Mg abundances in metal-poor halo stars as a tracer of early Galactic mixing
Mg abundances in metal-poor halo stars as a tracer of early Galactic mixing
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DOI：
10.1051/0004-6361:20041034
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发表时间：
2005-02
影响因子：
6.5
通讯作者：
E. Arnone;S. Ryan;D. Argast;J. Norris;T. Beers
中科院分区：
文献类型：
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作者：
E. Arnone;S. Ryan;D. Argast;J. Norris;T. Beers
我们给出了对23颗主序星进行详细化学分析的结果，这些主序星具有−3.4 ≤（Fe/H）≤− 2.2，这是一个在Teff和log（g）方面高度均匀的样本。我们调查的混合效率在早期银河系的（镁/铁）比的装置，并发现，所有的值都位于一个总的范围内的0.2德克斯，与标准偏差约为0.06德克斯的平均值，符合测量误差。这意味着在早期ISM中几乎没有或根本没有内在的散射，这也是高质量VLT观测的最新结果所表明的。这些结果与采用当前超新星（SN）II产额的非均匀银河系化学演化（iGCE）模型形成对比，该模型预测在非常低的金属丰度下（Mg/Fe）的峰-峰散射高达1 dex，相应的标准偏差约为0.4 dex。我们建议，冷却和混合的时间尺度应在iGCE模型中进行调查，以说明与目前的观测明显不一致。这里报道的恒定性和小的分散度（Mg/Fe）与（Ba/Fe）的完全不同的行为之间的对比表明，根据这种解释，Mg和Ba主要在不同的祖质量范围内合成。
We present results of a detailed chemical analysis performed on 23 main-sequence turnoff stars having −3.4 ≤ (Fe/H) ≤− 2.2, a sample selected to be highly homogeneous in Teff and log(g). We investigate the efficiency of mixing in the early Galaxy by means of the (Mg/Fe) ratio, and find that all values lie within a total range of 0.2 dex, with a standard deviation about the mean of 0.06 dex, consistent with measurement errors. This implies there is little or no intrinsic scatter in the early ISM, as suggested also by the most recent results from high-quality VLT observations. These results are in contrast with inhomogeneous Galactic chemical evolution (iGCE) models adopting present supernova (SN) II yields, which predict a peak- to-peak scatter in (Mg/Fe) as high as 1 dex at very low metallicity, with a corresponding standard deviation of about 0.4 dex. We propose that cooling and mixing timescales should be investigated in iGCE models to account for the apparent disagreement with present observations. The contrast between the constancy and small dispersion of (Mg/Fe) reported here and the quite different behaviour of (Ba/Fe) indicates, according to this interpretation, that Mg and Ba are predominantly synthesised in different progenitor mass ranges.