Burgasser, Adam J.Kirkpatrick, J. DavyBrown, Michael E.Reid, I. NeillGizis, John E.Dahn, Conard C.Monet, David G.Beichman, Charles A.Liebert, JamesCutri, Roc M.Skrutskie, Michael F.2024-04-262024-04-26199910.1086/312221https://hdl.handle.net/20.500.14394/2635This is a pre-published version which is collected from arXiv. The published version is at http://iopscience.iop.org/1538-4357/522/1/L65/fulltext.We report the discovery of four field methane ("T"-type) brown dwarfs using Two Micron All-Sky Survey (2MASS) data. One additional methane dwarf, previously discovered by the Sloan Digital Sky Survey, was also identified. Near-infrared spectra clearly show the 1.6 and 2.2 m CH4 absorption bands characteristic of objects with Teff 1300 K as well as broadened H2O bands at 1.4 and 1.9 m. Comparing the spectra of these objects with that of Gl 229B, we propose that all new 2MASS T dwarfs are warmer than 950 K, in order from warmest to coolest: 2MASS J1217-03, 2MASS J1225-27, 2MASS J1047+21, and 2MASS J1237+65. Based on this preliminary sample, we find a warm T dwarf surface density of 0.0022 T dwarfs deg-2, or 90 warm T dwarfs over the whole sky detectable to J < 16. The resulting space density upper limit, 0.01 T dwarfs pc-3, is comparable to that of the first L dwarf sample from Kirkpatrick et al.Astrophysics and Astronomyarticle