AGB星中i过程中子俘获核合成期间锕系元素和短寿命放射性核素的合成
Synthesis of actinides and short-lived radionuclides during i-process nucleosynthesis in AGB stars
AI总结：
本文利用STAREVOL程序研究AGB星质子摄入事件驱动的i过程核合成，发现低金属丰度模型可产生锕系元素及多种短寿命放射性核素，为星系化学增丰提供潜在来源。
摘要：
在渐近巨星支（AGB）恒星中，混合与核合成之间存在复杂的相互作用。除了慢中子俘获过程（s过程）之外，在质子摄入事件（PIEs）期间还可能发展出中间中子俘获过程（i过程）。本文在简要回顾了迄今已识别出的AGB恒星中重元素的不同产生模式之后，研究了i过程核合成期间锕系元素和其他短寿命放射性核素（SLRs，$^{60}$Fe、$^{107}$Pd、$^{126}$Sn、$^{129}$I、$^{135}$Cs和$^{182}$Hf）的合成。使用恒星演化程序STAREVOL计算了初始质量为$1 \leq M_{\rm ini}/M_{\odot} \leq 3$、金属丰度为$-3 \leq $ [Fe/H] $ \leq 0$且具有不同超射强度的AGB恒星模型。在质子摄入事件期间，使用包含1160种同位素的核反应网络并将其与输运方程耦合。我们发现，[Fe/H] $<-2$的AGB模型可以合成锕系元素，其丰度有时高于太阳丰度。$^{60}$Fe的产额随初始金属丰度成比例变化，而$^{107}$Pd、$^{126}$Sn、$^{129}$I、$^{135}$Cs和$^{182}$Hf的产额作为金属丰度的函数遵循相似的模式，在[Fe/H] $\simeq -1.3$处出现产生峰值。在[Fe/H] $<-1$时，预测奇Ba同位素比例$f_{\rm Ba,odd}$根据初始质量和金属丰度的不同在0.6至0.8之间变化。我们$1 M_{\odot}$、[Fe/H] $=-2.5$模型上的核不确定性导致$f_{\rm Ba,odd}$在0.27至0.76之间变化，这明显高于s过程的值。经历质子摄入事件的AGB恒星似乎是锕系元素和短寿命放射性核素的潜在产生者，尤其是在低金属丰度条件下（$^{60}$Fe除外）。需要星系化学演化模型来评估它们对星系增丰的可能贡献。
英文摘要：
A complex interplay between mixing and nucleosynthesis is at work in asymptotic giant branch (AGB) stars. In addition to the slow neutron capture process (s-process), the intermediate neutron capture process (i-process) can develop during protons ingestion events (PIEs). In this paper, after quickly reviewing the different modes of production of heavy elements in AGB stars that were identified so far, we investigate the synthesis of actinides and other short-lived radioactive nuclei (SLRs, $^{60}$Fe, $^{107}$Pd, $^{126}$Sn, $^{129}$I, $^{135}$Cs and $^{182}$Hf) during i-process nucleosynthesis. AGB stellar models with initial masses $1 \leq M_{\rm ini}/M_{\odot} \leq 3$, metallicities $-3 \leq $ [Fe/H] $ \leq 0$ and different overshoot strengths were computed with the stellar evolution code STAREVOL. During PIEs, a nuclear network of 1160 isotopes is used and coupled to the transport equations. We found that AGB models with [Fe/H] $<-2$ can synthesize actinides with sometimes abundances greater than solar. The $^{60}$Fe yield scales with the initial metallicity while the $^{107}$Pd, $^{126}$Sn, $^{129}$I, $^{135}$Cs and $^{182}$Hf yields follow a similar pattern as a function of metallicity, with a production peak at [Fe/H] $\simeq -1.3$. At [Fe/H] $<-1$, the fraction of odd Ba isotopes $f_{\rm Ba,odd}$ is predicted to vary between 0.6 and 0.8 depending on the initial mass and metallicity. Nuclear uncertainties on our $1 M_{\odot}$, [Fe/H] $=-2.5$ model lead to $f_{\rm Ba,odd}$ ranging between 0.27 and 0.76, which is clearly above the s-process value. AGB stars experiencing PIEs appear to be potential producers of actinides and SLRs, particularly at low metallicity (except for $^{60}$Fe). Galactic chemical evolution modeling are required to assess their possible contribution to the galactic enrichment.
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