Discovery of the Remarkably Red L/T Transition Object VHS J183135.58-551355.9

TL;DR

This paper reports the discovery of VHS J183135.58-551355.9, an extremely red L/T transition dwarf likely belonging to the β Pictoris moving group, characterized by its unique spectral features and potential youth indicators.

Contribution

The discovery of an unusually red L/T transition dwarf with detailed spectroscopic analysis and probable membership in the β Pictoris moving group is a novel addition to substellar object studies.

Findings

Identified a highly red L/T transition dwarf with unique spectral features.

Spectroscopic confirmation of low temperature and youth indicators.

Probable membership in the β Pictoris moving group with 85% confidence.

Abstract

We present the discovery of VHS J183135.58$-$551355.9 (hereafter VHS J1831$-$5513), an L/T transition dwarf identified as a result of its unusually red near-infrared colors ($J-K_{\rm S}=3.633\pm0.277$ mag; $J-W2=6.249\pm0.245$ mag) from the VISTA Hemisphere Survey and CatWISE2020 surveys. We obtain low resolution near-infrared spectroscopy of VHS J1831$-$5513 using Magellan/FIRE to confirm its extremely red nature and assess features sensitive to surface gravity (i.e., youth). Its near-infrared spectrum shows multiple CH$_{\rm 4}$ absorption features, indicating an exceptionally low effective temperature for its spectral type. Based on proper motion measurements from CatWISE2020 and a photometric distance derived from its $K_{\rm S}$-band magnitude, we find that VHS J1831$-$5513 is a likely ($\sim$85$\%$ probability) kinematic member of the $\beta$ Pictoris moving group. Future radial velocity and trigonometric parallax measurements will clarify such membership. Follow-up mid-infrared or higher resolution near-infrared spectroscopy of this object will allow for further investigation as to the cause(s) of its redness, such as youth, clouds, and viewing geometry.