2000ApJ...531L..57B

We report the discovery of a widely separated (258".3±0".4) T dwarf companion to the Gl 570ABC system. This new component, Gl 570D, was initially identified from the Two Micron All-Sky Survey. Its near-infrared spectrum shows the 1.6 and 2.2 µm CH₄ absorption bands characteristic of T dwarfs, while its common proper motion with the Gl 570ABC system confirms companionship. Gl 570D (M_J=16.47±0.07) is nearly a full magnitude dimmer than the only other known T dwarf companion, Gl 229B, and estimates of L=(2.8±0.3)x10^–6 L_☉ and T_eff=750±50 K make it significantly cooler and less luminous than any other known brown dwarf companion. Using evolutionary models by Burrows et al. and an adopted age of 2-10 Gyr, we derive a mass estimate of 50±20 M_Jup for this object.