The GAPS programme at TNG

XL. A puffy and warm Neptune-sized planet and an outer Neptune-mass candidate orbiting the solar-type star TOI-1422

¹ Department of Physics, University of Rome “Tor Vergata”, Via della Ricerca Scientifica 1, 00133 Rome, Italy
e-mail: luca.naponiello@unifi.it
² Department of Physics and Astronomy, University of Florence, Largo Enrico Fermi 5, 50125 Firenze, Italy
³ INAF – Turin Astrophysical Observatory, via Osservatorio 20, 10025 Pino Torinese, Italy
⁴ Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁵ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone (RM), Italy
⁶ Aix-Marseille Université, CNRS, CNES, LAM, Marseille, France
⁷ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁸ Dipartimento di Fisica, Universitá degli Studi di Torino, via Pietro Giuria 1, 10125 Torino, Italy
⁹ Centro de Astrobiología, Depto. de Astrofísica, ESAC campus, 28692, Villanueva de la Cañada (Madrid), Spain
¹⁰ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
¹¹ Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, MA 02138, USA
¹² INAF – Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
¹³ INAF – Osservatorio Astronomico di Capodimonte, Salita Moiariello 16, 80131 Naples, Italy
¹⁴ INAF – Osservatorio Astrofísico di Catania, via S. Sofia 78, 95123 Catania, Italy
¹⁵ INAF – Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
¹⁶ INAF – Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius (CA), Italy
¹⁷ Dipartimento di Fisica e Astronomia “Galileo Galilei” – Università di Padova, Vicolo dell’Osservatorio 2, 35122 Padova, Italy
¹⁸ INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate (LC), Italy
¹⁹ Fundación Galileo Galilei – INAF, Rambla José Ana Fernandez Pérez 7, 38712 Brena Baja, TF, Spain
²⁰ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
²¹ Institut d’Astrophysique de Paris, CNRS, UMR 7095 & Sorbonne Université, UPMC Paris 6, 98bis Bd Arago, 75014 Paris, France
²² Observatoire de Haute-Provence, CNRS, Université d’Aix-Marseille, 04870 Saint-Michel-l’Observatoire, France
²³ Aix-Marseille Université, CNRS, CNES, LAM, Marseille, France
²⁴ Université Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
²⁵ Department of Physics, Shahid Beheshti University, Tehran, Iran
²⁶ Laboratoire J.-L. Lagrange, OCA, Université de Nice-Sophia Antipolis, CNRS, Campus Valrose, 06108 Nice Cedex 2, France
²⁷ IRAP, Université de Toulouse, CNRS, UPS, CNES, 31400 Toulouse, France
²⁸ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²⁹ NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
³⁰ Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
³¹ Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
³² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
³³ Department of Physics and Astronomy, University of New Mexico, 210 Yale Blvd NE, Albuquerque, NM 87106, USA
³⁴ NASA Ames Research Center, Moffett Field, CA 94035, USA
³⁵ SETI Institute, Mountain View, CA 94043, USA
³⁶ Space Science & Astrobiology Division MS 245-3, NASA Ames Research Center, Moffett Field, CA 94035, USA
³⁷ INAF-Telescopio Nazionale Galileo, Apartado 565, 38700, Santa Cruz de La Palma, Spain
³⁸ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
³⁹ Astrophysics Group, Keele University, Staffordshire ST5 5BG, UK
⁴⁰ Department of Aeronautics and Astronautics, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA

Received: 21 May 2022
Accepted: 7 July 2022

Abstract

Context. Neptunes represent one of the main types of exoplanets and have chemical-physical characteristics halfway between rocky and gas giant planets. Therefore, their characterization is important for understanding and constraining both the formation mechanisms and the evolution patterns of planets.

Aims. We investigate the exoplanet candidate TOI-1422 b, which was discovered by the TESS space telescope around the high proper-motion G2 V star TOI-1422 (V = 10.6 mag), 155 pc away, with the primary goal of confirming its planetary nature and characterising its properties.

Methods. We monitored TOI-1422 with the HARPS-N spectrograph for 1.5 yr to precisely quantify its radial velocity (RV) variation. We analyse these RV measurements jointly with TESS photometry and check for blended companions through high-spatial resolution images using the AstraLux instrument.

Results. We estimate that the parent star has a radius of R_⋆ = 1.019_−0.013^+0.014 R_⊙, and a mass of M_⋆ = 1.019_−0.013^+0.014 M_⊙. Our analysis confirms the planetary nature of TOI-1422 b and also suggests the presence of a Neptune-mass planet on a more distant orbit, the candidate TOI-1422 c, which is not detected in TESS light curves. The inner planet, TOI-1422 b, orbits on a period of P_b = 12.9972 ± 0.0006 days and has an equilibrium temperature of T_eq,b = 867 ± 17 K. With a radius of R_b = 3.96_−0.11^+0.13 R_⊕, a mass of M_b = 9.0_−2.0^+2.3 M_⊕ and, consequently, a density of ρ_b = 0.795_−0.235^+0.290g cm⁻³, it can be considered a warm Neptune-sized planet. Compared to other exoplanets of a similar mass range, TOI-1422 b is among the most inflated, and we expect this planet to have an extensive gaseous envelope that surrounds a core with a mass fraction around 10% – 25% of the total mass of the planet. The outer non-transiting planet candidate, TOI-1422 c, has an orbital period of P_c = 29.29_−0.20^+0.21 days, a minimum mass, M_csin i, of 11.1_−2.3^+2.6 M_⊕, an equilibrium temperature of T_eq,c = 661 ± 13 K and, therefore, if confirmed, could be considered as another warm Neptune.