A Close-in Puffy Neptune with Hidden Friends: The Enigma of TOI 620
Bieryla, Allyson; Latham, David W.; Quinn, Samuel N.; Mahadevan, Suvrath; Terrien, Ryan; Feliz, Dax L.; Gaidos, Eric; Howell, Steve B.; Crossfield, Ian J. M.; Wright, Jason T.; Bean, Jacob; Collins, Karen A.; Jenkins, Jon M.; Beichman, Charles A.; Teske, Johanna; Collins, Kevin I.; Ciardi, David R.; Livingston, John H.; Eigmüller, Philipp; Fukui, Akihiko; Narita, Norio; Palle, Enric; Lendl, Monika; Osborn, Ares; Gagné, Jonathan; Kasper, David; Luque, Rafael; Bryant, Edward M.; Boyd, Patricia T.; Matthews, Elisabeth; Guerrero, Natalia; Schlieder, Joshua; Bouchy, François; Dressing, Courtney D.; Zechmeister, Mathias; Gao, Peter; Murgas, Felipe; Tanner, Angelle; Zohrabi, Farzaneh; Stassun, Keivan; Geneser, Claire; Irwin, Jonathan; Wang, Sharon X.; Stefánsson, Guðmundur; Lin, Andrea; Cañas, Caleb I.; Kanodia, Shubham; Hearty, Fred; Robertson, Paul; Roy, Arpita; Schwab, Christian; Reefe, Michael A.; Bonfils, Xavier; Beard, Corey; Lubin, Jack; Gnilka, Crystal L.; Plavchan, Peter P.; Cointepas, Marion; Cale, Bryson L.; Parviainen, Hannu; Eastman, Jason; Kidwell, Richard C.; McDermott, Scott; Fong, William; Almenara-Villa, Jose-Manuel; Berberian, John; Brady, Madison; Cacciapuoti, Luca; El Mufti, Mohammed; Esparza-Borges, Emma; Gonzales, Erica; Gupta, Arvind F.; Halverson, Sam; Kodama, Takanori; Kostov, Veselin; Matson, Rachel; Newman, Patrick; Ninan, Joe; Seifahrt, Andreas; Smith, Gareth D.; Sohani, Ahmad; Stevens, Daniel; Stürmer, Julian; Vermilion, David; Wittrock, Justin
United States, Spain, France, Switzerland, Canada, United Kingdom, Italy, Germany, Japan, Australia, China
Abstract
We present the validation of a transiting low-density exoplanet orbiting the M2.5 dwarf TOI 620 discovered by the NASA Transiting Exoplanet Survey Satellite (TESS) mission. We utilize photometric data from both TESS and ground-based follow-up observations to validate the ephemerides of the 5.09 day transiting signal and vet false-positive scenarios. High-contrast imaging data are used to resolve the stellar host and exclude stellar companions at separations ≳0.″2. We obtain follow-up spectroscopy and corresponding precise radial velocities (RVs) with multiple precision radial velocity (PRV) spectrographs to confirm the planetary nature of the transiting exoplanet. We calculate a 5σ upper limit of M P < 7.1 M ⊕ and ρ P < 0.74 g cm-3, and we identify a nontransiting 17.7 day candidate. We also find evidence for a substellar (1-20 M J ) companion with a projected separation ≲20 au from a combined analysis of Gaia, adaptive optics imaging, and RVs. With the discovery of this outer companion, we carry out a detailed exploration of the possibilities that TOI 620 b might instead be a circum-secondary planet or a pair of eclipsing binary stars orbiting the host in a hierarchical triple system. We find, under scrutiny, that we can exclude both of these scenarios from the multiwavelength transit photometry, thus validating TOI 620 b as a low-density exoplanet transiting the central star in this system. The low density of TOI 620 b makes it one of the most amenable exoplanets for atmospheric characterization, such as with the James Webb Space Telescope and Ariel, validated or confirmed by the TESS mission to date.