标题： 钙粒包层初始内部结构对尘埃粒径分布的依赖性 显示英文标题

标题： Dependence of the initial internal structure of chondrule rim on dust size distribution

摘要： 在球粒陨石中的粗大物体，如球粒和CAIs，通常被细粒边（FGRs）覆盖。 FGRs可以在湍流星云中自由漂浮的球粒表面形成，同时也会发生尘埃聚集。 一项先前的研究报告称，附着在球粒上的尘埃种群的形态会影响FGRs的初始结构。 研究发现，如果单体颗粒附着在球粒上，较小的颗粒倾向于集中在球粒表面附近，FGRs表现出从底部到顶部的颗粒尺寸变粗。 然而，该研究没有考虑尘埃团块的时间生长对FGRs形成的影响。 在本研究中，我们计算了多分散单体颗粒的聚集及其在球粒上的附着。 可以识别出两种不同的尘埃聚集阶段：单体聚集阶段和类似BCCA的阶段。 在单体聚集阶段，当平均团块尺寸达到单体尺寸时，单体颗粒被纳入团块中。 在类似BCCA的阶段，团块以类似于单体尺寸颗粒的方式呈分形演化。 基于之前研究的结果，我们获得了球粒获得单体附着FGRs的必要条件，这些FGRs的颗粒尺寸变粗现象在一些球粒陨石中被观察到。 在与星际介质（ISM）相似的尺寸分布情况下，最大颗粒尺寸为$>$ $1$ $\mu$ 米时，广泛需要（$\alpha$ $<$ $10^{-3}$）用于单体吸积，而如果星云中的湍流强度非常弱（$\alpha$$<$ $10^{-5}$），则需要最大颗粒尺寸$\sim$ $10$ $\mu$ 米。 在大颗粒中具有较大质量分数的单体尺寸分布，可能是有效颗粒尺寸粗化的必要条件。 显示英文摘要

摘要： Coarse objects in chondrites such as chondrules and CAIs are mostly coated with fine-grained rims (FGRs). FGRs can be formed on the surface of free floating chondrules in a turbulent nebula, where dust aggregation also occurs. A former study has reported that the morphology of the dust populations accreting onto chondrules affects the initial structures of FGRs. It was revealed that, if monomer grains accrete onto chondrules, the smaller grains tend to accumulate near the surface of chondrules, and FGRs exhibit grain size coarsening from the bottom to the top. However, the study did not consider the effect of temporal growth of dust aggregates on FGRs formation. In this study, we calculate the aggregation of polydisperse monomer grains and their accretion onto chondrules. The following two different stages of dust aggregation can be identified: the monomer-aggregation stage and the BCCA-like stage. In the monomer-aggregation stage, monomer grains are incorporated into aggregates when the average aggregate size reaches the size of the monomer. In the BCCA-like stage, aggregates evolve fractally in a fashion similar to that of single size monomer grains. Based on the results of the previous study, we obtain the requisite conditions for chondrules to acquire monomer-accreting FGRs with grain size coarsening observed in some chondrites. In the case of similar size distribution as that of Inter Stellar Medium (ISM), the maximum grain size of $>$ $1$ $\mu$m is widely ($\alpha$ $<$ $10^{-3}$) required for monomer accretion, while if turbulent intensity in a nebula is extremely weak ($\alpha$ $<$ $10^{-5}$), a maximum grain size $\sim$ $10$ $\mu$m is required. The monomer size distributions having larger mass fraction in the large grains compared to ISM might be necessary for the effective grain size coarsening.