TOI-2266 b: A keystone super-Earth at the edge of the M dwarf radius valley

¹ Dept. Astrofisica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
² Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna, Tenerife, Spain
³ Department of Astronomy & Astrophysics, University of Chicago, Chicago, IL 60637, USA
⁴ Centro de Astrobiologia (CSIC-INTA), Carretera de Ajalvir km 4, 28850 Torrejon de Ardoz, Madrid, Spain
⁵ Lund Observatory, Division of Astrophysics, Department of Physics, Lund University, Box 43, 22100 Lund, Sweden
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 Department of Space, Earth and Environment, Chalmers University of Technology, 412 96 Gothenburg, Sweden
¹⁰ Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023, PR China
¹¹ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
¹² Department of Multi-Disciplinary Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
¹³ Okayama Observatory, Kyoto University, 3037-5 Honjo, Kamogatacho, Asakuchi, Okayama 719-0232, Japan
¹⁴ Department of Physical Sciences, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan
¹⁵ Freie Universität Berlin, Institute of Geological Sciences, Malteserstr. 74-100, 12249 Berlin, Germany
¹⁶ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹⁷ Department of Astronomical Science, The Graduated University of Advanced Studies, SOKENDAI, 2-21-1, Osawa, Mitaka, Tokyo, 181-8588, Japan
¹⁸ Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudzia̧dzka 5, 87-100 Toruń, Poland
¹⁹ Department of Astronomy, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
²⁰ Institute of Astronomy and Astrophysics, Academia Sinica, PO Box 23-141, Taipei 10617, Taiwan, ROC
²¹ Department of Astrophysics, National Taiwan University, Taipei 10617, Taiwan, ROC
²² NASA Exoplanet Science Institute – Caltech/IPAC, Pasadena, CA 91125, USA
²³ Department of Astronomy, University of California Berkeley, Berkeley, CA 94720, USA
²⁴ Department of Astronomy, University of Maryland, College Park, MD 20742, USA
²⁵ Kavli Center for Particle Astrophysics and Cosmology, Stanford University, Stanford, CA 94305, USA
²⁶ Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK
²⁷ Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA
²⁸ George Mason University, 4400 University Drive, Fairfax, VA 22030, USA
²⁹ Astrobiology Research Unit, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
³⁰ Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
³¹ Oukaimeden Observatory, High Energy Physics and Astrophysics Laboratory, Faculty of sciences Semlalia, Cadi Ayyad University, Marrakech, Morocco
³² Departamento de Fisica e Astronomia, Faculdade de Ciencias, Universidade do Porto, Rua do Campo Alegre, 4169-007 Porto, Portugal
³³ Instituto de Astrofisica e Ciencias do Espaco, Universidade do Porto, CAUP, Rua das Estrelas, 150-762 Porto, Portugal
³⁴ Proto-Logic LLC, 1718 Euclid Street NW, Washington, DC 20009, USA
³⁵ NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
³⁶ Royal Astronomical Society, Burlington House, Piccadilly, London W1J 0BQ, UK
³⁷ SETI Institute, Mountain View, CA 94043, USA/NASA Ames Research Center, Moffett Field, CA 94035, USA
³⁸ Department of Astronomy and Tsinghua Centre for Astrophysics, Tsinghua University, Beijing 100084, PR China
³⁹ SUPA Physics and Astronomy, University of St. Andrews, Fife, KY16 9SS Scotland, UK
⁴⁰ Dept. of Physics & Astronomy, Swarthmore College, Swarthmore, PA 19081, USA
⁴¹ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁴² Kotizarovci Observatory, Sarsoni 90, 51216 Viskovo, Croatia
⁴³ Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁴⁴ Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁴⁵ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
⁴⁶ Department of Physics and Astronomy, University of New Mexico, 1919 Lomas Blvd NE, Albuquerque, NM 87131, USA

e-mail: hannu@iac.es

Received: 11 July 2023
Accepted: 8 January 2024

Abstract

We validate the Transiting Exoplanet Survey Satellite (TESS) object of interest TOI-2266.01 (TIC 8348911) as a small transiting planet (most likely a super-Earth) orbiting a faint M5 dwarf (V = 16.54) on a 2.33 d orbit. The validation is based on an approach where multicolour transit light curves are used to robustly estimate the upper limit of the transiting object's radius. Our analysis uses SPOC-pipeline TESS light curves from Sectors 24, 25, 51, and 52, simultaneous multicolour transit photometry observed with MuSCAT2, MuSCAT3' and HiPERCAM, and additional transit photometry observed with the LCOGT telescopes. TOI-2266 b is found to be a planet with a radius of 1.54 ± 0.09 R_⊕, which locates it at the edge of the transition zone between rocky planets, water-rich planets, and sub-Neptunes (the so-called M dwarf radius valley). The planet is amenable to ground-based radial velocity mass measurement with red-sensitive spectrographs installed in large telescopes, such as MAROON-X and Keck Planet Finder (KPF), which makes it a valuable addition to a relatively small population of planets that can be used to probe the physics of the transition zone. Further, the planet's orbital period of 2.33 days places it inside a ‘keystone planet’ wedge in the period-radius plane where competing planet formation scenarios make conflicting predictions on how the radius valley depends on the orbital period. This makes the planet also a welcome addition to the small population of planets that can be used to test small-planet formation scenarios around M dwarfs.