Direct imaging and dynamical mass of a benchmark T-type brown dwarf companion to HD 167665^★

¹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
² STAR Institute, Université de Liège, Allée du Six Août 19c, 4000 Liège, Belgium
³ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
⁴ Department of Physics & Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA
⁵ Space Telescope Science Institute (STScI), 3700 San Martin Drive, Baltimore, MD 21218, USA
⁶ INAF – Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
⁷ LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
⁸ European Southern Observatory (ESO), Karl-Schwarzschild-Straße 2, 85748 Garching, Germany
⁹ Université Lyon 1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon, UMR5574, 69230, Saint-Genis-Laval, France
¹⁰ Observatoire de Genève, Université de Genève, Chemin Pegasi 51, 1290 Versoix, Switzerland
¹¹ Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh EH9 3HJ, UK
¹² INAF – Osservatorio Astrofisico di Catania, Via Santa Sofia 78, 95123 Catania, Italy
¹³ Institutionen för astronomi, Stockholms universitet, AlbaNova universitetscentrum, Roslagstullsbacken 21, 106 91 Stockholm, Sweden
¹⁴ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago, Chile
¹⁵ Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile
¹⁶ Millennium Nucleus on Young Exoplanets and their Moons (YEMS), Santiago, Chile
¹⁷ Aix-Marseille Univ., CNRS, CNES, LAM, Marseille, France
¹⁸ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
¹⁹ Max Planck Institute for Extraterrestrial Physics, Giessenbachstraße 1, 85748 Garching, Germany
²⁰ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
²¹ Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, North-western University, Evanston, IL 60208, USA
²² Unidad Mixta Internacional Franco-Chilena de Astronomía CNRS/INSU UMI 3386 and Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
²³ Astronomy Department, University of Michigan, Ann Arbor, MI 48109, USA
²⁴ University of Exeter, Physics Building, Stocker Road, Exeter EX4 4QL, UK
²⁵ Universidade de Lisboa - Faculdade de Ciências, Campo Grande, 1749-016 Lisboa, Portugal
²⁶ CENTRA - Centro de Astrofísica e Gravitação, IST, Universidade de Lisboa, 1049-001 Lisboa, Portugal
²⁷ Department of Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
²⁸ Department of Astrophysical and Planetary Sciences, JILA, Duane Physics Bldg., 2000 Colorado Ave, University of Colorado, Boulder, CO 80309, USA
²⁹ I. Institute of Physics, University of Cologne, Zülpicher Straße 77, 50937 Cologne, Germany
³⁰ Max Planck Institute for Radio Astronomy, Auf dem Hügel 69, 53121 Bonn, Germany
³¹ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
³² Universidade do Porto, Faculdade de Engenharia, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal
³³ School of Physics, University College Dublin, Belfield, Dublin 4, Ireland
³⁴ Academia Sinica, Institute of Astronomy and Astrophysics, 11F Astronomy-Mathematics Building, NTU/AS campus, No. 1, Section 4, Roosevelt Rd., Taipei 10617, Taiwan
³⁵ European Space Agency (ESA), ESA Office, STScI, 3700 San Martin Drive, Baltimore, MD 21218, USA
³⁶ ORIGINS Excellence Cluster, Boltzmannstraße 2, 85748 Garching, Germany
³⁷ Max Planck Institute for Astrophysics, Karl-Schwarzschild-Straße 1, 85748 Garching, Germany
³⁸ Departments of Physics and Astronomy, Le Conte Hall, University of California, Berkeley, CA 94720, USA
³⁹ Advanced Concepts Team, European Space Agency, TEC-SF, ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands
⁴⁰ Department of Earth & Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA

^★★ Corresponding author; annelisekatia.maire@gmail.com

Received: 19 June 2024
Accepted: 5 September 2024

Abstract

Context. A low-mass companion potentially in the brown dwarf mass regime was discovered on a ~12 yr orbit (~5.5 au) around HD 167665 using radial velocity (RV) monitoring. Joint RV–astrometry analyses confirmed that HD 167665B is a brown dwarf with precisions on the measured mass of ~4–9%. Brown dwarf companions with measured mass and luminosity are valuable for testing formation and evolutionary models. However, its atmospheric properties and luminosity are still unconstrained, preventing detailed tests of evolutionary models.

Aims. We further characterize the HD 167665 system by measuring the luminosity and refining the mass of its companion and reassessing the stellar age.

Methods. We present new high-contrast imaging data of the star and of its close-in environment from SPHERE and GRAVITY, which we combined with RV data from CORALIE and HIRES and astrometry from HIPPARCOS and Gaia.

Results. The analysis of the host star properties indicates an age of 6.20 ± 1.13 Gyr. GRAVITY reveals a point source near the position predicted from a joint fit of RV data and HIPPARCOS–Gaia proper motion anomalies. Subsequent SPHERE imaging confirms the detection and reveals a faint point source of contrast of ∆H2 = 10.95 ± 0.33 mag at a projected angular separation of ~180 mas. A joint fit of the high-contrast imaging, RV, and HIPPARCOS intermediate astrometric data together with the Gaia astrometric parameters constrains the mass of HD 167665B to ~1.2%, 60.3 ± 0.7 M_J. The SPHERE colors and spectrum point to an early or mid-T brown dwarf of spectral type T4₋₂⁺¹. Fitting the SPHERE spectrophotometry and GRAVITY spectrum with synthetic spectra suggests an effective temperature of ~1000–1150 K, a surface gravity of ~5.0–5.4 dex, and a bolometric luminosity log(L/L_⊙)=−4.892_−0.028^+0.024 dex. The mass, luminosity, and age of the companion can only be reproduced within 3σ by the hybrid cloudy evolutionary models of Saumon & Marley (2008, ApJ, 689, 1327), whereas cloudless evolutionary models underpredict its luminosity.