Two sub-Neptunes around the M dwarf TOI-1470

¹ Centro de Astrobiología (CAB), CSIC-INTA, Carretera de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
² Departamento de Física de la Tierra y Astrofísica & IPARCOS-UCM (Instituto de Física de Partículas y del Cosmos de la UCM), Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
e-mail: estgon11@ucm.es
³ Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna, Tenerife, Spain
⁴ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
⁵ Komaba Institute for Science, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
⁶ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
⁷ Department of Multi-Disciplinary Sciences, Graduate School of Arts and Sciences, The University of Tokyo, 3-8-1 Komaba, Meguro, Tokyo 153-8902, Japan
⁸ Astrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁹ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹⁰ Department of Astronomical Science, The Graduated University for Advanced Studies, SOKENDAI, 2-21-1, Osawa, Mitaka, Tokyo 181-8588, Japan
¹¹ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹² Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
¹³ Homer L. Dodge Department of Physics and Astronomy, University of Oklahoma, 440 West Brooks Street, Norman, OK 73019, USA
¹⁴ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
¹⁵ Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
¹⁶ NASA Exoplanet Science Institute, Caltech/IPAC, Mail Code 100-22, 1200 E. California Blvd., Pasadena, CA 91125, USA
¹⁷ Centro Astronómico Hispano en Andalucía CAHA, Observatorio Astronómico de Calar Alto, Sierra de los Filabres, 04550 Gérgal, Spain
¹⁸ American Association of Variable Star Observers, 185 Alewife Brook Parkway, Suite 410, Cambridge, MA 02138, USA
¹⁹ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
²⁰ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
²¹ NASA Goddard Space Flight Center, 8800 Greenbelt Rd, Greenbelt, MD 20771, USA
²² Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
²³ Intelligent Systems Division, NASA Ames Research Center, Moffett Field, CA 94035, USA
²⁴ Villa ’39 Observatory, Landers, CA 92285, USA
²⁵ Google, Cambridge, MA 02142, USA
²⁶ School of Physics and Astronomy, Tel Aviv University, Tel Aviv 6997801, Israel
²⁷ Institut für Astrophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
²⁸ Institut de Ciències de l’Espai (IEEC-CSIC), Campus UAB, Carrer de Can Magrans s/n, 08193 Bellaterra, Spain
²⁹ Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
³⁰ Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
³¹ Kotizarovci Observatory, Sarsoni 90, 51216 Viskovo, Croatia
³² SETI Institute/NASA Ames Research Center, Moffett Field, CA 94305, USA
³³ Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
³⁴ Division of Science, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
³⁵ Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Received: 1 March 2023
Accepted: 7 June 2023

Abstract

Aims. A transiting planet candidate with a sub-Neptune radius orbiting the nearby (d = 51.9 ± 0.07 pc) M1.5 V star TOI-1470 with a period of ~2.5 d was announced by the NASA Transiting Exoplanet Survey Satellite (TESS), which observed the field of TOI-1470 in four different sectors. We aim to validate its planetary nature using precise radial velocities (RVs) taken with the CARMENES spectrograph.

Methods. We obtained 44 RV measurements with CARMENES spanning eight months between 3 June 2020 and 17 January 2021. For a better characterization of the parent star activity, we also collected contemporaneous optical photometric observations at the Joan Oró and Sierra Nevada Observatories, and we retrieved archival photometry from the literature. We used ground-based photometric observations from MuSCAT and also from MuSCAT2 and MuSCAT3 to confirm the planetary transit signals. We performed a combined photometric and spectroscopic analysis by including Gaussian processes and Keplerian orbits to simultaneously account for the stellar activity and planetary signals.

Results. We estimate that TOI-1470 has a rotation period of 29 ± 3d based on photometric and spectroscopic data. The combined analysis confirms the discovery of the announced transiting planet, TOI-1470 b, with an orbital period of 2.527093 ± 0.000003 d, a mass of 7.32_-1.24^+1.21M_⊕, and a radius of 2.18_-0.04^+0.04R_⊕. We also discover a second transiting planet that was not announced previously by TESS, TOI-1470 c, with an orbital period of 18.08816 ± 0.00006 d, a mass of 7.24_-2.77^+2.87M_⊕, and a radius of 2.47_-0.02^+0.02R_⊕ . The two planets are placed on the same side of the radius valley of M dwarfs and lie between TOI-1470 and the inner border of its habitable zone.