期刊
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
卷 458, 期 1, 页码 L59-L63出版社
OXFORD UNIV PRESS
DOI: 10.1093/mnrasl/slw013
关键词
galaxies: individual: Draco II; galaxies: kinematics and dynamics; Local Group
资金
- Strasbourg IDEX (Initiative d'Excellence) grant - University of Strasbourg
- CNRS through PICS [PICS06183]
- DFG [SFB 881]
- W.M. Keck Foundation
- National Aeronautics and Space Administration through the Planetary Science Division of the NASA Science Mission Directorate [NNX08AR22G]
- National Science Foundation [AST-1238877]
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [1238877] Funding Source: National Science Foundation
We present the first spectroscopic analysis of the faint and compact stellar system Draco II (Dra II, M-V = -2.9 +/- 0.8, r(h) = 19(-6)(+8) pc), recently discovered in the Panoramic Survey Telescope and Rapid Response System 1 3 pi survey. The observations, conducted with DEIMOS on the Keck II telescope, establish some of its basic characteristics: the velocity data reveal a narrow peak with nine member stars at a systemic heliocentric velocity < vr > = -347.6(-1.8)(+1.7) km s(-1), thereby confirming Dra II is a satellite of the Milky Way; we infer a velocity dispersion with sigma(vr) = 2.9 +/- 2.1 kms(-1) (<8.4 kms(-1) at the 95 per cent confidence level), which implies log(10) (M-1/2) = 5.5(-0.6)(+0.4) and log(10) ((M/L)(1/2)) = 2.7(-0.8)(+0.5), in Solar units; furthermore, very weak calcium triplet lines in the spectra of the high signal-to-noise member stars imply [Fe/H] < -2.1, whilst variations in the line strengths of two stars with similar colours and magnitudes suggest a metallicity spread in Dra II. These new data cannot clearly discriminate whether Draco II is a star cluster or amongst the faintest, most compact, and closest dwarf galaxies. However, the sum of the three - individually inconclusive - pieces of evidence presented here seems to favour the dwarf galaxy interpretation.
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