TOI-1442 b and TOI-2445 b: Two potentially rocky ultra-short period planets around M dwarfs

¹ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
e-mail: giuseppe.morello-ext@iac.es
² Departamento de Astroffsica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
³ INAF – Palermo Astronomical Observatory, Piazza del Parlamento 1, 90134 Palermo, Italy
⁴ Department of Space, Earth and Environment, Chalmers University of Technology, 412 96 Gothenburg, Sweden
⁵ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122, Padova, Italy
⁶ Komaba Institute for Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153–8902, Japan
⁷ Astrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁸ Center for Astrophysics, Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
⁹ The Maury Lewin Astronomical Observatory, Glendora, CA 91741, USA
¹⁰ Université de Montréal, Département de Physique, IREX, Montréal, QC H3C 3J7, Canada
¹¹ Observatoire du Mont-Mégantic, Université de Montréal, Montréal, QC H3C 3J7, Canada
¹² European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
¹³ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹⁴ Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
¹⁵ Okayama Observatory, Kyoto University, 3037-5 Honjo, Kamogatacho, Asakuchi, Okayama 719-0232, Japan
¹⁶ Department of Multi-Disciplinary Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
¹⁷ Department of Astronomical Science, The Graduated University for Advanced Studies, SOKENDAI, 2-21-1, Osawa, Mitaka, Tokyo, 181-8588, Japan
¹⁸ Department of Space, Earth and Environment, Astronomy and Plasma Physics, Chalmers University of Technology, 412 96 Gothenburg, Sweden
¹⁹ Division of Astrophysics, Department of Physics, Lund University, Box 43, 22100 Lund, Sweden
²⁰ Lund Observatory, Department of Astronomy and Theoretical Physics, Lund University, Box 43, SE-221 00 Lund, Sweden
²¹ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
²² Institute of Astronomy and Astrophysics, Academia Sinica, PO Box 23-141, Taipei 10617, Taiwan, R.O.C.
²³ Department of Astrophysics, National Taiwan University, Taipei 10617, Taiwan, R.O.C.
²⁴ Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
²⁵ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
²⁶ Astrobiology Research Unit, Université de Liège, 19C Allée du 6 Août, 4000 Liège, Belgium
²⁷ Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
²⁸ Space sciences, Technologies and Astrophysics Research (STAR) Institute, Université de Liège, Belgium
²⁹ Oukaimeden Observatory, High Energy Physics and Astrophysics Laboratory, Cadi Ayyad University, Marrakech, Morocco
³⁰ Departamento de Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
³¹ Instituto de Astrofisica e Ciencias do Espaco, Universidade do porto, CAUP, Rua das Estrelas, 150-762 Porto, Portugal
³² George Mason University, 4400 University Drive, Fairfax, VA, 22030, USA

Received: 20 March 2022
Accepted: 6 March 2023

Abstract

Context. Exoplanets with orbital periods of less than one day are known as ultra-short period (USP) planets. They are relatively rare products of planetary formation and evolution processes, but especially favourable for characterisation with current planet detection methods. At the time of writing, 125 USP planets have already been confirmed.

Aims. Our aim is to validate the planetary nature of two new transiting planet candidates around M dwarfs announced by the NASA Transiting Exoplanet Survey Satellite (TESS), registered as TESS Objects of Interest (TOIs) TOI-1442.01 and TOI-2445.01.

Methods. We used TESS data, ground-based photometric light curves, and Subaru/IRD spectrograph radial velocity (RV) measurements to validate both planetary candidates and to establish their physical properties.

Results. TOI-1442 bis a validated exoplanet with an orbital period of P = 0.4090682 ± 0.0000004 day, a radius of R_p = 1.15 ± 0.06 R_⊕, and equilibrium temperature of T_p,eq = 1357₋₄₂⁺⁴⁹ K. TOI-2445 b is also validated with an orbital period of P = 0.3711286 ± 0.0000004 day, a radius of R_p = 1.33 ± 0.09 R_⊕, and equilibrium temperature of T_p,eq = 1330₋₅₆⁺⁶¹ K. Their physical properties align with current empirical trends and formation theories of USP planets. Based on the RV measurements, we set 3σ upper mass limits of 8 M_⊕ and 20 M_⊕, thus confirming the non-stellar, sub-Jovian nature of both transiting objects. More RV measurements will be needed to constrain the planetary masses and mean densities, and the predicted presence of outer planetary companions. These targets extend the small sample of USP planets orbiting around M dwarfs up to 21 members. They are also among the 20 most suitable terrestrial planets for atmospheric characterisation via secondary eclipse with the James Webb Space Telescope, according to a widespread emission spectroscopy metric.