The Gaia Ultracool Dwarf Sample -- IV. GTC/OSIRIS optical spectra of Gaia late-M and L dwarfs

TL;DR

This study provides optical spectra, spectral classifications, and kinematic data for 53 late-M and L ultracool dwarfs, revealing their physical properties and membership in stellar populations, including young groups and potential outliers.

Contribution

It presents new optical spectra, spectral types, and radial velocities for poorly investigated ultracool dwarfs, enhancing understanding of their physical and kinematic properties.

Findings

Identification of two ultracool dwarfs outside the thin disc

Detection of four ultracool dwarfs in young stellar groups

Measurement of radial velocities for 46 objects, including 29 new measurements

Abstract

As part of our comprehensive, ongoing characterisation of the low-mass end of the main sequence in the Solar neighbourhood, we used the OSIRIS instrument at the 10.4 m Gran Telescopio Canarias to acquire low- and mid-resolution (R$\approx$300 and R$\approx$2500) optical spectroscopy of 53 late-M and L ultracool dwarfs. Most of these objects are known but poorly investigated and lacking complete kinematics. We measured spectral indices, determined spectral types (six of which are new) and inferred effective temperature and surface gravity from BT-Settl synthetic spectra fits for all objects. We were able to measure radial velocities via line centre fitting and cross correlation for 46 objects, 29 of which lacked previous radial velocity measurements. Using these radial velocities in combination with the latest Gaia DR3 data, we also calculated Galactocentric space velocities. From their kinematics, we identified two candidates outside of the thin disc and four in young stellar kinematic groups. Two further ultracool dwarfs are apparently young field objects: 2MASSW J1246467$+$402715 (L4$\beta$), which has a potential, weak lithium absorption line, and G 196$-$3B (L3$\beta$), which was already known as young due to its well-studied primary companion.