s-process Nucleosynthesis in Asymptotic Giant Branch Stars

机译：渐近巨支星的s-过程核合成

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We have made a parametric study of s-process nucleosynthesis in the metal poor ([Fe/H] = ―2.7) stars LP 625-44 and LP 706-7. We find that a high neutron exposure and a small overlap factor are necessary to fit the abundance pattern observed in these two metal-deficient stars, particularly the abundance ratios, Pb/Ba ≈ 1 and Ba/Sr ≈10. We have also constructed stellar models to better understand how such s-process conditions could arise. We have calculated a 2solar mass model star with metallicity [Fe/H] =―2.7 from the ZAMS up to AGB phase. We find that for such low-metallicity stars the He convective shell reaches the bottom of the overlying H-rich envelope at the second thermal pulse. Protons are then carried into the hotter He burning layers and ~(13)C is formed as protons mix into the He shell. Subsequently, material in the H-flash driven convective zone experiences a high neutron exposure due to the ~(13)C(α, n)~(16)O reaction. This results in a new neutron-capture s-process paradigm in which the abundances are characterized by only a few neutron exposures. We suggest that this new s-process site may be a significant contributor to the s-process abundances in low-metallicity ([Fe/H] ≤ ―2.5) stars.

机译：我们已经对贫金属（[Fe / H] = 2.7）恒星LP 625-44和LP 706-7中的S过程核合成进行了参数研究。我们发现，需要高中子辐照度和小的重叠因子来拟合在这两个缺金属恒星中观察到的丰度模式，特别是丰度比Pb / Ba≈1和Ba / Sr≈10。我们还构建了恒星模型，以更好地理解这种s过程条件是如何产生的。我们已经计算了从ZAMS到AGB相的金属质量[Fe / H] = -2.7的2太阳质量模型恒星。我们发现，对于这样的低金属恒星，He对流壳在第二个热脉冲时到达上覆H富集层的底部。然后，质子被带入较热的He燃烧层，当质子混合到He壳中时形成〜（13）C。随后，由于〜（13）C（α，n）〜（16）O反应，H-flash驱动的对流区内的材料经历了高中子暴露。这导致了一种新的中子俘获s过程范式，其中丰度仅以少数中子暴露为特征。我们建议，这个新的S过程位置可能是低金属（[Fe / H]≤― 2.5）恒星中S过程丰度的重要贡献。

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《》|2002年|p.5-9|共5页
会议地点 Tokai(JP)
作者
Nobuyuki Iwamoto;
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National Astronomical Observatory of Japan;

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正文语种 eng
中图分类 O5;
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s-process Nucleosynthesis in Asymptotic Giant Branch Stars

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