Astronomy and Astrophysics Discovery of a Faint Field Methane Brown Dwarf from Es0 Ntt and Vlt Observations

We report the discovery of an isolated brown dwarf with similar properties to the binary object Gliese 229B and to the newly discovered field brown dwarf SDSS 1624+00. Although exhibiting similar colors, its magnitude of ∼ 20.5 is about 6 and 5 magnitudes fainter than Gliese 229B and SDSS 1624+00 respectively. This is the third methane brown dwarf reported to date, the second isolated one in the field and by far the most distant at ∼ 100 pc. Its IR spectrum, although at low S/N given the faintness of the object, is remarkably similar to those of the 2 other methane brown dwarfs.