The GAPS programme at TNG

LVII. TOI-5076b: A warm sub-Neptune planet orbiting a thin-to-thick-disk transition star in a wide binary system^★

¹ INAF – Osservatorio Astrofisico di Catania, Via Santa Sofia 78, 95123 Catania, Italy
e-mail: marco.montalto@inaf.it
² Dipartimento di Fisica e Astronomia “Ettore Majorana”, Università di Catania, Via S. Sofia 64, 95123 Catania, Italy
³ Scuola Superiore di Catania, Università di Catania, Via Valdisavoia 9, 95123 Catania, Italy
⁴ Department of Physics, University of Rome “Tor Vergata”, Via della Ricerca Scientifica 1, 00133 Rome, Italy
⁵ INAF – Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
⁶ Department of Physics, Engineering and Astronomy, Stephen F. Austin State University, 1936 North St, Nacogdoches, TX 75962, USA
⁷ Cerro Tololo Inter-American Observatory, Casilla 603, La Serena, Chile
⁸ Department of Physics and Astronomy, The University of North Carolina at Chapel Hill, Chapel Hill, NC 2599-3255, USA
⁹ Sternberg Astronomical Institute of Lomonosov Moscow State University, Moscow 119234, Russia
¹⁰ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹¹ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monte Porzio Catone (RM), Italy
¹² Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
¹³ International Institute for Advanced Scientific Studies (IIASS), Via G. Pellegrino 19, 84019 Vietri sul Mare (SA), Italy
¹⁴ Dipartimento di Fisica e Astronomia “Galileo Galilei”, Università degli Studi di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
¹⁵ INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
¹⁶ Fundación Galileo Galilei–INAF, Rambla José Ana Fernandez Pérez 7, 38712, Breña Baja, TF, Spain
¹⁷ INAF – Osservatorio Astronomico di Palermo “G.S. Vaiana”, Piazza del Parlamento 1, 90134 Palermo, Italy
¹⁸ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
¹⁹ Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
²⁰ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²¹ Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
²² Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
²³ University of Southern Queensland, Centre for Astrophysics, West Street, Toowoomba, QLD 4350, Australia
²⁴ NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA

Received: 22 December 2023
Accepted: 19 April 2024

Abstract

Aims. We report the confirmation of a new transiting exoplanet orbiting the star TOI-5076.

Methods. We present our vetting procedure and follow-up observations which led to the confirmation of the exoplanet TOI-5076b. In particular, we employed high-precision TESS photometry, high-angular-resolution imaging from several telescopes, and high-precision radial velocities from HARPS-N.

Results. From the HARPS-N spectroscopy, we determined the spectroscopic parameters of the host star: T_eff = (5070±143) K, log 𝑔 = (4.6±0.3), [Fe/H] = (+0.20±0.08), and [α/Fe] = 0.05±0.06. The transiting planet is a warm sub-Neptune with a mass m_p = (16±2) M_⊙, a radius r_p =(3.2±0.l) R_⊙ yielding a density ρ_p = (2.8±0.5) g cm⁻³. It revolves around its star approximately every 23.445 days.

Conclusions. The host star is a metal-rich, K2V dwarf, located at about 82 pc from the Sun with a radius of R_⋆ = (0.78±0.01) R_⊙ and a mass of M_⋆ = (0.80±0.07) M_⊙. It forms a common proper motion pair with an M-dwarf companion star located at a projected separation of 2178 au. The chemical analysis of the host-star and the Galactic-space velocities indicate that TOI-5076 belongs to the old population of thin-to-thick-disk transition stars. The density of TOI-5076b suggests the presence of a large fraction by volume of volatiles overlying a massive core. We found that a circular orbit solution is marginally favored with respect to an eccentric orbit solution for TOI-5076b.