TOI-220 b: a warm sub-Neptune discovered by TESS
Bouchy, F.; Deeg, H.; Deleuil, M.; Fridlund, M.; Pallé, E.; de Medeiros, J. R.; Barragán, O.; Gandolfi, D.; Korth, J.; Grziwa, S.; Hatzes, A. P.; Cabrera, J.; Cochran, W. D.; Persson, C. M.; Sabotta, S.; Van Eylen, V.; Winn, J. N.; Knudstrup, E.; Serrano, L. M.; Adibekyan, V.; Hoyer, S.; Barrado, D.; Barros, S. C. C.; Collins, K. A.; Collins, K. I.; Esposito, M.; Goffo, E.; Jenkins, J. M.; Luque, R.; Osborn, H. P.; Redfield, S.; Rodler, F.; Santos, N. C.; Seager, S.; Twicken, J. D.; Udry, S.; Sousa, S.; Lillo-Box, J.; Figueira, P.; Mousis, O.; Wheatley, P. J.; Strøm, P. A.; Cortés-Zuleta, P.; Almenara, J. M.; Díaz, R. F.; Latham, D. W.; Vanderspek, R.; Fong, W.; Dumusque, X.; Demangeon, O.; Furlan, E.; Kabáth, P.; Boyd, P. T.; Santerne, A.; Mullally, S. E.; Jensen, E. L. N.; Howell, S. B.; Doty, J. P.; Acuña, L.; Hojjatpanah, S.; Nielsen, L. D.; Armstrong, D. J.; Otegi, J. F.; Bayliss, D.; Bryant, E. M.; Cooke, B. F.; Lopez, T. A.; Osborn, A.; Scott, N. J.; Leão, I. C.; Šubjak, J.; Livingston, J. H.; Smith, J.; Stockdale, C.; Delgado Mena, E.; Canto Martins, B. L.; Matson, R. A.; Aguichine, A.; Jackman, J.; Yahalomi, D. A.
France, Italy, United Kingdom, Brazil, Spain, Portugal, Netherlands, Sweden, United States, Argentina, Germany, Switzerland, Chile, Australia, Czech Republic, Denmark, Japan
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 $\rm {g\,cm}^{-3}$. 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.