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A Close-in Puffy Neptune with Hidden Friends: The Enigma of TOI 620

Michael A. Reefe Rafael Luque Eric Gaidos Corey Beard Peter P. Plavchan Marion Cointepas 1 Bryson L. Cale Enric Palle Hannu Parviainen Dax L. Feliz Jason Eastman Keivan Stassun Jonathan Gagné Jon M. Jenkins Patricia T. Boyd Richard C. Kidwell Scott Mcdermott Karen A. Collins William Fong Natalia Guerrero Jose-Manuel Almenara-Villa 1 Jacob Bean Charles A. Beichman John Berberian Allyson Bieryla Xavier Bonfils 1 François Bouchy Madison Brady Edward M. Bryant Luca Cacciapuoti Caleb I. Cañas David R. Ciardi Kevin I. Collins Ian J. M. Crossfield Courtney D. Dressing Philipp Eigmüller Mohammed El Mufti Emma Esparza-Borges Akihiko Fukui Peter Gao Claire Geneser Crystal L. Gnilka Erica Gonzales Arvind F. Gupta Sam Halverson Fred Hearty Steve B. Howell Jonathan Irwin Shubham Kanodia David Kasper Takanori Kodama Veselin Kostov David W. Latham Monika Lendl Andrea Lin John H. Livingston Jack Lubin Suvrath Mahadevan Rachel Matson Elisabeth Matthews Felipe Murgas 1 Norio Narita Patrick Newman Joe Ninan Ares Osborn Samuel N. Quinn Paul Robertson Arpita Roy Joshua Schlieder Christian Schwab Andreas Seifahrt Gareth D. Smith Ahmad Sohani Guðmundur Stefánsson Daniel Stevens Julian Stürmer Angelle Tanner Ryan Terrien Johanna Teske David Vermilion Sharon X. Wang Justin Wittrock Jason T. Wright Mathias Zechmeister Farzaneh Zohrabi 
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.
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Submitted on : Monday, June 27, 2022 - 12:29:50 PM
Last modification on : Wednesday, June 29, 2022 - 3:09:34 AM

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Michael A. Reefe, Rafael Luque, Eric Gaidos, Corey Beard, Peter P. Plavchan, et al.. A Close-in Puffy Neptune with Hidden Friends: The Enigma of TOI 620. The Astronomical Journal, 2022, 163, ⟨10.3847/1538-3881/ac658b⟩. ⟨insu-03705343⟩

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