THE CHEMICAL EVOLUTION OF THE DRACO DWARF SPHEROIDAL GALAXY

被引:163
作者
Cohen, Judith G. [1 ]
Huang, Wenjin [1 ]
机构
[1] CALTECH, Palomar Observ, Pasadena, CA 91125 USA
关键词
galaxies: abundances; galaxies: dwarf; galaxies: individual (Draco); METAL-POOR STARS; VELOCITY DISPERSION PROFILES; GIANT BRANCH STARS; URSA-MINOR; GALACTIC EVOLUTION; LINE FORMATION; CARBON STARS; METALLICITY DISTRIBUTION; VLT/UVES ABUNDANCES; ELEMENT ABUNDANCES;
D O I
10.1088/0004-637X/701/2/1053
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We present an abundance analysis based on high-resolution spectra of eight stars selected to span the full range in metallicity in the Draco dwarf spheroidal (dSph) galaxy. We find that [Fe/H] for the sample stars ranges from -1.5 to -3.0 dex. Combining our sample with previously published work for a total of 14 luminous Draco giants, we show that the abundance ratios [Na/Fe], [Mg/Fe], and [Si/Fe] for the Draco giants overlap those of Galactic halo giants at the lowest [Fe/H] probed, but are significantly lower for the higher Fe-metallicity Draco stars. For the explosive a-elements Ca and Ti, the abundance ratios for Draco giants with [Fe/H] > -2.4 dex are approximately constant and slightly subsolar, well below values characteristic of Galactic halo stars. The s-process contribution to the production of heavy elements begins at significantly lower Fe metallicity than in the Galactic halo. Using a toy model we compare the behavior of the abundance ratios within the sample of Draco giants with those from the literature of Galactic globular clusters, and the Carina and Sgr dSph galaxies. The differences appear to be related to the timescale for buildup of the heavy elements, with Draco having the slowest rate. We note the presence of a Draco giant with [Fe/H] < -3.0 dex in our sample, and reaffirm that the inner Galactic halo could have been formed by early accretion of Galactic satellite galaxies and dissolution of young globular clusters, while the outer halo could have formed from those satellite galaxies accreted later.
引用
收藏
页码:1053 / 1075
页数:23
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