Discovery of a Brown Dwarf Companion to Gliese 570ABC: A 2MASS T Dwarf Significantly Cooler than Gliese 229B.

We report the discovery of a widely separated (258&farcs;3+/-0&farcs;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.