Eight New Substellar Hyades Candidates from the UKIRT Hemisphere Survey

TL;DR

This study identified eight new substellar candidates in the Hyades cluster using multiple surveys, confirmed them as brown dwarfs through spectroscopy, and analyzed their properties and potential cluster membership.

Contribution

The paper reports the discovery and spectroscopic confirmation of eight new brown dwarf members of the Hyades, including the coldest and lowest-mass free-floating member known.

Findings

All eight objects are confirmed brown dwarfs with spectral types L6 to T5.

CWISE J042356.23+130414.3 is the coldest and lowest-mass Hyades member discovered.

Substellar Hyades members tend to have redder near-infrared colors than field brown dwarfs.

Abstract

We have used the UKIRT Hemisphere Survey (UHS) combined with the UKIDSS Galactic Cluster Survey (GCS), the UKIDSS Galactic Plane Survey (GPS), and the CatWISE2020 catalog to search for new substellar members of the nearest open cluster to the Sun, the Hyades. Eight new substellar Hyades candidate members were identified and observed with the Gemini/GNIRS near-infrared spectrograph. All eight objects are confirmed as brown dwarfs with spectral types ranging from L6 to T5, with two objects showing signs of spectral binarity and/or variability. A kinematic analysis demonstrates that all eight new discoveries likely belong to the Hyades cluster, with future radial velocity and parallax measurements needed to confirm their membership. CWISE J042356.23$+$130414.3, with a spectral type of T5, would be the coldest ($T_{\rm eff}$$\approx$1100 K) and lowest-mass ($M$$\approx$30 $M_{\rm Jup}$) free-floating member of the Hyades yet discovered. We further find that high-probability substellar Hyades members from this work and previous studies have redder near-infrared colors than field-age brown dwarfs, potentially due to lower surface gravities and super-solar metallicities.