SILICON CARBIDE GRAINS OF TYPE C PROVIDE EVIDENCE FOR THE PRODUCTION OF THE UNSTABLE ISOTOPE 32Si IN SUPERNOVAE
SILICON CARBIDE GRAINS OF TYPE C PROVIDE EVIDENCE FOR THE PRODUCTION OF THE UNSTABLE ISOTOPE 32Si IN SUPERNOVAE
复制标题
C 型碳化硅颗粒为超新星中不稳定同位素 32Si 的产生提供了证据
DOI：
--
复制
发表时间：
2013
期刊：
影响因子：
--
通讯作者：
F. Thielemann
中科院分区：
文献类型：
--
作者：
M. Pignatari;E. Zinner;M. Bertolli;R. Trappitsch;P. Hoppe;T. Rauscher;C. Fryer;F. Herwig;R. Hirschi;F. Timmes;F. Thielemann
在最近的核心坍缩超新星（SNe）爆炸后一年内，观测到富含碳的颗粒在喷出物中凝结。X型碳化硅颗粒是富碳颗粒，具有超新星爆发核合成的同位素特征。更罕见的C型碳化硅颗粒是来自SNe的SiC颗粒的特殊亚组。它们显示出特殊的丰度签名的Si和S，同位素重Si，和同位素轻S，这似乎与模型预测不一致。我们建议，C颗粒主要是由富C恒星材料暴露于较低的SN冲击温度比更常见的X型颗粒。在这种情况下，在C颗粒中观察到的极端32 S富集可以通过喷出物中存在短寿命的32 Si（τ1/2 = 153年）来解释，这些32 Si是由稳定的Si同位素开始的中子捕获过程产生的。不需要来自更深的富Si材料的混合和/或由于分子化学导致的Si与S的分馏来解释32 S富集。晶粒中32 Si的丰度可以对富C He壳材料中SN爆炸期间达到的中子密度提供约束。在32 Si区域的中子俘获截面的大的不确定性的影响进行了讨论。
Carbon-rich grains are observed to condense in the ejecta of recent core-collapse supernovae (SNe) within a year after the explosion. Silicon carbide grains of type X are C-rich grains with isotopic signatures of explosive SN nucleosynthesis have been found in primitive meteorites. Much rarer silicon carbide grains of type C are a special sub-group of SiC grains from SNe. They show peculiar abundance signatures for Si and S, isotopically heavy Si, and isotopically light S, which appear to be in disagreement with model predictions. We propose that C grains are formed mostly from C-rich stellar material exposed to lower SN shock temperatures than the more common type X grains. In this scenario, extreme 32S enrichments observed in C grains may be explained by the presence of short-lived 32Si (τ1/2 = 153 yr) in the ejecta, produced by neutron capture processes starting from the stable Si isotopes. No mixing from deeper Si-rich material and/or fractionation of Si from S due to molecular chemistry is needed to explain the 32S enrichments. The abundance of 32Si in the grains can provide constraints on the neutron density reached during the SN explosion in the C-rich He shell material. The impact of the large uncertainty of the neutron capture cross sections in the 32Si region is discussed.