Where have all the interstellar silicon carbides gone?
Where have all the interstellar silicon carbides gone?
复制标题
星际碳化硅都到哪里去了？
DOI：
10.1093/mnras/stab3175
复制
发表时间：
2021
影响因子：
4.8
通讯作者：
Zhou, C T
中科院分区：
文献类型：
--
作者：
Chen, Tao;Xiao, C Y;Li, Aigen;Zhou, C T
对富碳演化恒星的Si-C伸展的11.3发射特征的探测表明，碳化硅尘埃颗粒在碳星的流出中凝聚。碳化硅尘埃可能是星际尘埃的重要组成部分，因为人们普遍认为碳星向星际介质(ISM)注入了相当数量的尘埃。在原始陨石中发现了恒星起源的太阳前碳化硅颗粒，也支持了ISM中碳化硅尘埃的存在。然而，在ISM中从来没有看到过碳化硅的11.3吸附特性，经常会提到碳化硅的氧化破坏。在这项工作中，我们在分子动力学模拟和密度泛函理论计算的基础上，定量地探讨了星际碳化硅粉尘通过氧化的破坏。我们发现，氧原子与碳化硅分子和碳化硅团簇的反应是放热的，会导致CO的损失。然而，即使这可以推断为散装的碳化硅粉尘，通过氧化的碳化硅粉尘的破坏速度仍然可能比(目前认为的)碳星喷射率要小得多。因此，ISM中缺乏碳化硅粉尘的11.3吸收特性仍然是一个谜。一个可能的解决方案可能在于目前认为的恒星注入碳化硅的速度(可能被高估了)和/或碳化硅尘埃的大小(实际上可能比亚微米小得多)。
The detection of the 11.3emission feature characteristic of the Si–C stretch in carbon-rich evolved stars reveals that silicon carbide (SiC) dust grains are condensed in the outflows of carbon stars. SiC dust could be a significant constituent of interstellar dust since it is generally believed that carbon stars inject a considerable amount of dust into the interstellar medium (ISM). The presence of SiC dust in the ISM is also supported by the identification of pre-solar SiC grains of stellar origin in primitive meteorites. However, the 11.3absorption feature of SiC has never been seen in the ISM, and oxidative destruction of SiC is often invoked. In this work, we quantitatively explore the destruction of interstellar SiC dust through oxidation based on molecular dynamics simulations and density functional theory calculations. We find that the reaction of an oxygen atom with SiC molecules and clusters is exothermic and could cause CO-loss. Nevertheless, even if this is extrapolable to bulk SiC dust, the destruction rate of SiC dust through oxidation could still be considerably smaller than the (currently believed) injection rate from carbon stars. Therefore, the lack of the 11.3absorption feature of SiC dust in the ISM remains a mystery. A possible solution may lie in the currently believed stellar injection rate of SiC (which may have been overestimated) and/or the size of SiC dust (which may actually be considerably smaller than submicron in size).