Barium Abundances in Extremely Metal-poor Stars
Barium Abundances in Extremely Metal-poor Stars
复制标题
DOI：
10.1086/300289
复制
发表时间：
1998-04
期刊：
影响因子：
--
通讯作者：
A. McWilliam
中科院分区：
文献类型：
--
作者：
A. McWilliam
McWilliam 等人 1995 年样本中 33 颗金属极度贫乏的晕星的新的、改进的钡丰度。已经计算出来了。 [Fe/H] ≤ -2.4 的恒星的平均 [Ba/Eu] 比率为 -0.69 ± 0.06 dex，与测量不确定度内的纯 r 过程核合成一致。尽管[Sr/Fe]和[Ba/Fe]丰度比的范围为2.6 dex，但平均值与[Fe/H]近似恒定。这与化学演化模型一致，其中母云因少量超新星事件而丰富。在此模型中，随着 [Fe/H] 的增加，重元素色散减小，这仅仅是由于许多超新星在较高 [Fe/H] 下的元素产量的平均值所致；然而，为了证实这一图景，有必要增加已知的极度贫金属恒星的数量。除了来自 r 过程的随机 Sr 成分之外，[Sr/Ba] 比率表明还有来自尚未确定的核合成位点的第二个也是随机的 Sr 来源。
New, improved, barium abundances for 33 extremely metal-poor halo stars from the 1995 sample of McWilliam et al. have been computed. The mean [Ba/Eu] ratio for stars with [Fe/H] ≤ -2.4 is -0.69 ± 0.06 dex, consistent with pure r-process nucleosynthesis within the measurement uncertainties. Although the [Sr/Fe] and [Ba/Fe] abundance ratios span a range of 2.6 dex, the mean values are approximately constant with [Fe/H]. This is consistent with a model of chemical evolution in which the parent clouds were enriched by small numbers of supernova events. In this model, the decreasing heavy-element dispersion with increasing [Fe/H] is simply due to the averaging of element yields from many supernovae at higher [Fe/H]; however, it is necessary to increase the number of extremely metal-poor stars known in order to confirm this picture. In addition to the random Sr component from the r-process, the [Sr/Ba] ratios indicate that there is a second, also random, source of Sr from an as yet unidentified nucleosynthesis site.