TOI-4336 A b: A temperate sub-Neptune ripe for atmospheric characterization in a nearby triple M-dwarf system

¹ Astrobiology Research Unit, Université de Liège, 19C Allée du 6 Août, 4000 Liège, Belgium
e-mail: mathilde.timmermans@uliege.be
² School of Physics & Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
³ Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
⁴ Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁵ Department of Physics, UC San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
⁶ Kavli Institute for Particle Astrophysics & Cosmology, Stanford University, Stanford, CA 94305, USA
⁷ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
⁸ Cerro Tololo Inter-American Observatory/NSF’s NOIRLab, Casilla 603, La Serena 1700000, Chile
⁹ Department of Astronomy & Astrophysics, UC San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
¹⁰ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA, 02138, USA
¹¹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
¹² Observatoire de Genève, Département d’Astronomie, Université de Genève, Chemin Pegasi 51b, 1290 Versoix, Switzerland
¹³ Dpto. Física Teórica y del Cosmos, Universidad de Granada, 18071 Granada, Spain
¹⁴ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
¹⁵ AIM, CEA, CNRS, Université Paris-Saclay, Université de Paris, 91191 Gif-sur-Yvette, France
¹⁶ Department of Physics & Astronomy, Vanderbilt University, 6301 Stevenson Center Ln., Nashville, TN 37235, USA
¹⁷ Department of Physics, Engineering and Astronomy, Stephen F. Austin State University, 1936 North St, Nacogdoches, TX 75962, USA
¹⁸ Carl Sagan Institute, Cornell University, 302 Space Science Building, 14850 Ithaca, NY, USA
¹⁹ Department of Astrophysical and Planetary Sciences, University of Colorado Boulder, Boulder, CO 80309, USA
²⁰ Laboratoire d’Astrophysique de Bordeaux, CNRS and Université de Bordeaux, Allée Geoffroy St. Hilaire, 33165 Pessac, France
²¹ Oukaimeden Observatory, High Energy Physics and Astrophysics Laboratory, Faculty of sciences Semlalia, Cadi Ayyad University, Marrakech, Morocco
²² Caltech/IPAC-NASA Exoplanet Science Institute, 770 S. Wilson Avenue, Pasadena, CA 91106, USA
²³ Space Sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
²⁴ Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012, Bern, Switzerland
²⁵ Center for Computational Astrophysics, Flatiron Institute, New York, NY, USA
²⁶ Universidad Nacional Autónoma de México, Instituto de Astronomía, AP 70-264, Ciudad de México 04510, Mexico
²⁷ Cavendish Laboratory, JJ Thomson Avenue, Cambridge CB3 0HE, UK
²⁸ SUPA Physics and Astronomy, University of St. Andrews, Fife, KY16 9SS, Scotland, UK
²⁹ European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
³⁰ NASA Ames Research Center, Moffett Field, CA 94035, USA
³¹ Department of Physics and Astronomy, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255, USA
³² Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
³³ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
³⁴ ETH Zurich, Department of Physics, Wolfgang-Pauli-Strasse 2, 8093 Zurich, Switzerland
³⁵ Royal Astronomical Society, Burlington House, Piccadilly, London W1J 0BQ, UK
³⁶ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
³⁷ Istituto Nazionale di Astrofisica, Osservatorio Astrofisico di Torino, Strada Osservatorio 20, 10025 Pino Torinese, Italy
³⁸ Kotizarovci Observatory, Sarsoni 90, 51216 Viskovo, Croatia
³⁹ SETI Institute, Mountain View, CA 94043 USA NASA Ames Research Center, Moffett Field, CA 94035, USA
⁴⁰ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA

Received: 15 September 2023
Accepted: 18 April 2024

Abstract

Context. Small planets transiting bright nearby stars are essential to our understanding of the formation and evolution of exoplanetary systems. However, few constitute prime targets for atmospheric characterization, and even fewer are part of multiple star systems.

Aims. This work aims to validate TOI-4336 A b, a sub-Neptune-sized exoplanet candidate identified by the TESS space-based transit survey around a nearby M dwarf.

Methods. We validated the planetary nature of TOI-4336 A b through the global analysis of TESS and follow-up multi-band high-precision photometric data from ground-based telescopes, medium- and high-resolution spectroscopy of the host star, high-resolution speckle imaging, and archival images.

Results. The newly discovered exoplanet TOI-4336 A b has a radius of 2.1 ± 0.1 R_⊕. Its host star is an M3.5-dwarf star with a mass of 0.33 ± 0.01 M_⊙ and a radius of 0.33 ± 0.02 R_⊙, and is a member of a hierarchical triple M-dwarf system 22 pc away from the Sun. The planet’s orbital period of 16.3 days places it at the inner edge of the habitable zone of its host star, which is the brightest of the inner binary pair. The parameters of the system make TOI-4336 A b an extremely promising target for the detailed atmospheric characterization of a temperate sub-Neptune by transit transmission spectroscopy with JWST.