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

3 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
Externally publishedYes

Bibliographical note

Funding Information:
R.L. acknowledges financial support from the Spanish Ministerio de Ciencia e Innovación, through project PID2019-109522GB-C52, and the Centre of Excellence “Severo Ochoa” award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709).

Funding Information:
Based on data collected under the ExTrA project at the ESO La Silla Paranal Observatory. ExTrA is a project of Institut de Planétologie et d’Astrophysique de Grenoble (IPAG/CNRS/UGA), funded by the European Research Council under the ERC Grant Agreement No. 337591-ExTrA. This work has been supported by a grant from Labex OSUG@2020 (Investissements d’avenir—ANR10 LABX56).

Funding Information:
Observations in this paper made use of the NN-EXPLORE Exoplanet and Stellar Speckle Imager (NESSI). NESSI was funded by the NASA Exoplanet Exploration Program and the NASA Ames Research Center. NESSI was built at the Ames Research Center by Steve B. Howell, Nic Scott, Elliott P. Horch, and Emmett Quigley.

Funding Information:
The development of the MAROON-X spectrograph was funded by the David and Lucile Packard Foundation, the Heising-Simons Foundation, the Gemini Observatory, and the University of Chicago. We thank the staff of the Gemini Observatory for their assistance with the commissioning and operation of the instrument. The MAROON-X observing program is supported by NSF grant No. 2108465.

Funding Information:
This work is partly supported by JSPS KAKENHI grant No. P17H04574, JP18H05439, JP20K14518, JP21K13975, JST CREST grant No. JPMJCR1761, and the Astrobiology Center of National Institutes of Natural Sciences (NINS) (grant Nos. AB022006, AB031010, AB031014). This work is partly financed by the Spanish Ministry of Economics and Competitiveness through grant No. PGC2018-098153-B-C31.

Funding Information:
Based on data collected under the NGTS project at the ESO La Silla Paranal Observatory. The NGTS facility is operated by the consortium institutes with support from the UK Science and Technology Facilities Council (STFC) projects ST/M001962/1 and ST/S002642/1. This work has made use of data from the European Space Agency (ESA) mission Gaia ( https://www.cosmos.esa.int/gaia ), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https://www.cosmos.esa.int/web/gaia/dpac/consortium ). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.

Funding Information:
Some of the observations in the paper made use of the High-Resolution Imaging instrument Zorro obtained under Gemini LLP Proposal Number GN/S-2021A-LP-105. Zorro was funded by the NASA Exoplanet Exploration Program and built at the NASA Ames Research Center by Steve B. Howell, Nic Scott, Elliott P. Horch, and Emmett Quigley. Zorro was mounted on the Gemini South telescope of the international Gemini Observatory, a program of NSF's OIR Lab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. on behalf of the Gemini partnership: the National Science Foundation (United States), National Research Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia, Tecnología e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações (Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea).

Funding Information:
We acknowledge support from NSF grant Nos. AST-190950 and 1910954.

Funding Information:
M.A.R. and P.P.P. acknowledge support from NASA (Exoplanet Research Program Award #80NSSC20K0251, TESS Cycle 3 Guest Investigator Program Award #80NSSC21K0349, JPL Research and Technology Development, and Keck Observatory Data Analysis) and the NSF (Astronomy and Astrophysics grant Nos. 1716202 and 2006517), and the Mt Cuba Astronomical Foundation.

Funding Information:
V.K. gratefully acknowledges support from NASA via grant No. NNX17AF81G.

Funding Information:
This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under grant No. DGE 1746045.

Funding Information:
C.I.C. acknowledges support by NASA Headquarters under the NASA Earth and Space Science Fellowship Program through grant No. 80NSSC18K1114.

Funding Information:
NEID is funded by NASA/JPL under contract 1547612.

Funding Information:
M.L. acknowledges support from the Swiss National Science Foundation under grant No. PCEFP2_194576. The contribution of M.L. has been carried out within the framework of the NCCR PlanetS supported by the Swiss National Science Foundation.

Publisher Copyright:
© 2022. The Author(s). Published by the American Astronomical Society.


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