Physical and Chemical Evolution of Dust Aggregate and their Physical Properties in the Primordial Solar Nebula

在该赠款资助期间，对以下主题进行了调查。(1)散射特性及其对尘埃聚集体结构和化学组成的依赖性：采用离散偶极子近似研究了散射特性对尘埃聚集体结构和化学组成的依赖性。结果表明，前向散射光的行为清楚地反映了尘埃聚集体的总体尺寸和平均化学成分，而后向散射光的行为则对尘埃聚集体表面粗糙度敏感。(2)原始太阳星云中尘埃聚集体的形成过程：讨论了一种自洽处理原始太阳星云中尘埃聚集体的形成过程及其结构的方法，但没有进行详细的计算。(3)彗星尘埃中硅酸盐成分的结晶度：根据格林伯格的星际尘埃模型，研究了彗星尘埃中结晶硅酸盐成分的来源，并与P/Halley彗星的观测结果进行了比较，估计其结晶成分的体积约为10 ~ 20%。这一估算值可以通过在星际尘埃到彗星尘埃演化框架内发展的硅酸盐组分结晶机制来实现。(4)天体物理环境中尘埃颗粒的形成研究了演化恒星星周包层中尘埃颗粒的形成。研究了由SiC核和碳幔组成的核幔颗粒的形成过程，以重现对碳星观察到的11.3 μ m特征。在富氧的AGB星中，观测到的13 μ m特征可以归因于由Al_2O_3核和硅酸盐地幔组成的尘埃颗粒。讨论了Ia超新星中尘埃颗粒形成的可能性。

The following subject had been investigated during the period supported by this grant.(1) Scattering properties and their dependence on the strusture and the chemical composition of dust aggregates : The discrete dipole approximation was applied to investigate the dependence of the scattering properties on the structure and the chemical composition of dust aggregates. The results show that the behavior of forward scattered light clearly reflects the overall size and the mean chemical composition of dust aggregates, otherwise the backward scattering is sensitive to the roughness of surface layr of dust aggregates.(2) Formation process of dust aggregates in the primordial solar nebula : A method was discussed to treat the formation process and the resulting structure of dust aggregates self-consistently in the primordial solar nebula, but the detailed calculation was not performed.(3) The crystallinity of silicate component in comet dust : On the basis of the Greenberg's interstellar dust model, the origin of crystalline silicate component in cometary dust was investigated ; in comparison with the observation of comet P/Halley the crystalline component was estimated to be the order of 10 to 20% in volume. The estimated value can be realized by the mechanism for the crystallization of silicate component developed in the framework of the evolution from interstellar dust to cometary dust.(4) Formation of dust grains in astrophysical environments ; The formation of dust grains was investigated in circumstellar envelopes of evolved stars. The formation process of core-mantle grains consisting of a SiC core and a carbon mantle was investigated to reproduce the 11.3mum feature observed towards carbon stars. In oxygen-rich AGB stars the observed 13mum feature can be attributed to dust grains consisting of a Al_2O_3 core and a silicate mantle. The possibility of the formation of dust grains in Ia supernovae was discussed.