Journal
ASTRONOMY & ASTROPHYSICS
Volume 497, Issue 2, Pages 619-633Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361/200810314
Keywords
stars: low-mass, brown dwarfs; stars: late-type
Categories
Funding
- Alfred P. Sloan Foundation
- Participating Institutions
- National Science Foundation
- U. S. Department of Energy
- National Aeronautics and Space Administration
- Japanese Monbukagakusho
- Max Planck Society
- Higher Education Funding Council for England
- Natural Science Foundation of China [10521001, 10433030, 10503010]
- CAS Research Fellowship
- STFC [ST/G002622/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/G002622/1] Funding Source: researchfish
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Aims. We try to identify ultra-cool dwarfs from the seventh Data Release of the Sloan Digital Sky Survey (SDSS DR7) with SDSS i-z and r-z colors. We also obtain proper motion data from SDSS, 2MASS, and UKIDSS and improve spectral typing from SDSS and 2MASS photometric colors. Methods. We selected ultra-cool dwarf candidates from the SDSS DR7 with new photometric selection criteria, which are based on a parameterization study of known L and T dwarfs. The objects are then cross-identified with the Two Micron All Sky Survey and the Fourth Data Release of the UKIRT Infrared Deep Sky Survey (UKIDSS DR4). We derive proper motion constraints by combining SDSS, 2MASS, and UKIDSS positional information. In this way we are able to assess, to some extent, the credence of our sample using a multi epoch approach, which complements spectroscopic confirmation. Some of the proper motions are affected by short baselines, but, as a general tool, this method offers great potential to confirm faint L dwarfs as UKIDSS coverage increases. In addition we derive updated color-spectral type relations for L and T dwarfs with SDSS and 2MASS magnitudes. Results. We present 59 new nearby M and L dwarfs selected from the imaging catalog of the SDSS DR7, including proper motions and spectral types calculated from the updated color-spectral type relations. and obtain proper motions from SDSS, 2MASS, and UKIDSS for all of our objects.
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