TOI-3785 b: A Low-density Neptune Orbiting an M2-dwarf Star
Kobulnicky, Henry A.; Cochran, William D.; Mahadevan, Suvrath; Wisniewski, John; Wright, Jason T.; Monson, Andrew; Cañas, Caleb I.; Kanodia, Shubham; Ninan, Joe P.; Hebb, Leslie; Bender, Chad F.; Metcalf, Andrew J.; Robertson, Paul; Schwab, Christian; Lin, Andrea S. J.; Libby-Roberts, Jessica; Stefánsson, Guđmundur; Gupta, Arvind F.; Parker, Brock A.; Swaby, Tera N.; Jones, Sinclaire; Powers, Luke C.
United States, Switzerland, India, Australia
Abstract
Using both ground-based transit photometry and high-precision radial velocity spectroscopy, we confirm the planetary nature of TOI-3785 b. This transiting Neptune orbits an M2-Dwarf star with a period of ~4.67 days, a planetary radius of 5.14 ± 0.16 R ⊕, a mass of ${14.95}_{-3.92}^{+4.10}$ M ⊕, and a density of $\rho ={0.61}_{-0.17}^{+0.18}$ g cm-3. TOI-3785 b belongs to a rare population of Neptunes (4 R ⊕ < R p < 7 R ⊕) orbiting cooler, smaller M-dwarf host stars, of which only ~10 have been confirmed. By increasing the number of confirmed planets, TOI-3785 b offers an opportunity to compare similar planets across varying planetary and stellar parameter spaces. Moreover, with a high-transmission spectroscopy metric of ~150 combined with a relatively cool equilibrium temperature of T eq = 582 ± 16 K and an inactive host star, TOI-3785 b is one of the more promising low-density M-dwarf Neptune targets for atmospheric follow up. Future investigation into atmospheric mass-loss rates of TOI-3785 b may yield new insights into the atmospheric evolution of these low-mass gas planets around M dwarfs.