Europium Isotope Ratios in s-Process Element-enhanced Metal-poor Stars: A New Probe of the 151Sm Branching
Europium Isotope Ratios in s-Process Element-enhanced Metal-poor Stars: A New Probe of the 151Sm Branching
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DOI：
10.1086/377681
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发表时间：
2003-06
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影响因子：
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通讯作者：
W. Aoki;S. Ryan;N. Iwamoto;T. Beers;J. Norris;H. Ando;T. Kajino;G. Mathews;M. Fujimoto
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作者：
W. Aoki;S. Ryan;N. Iwamoto;T. Beers;J. Norris;H. Ando;T. Kajino;G. Mathews;M. Fujimoto
我们报告了对 s 过程元素增强贫金属恒星中 Eu 同位素分数（151Eu 和 153Eu）的首次测量。我们使用这些比率来研究 s 过程核合成的 151Sm 分支。该测量是通过对Eu II谱线的详细研究进行的，这些谱线受到用斯巴鲁望远镜高色散摄谱仪观察的富碳贫金属恒星LP 625-44和CS 31062-050光谱中的超精细分裂和同位素位移的显着影响。 LP 625-44 和 CS 31062-050 得出的 151Eu 分数 [fr(151Eu) = 151Eu/(151Eu + 153Eu)] 分别为 0.60 和 0.55，不确定性约为 ±0.05。这些值高于太阳系材料中的值，但与最近 s 过程模型的预测非常吻合。我们根据 151Eu 分数的脉冲 s 过程模型的计算得出了 s 过程期间温度和中子密度的新约束。
We report on the first measurement of the Eu isotope fractions (151Eu and 153Eu) in s-process element-enhanced metal-poor stars. We use these ratios to investigate the 151Sm branching of s-process nucleosynthesis. The measurement was made by detailed study of Eu II lines that are significantly affected by hyperfine splitting and isotope shifts in spectra of the carbon-rich very metal poor stars LP 625-44 and CS 31062-050, observed with the Subaru Telescope High Dispersion Spectrograph. The 151Eu fractions [fr(151Eu) = 151Eu/(151Eu + 153Eu)] derived for LP 625-44 and CS 31062-050 are 0.60 and 0.55, respectively, with uncertainties of about ±0.05. These values are higher than found in solar system material but agree well with the predictions of recent s-process models. We derive new constraints on the temperature and neutron density during the s-process based on calculations of pulsed s-process models for the 151Eu fraction.