A detailed analysis of the Gl 486 planetary system

¹ Centro de Astrobiología (CSIC-INTA), ESAC, Camino bajo del castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
e-mail: caballero@cab.inta-csic.es
² Centro de Astrobiología (CSIC-INTA), Carretera de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
³ Department of Astronomy and Astrophysics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA
⁴ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁵ Departament of Astronomy, Sofijski universitet “Sv. Kliment Ohridski”, 5 James Bourchier Boulevard, 1164 Sofia, Bulgaria
⁶ Louisiana State University, 202 Nicholson Hall, Baton Rouge, LA 70803, USA
⁷ Universität Zürich, Institute for Computational Science, Winterthurerstrasse 190, CH-8057, Zürich, Switzerland
⁸ Universitäts-Sternwarte, Ludwig-Maximilians-Universität München, Scheinerstrasse 1, 81679 München, Germany
⁹ Exzellenzcluster Origins, Boltzmannstrasse 2, 85748 Garching, Germany
¹⁰ Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
¹¹ Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹² Departamento de Física Teórica y del Cosmos, Universidad de Granada, 18071 Granada, Spain
¹³ The CHARA Array of Georgia State University, Mount Wilson Observatory, Mount Wilson, CA 91203, USA
¹⁴ Instituto de Astrofísica de Canarias (IAC), 38200 La Laguna, Tenerife, Spain
¹⁵ Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
¹⁶ Astrophysics Group, Department of Physics & Astronomy, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
¹⁷ Institut für Astrophysik und Geophysik, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
¹⁸ AstroLAB IRIS, Provinciaal Domein “De Palingbeek”, Verbrande-molenstraat 5, 8902 Zillebeke, Ieper, Belgium
¹⁹ Astronomy Department, University of Michigan, Ann Arbor, MI 48109, USA
²⁰ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
²¹ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
²² Institut de Ciències de l’Espai (ICE, CSIC), Campus UAB, Can Magrans s/n, 08193 Bellaterra, Barcelona, Spain
²³ Institut d’Estudis Espacials de Catalunya (IEEC), 08034 Barcelona, Spain
²⁴ European Southern Observatory, Casilla 19001 Santiago 19, Chile
²⁵ Institut de Planetologie et d’Astrophysique de Grenoble, Grenoble 38058, France
²⁶ Department of Physics and Astronomy, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
²⁷ 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
²⁸ Centro Astronómico Hispano en Andalucía, Observatorio de Calar Alto, Sierra de los Filabres, 04550 Gérgal, Almería, Spain
²⁹ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
³⁰ Centre for Earth Evolution and Dynamics, Department of Geo-sciences, Universitetet i Oslo, Sem Sœlands vei 2b, 0315 Oslo, Norway
³¹ Department of Physics, Ariel University, Ariel 40700, Israel
³² Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, NJ 08540, USA
³³ Vereniging Voor Sterrenkunde, Oude Bleken 12, 2400 Mol, Belgium
³⁴ Centre for Mathematical Plasma Astrophysics, Katholieke Universiteit Leuven, Celestijnenlaan 200B, bus 2400, 3001 Leuven, Belgium
³⁵ Lowell Observatory, 1400 W. Mars Hill Road, Flagstaff, AZ 86001, USA
³⁶ Exoplanets and Stellar Astrophysics Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA

Received: 14 March 2022
Accepted: 7 June 2022

Abstract

Context. The Gl 486 system consists of a very nearby, relatively bright, weakly active M3.5 V star at just 8 pc with a warm transiting rocky planet of about 1.3 R_⊕ and 3.0 M_⊕. It is ideal for both transmission and emission spectroscopy and for testing interior models of telluric planets.

Aims. To prepare for future studies, we aim to thoroughly characterise the planetary system with new accurate and precise data collected with state-of-the-art photometers from space and spectrometers and interferometers from the ground.

Methods. We collected light curves of seven new transits observed with the CHEOPS space mission and new radial velocities obtained with MAROON-X at the 8.1 m Gemini North telescope and CARMENES at the 3.5 m Calar Alto telescope, together with previously published spectroscopic and photometric data from the two spectrographs and TESS. We also performed near-infrared interferometric observations with the CHARA Array and new photometric monitoring with a suite of smaller telescopes (AstroLAB, LCOGT, OSN, TJO). This extraordinary and rich data set was the input for our comprehensive analysis.

Results. From interferometry, we measure a limb-darkened disc angular size of the star Gl 486 at θ_LDD = 0.390 ± 0.018 mas. Together with a corrected Gaia EDR3 parallax, we obtain a stellar radius R_* = 0.339 ± 0.015 R_⊕. We also measure a stellar rotation period at P_rot = 49.9 ± 5.5 days, an upper limit to its XUV (5-920 A) flux informed by new Hubble/STIS data, and, for the first time, a variety of element abundances (Fe, Mg, Si, V, Sr, Zr, Rb) and C/O ratio. Moreover, we imposed restrictive constraints on the presence of additional components, either stellar or sub-stellar, in the system. With the input stellar parameters and the radial-velocity and transit data, we determine the radius and mass of the planet Gl 486 b at R_p = 1.343_−0.062^+0.063 R_⊕ and M_p = 3.00_−0.12^+0.13 M_⊕, with relative uncertainties of the planet radius and mass of 4.7% and 4.2%, respectively. From the planet parameters and the stellar element abundances, we infer the most probable models of planet internal structure and composition, which are consistent with a relatively small metallic core with respect to the Earth, a deep silicate mantle, and a thin volatile upper layer. With all these ingredients, we outline prospects for Gl 486 b atmospheric studies, especially with forthcoming James Webb Space Telescope (Webb) observations.