Discovery of Four Field Methane (T-Type) Dwarfs with the Two Micron All-Sky Survey
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 CH4 absorption bands characteristic of objects with Teff<~1300 K as well as broadened H2O 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.
Portions of the data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by generous financial support of the W. M. Keck Foundation.- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 1999
- DOI:
- arXiv:
- arXiv:astro-ph/9907019
- Bibcode:
- 1999ApJ...522L..65B
- Keywords:
-
- INFRARED: STARS;
- STARS: FUNDAMENTAL PARAMETERS;
- STARS: INDIVIDUAL: ALPHANUMERIC: 2MASSI J1047539+212423;
- STARS: INDIVIDUAL: ALPHANUMERIC: 2MASSW J1217111-031113;
- STARS: INDIVIDUAL: ALPHANUMERIC: 2MASSW J1225543-273947;
- STARS: INDIVIDUAL: ALPHANUMERIC: 2MASSW J1237392+652615;
- STARS: INDIVIDUAL: ALPHANUMERIC: 2MASSW J1346464-003150;
- STARS: LOW-MASS;
- BROWN DWARFS;
- Infrared: Stars;
- Stars: Fundamental Parameters;
- Stars: Individual: Alphanumeric: 2MASSI J1047539+212423;
- Stars: Individual: Alphanumeric: 2MASSW J1217111-031113;
- Stars: Individual: Alphanumeric: 2MASSW J1225543-273947;
- Stars: Individual: Alphanumeric: 2MASSW J1237392+652615;
- Stars: Individual: Alphanumeric: 2MASSW J1346464-003150;
- Stars: Low-Mass;
- Brown Dwarfs;
- Astrophysics
- E-Print:
- 12 pages, 2 figures, 2 tables, to appear in ApJ Letters v. 520