Empirical Abundance Scaling Laws and Implications for the Gamma Process in Core-Collapse Supernovae
Empirical Abundance Scaling Laws and Implications for the Gamma Process in Core-Collapse Supernovae
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DOI：
10.1086/589938
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发表时间：
2008-10
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通讯作者：
T. Hayakawa;N. Iwamoto;T. Kajino;T. Shizuma;H. Umeda;K. Nomoto
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作者：
T. Hayakawa;N. Iwamoto;T. Kajino;T. Shizuma;H. Umeda;K. Nomoto
通过对太阳系丰度的分析，我们发现了相同原子序数的p核和S核的两个经验丰度标度律。第一个标度律是，在很宽的原子序数范围内，S/p比几乎是恒定的，其中p核比S核轻2或4个中子。第二定律是，当第二个p核比第一个p核轻2个中子时，p/p比几乎是恒定的。这些标度提供的证据表明，在超新星爆炸中，大多数p核主要是由γ过程合成的。这些标度导致了“γ过程的普适性”的新概念，即由单个γ过程产生的核的S/p和p/p比率几乎是恒定的。我们根据核坍塌超新星爆炸模型计算了不同天体物理条件下γ过程产生的比例，发现标度适用于单个γ过程产生的物质，而与所假定的天体物理条件无关。这种普适性源于三种机制：γ过程层移动以保持其峰值温度，前新星中弱的S过程和S/p比不受核反应的影响。结果进一步表明，γ过程层中的S过程丰度比不仅是常数，而且以一个特定值3为中心。根据这个特定值和第一标度定律，我们估计对于A>；90的S过程核，AGB星对大质量恒星的S过程丰度贡献之比将接近6.7。我们发现，Ce、Er和W的S/p比值的大幅增加是弱S过程实际上发生在超新星之前的证据。
Analyzing solar system abundances, we have found two empirical abundance scaling laws for p- and s-nuclei with the same atomic number. The first scaling law is that s/p ratios are almost constant over a wide range of atomic numbers where the p-nuclei are lighter than the s-nuclei by 2 or 4 neutrons. The second law is that p/p ratios are almost constant where the second p-nuclei are lighter than the first p-nuclei by 2 neutrons. These scalings provide evidence that most p-nuclei are dominantly synthesized by the γ-process in supernova explosions. These scalings lead to a novel concept of the “universality of the γ-process,” in that the s/p and p/p ratios of nuclei produced by individual γ-processes are almost constant. We have calculated the ratios produced by the γ-process based on core-collapse supernova explosion models under various astrophysical conditions, and found that the scalings hold for materials produced by individual γ-processes independent of the astrophysical conditions assumed. The universality originates from three mechanisms: the shifting of the γ-process layers in order to keep their peak temperature, the weak s-process in presupernovae, and the independence of the s/p ratios from nuclear reactions. The results further suggest an extended universality, that the s/p ratios in the γ-process layers are not only constant but also centered on a specific value of 3. With this specific value and the first scaling law, we estimate that the ratio of s-process abundance contributions from AGB stars to massive stars will be almost 6.7 for the s-nuclei of A > 90. We find that large enhancements of the s/p ratios for Ce, Er, and W are evidence that the weak s-process actually occurred before supernovae.