Detection and characterisation of a 106-day transiting Jupiter: TOI-2449 b/NGTS-36 b^★

¹ Leiden Observatory, Leiden University, PO.Box 9513, 2300 RA Leiden, The Netherlands
² Observatoire Astronomique de l’Université de Genève, Chemin Pegasi 51b, 1290 Versoix, Switzerland
³ Space Research and Planetary Sciences, Physics Institute, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
⁴ Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁵ Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
⁶ Millennium Institute for Astrophysics, Santiago, Chile
⁷ Facultad de Ingeniería y Ciencias, Universidad Adolfo Ibáñez, Av. Diagonal las Torres 2640, Peñalolén, Santiago, Chile
⁸ Data Observatory Foundation, Santiago, Chile
⁹ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁰ Instituto de Astronomía, Universidad Católica del Norte, Angamos 0610, 1270709, Antofagasta, Chile
¹¹ Astronomy Unit, Queen Mary University of London, G.O. Jones Building, Bethnal Green, London E1 4NS, UK
¹² Space Research Institute, Austrian Academy of Sciences, Schmiedl-strasse 6, 8042 Graz, Austria
¹³ Cerro Tololo Inter-American Observatory, Casilla 603, La Serena, Chile
¹⁴ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
¹⁵ School of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
¹⁶ Center for Astrophysics || Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
¹⁷ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹⁸ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁹ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
²⁰ NASA Exoplanet Science Institute, Caltech/IPAC, Mail Code 100-22, 1200 E. California Blvd., Pasadena, CA 91125, USA
²¹ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²² University of Zurich, Department of Astrophysics, Winterthurerstr. 190, 8057 Zurich, Switzerland
²³ NASA Ames Research Center, Moffett Field, CA 94035, USA
²⁴ SETI Institute, Mountain View, CA 94043, USA
²⁵ Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile
²⁶ Centro de Astrofísica y Tecnologías Afines (CATA), Casilla 36-D, Santiago, Chile
²⁷ ESO – European Southern Observatory, Av. Alonso de Cordova 3107, Vitacura, Santiago, Chile
²⁸ Department of Physics and Astronomy, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255, USA
²⁹ Bay Area Environmental Research Institute, Moffett Field, CA 94035, USA
³⁰ Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
³¹ STAR Institute, Université de Liège, Liège, Belgium
³² Institute of Space Sciences (ICE, CSIC), Carrer de Can Magrans S/N, Campus UAB, Cerdanyola del Valles, 08193 Spain
³³ Institut d’Estudis Espacials de Catalunya (IEEC), 08860 Castellde-fels (Barcelona), Spain
³⁴ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK
³⁵ Center for Data Intensive and Time Domain Astronomy, Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA
³⁶ Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile
³⁷ Department of Astronomy/Steward Observatory, The University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
³⁸ Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
³⁹ Department of Aeronautics and Astronautics, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
⁴⁰ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
⁴¹ Department of Astronomy, The Ohio State University, 140 W. 18th Ave., Columbus, OH 43210, USA
⁴² Landessternwarte, Zentrum für Astronomie der Universtät Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
⁴³ Department of Astronomy, Sofia University St Kliment Ohridski, 5 James Bourchier Blvd, 1164 Sofia, Bulgaria
⁴⁴ Institute of Physics, École Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, Chemin Pegasi 51b, 1290 Versoix, Switzerland
⁴⁵ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
⁴⁶ University of Southern Queensland, Centre for Astrophysics, West Street, Toowoomba, QLD 4350, Australia
⁴⁷ Department of Physics, Engineering and Astronomy, Stephen F. Austin State University, 1936 North St, Nacogdoches, TX 75962, USA

^★★ Corresponding author: ulmer-moll@strw.leidenuniv.nl

Received: 15 April 2025
Accepted: 18 September 2025

Abstract

Context. Only a handful of transiting giant exoplanets with orbital periods longer than 100 days are known. These warm exoplanets are valuable objects, as their radius and mass can be measured and lead to an in-depth characterisation of the planet’s properties. Thanks to low levels of stellar irradiation and large orbital distances, the atmospheric properties and orbital parameters of warm exoplanets remain relatively unaltered by their host star, giving new insights into planetary formation and evolution.

Aims. Our aim is to increase the sample of warm giant exoplanets with precise radii and masses. Our goal is to identify suitable candidates in the Transiting Exoplanet Survey Satellite data and perform follow-up observations with ground-based instruments.

Methods. We used the Next Generation Transit Survey (NGTS) to detect additional transits of planetary candidates in order to pinpoint their orbital period. We also monitored the target with several high-resolution spectrographs to measure the planetary mass and eccentricity. We studied the planet’s interior composition with a planetary evolution code to determine the planet’s metallicity.

Results. We report the discovery of a 106-day period Jupiter-sized planet around the G-type star TOI-2449/NGTS-36. We jointly modelled the photometric and radial velocity data and find that the planet has a mass of 0.70_−0.04^+0.05 M_J and a radius of 1.001 ± 0.009 R_J. The planetary orbit has a semi-major axis of 0.449 au and is slightly eccentric (e = 0.0098_−0.030^+0.028). We detected an additional 3-year signal in the radial velocity data that is likely due to the stellar magnetic cycle. Based on the planetary evolution models considered here, we find that TOI-2449 b/NGTS-36 b contains 11₋₅⁺⁶ M_⊕ of heavy elements and has a marginal planet-to-star metal enrichment of 3.3_−1.8^+2.5. Assuming a Jupiter-like bond albedo, TOI-2449 b/NGTS-36 b has an equilibrium temperature of 400 K and is a good target for understanding nitrogen chemistry in cooler atmospheres.