TOI-1468: A system of two transiting planets, a super-Earth and a mini-Neptune, on opposite sides of the radius valley^★

¹ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
e-mail: priyanka@tls-tautenburg.de
² Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
e-mail: pbluhm@lsw.uni-heidelberg.de
³ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
⁴ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
⁵ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
⁶ Department of Astronomy and Astrophysics, University of Chicago, 5640 S. Ellis Avenue, Chicago, IL 60637, USA
⁷ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
⁸ Universitäts-Sternwarte, Ludwig-Maximilians-Universität München, Scheinerstrasse 1, 81679 München, Germany
⁹ Exzellenzcluster Origins, Boltzmannstrasse 2, 85748 Garching, Germany
¹⁰ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹¹ Centro de Astrobiología (CSIC-INTA), ESAC, Camino bajo del castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
¹² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹³ IPAC, Mail Code 314-6, Caltech, 1200 E. California Blvd., Pasadena, CA 91125, USA
¹⁴ Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹⁵ University of Maryland, Baltimore, MD 21250, USA
¹⁶ NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
¹⁷ Centro Astronómico Hispano en Andalucía, Observatorio de Calar Alto, Sierra de los Filabres, 04550 Gérgal, Spain
¹⁸ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
¹⁹ George Mason University, 4400 University Drive, Fairfax, VA 22030, USA
²⁰ Komaba Institute for Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
²¹ NASA Ames Research Center, Moffett Field, CA 94035, USA
²² Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²³ Observatori Astronomic Albanyà, Camí de Bassegoda s/n, Albanyá 17733, Girona, Spain
²⁴ Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, Can Magrans s/n, 08193 Bellaterra, Spain
²⁵ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
²⁶ Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-weg 3, 37077 Göttingen, Germany
²⁷ Department of Physics and Astronomy, Swarthmore College, Swarthmore, PA 19081, USA
²⁸ 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
²⁹ Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
³⁰ Astrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
³¹ Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019, USA
³² Institut für Astrophysik and Geophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
³³ Department of Astronomy/Steward Observatory, The University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
³⁴ Patashnick Voorheesville Observatory, Voorheesville, NY 12186, USA
³⁵ Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08540, USA
³⁶ Hazelwood Observatory DO3-32, VIC, Australia
³⁷ Department of Physics, Ariel University, Ariel 40700, Israel
³⁸ SETI Institute, Mountain View, CA 94043, USA
³⁹ Vereniging Voor Sterrenkunde, Brieversweg 147, 8310, Brugge, Belgium
⁴⁰ Centre for Mathematical Plasma-Astrophysics, Department of Mathematics, KU Leuven, Celestijnenlaan 200B, 3001 Heverlee, Belgium
⁴¹ AstroLAB IRIS, Provinciaal Domein “De Palingbeek”, Verbrande-molenstraat 5, 8902 Zillebeke, Ieper, Belgium
⁴² Tsinghua International School, Beijing 100084, PR China
⁴³ Planetary Discoveries, Fredericksburg, VA 22405, USA

Received: 19 May 2022
Accepted: 5 August 2022

Abstract

We report the discovery and characterization of two small transiting planets orbiting the bright M3.0V star TOI-1468 (LSPM J0106+1913), whose transit signals were detected in the photometric time series in three sectors of the TESS mission. We confirm the planetary nature of both of them using precise radial velocity measurements from the CARMENES and MAROON-X spectrographs, and supplement them with ground-based transit photometry. A joint analysis of all these data reveals that the shorter-period planet, TOI-1468 b (P_b = 1.88 d), has a planetary mass of M_b = 3.21 ± 0.24M_⊕ and a radius of R_b = 1.280_−0.039^+0.038 R_⊕, resulting in a density of ρ_b = 8.39_−0.92^+1.05 g cm⁻³, which is consistent with a mostly rocky composition. For the outer planet, TOI-1468 c (P_c = 15.53 d), we derive a mass of M_c = 6.64_−0.68^+0.67 M_⊕,aradius of R_c = 2.06 ± 0.04 R_⊕, and a bulk density of ρ_c = 2.00_−0.19^+0.21 g cm⁻³, which corresponds to a rocky core composition with a H/He gas envelope. These planets are located on opposite sides of the radius valley, making our system an interesting discovery as there are only a handful of other systems with the same properties. This discovery can further help determine a more precise location of the radius valley for small planets around M dwarfs and, therefore, shed more light on planet formation and evolution scenarios.