Stardust grains that originated in ancient stars and supernovae are recovered from meteorites and carry the detailed composition of their astronomical sites of origin. We present evidence that the majority of large ($\mu$m-sized) meteoritic silicon carbide (SiC) grains formed in C-rich asymptotic giant branch (AGB) stars that were more metal-rich than the Sun. In the framework of the slow neutron-captures (the s process) that occurs in AGB stars the lower-than-solar 88Sr/86Sr isotopic ratios measured in the large SiC grains can only be accompanied by Ce/Y elemental ratios that are also lower than solar, and predominately observed in metal-rich barium stars - the binary companions of AGB stars. Such an origin suggests that these large grains represent the material from high-metallicity AGB stars needed to explain the s-process nucleosynthesis variations observed in bulk meteorites (Ek et al. 2020). In the outflows of metal-rich, C-rich AGB stars SiC grains are predicted to be small ($\simeq$ 0.2 $\mu$m-sized); large ($\simeq$ $\mu$m-sized) SiC grains can grow if the number of dust seeds is two to three orders of magnitude lower than the standard value of $10^{-13}$ times the number of H atoms. We therefore predict that with increasing metallicity the number of dust seeds might decrease, resulting in the production of larger SiC grains.

中文翻译：

---

富金属AGB星中大陨石碳化硅星尘颗粒的成因

起源于古代恒星和超新星的星尘颗粒是从陨石中回收的，并带有它们起源天文地点的详细组成。我们提供的证据表明，大多数大型（$\mu$m 大小）陨石碳化硅 (SiC) 颗粒形成于富含 C 的渐近巨星分支 (AGB) 恒星，这些恒星比太阳的金属含量更高。在 AGB 星中发生的慢中子俘获（s 过程）的框架中，在大 SiC 晶粒中测量的低于太阳的 88Sr/86Sr 同位素比率只能伴随着同样较低的 Ce/Y 元素比率比太阳，并且主要在富含金属的钡星中观察到 - AGB 星的双星伴星。这样的起源表明，这些大颗粒代表了来自高金属度 AGB 恒星的物质，需要解释在大块陨石中观察到的 s 过程核合成变化（Ek et al. 2020）。在富含金属、富含 C 的 AGB 星的流出中，预计 SiC 晶粒很小（$\simeq$ 0.2 $\mu$m 大小）；如果尘埃种子的数量比标准值 $10^{-13}$ 乘以 H 原子数量低两到三个数量级，那么大（$\simeq$ $\mu$m 大小）的 SiC 晶粒可以生长. 因此，我们预测随着金属丰度的增加，尘埃种子的数量可能会减少，从而产生更大的 SiC 晶粒。如果尘埃种子的数量比标准值 $10^{-13}$ 乘以 H 原子数量低两到三个数量级，那么大（$\simeq$ $\mu$m 大小）的 SiC 晶粒可以生长. 因此，我们预测随着金属丰度的增加，尘埃种子的数量可能会减少，从而产生更大的 SiC 晶粒。如果尘埃种子的数量比标准值 $10^{-13}$ 乘以 H 原子数量低两到三个数量级，那么大（$\simeq$ $\mu$m 大小）的 SiC 晶粒可以生长. 因此，我们预测随着金属丰度的增加，尘埃种子的数量可能会减少，从而产生更大的 SiC 晶粒。