VVV J165507.19-421755.5: A Nearby T Dwarf Hidden in the Galactic Plane

Abstract

We present the discovery of VVV J165507.19−421755.5, a mid-T dwarf found through ongoing unWISE-based proper motion searches. A near-infrared spectrum of this object obtained with the NIRES instrument on the Keck II telescope indicates a spectral classification of T5. Using data from the VISTA Variables in the Via Lactea (VVV) catalog with a 9 year baseline, we measure a proper motion of ( μαcos(δ) , μ δ ) = (−631.0 ± 1.3, −315.0 ± 1.4) mas yr−1 and a trigonometric parallax of π abs = 66.0 ± 4.8 mas, corresponding to a distance of 15.2 ± 1.1 pc. The trigonometric parallax agrees well with our photometric distance estimate (16.1 −3.9+5.1 pc) assuming that VVV J165507.19−421755.5 is a single T5 dwarf. VVV J165507.19−421755.5 is a new member of the 20 parsec census.