TOI-220 b: A Warm Sub-Neptune Discovered By TESS

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Monthly Notices Of The Royal Astronomical Society


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 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.


techniques: photometric, techniques: radial velocities, planets and satellites: fundamental parameters, planets and satellites: individual: TYC 8897-01263-1, stars: fundamental parameters


This article has been published in Monthly Notices Of The Royal Astronomical Society. © 2021 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.