TOI-1199 b and TOI-1273 b: Two new transiting hot Saturns detected and characterized with SOPHIE and TESS

¹ International Center for Advanced Studies (ICAS) and ICIFI (CON-ICET), ECyT-UNSAM, Campus Miguelete, 25 de Mayo y Francia, 1650 Buenos Aires, Argentina
e-mail: jserrano@unsam.edu.ar
² Institut d’astrophysique de Paris, CNRS, UMR 7095, Sorbonne Université, 98 bis bd Arago, 75014 Paris, France
³ Observatoire de Haute-Provence, St Michel 1’Observatoire, France
⁴ Laboratório Nacional de Astrofisica, Rua Estados Unidos 154, 37504-364 Itajubá, MG, Brazil
⁵ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal
⁶ Laboratoire d’astrophysique de Marseille, Univ. de Provence, UMR6110 CNRS, 38 r. F. Joliot Curie, 13388 Marseille cedex 13, France
⁷ Univ. Grenoble Alpes, CNRS, IPAG, 414 rue de la Piscine, 38400 St-Martin-d’Hères, France
⁸ INAF – Osservatorio Astrofisico di Catania, Via S. Sofia 78, 95123 Catania, Italy
⁹ Acton Sky Portal private observatory, Acton, MA, USA
¹⁰ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
¹¹ SETI Institute/NASA Ames Research Center, Moffett Field, CA 94035, USA
¹² IPAC-NASA Exoplanet Science Institute, 770 S. Wilson Avenue, Pasadena, CA 91106, USA
¹³ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
¹⁴ Astrophysics Group, University of Exeter, Exeter EX4 2QL, UK
¹⁵ Department of Multi-Disciplinary Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
¹⁶ Instituto de Astrofísica de Canarias (IAC), calle Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
¹⁷ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
¹⁸ Komaba Institute for Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
¹⁹ Crow Observatory, Portalegre, Portugal
²⁰ Bryant Space Science Center, Department of Astronomy, University of Florida, Gainesville, FL 32611, USA
²¹ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²² NASA Ames Research Center, Moffett Field, CA 94035, USA
²³ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
²⁴ Wild Boar Remote Observatory, San Casciano in val di Pesa, Firenze, Italy
²⁵ Gruppo Astrofili Catanesi, Catania, Italy
²⁶ Waffelow Creek Observatory, 10780 FM 1878, Nacogdoches, TX 75961, USA
²⁷ Université de Toulouse, CNRS, IRAP, 14 avenue Belin, 31400 Toulouse, France
²⁸ Astrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
²⁹ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
³⁰ Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA
³¹ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA

Received: 16 October 2023
Accepted: 3 January 2024

Abstract

We report the characterization of two planet candidates detected by the Transiting Exoplanet Survey Satellite (TESS), TOI-1199 b and TOI-1273 b, with periods of 3.7 and 4.6 days, respectively. Follow-up observations for both targets, which include several ground-based light curves, confirmed the transit events. High-precision radial velocities from the SOPHIE spectrograph revealed signals at the expected frequencies and phases of the transiting candidates and allowed mass determinations with a precision of 8.4% and 6.7% for TOI-1199 b and TOI-1273 b, respectively. The planetary and orbital parameters were derived from a joint analysis of the radial velocities and photometric data. We find that the planets have masses of 0.239 ± 0.020 M_J and 0.222 ± 0.015 M_J and radii of 0.938 ± 0.025 R_J and 0.99 ± 0.22 R_J, respectively. The grazing transit of TOI-1273 b translates to a larger uncertainty in its radius, and hence also in its bulk density, compared to TOI-1199 b. The inferred bulk densities of 0.358 ± 0.041 g cm⁻³ and 0.28 ± 0.11 g cm⁻³ are among the lowest known for exoplanets in this mass range, which, considering the brightness of the host stars (V≈11 mag), render them particularly amenable to atmospheric characterization via the transit spectroscopy technique. The better constraints on the parameters of TOI-1199 b provide a transmission spectroscopy metric of 134 ± 17, making it the better suited of the two planets for atmospheric studies.