CHEMICAL ABUNDANCES OF THE LEO II DWARF GALAXY
CHEMICAL ABUNDANCES OF THE LEO II DWARF GALAXY
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DOI：
10.1088/0004-6256/137/1/62
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发表时间：
2008-10
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影响因子：
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通讯作者：
M. Shetrone;M. Siegel;D. Cook;T. Bosler
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作者：
M. Shetrone;M. Siegel;D. Cook;T. Bosler
我们使用先前公布的中等分辨率光谱结合恒星大气模型，推导出第一个测量的化学丰度比在狮子座II矮椭球（dSPH）星系。我们发现，对于光谱的信噪比大于24，我们能够测量丰度弱钛，铁，镁线位于附近的钙红外三重态（CaT）。我们还量化和讨论从Fe i线和CaT功能估计的金属丰度之间的差异。我们发现，虽然大多数贫金属（[Fe/H] <-2.0]）的狮子座II型恒星的Ca和Ti丰度比与银河系球状星团相似，但更多金属丰富的恒星的Ti，Mg和Ca丰度比随着金属丰度的增加而逐渐下降。在这个遥远的，显然是动态稳定的dSph星系中发现这些趋势支持了这样一个假设，即dSph星系的缓慢化学富集历史是普遍的，独立于与银河系的任何相互作用。结合我们的光谱丰度与公布的宽带测光和更新的等时线，我们能够近似恒星年龄为我们的明亮的红巨星分支恒星的相对精度为2-3 Gyr。虽然Leo II的年龄-金属丰度关系暗示了一定程度的缓慢富集，但数据仍然在统计上与Leo II历史上没有富集相一致。
We use previously published moderate-resolution spectra in combination with stellar atmosphere models to derive the first measured chemical abundance ratios in the Leo II dwarf Spheroidal (dSph) galaxy. We find that for spectra with signal-to-noise ratio greater than 24, we are able to measure abundances from weak Ti, Fe, and Mg lines located near the calcium infrared triplet (CaT). We also quantify and discuss discrepancies between the metallicities measured from Fe i lines and those estimated from the CaT features. We find that while the most metal-poor ([Fe/H] <−2.0]) Leo II stars have Ca and Ti abundance ratios similar to those of Galactic globular clusters, the more metal-rich stars show a gradual decline of Ti, Mg, and Ca abundance ratio with increasing metallicity. Finding these trends in this distant and apparently dynamically stable dSph galaxy supports the hypothesis that the slow chemical enrichment histories of the dSph galaxies is universal, independent of any interaction with the Milky Way. Combining our spectroscopic abundances with published broadband photometry and updated isochrones, we are able to approximate stellar ages for our bright red giant branch stars to a relative precision of 2–3 Gyr. While the derived age-metallicity relationship of Leo II hints at some amount of slow enrichment, the data are still statistically consistent with no enrichment over the history of Leo II.