Discovery of a bright field methane (T-type) brown dwarf by 2MASS

We report the discovery of a bright (J = 13.83 +/- 0.03) methane brown dwar f, or T dwarf, by the Two Micron All Sky Survey. This object, 2MASSI J05591 91-140448, is the first brown dwarf identified by the newly commissioned Co rMASS instrument mounted on the Palomar 60 inch (1.5 m) telescope. Near-inf rared spectra from 0.9 to 2.35 mu m show characteristic CH4 bands at 1.1, 1 .3, 1.6, and 2.2 mu m, which are significantly shallower than those seen in other T dwarfs discovered to date. Coupled with the detection of an FeH ba nd at 0.9896 mu m and two sets of K I doublets at J band, we propose that 2 MASS J0559-14 is a warm T dwarf, close to the transition between L and T sp ectral classes. The brightness of this object makes it a good candidate for detailed investigation over a broad wavelength regime and at higher resolu tion.