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

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.

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Journal
Astronomy and Astrophysics
Published
2025-10-16
DOI
https://doi.org/10.1051/0004-6361/202555168
Primary Topic
Astro and Planetary Science
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article
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article

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

X. Dumusque, A. Bonfanti, Marziye Jafariyazani, Maximiliano Moyano et al.
Astronomy and Astrophysics
Astro and Planetary Science
article

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

X. Dumusque, A. Bonfanti, Marziye Jafariyazani, Maximiliano Moyano, F. Bouchy, B. Falk, M.R. Burleigh, J. McCormac, P. Figueira, R. Brahm, James J. Eberhardt, Marcelo Tala Pinto, Martin Schlecker, Soléne Ulmer-Moll, D. Bayliss, Angelica Psaridi, M.I. Jones, C. Ziegler, C.A. Watson, A.W. Mann, C. Mordasini, E. Furlan, J.M. Jenkins, M. R. Goad, J. P. Faria, J.E. Rodriguez, C. Pezzotti, Alicia Kendall, Samuel Gill, Sara Seager, R. Helled, E.M. Bryant, S.N. Quinn, C. Briceño, F. Hawthorn, Nicholas M. Law, K. A. Collins, J.N. Winn, Colin Littlefield, A. Jordán, R.F. Goeke, J.S. Jenkins, M. Lendl, J. Hagelberg, S.B. Howell, George Zhou, José Fernández, Trifon Trifonov, José I Vines, D. R. Anderson, H. Osborn, Suman Saha, P.J. Wheatley, M. Fridlund, Matthew P. Battley, Mélissa J. Hobson, Khaled Al Moulla, Felipe Rojas, A. Deline, T. G. Wilson, S. Udry, N. Espinoza, Alastair B Claringbold, Toby Rodel, Giordano Viviani, S. G. Sousa, Th. Henning
article en

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.

Astronomy and AstrophysicsVol. 703
University of North Carolina at Chapel Hill (US), University of Geneva (CH), University of Bern (CH), Leiden University (NL), Queen's University Belfast (GB), Ames Research Center (US), Space Telescope Science Institute (US), Institute of Space Sciences (ES), University of Arizona (US), Austrian Academy of Sciences (AT), University of Leicester (GB), University of Liège (BE), Pontificia Universidad Católica de Chile (CL), Queen Mary University of London (GB), Universidade do Porto (PT), University of Southern Queensland (AU), Princeton University (US), Stephen F. Austin State University (US), University of Zurich (CH), Adolfo Ibáñez University (CL), Heidelberg University (DE), NASA Exoplanet Science Institute (US), Universidad Católica del Norte (CL), University of Warwick (GB), Institute of Astrophysics and Space Sciences (PT), Institut d'Estudis Espacials de Catalunya (ES), Kavli Institute for Particle Astrophysics and Cosmology (US), Millennium Institute of Astrophysics (CL), Max Planck Institute for Astronomy (DE), Bay Area Environmental Research Institute (US), Osservatorio Astrofisico di Catania (IT), FZU ‒ Institute of Physics of the Academy of Sciences of the Czech Republic (CZ), Center for Astrophysics Harvard & Smithsonian (US), European Southern Observatory (CL), Cerro Tololo Inter-American Observatory (CL), Astronomy and Space (AU), Data Observatory Foundation, University College London (GB), American Institute of Aeronautics and Astronautics (US), École Polytechnique Fédérale de Lausanne (CH), The Ohio State University (US), Sofia University "St. Kliment Ohridski" (BG), Massachusetts Institute of Technology (US), Chalmers University of Technology (SE), Search for Extraterrestrial Intelligence (US), Universidad Diego Portales (CL)
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