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Discovery of Four Field Methane (T-Type) Dwarfs with the Two Micron All-Sky Survey

By Adam J. Burgasser, J. Davy Kirkpatrick, Michael E. Brown, I. Neill Reid, John E. Gizis, Conard C. Dahn, David G. Monet, Charles A. Beichman, James Liebert, Roc M. Cutri and Michael F. Skrutskie

Abstract

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 μm CH_4 absorption bands characteristic of objects with T_(eff) ≾ 1300 K as well as broadened H_2O bands at 1.4 and 1.9 μm. 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

Publisher: American Astronomical Society
Year: 1999
OAI identifier: oai:authors.library.caltech.edu:34549
Provided by: Caltech Authors

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