The Near-Infrared Spectrum of the Brown Dwarf Gliese 229B

A medium-resolution 1.0--2.5 mu m spectrum of the brown dwarf Gliese 229B has been obtained using the facility spectrometer CGS4 on the United Kingdom Infrared Telescope. In addition to the broad spectral structure seen in earlier low-resolution observations, the new spectrum reveals a large number of absorption lines, many of which can be identified with water vapor. Water and methane are both shown to be strong absorbers in the near-infrared spectrum of the object. Several spectral features in Gl 229B that are attributable to methane match ones seen in reflection in the giant outer planets and, in particular, Titan.