Planetary companions orbiting the M dwarfs GJ 724 and GJ 3988

A CARMENES and IRD collaboration^★

¹ Institut für Astrophysik und Geophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
e-mail: [email protected]
² Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
³ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁴ Astrobiology Center, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁵ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁶ Department of Astronomical Science, The Graduate University for Advanced Studies, SOKENDAI, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
⁷ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁸ Centro de Astrobiología (CSIC-INTA), ESAC Campus, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
⁹ Subaru Telescope, 650 North A’ohoku Place, Hilo, HI 96720, USA
¹⁰ Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, Can Magrans s/n, 08193 Bellaterra, Spain
¹¹ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
¹² Instituto de Astrofísica de Canarias, Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
¹³ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
¹⁴ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
¹⁵ Centro Astronómico Hispano en Andalucía (CAHA), Observatorio de Calar Alto, Sierra de los Filabres, 04550 Gérgal, Almería, Spain
¹⁶ Departamento de Física de la Tierra y Astrofísica and IPARCOSUCM (Instituto de Física de Partículas y del Cosmos de la UCM), Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
¹⁷ Department of Earth and Planetary Sciences, School of Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo 152-8551, Japan
¹⁸ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
¹⁹ Centre for Earth Evolution and Dynamics, Department of Geosciences, University of Oslo, Sem Saelands vei 2b 0315 Oslo, Norway
²⁰ Department of Physics, Ariel University, Ariel 40700, Israel
²¹ Department of Astronomy, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Received: 6 June 2023
Accepted: 15 September 2023

Abstract

We report the discovery of two exoplanets around the M dwarfs GJ 724 and GJ 3988 using the radial velocity (RV) method. We obtained a total of 153 3.5 m Calar Alto/CARMENES spectra for both targets and measured their RVs and activity indicators. We also added archival ESO/HARPS data for GJ 724 and infrared RV measurements from Subaru/IRD for GJ 3988. We searched for periodic and stable signals to subsequently construct Keplerian models, considering different numbers of planets, and we selected the best models based on their Bayesian evidence. Gaussian process (GP) regression was included in some models to account for activity signals. For both systems, the best model corresponds to one single planet. The minimum masses are 10.75_−0.87^+0.96 and 3.69_−0.41^+0.42 Earth-masses for GJ 724 b and GJ 3988 b, respectively. Both planets have short periods (P < 10 d) and, therefore, they orbit their star closely (a < 0.05 au). GJ 724 b has an eccentric orbit (e = 0.577_−0.052^+0.055), whereas the orbit of GJ 3988 b is circular. The high eccentricity of GJ 724 b makes it the most eccentric single exoplanet (to this date) around an M dwarf. Thus, we suggest a further analysis to understand its configuration in the context of planetary formation and architecture. In contrast, GJ 3988 b is an example of a common type of planet around mid-M dwarfs.