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

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_ S=3.633±0.277 mag; J-W2=6.249±0.245 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_ 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_ S-band magnitude, we find that VHS J1831-5513 is a likely (∼85% probability) kinematic member of the β 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.