论文标题
在渐近巨型分支星星中的thor和铀的合成
Synthesis of thorium and uranium in asymptotic giant branch stars
论文作者
论文摘要
中间中子捕获过程（I-Process）以缓慢和快速中子捕获过程之间的中子密度运行。它可以通过在对流氦燃烧区域摄入质子来触发。一个可能的天体物理部位是低质量低金属渐近性巨型分支（AGB）星。我们在这里研究actinides（尤其是TH和U）的可能性可以通过AGB恒星中的I-Process核合成显着合成。我们用恒星进化代码starevol计算了[fe/h] $ = -2.5 $的1 $ m _ {\ odot} $模型。我们使用了一个从H到CF的1160种的核网络，耦合到运输过程。在质子摄入事件中，中子密度为$ \ sim 10^{15} $ cm $^{ - 3} $。虽然大多数核流式循环循环在富含中子的PB-BI-PO区域，但不可忽略的部分泄漏到较重的元素，并最终合成肌动剂。 TH和U中的表面富集受到核和天体物理模型的不确定性的影响，这些模型可能会在将来降低，尤其是通过对影响PB和PA之间的中子富含中子同位素的中子捕获速率的核输入的详细分析。在其频谱中。它的表面丰度证明我们的AGB模型可以很好地再现。与Cosmochronometry结合使用，这一发现为与I-Process事件的约会开辟了道路，从而获得了CEMP-R/S恒星年龄的下限。只有在同时提取Th和U的表面丰度时，预计这种日期才能准确。这项工作表明，可以通过I-Process在AGB恒星中合成actinides。结果，R过程可能不是生产U和Th的唯一机制。
The intermediate neutron capture process (i-process) operates at neutron densities between those of the slow and rapid neutron-capture processes. It can be triggered by the ingestion of protons in a convective helium-burning region. One possible astrophysical site is low-mass low-metallicity asymptotic giant branch (AGB) stars. We study here the possibility that actinides (particularly Th and U) may be significantly synthesized through i-process nucleosynthesis in AGB stars. We computed a 1 $M_{\odot}$ model at [Fe/H] $= -2.5$ with the stellar evolution code STAREVOL. We used a nuclear network of 1160 species from H to Cf coupled to the transport processes. During the proton ingestion event, the neutron density goes up to $\sim 10^{15}$ cm$^{-3}$. While most of the nuclear flow cycles in the neutron-rich Pb-Bi-Po region, a non-negligible fraction leaks towards heavier elements and eventually synthesizes actinides. The surface enrichment in Th and U is subject to nuclear and astrophysical model uncertainties that could be lowered in the future, in particular by a detailed analysis of the nuclear inputs that affect the neutron capture rates of neutron-rich isotopes between Pb and Pa. One stellar candidate that may confirm the production of actinides by the i-process is the carbon-enhanced metal-poor r/s star J0949-1617, which shows Th lines in its spectrum. Its surface abundance is shown to be reasonably well reproduced by our AGB model. Combined with cosmochronometry, this finding opens the way to dating the i-process event and thus obtaining a lower limit for the age of CEMP-r/s stars. Such a dating is expected to be accurate only if surface abundances of Th and U can be extracted simultaneously. This work shows that actinides can be synthesized in AGB stars through the i-process. As a consequence, the r-process may not be the sole mechanism for the production of U and Th.
