TOI-220 b: a warm sub-Neptune discovered by TESS

S. Hoyer (1) , D. Gandolfi (2) , D. J. Armstrong (1) , M. Deleuil (1) , L. Acu Na , J. R. De Medeiros , E. Goffo , J. Lillo-Box (3) , E. Delgado Mena , T. A. Lopez , A. Santerne (1) , S. Sousa (4) , M. Fridlund (5) , V. Adibekyan (6) , K. A. Collins , L. M. Serrano , P. Cortés-Zuleta , S. B. Howell , H. Deeg (7) , A. Aguichine (1) , O. Barragán , E. M. Bryant , B. L. Canto Martins (8) , K. I. Collins , B. F. Cooke , R. F. Diaz (9) , M. Esposito , E. Furlan , S. Hojjatpanah , J. Jackman , J. M. Jenkins , E. L. N. Jensen , D. W. Latham , I. C. Le Ao , R. A. Matson , L. D. Nielsen (10) , A. Osborn , J. F. Otegi , F. Rodler , S. Sabotta , N. J. Scott , S. Seager , C. Stockdale , P. A. Strøm , R. Vanderspek (11) , V. van Eylen , P. J. Wheatley (12) , J. N. Winn , J. M. Almenara (13) , D. Barrado (14) , S. C. C. Barros (1) , D. Bayliss (15) , F. Bouchy (16) , P. T. Boyd (17) , J. Cabrera (18) , W. D. Cochran , O. Demangeon (19) , J. P. Doty , X. Dumusque (16) , P. Figueira (20, 4) , W. Fong , S. Grziwa , A. P. Hatzes (21) , P. Kabáth (22) , E. Knudstrup , J. Korth , J. H. Livingston , R. Luque (23) , O. Mousis (1) , S. E. Mullally , H. P. Osborn (1) , E. Palle (24) , C. M. Persson , S. Redfield (25) , N. C. Santos (6, 26) , J. Smith , J. Šubjak , J. D. Twicken , S. Udry (16) , D. A. Yahalomi

1 LAM - Laboratoire d'Astrophysique de Marseille
2 Department of Brain and Behavioural Sciences
3 ESO - European Southern Observatory
4 IASTRO - Instituto de Astrofísica e Ciências do Espaço
5 RSSD - Research and Scientific Support Department, ESTEC
6 CAUP - Centro de Astrofísica da Universidade do Porto
7 IAP - Institut d'Astrophysique de Paris
8 GRAAL - Groupe de Recherche en Astronomie et Astrophysique du Languedoc
9 IAFE - Instituto de Astronomía y Física del Espacio [Buenos Aires]
10 IGN - Department of Geosciences and Natural Resource Management [Copenhagen]
11 CSR - Center for Space Research [Cambridge]
12 University of Warwick [Coventry]
13 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble
14 CAB - Centro de Astrobiologia [Madrid]
15 Department of Physics [Coventry]
16 ObsGE - Observatoire Astronomique de l'Université de Genève
17 IMAS - Institute for Marine and Antarctic Studies [Hobart]
18 IRSN/PSE-ENV/SEDRE/LETIS - Laboratoire d'étude et de recherche sur les transferts et les interactions dans les sous-sols
19 Universidade do Porto = University of Porto
20 ESO - European Southern Observatory [Santiago]
21 TLS - Thüringer Landessternwarte Tautenburg
22 ASU / CAS - Astronomical Institute of the Czech Academy of Sciences
23 Universidad de Córdoba = University of Córdoba [Córdoba]
24 IAC - Instituto de Astrofisica de Canarias
25 Wesleyan University
26 DFA/FCUP - Departamento de Física e Astronomia [Porto]

In this paper, we report the discovery of TOI-220 b, a new sub-Neptune detected by the Transiting Exoplanet Survey Satellite (TESS) and confirmed by radial velocity follow-up observations with the HARPS spectrograph. Based on the combined analysis of TESS transit photometry and high precision radial velocity measurements, we estimate a planetary mass of 13.8 ± 1.0 M⊕ and radius of 3.03 ± 0.15 R⊕, implying a bulk density of 2.73 ± 0.47 gcm−3⁠. TOI-220 b orbits a relative bright (V= 10.4) and old (10.1 ± 1.4 Gyr) K dwarf star with a period of ∼10.69 d. Thus, TOI-220 b is a new warm sub-Neptune with very precise mass and radius determinations. A Bayesian analysis of the TOI-220 b internal structure indicates that due to the strong irradiation it receives, the low density of this planet could be explained with a steam atmosphere in radiative–convective equilibrium and a supercritical water layer on top of a differentiated interior made of a silicate mantle and a small iron core.

Keywords: techniques: photometric; techniques: radial velocities; planets and satellites: fundamental parameters; planets and satellites: individual: TYC 8897-01263-1; stars: fundamental parameters; Astrophysics - Earth and Planetary Astrophysics

Domains: Physics [physics]; Astrophysics [astro-ph]; Earth and Planetary Astrophysics [astro-ph.EP]

S. Hoyer, D. Gandolfi, D. J. Armstrong, M. Deleuil, L. Acu Na, et al.. TOI-220 b: a warm sub-Neptune discovered by TESS. Monthly Notices of the Royal Astronomical Society: Letters, 2021, 505 (3), pp.3361-3379. ⟨10.1093/mnras/stab1427⟩. ⟨hal-03577487⟩