Precise mass and radius of a transiting super-Earth planet orbiting the M dwarf TOI-1235: a planet in the radius gap?

¹ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
e-mail: pbluhm@lsw.uni-heidelberg.de
² Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
³ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁴ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁵ Centro de Astrobiología (CSIC-INTA), ESAC, Camino bajo del castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁶ Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁷ Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
⁸ Department of Astronomy, University of Tokyo, 7-3-1 Hongo, Bunkyo-ky, Tokyo 113-0033, Japan
⁹ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey, RH5 6NT, UK
¹⁰ NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
¹¹ Sellers Exoplanet Environments Collaboration, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
¹² Deutsches Zentrum für Luft- und Raumfahrt, Institut für Planetenforschung, 12489 Berlin, Rutherfordstrasse 2., Germany
¹³ Centro de Astrobiología (CSIC-INTA), Carretera de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
¹⁴ Department of Physics and Astronomy, George Mason University, 4400 University Drive, Fairfax, VA 22030, USA
¹⁵ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
¹⁶ Center for Planetary Systems Habitability and McDonald Observatory, The University of Texas at Austin, Austin, TX 78730, USA
¹⁷ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
¹⁸ Departamento de Explotación y Prospección de Minas, Escuela de Minas, Energía y Materiales, Universidad de Oviedo, 33003 Oviedo, Spain
¹⁹ Instituto Universitario de Ciencias y Tecnologías del Espacio de Asturias, Independencia 13, 33004 Oviedo, Spain
²⁰ Department of Physics, University of Khartoum, Al-Gamaa Ave, Khartoum 11111, Sudan
²¹ Campo Catino Astronomical Observatory, Regione Lazio, 03010 Guarcino (FR), Italy
²² Leiden Observatory, Leiden University, 2333CA Leiden, The Netherlands
²³ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
²⁴ Department of Earth Sciences, University of Hawai’i at Māanoa, Honolulu, HI 96822 USA
²⁵ IRFU, CEA, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
²⁶ AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, 91191 Gif-sur-Yvette, France
²⁷ Observatori Astronòmic Albanyà, Camí de Bassegoda s/n, 17733 Albanyà, Girona, Spain
²⁸ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
²⁹ Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, Can Magrans s/n, 08193 Bellaterra, Spain
³⁰ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
³¹ NASA 31 Research Center, Moffett Field, CA 94035, USA
³² Department of Physics & Astronomy, Swarthmore College, Swarthmore PA 19081, USA
³³ Astronomical Institute, Czech Academy of Sciences, Fričova 298, 25165, Ondřejov, Czech Republic
³⁴ Rheinisches Institut für Umweltforschung an der Universität zu Köln, Aachener Strasse 209, 50931 Köln, Germany
³⁵ Departamento de Física de la Tierra y Astrofísica and IPARCOS-UCM (Instituto de Física de Partículas y del Cosmos de la UCM), Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040, Madrid, Spain
³⁶ Komaba Institute forScience, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
³⁷ JST, PRESTO, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
³⁸ Astrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
³⁹ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
⁴⁰ Homer L. Dodge Departmentof Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019, USA
⁴¹ Centro Astronómico Hispano-Alemán, Observatorio de Calar Alto, Sierra de los Filabres, 04550 Gérgal, Spain
⁴² Zentrum für Astronomie und Astrophysik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
⁴³ Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstr. 74-100, 12249 Berlin, Germany
⁴⁴ Astronomy Department and Van Vleck Observatory, Wesleyan University, Middletown, CT 06459, USA
⁴⁵ Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁴⁶ Space Science Institute, 4765 Walnut St., Suite B, Boulder, CO 80301, USA
⁴⁷ Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
⁴⁸ Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
⁴⁹ School of Physics and Astronomy, Queen Mary University London, 327 Mile End Road, London E1 4NS, UK
⁵⁰ Department of Physics, Ariel University, Ariel 40700, Israel
⁵¹ Vereniging Voor Sterrenkunde, Brugge, Belgium & Centre for mathematical Plasma-Astrophysics, Department of Mathematics, KU Leuven, Celestijnenlaan 200B, 3001 Heverlee, Belgium
⁵² AstroLAB IRIS, Provinciaal Domein “De Palingbeek”, Verbrandemolenstraat 5, 8902 Zillebeke, Ieper, Belgium
⁵³ Department of Physics and Astronomy, Mississippi State University, 355 Lee Boulevard, Mississippi State, MS 39762, USA

Received: 13 April 2020
Accepted: 16 June 2020

Abstract

We report the confirmation of a transiting planet around the bright weakly active M0.5 V star TOI-1235 (TYC 4384–1735–1, V ≈ 11.5 mag), whose transit signal was detected in the photometric time series of sectors 14, 20, and 21 of the TESS space mission. We confirm the planetary nature of the transit signal, which has a period of 3.44 d, by using precise RV measurements with the CARMENES, HARPS-N, and iSHELL spectrographs, supplemented by high-resolution imaging and ground-based photometry. A comparison of the properties derived for TOI-1235 b with theoretical models reveals that the planet has a rocky composition, with a bulk density slightly higher than that of Earth. In particular, we measure a mass of M_p = 5.9 ± 0.6 M_⊕ and a radius of R_p = 1.69 ± 0.08 R_⊕, which together result in a density of ρ_p = 6.7_{− 1.1}^{+ 1.3} g cm⁻³. When compared with other well-characterized exoplanetary systems, the particular combination of planetary radius and mass places our discovery in the radius gap, which is a transition region between rocky planets and planets with significant atmospheric envelopes. A few examples of planets occupying the radius gap are known to date. While the exact location of the radius gap for M dwarfs is still a matter of debate, our results constrain it to be located at around 1.7 R_⊕ or larger at the insolation levels received by TOI-1235 b (~60 S_⊕). This makes it an extremely interesting object for further studies of planet formation and atmospheric evolution.