贫金属星的铕、钐和钕同位素分馏
Europium, Samarium, and Neodymium Isotopic Fractions in Metal-Poor Stars
摘要：
我们推导出了两颗贫金属巨星中铕、钐和钕的同位素分数，它们具有不同的中子俘获核合成历史。这些同位素分数是从麦克唐纳天文台2.7米史密斯望远镜的2d Coude摄谱仪获得的新的高分辨率（R ~ 120，000），高信噪比（S/N ~ 160-1000）光谱中测量的。合成光谱是使用最近的高精度实验室测量这些元素的几个过渡的超精细和同位素子成分，并定量匹配所观察到的光谱。我们解释我们的同位素分数的恒星模型，再现S-过程核合成的物理条件下，预期在低质量，热脉冲星的AGB的核合成预测，和经典的方法，它近似S-过程核合成的稳定中子通量撞击在Fe峰种子核。我们在HD 175305中的Eu同位素分数与经典方法的r-过程起源一致，并且与恒星模型的r-或s-过程起源一致。我们的Sm同位素馏分HD 175305建议一个主要的r-过程的起源，和我们的Sm同位素馏分HD 196944是一致的S-过程的起源。钕同位素分数，而符合r-过程或s-过程的起源，有非常小的能力来区分任何物理值的同位素分数在任何恒星。这项研究首次将贫金属恒星中多种稀土元素的n-捕获起源从元素丰度扩展到同位素水平，加强了HD 175305的r-过程解释和HD 196944的s-过程解释。
英文摘要：
We have derived isotopic fractions of europium, samarium, and neodymium in two metal-poor giants with differing neutron-capture nucleosynthetic histories. These isotopic fractions were measured from new high resolution (R ~ 120,000), high signal-to-noise (S/N ~ 160-1000) spectra obtained with the 2dCoude spectrograph of McDonald Observatory's 2.7m Smith telescope. Synthetic spectra were generated using recent high-precision laboratory measurements of hyperfine and isotopic subcomponents of several transitions of these elements and matched quantitatively to the observed spectra. We interpret our isotopic fractions by the nucleosynthesis predictions of the stellar model, which reproduces s-process nucleosynthesis from the physical conditions expected in low-mass, thermally-pulsing stars on the AGB, and the classical method, which approximates s-process nucleosynthesis by a steady neutron flux impinging upon Fe-peak seed nuclei. Our Eu isotopic fraction in HD 175305 is consistent with an r-process origin by the classical method and is consistent with either an r- or an s-process origin by the stellar model. Our Sm isotopic fraction in HD 175305 suggests a predominantly r-process origin, and our Sm isotopic fraction in HD 196944 is consistent with an s-process origin. The Nd isotopic fractions, while consistent with either r-process or s-process origins, have very little ability to distinguish between any physical values for the isotopic fraction in either star. This study for the first time extends the n-capture origin of multiple rare earths in metal-poor stars from elemental abundances to the isotopic level, strengthening the r-process interpretation for HD 175305 and the s-process interpretation for HD196944.
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