The Chemical Evolution of the Ursa Minor Dwarf Spheroidal Galaxy

We present an abundance analysis based on high-resolution spectra of 10 stars selected to span the full range in metallicity in the Ursa Minor (UMi) dwarf spheroidal (dSph) galaxy. We find that [Fe/H] for the sample stars ranges from -1.35 to -3.10 dex. Combining our sample with previously published...

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Bibliographic Details
Published in:The Astrophysical journal 2010-08, Vol.719 (1), p.931-949
Main Authors: Cohen, Judith G, Huang, Wenjin
Format: Article
Language:English
Subjects:
ABUNDANCE
Astronomy
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
BARYON REACTIONS
Earth, ocean, space
EVOLUTION
Exact sciences and technology
GALAXIES
HADRON REACTIONS
MAIN SEQUENCE STARS
MILKY WAY
NEUTRON REACTIONS
NUCLEAR REACTIONS
NUCLEON REACTIONS
R PROCESS
S PROCESS
SATELLITES
STAR EVOLUTION
STARS
SUN
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Summary:We present an abundance analysis based on high-resolution spectra of 10 stars selected to span the full range in metallicity in the Ursa Minor (UMi) dwarf spheroidal (dSph) galaxy. We find that [Fe/H] for the sample stars ranges from -1.35 to -3.10 dex. Combining our sample with previously published work for a total of 16 luminous UMi giants, we establish the trends of abundance ratios [X/Fe] as functions of [Fe/H] for 15 elements. In key cases, particularly for the {alpha}-elements, these trends resemble those for stars in the outer part of the Galactic halo, especially at the lowest metallicities probed. The neutron-capture elements show an r-process distribution over the full range of Fe metallicity reached in this dSph galaxy. This suggests that the duration of star formation in the UMi dSph was shorter than in other dSph galaxies. The derived ages for a larger sample of UMi stars with more uncertain metallicities also suggest a population dominated by uniformly old ({approx}13 Gyr) stars, with a hint of an age-metallicity relationship. Upon comparing our results for UMi, our earlier work in Draco, and published studies of more metal-rich dSph Galactic satellites, there appears to be a pattern of moving from a chemical inventory for dSph giants with [Fe/H] {approx} - 1.5 dex leads to a chemical inventory wildly discrepant from that of any component of the Milky Way. We note the presence of two UMi giants with [Fe/H]
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/719/1/931