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

S. Hoyer, D. Gandolfi, D. J. Armstrong, M. Deleuil, L. Acuña, J. R. de Medeiros, E. Goffo, J. Lillo-Box, E. Delgado Mena, T. A. Lopez, A. Santerne, S. G. Sousa, M. Fridlund, V. Zh. Adibekyan, K. A. Collins, L. M. Serrano, P. Cortés-Zuleta, S. B. Howell, H. J. Deeg, A. Aguichine, O. Barragán, E. M. Bryant, B. L. Canto Martins, K. I. Collins, B. F. Cooke, R. F. Díaz, M. Esposito, E. Furlan, S. Hojjatpanah, J. Jackman, J. M. Jenkins, E. L. N. Jensen, D. W. Latham, I. C. Leão, R. A. Matson, L. D. Nielsen, A. Osborn, J. F. Otegi, F. Rodler, S. Sabotta, N. J. Scott, S. Seager, C. Stockdale, P. A. Strøm, R. K. Vanderspek, V. Van Eylen, P. J. Wheatley, J. N. Winn, J.-M. Almenara, D. Barrado, S. C. C. Barros, D. Bayliss, F. Bouchy, P. T. Boyd, J. Cabrera, W. D. Cochran, O. Demangeon, J. P. Doty, X. Dumusque, P. Figueira, W. Fong, S. Grziwa, A. Hatzes, P. Kabáth, E. Knudstrup, J. Korth, J. H. Livingston, R. Luque, O. Mousis, S. E. Mullally, H. P. Osborn, E. Pallé, C. M. Persson, S. Redfield, N. C. Santos, J. C. Smith, J. ¦ubjak, J. D. Twicken, S. Udry, D. A. Yahalomi

Abstract
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

Monthly Notices of the Royal Astronomical Society
Volume 505, Issue 3, Page 3361
2021 August

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia