TESS and HARPS-N unveil two planets transiting TOI-1453

A super-Earth and one of the lowest mass sub-Neptunes^★

¹ Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
² Astrobiology Research Unit, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
³ School of Physics & Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
⁴ Department of Physics, University of Oxford, OX13RH Oxford, UK
⁵ Weltraumforschung und Planetologie, Physikalisches Institut, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
⁶ Dipartimento di Fisica e Astronomia ‘Galileo Galilei’, Universitá di Padova, Vicolo del l’Osservatorio 3, 35122 Padova, Italy
⁷ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, Padova 35122, Italy
⁸ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
⁹ Instituto de Astrofísica de Canarias, C/Vía Láctea s/n, 38205 La Laguna (Tenerife), Canary Islands, Spain
¹⁰ Departamento de Astrofísica, Univ. de La Laguna, Av. del Astrofísico Francisco Sánchez s/n, 38205 La Laguna (Tenerife), Canary Islands, Spain
¹¹ DTU Space, Technical University of Denmark, Elektrovej 328, 2800 Kgs. Lyngby, Denmark
¹² Département d’Astronomie, Université de Genève, Chemin Pegasi 51b, 1290 Versoix, Switzerland
¹³ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
¹⁴ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁵ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
¹⁶ Fundación Galileo Galilei – INAF (Telescopio Nazionale Galileo), Rambla José Ana Fernández Perez 7, 38712 Breña Baja (La Palma), Canary Islands, Spain
¹⁷ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00078 Monte Porzio Catone, Italy
¹⁸ Physics Department, Austin College, Sherman, TX 75090, USA
¹⁹ NASA Exoplanet Science Institute, IPAC, California Institute of Technology, Pasadena, CA 91125, USA
²⁰ INAF – Osservatorio Astrofisico di Torino, Via Osservatorio 20, 10025 Pino Torinese, Italy
²¹ Komaba Institute for Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
²² Astrophysics Group, University of Exeter, Exeter EX4 2QL, UK
²³ NASA Ames Research Center, Moffett Field, CA 94035, USA
²⁴ The Maury Lewin Astronomical Observatory, Glendora, CA 91741, USA
²⁵ Centro de Astrobiología (CAB), CSIC-INTA, ESAC campus, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada (Madrid), Spain
²⁶ Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²⁷ Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²⁸ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
²⁹ Department of Physics, Engineering and Astronomy, Stephen F. Austin State University, 1936 North St, Nacogdoches, TX 75962, USA

^★★ Corresponding author; manu.stalport@uliege.be

Received: 12 November 2024
Accepted: 23 February 2025

Abstract

Context. The TESS mission is searching for transiting planets over the entire sky, including two continuous viewing zones. Data from the continuous viewing zones span a long time baseline and offer ideal conditions for precise planet radius estimations, enabling the community to prepare for the PLATO mission.

Aims. We report on the validation and characterisation of two transiting planets around TOI-1453, a K-dwarf star in the TESS northern continuous viewing zone.

Methods. In addition to the TESS data, we used ground-based photometric, spectroscopic, and high-resolution imaging follow-up observations to validate the two planets. We obtained 100 HARPS-N high-resolution spectra over two seasons and used them together with the TESS light curve to constrain the mass, radius, and orbit of each planet.

Results. TOI-1453 b is a super-Earth with an orbital period of P_b=4.314 days, a radius of R_b=1.17±0.06R_⊕, and a mass lower than 2.32 M_⊕ (99%). TOI-1453 c is a sub-Neptune with a period of P_c =6.589 days, radius of R_c=2.22±0.09 R_⊕, and mass of M_c=2.95_−0.84^+0.83 M_⊕. The two planets orbit TOI-1453 with a period ratio close to 3/2, although they are not in a mean motion resonance (MMR) state. We did not detect any transit timing variations in our attempt to further constrain the planet masses. TOI-1453 c has a very low bulk density and is one of the least massive sub-Neptunes discovered to date. It is compatible with having either a water-rich composition or a rocky core surrounded by a thick H/He atmosphere. However, we set constraints on the water mass fraction in the envelope according to either a water-rich or water-poor formation scenario. The star TOI-1453 belongs to the Galactic thin disc based on Gaia kinematics and has a sub-solar metallicity. This system is orbited by a fainter stellar companion at a projected distance of ∼150 AU, classifying TOI-1453 b and c of S-type planets. These various planetary and stellar characteristics make TOI-1453 a valuable system for understanding the origin of super-Earths and sub-Neptunes.