Ia型超新星前身星碳沸腾过程中的中子化
Neutronization During Carbon Simmering In Type Ia Supernova Progenitors
摘要：
当Ia型超新星（SN Ia）的前身首先点燃核心中的碳时，它在热核失控开始之前经历了${\sim} \,10^{3}-10^{4} \,$年的对流燃烧。这个碳沸腾阶段对于确定白矮星的热剖面和成分很重要。使用\texttt{MESA}恒星演化代码，我们遵循这种对流燃烧，并检查富中子同位素的生产。SN燃料的中子含量对随后的核合成具有重要影响，特别是对次级Fe峰核如Mn和稳定Ni的产生具有重要影响。这些元素已经在超新星遗迹如第谷、开普勒和3C 397的X射线光谱中被观测到，它们的产额可以为研究Ia超新星的物理学及其祖先的性质提供有价值的见解。我们发现慢炖过程中的弱反应最多只能产生${\approx} \, 3 \times 10^{-4}$的中子过剩。这是${\approx} \, 8 \times 10^{-4}$低于在以前的研究中发现的，没有考虑到整个密度和温度分布的沸腾区域。我们的研究结果表明，祖金属丰度是主要贡献者的中子过剩的超新星Ia燃料$Z \gtrsim 1/3 \, Z_{\odot}$。或者，在较低的金属丰度，这种中子过剩提供了一个地板，应该存在于任何中心点燃的SN~Ia的情况。
英文摘要：
When a Type Ia supernova (SN Ia) progenitor first ignites carbon in its core, it undergoes ${\sim} \,10^{3}-10^{4} \,$yr of convective burning prior to the onset of thermonuclear runaway. This carbon simmering phase is important for setting the thermal profile and composition of the white dwarf. Using the \texttt{MESA} stellar evolution code, we follow this convective burning and examine the production of neutron-rich isotopes. The neutron content of the SN fuel has important consequences for the ensuing nucleosynthesis, and, in particular, for the production of secondary Fe-peak nuclei like Mn and stable Ni. These elements have been observed in the X-ray spectra of SN remnants like Tycho, Kepler, and 3C 397, and their yields can provide valuable insights into the physics of SNe Ia and the properties of their progenitors. We find that weak reactions during simmering can at most generate a neutron excess of ${\approx} \, 3 \times 10^{-4}$. This is ${\approx} \, 8 \times 10^{-4}$ lower than that found in previous studies that do not take the full density and temperature profile of the simmering region into account. Our results imply that the progenitor metallicity is the main contributor to the neutron excess in SN Ia fuel for $Z \gtrsim 1/3 \, Z_{\odot}$. Alternatively, at lower metallicities, this neutron excess provides a floor that should be present in any centrally-ignited SN~Ia scenario.
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