⊕</sub>(0.39 ± 0.07<italic>M</italic><sub>J</sub>) and 10.4 ± 0.7<italic>R</italic><sub>⊕</sub>(0.92 ± 0.06<italic>R</italic><sub>J</sub>), respectively. The spectroscopic and photometric analysis of the host star TOI-5688 A shows that it is a metal-rich ([Fe/H] = 0.47 ± 0.16 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 ~5″ (1110 au) and is an M4V, making TOI-5688 A b part of the growing number of GEMS in wide-separation binary systems.</p>American Astronomical Society Journals2025-03-0310651340The Astronomical Journal16931870004-6256https://doi.org/10.3847/1538-3881/ada7ea2108493; 2108801; 2538457; 2108616; 2108512National Science Foundation