Near-infrared spectroscopic characterisation of Gaia ultra-cool dwarf candidates

Spectral types and peculiarities^★,★★

¹ Université de Franche-Comté, CNRS UMR6213, Institut UTINAM, OSU THETA Franche-Comté-Bourgogne, Observatoire de Besançon, BP 1615, 25010 Besançon Cedex, France
e-mail: thomas.ravinet@univ-fcomte.fr
² Laboratoire d’Astrophysique de Bordeaux, Université Bordeaux, CNRS, B18N, Allée Geoffroy Saint-Hilaire, 33615 Pessac, France
³ Department of Astronomy & Astrophysics, University of California San Diego, La Jolla, CA 92093, USA
⁴ Istituto Nazionale di Astrofisica, Osservatorio Astrofisico di Torino, Strada Osservatorio 20, I-10025 Pino Torinese, Italy
⁵ Instituto Multidisciplinario de Investigación y Postgrado, Universidad de La Serena, Raúl Bitrán 1305, La Serena, Chile
⁶ Departamento de Astronomía, Universidad de La Serena, Av. Cisternas 1200, La Serena, Chile
⁷ IPAC, Mail Code 100-22, Caltech, 1200 E. California Boulevard, Pasadena, CA 91125, USA
⁸ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁹ Centre for Astrophysics Research, University of Hertfordshire, Hatfield, Hertfordshire, AL10 9AB, UK
¹⁰ Hunter College, Physics and Astronomy, 695 Park Avenue, New York, NY 10065, USA
¹¹ Instituto de Astronomía, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta, Chile
¹² Aperio Software Ltd., Insight House, Riverside Business Park, Stoney Common Road, Stansted, Essex, CM24 8PL, UK
¹³ Dpto. de Inteligencia Artificial, UNED, c/ Juan del Rosal 16, 28040 Madrid, Spain

Received: September 2023
Accepted: 30 January 2024

Abstract

Context. The local census of very low-mass stars and brown dwarfs is crucial to improving our understanding of the stellar-substellar transition and their formation history. These objects, known as ultra-cool dwarfs (UCDs), are essential targets for searches of potentially habitable planets. However, their detection poses a challenge because of their low luminosity. The Gaia survey has identified numerous new UCD candidates thanks to its large survey and precise astrometry.

Aims. We aim to characterise 60 UCD candidates detected by Gaia in the solar neighbourhood with a spectroscopic follow-up to confirm that they are UCDs, as well as to identify peculiarities.

Methods. We acquired the near-infrared (NIR) spectra of 60 objects using the SOFI spectrograph between 0.93 and 2.5 µm (R~ 600). We identified their spectral types using a template-matching method. Their binarity is studied using astrometry and spectral features.

Results. We confirm that 60 objects in the sample have ultra-cool dwarf spectral types close to those expected from astrometry. Their NIR spectra reveal that seven objects could host an unresolved coolest companion and seven UCDs share the same proper motions as other stars. The characterisation of these UCDs is part of a coordinated effort to improve our understanding of the Solar neighbourhood.