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 dwarf, or T dwarf, by the Two Micron All Sky Survey. This object, 2MASSI J0559191-140448, is the first brown dwarf identified by the newly commissioned CorMASS instrument mounted on the Palomar 60 inch (1.5 m) telescope. Near-infrared spectra from 0.9 to 2.35 μm show characteristic CH₄ bands at 1.1, 1.3, 1.6, and 2.2 μm, which are significantly shallower than those seen in other T dwarfs discovered to date. Coupled with the detection of an FeH band at 0.9896 μm and two sets of K I doublets at J band, we propose that 2MASS J0559-14 is a warm T dwarf, close to the transition between L and T spectral classes. The brightness of this object makes it a good candidate for detailed investigation over a broad wavelength regime and at higher resolution.