# A new L5 brown dwarf member of the Hyades cluster with chromospheric activity

## TL;DR

This study identifies a new L5 brown dwarf in the Hyades cluster, exhibiting chromospheric activity, and characterizes its properties to enhance understanding of substellar objects in this nearby cluster.

## Contribution

The paper reports the discovery and spectroscopic confirmation of a new L5 brown dwarf member of the Hyades, including its chromospheric activity and kinematic properties.

## Key findings

- Identified a brown dwarf with 94.5% membership probability in Hyades.
- Detected Hα emission indicating chromospheric activity.
- Determined the brown dwarf's spectral type as L5.0±0.5.

## Abstract

Our aim is to identify brown dwarf members of the nearby Hyades open star cluster to determine the photometric and spectroscopic properties of brown dwarfs at moderately old ages and extend the knowledge of the substellar mass function of the cluster. We cross-matched the 2MASS and AllWISE public catalogues and measured proper motions to identify low-mass stars and brown dwarf candidates in an area of radius eight degrees around the central region of the Hyades cluster. We identified objects with photometry and proper motions consistent with cluster membership. For the faintest ($J$\,=\,17.2 mag) most promising astrometric and photometric low-mass candidate 2MASS\,J04183483$+$2131275\@, with a membership probability of 94.5\%, we obtained low-resolution (R\,=\,300--1000) and intermediate-resolution (R\,=\,2500) spectroscopy with the 10.4m Gran Telescopio Canarias. From the low-resolution spectra we determined a L5.0$\pm$0.5 spectral type, consistent with the available photometry. In the intermediate dispersion spectrum we detected H$\alpha$ in emission (marginally resolved with a full width half maximum of $\sim$2.8 \AA{}) and determined a $\log ($L$_{\rm{H}\alpha}$/L$_{\rm bol})=-6.0$ dex. From H$\alpha$ we obtained a radial velocity of 38.0$\pm$2.9 km$\cdot$s$^{-1}$, which combined with the proper motion leads to space velocities which are fully consistent with membership in the Hyades cluster.