TOI-532b: The Habitable-zone Planet Finder confirms a Large Super Neptune in the Neptune Desert orbiting a metal-rich M-dwarf host
Kobulnicky, Henry A.; Cochran, William D.; Mahadevan, Suvrath; Wisniewski, John; Wright, Jason T.; Monson, Andrew; Kopparapu, Ravi; Cañas, Caleb I.; Kanodia, Shubham; Ninan, Joe P.; Hebb, Leslie; Bender, Chad F.; Diddams, Scott A.; Fredrick, Connor; Halverson, Samuel; Hearty, Fred; Maney, Marissa; Metcalf, Andrew J.; Ramsey, Lawrence W.; Robertson, Paul; Roy, Arpita; Schwab, Christian; Terrien, Ryan C.; Lin, Andrea S. J.; Beard, Corey; Lubin, Jack; Gupta, Arvind F.; Stefansson, Gudmundur; Parker, Brock A.; Jones, Sinclaire; Schutte, Maria; Rothenberg, Jason; Hawley, Suzanne
United States, Australia
Abstract
We confirm the planetary nature of TOI-532b, using a combination of precise near-infrared radial velocities with the Habitable-zone Planet Finder, Transiting Exoplanet Survey Satellite (TESS) light curves, ground-based photometric follow up, and high-contrast imaging. TOI-532 is a faint (J ~ 11.5) metal-rich M dwarf with Teff = 3957 ± 69 K and [Fe/H] = 0.38 ± 0.04; it hosts a transiting gaseous planet with a period of ~2.3 days. Joint fitting of the radial velocities with the TESS and ground-based transits reveal a planet with radius of 5.82 ± 0.19 R⊕, and a mass of ${61.5}_{-9.3}^{+9.7}$ M⊕. TOI-532b is the largest and most massive super Neptune detected around an M dwarf with both mass and radius measurements, and it bridges the gap between the Neptune-sized planets and the heavier Jovian planets known to orbit M dwarfs. It also follows the previously noted trend between gas giants and host-star metallicity for M-dwarf planets. In addition, it is situated at the edge of the Neptune desert in the Radius-Insolation plane, helping place constraints on the mechanisms responsible for sculpting this region of planetary parameter space.