The GAPS Programme at TNG

XXVIII. A pair of hot-Neptunes orbiting the young star TOI-942^★,★★

¹ Astronomy Department and Van Vleck Observatory, Wesleyan University, Middletown, CT 06459, USA
e-mail: icarleo@wesleyan.edu
² INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
³ Aix Marseille Univ, CNRS, CNES, LAM, Marseille, France
⁴ Dipartimento di Fisica e Astronomia Galileo Galilei, Universitá di Padova, Vicolo dellOsservatorio 3, 35122 Padova, Italy
⁵ INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
⁶ Department of Astronomy, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
⁷ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento, 1, 90134 Palermo, Italy
⁸ Institute for Space Astrophysics and Planetology INAF-IAPS Via Fosso del Cavaliere 100, 00133 Roma, Italy
⁹ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate, Italy
¹⁰ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
¹¹ INAF – Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, 50125 Firenze, Italy
¹² ETH Zürich, Institute for Particle Physics and Astrophysics, Wolfgang-Pauli-Str. 27, 8093 Zürich, Switzerland
¹³ INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34143 Trieste, Italy
¹⁴ Fundación Galileo Galilei-INAF, Rambla José Ana Fernandez Pérez 7, 38712 Breña Baja, TF, Spain
¹⁵ INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Napoli, Italy
¹⁶ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenberg, Germany
¹⁷ Dipartimento di Fisica G. Occhialini, Università degli Studi di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
¹⁸ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
¹⁹ Department of Physics, University of Rome “Tor Vergata”, Via della Ricerca Scientifica 1, 00133 Rome, Italy
²⁰ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
²¹ INAF – Osservatorio Astronomico di Cagliari & REM, Via della Scienza, 5, 09047 Selargius CA, Italy

Received: 27 July 2020
Accepted: 25 November 2020

Abstract

Context. Young stars and multi-planet systems are two types of primary objects that allow us to study, understand, and constrain planetary formation and evolution theories.

Aims. We validate the physical nature of two Neptune-sized planets transiting TOI-942 (TYC 5909-319-1), a previously unacknowledged young star (50₋₂₀⁺³⁰ Myr) observed by the TESS space mission in Sector 5.

Methods. Thanks to a comprehensive stellar characterization, TESS light curve modeling and precise radial-velocity measurements, we validated the planetary nature of the TESS candidate and detected an additional transiting planet in the system on a larger orbit.

Results. From photometric and spectroscopic observations we performed an exhaustive stellar characterization and derived the main stellar parameters. TOI-942 is a relatively active K2.5V star (log R′_HK = −4.17 ± 0.01) with rotation period P_rot = 3.39 ± 0.01 days, a projected rotation velocity v sin i_⋆ = 13.8 ± 0.5 km s⁻¹, and a radius of ~0.9 R_⊙. We found that the inner planet, TOI-942 b, has an orbital period P_b = 4.3263 ± 0.0011 days, a radius R_b = 4.242_−0.313^+0.376 R_⊕, and a mass upper limit of 16 M_⊕ at 1σ confidence level. The outer planet, TOI-942 c, has an orbital period P_c = 10.1605_−0.0053^+0.0056 days, a radius R_c = 4.793_−0.351^+0.410 R_⊕, and a mass upper limit of 37 M_⊕ at 1σ confidence level.