The HD 260655 system: Two rocky worlds transiting a bright M dwarf at 10 pc

¹ Instituto de Astrofisica de Andalucia (IAA-CSIC), Glorieta de la Astronomia s/n, 18008 Granada, Spain
² Department of Astronomy & Astrophysics, University of Chicago, Chicago, IL 60637 USA
e-mail: rluque@uchicago.edu
³ Division of Geological and Planetary Sciences, California Institute of Technology, 1200 East California Blvd, Pasadena, CA 91125 USA
⁴ Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
⁵ Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
⁶ Astrophysics Group, Keele University, Keele ST5 6BG, UK
⁷ Center of Excellence in Information Systems, Tennessee State University, Nashville, TN 37209-1561 USA
⁸ Universitäts-Sternwarte, Ludwig-Maximilians-Universität München, Scheinerstrasse 1, 81679 München, Germany
⁹ Exzellenzcluster Origins, Boltzmannstraβe 2, 85748 Garching, Germany
¹⁰ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹¹ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
¹² Instituto de Astrofisica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
¹³ Departamento de Astrofisica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
¹⁴ Space Sciences, Technologies and Astrophysics Research (STAR) Institute, Universitde Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
¹⁵ Astrobiology Research Unit, Université de Liège, Allée du 6 Août 19C, 4000 Liège, Belgium
¹⁶ Center for Earth Evolution and Dynamics, Department of Geosciences, University of Oslo, Sem Saelands vei 2b 0315 Oslo, Norway
¹⁷ Institut de Ciències de l’Espai (CSIC), Campus UAB, c/de Can Magrans s/n, 08193 Bellaterra, Barcelona, Spain
¹⁸ Centro Astronómico Hispano Alemán, Observatorio de Calar Alto, Sierra de los Filabres, 04550 Gérgal, Almeria, Spain
¹⁹ NASA Exoplanet Science Institute, Caltech/IPAC, Mail Code 100-22, 1200 E. California Blvd., Pasadena, CA 91125 USA
²⁰ Centro de Astrobiologia (INTA-CSIC), ESAC Campus, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
²¹ Center for Astrophysics I Harvard & Smithsonian, 60 Garden St, Cambridge, MA 02138, USA
²² Vereniging Voor Sterrenkunde, Oostmeers 122 C, 8000 Brugge, Belgium
²³ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 USA
²⁴ NSF’s Optical Infrared Astronomy Research Laboratory, 950 North Cherry Avenue Tucson, AZ 85719 USA
²⁵ Department of Astronomy, Yale University, 52 Hillhouse Avenue, New Haven, CT 06511 USA
²⁶ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
²⁷ Space Science & Astrobiology Division, NASA Ames Research Center, Moffett Field, CA 94035 USA
²⁸ Department of Astronomy, The University of California, Berkeley, CA 94720 USA
²⁹ Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
³⁰ Department of Earth and Planetary Sciences, University of California, Riverside, CA 92521 USA
³¹ Departamento de Física de la Tierra y Astrofísica & IPARCOSUCM (Instituto de Física de Particulas y del Cosmos de la UCM), Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
³² Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
³³ Institut d’Estudis Espacials de Catalunya, 08034 Barcelona, Spain
³⁴ Department of Astronomy/Steward Observatory, The University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721 USA
³⁵ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
³⁶ Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139 USA
³⁷ Department of Aeronautics and Astronautics, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139 USA
³⁸ Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 USA
³⁹ Department of Physics, Ariel University, Ariel 40700 Israel
⁴⁰ Department of Astronomy, Sofia University “St Kliment Ohridski”, 5 James Bourchier Blvd, 1164 Sofia, Bulgaria
⁴¹ AstroLAB IRIS, Provinciaal Domein “De Palingbeek”, Verbrandemolenstraat 5, 8902 Zillebeke, Ieper, Belgium
⁴² Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08544, USA
⁴³ Centro de Astrobiologia (CSIC-INTA), Carretera de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain

Received: 21 April 2022
Accepted: 13 June 2022

Abstract

We report the discovery of a multiplanetary system transiting the M0 V dwarf HD 260655 (GJ 239, TOI-4599). The system consists of at least two transiting planets, namely HD 260655 b, with a period of 2.77 d, a radius of R_b = 1.240 ± 0.023 R_⊕, a mass of M_b = 2.14 ± 0.34 M_⊕, and a bulk density of ρ_b = 6.2 ± 1.0 g cm⁻³, and HD 260655 c, with a period of 5.71 d, a radius of , a mass of M_c = 3.09 ± 0.48 M_⊕, and a bulk density of g cm⁻³. The planets have been detected in transit by the Transiting Exoplanet Survey Satellite (TESS) mission and confirmed independently with archival and new precise radial velocities obtained with the HIRES and CARMENES instruments since 1998 and 2016, respectively. At a distance of 10 pc, HD 260655 has become the fourth closest known multitransiting planet system after HD 219134, LTT 1445 A, and AU Mic. Due to the apparent brightness of the host star (J = 6.7 mag), both planets are among the most suitable rocky worlds known today for atmospheric studies with the James Webb Space Telescope, both in transmission and emission.