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, 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 GuerreroJose Manuel Almenara-Villa, Jacob Bean, Charles A. Beichman, John Berberian, Allyson Bieryla, Xavier Bonfils, 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, 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

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


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.

Original languageEnglish (US)
Article number269
JournalAstronomical Journal
Issue number6
StatePublished - Jun 1 2022

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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