碳星外流中MgS的凝聚
Condensation of MgS in outflows from carbon stars
摘要：
本文讨论了AGB尖端富碳恒星外流中MgS广泛凝聚的基本机制，旨在建立一个可用于恒星风尘埃形成模型计算的凝聚模型。通过一些热化学计算和对恒星风中颗粒生长动力学的详细分析，探讨了在碳星外流的化学环境中如何形成MgS的不同可能性。计算了具有MgS地幔的核幔颗粒的光学性质，以证明这种颗粒再现了所观察到的30 $μ$ m特征的结构。这些考虑得到了碳星周围拱星尘埃壳模型计算的补充。据认为，MgS是通过在碳化硅颗粒上沉淀形成的。这种形成机制解释了碳星周围尘埃壳中MgS凝聚的一些基本观测特征。在33度左右有一个弱的次峰... 36 $μ$ m被证明存在于某些情况下，如果MgS在SiC上形成涂层。
英文摘要：
The basic mechanism responsible for the widespread condensation of MgS in the outflows from carbon rich stars on the tip of the AGB is discussed with the aim of developing a condensation model that can be applied in model calculations of dust formation in stellar winds. The different possibilities how MgS may be formed in the chemical environment of outflows from carbon stars are explored by some thermochemical calculations and by a detailed analysis of the growth kinetics of grains in stellar winds. The optical properties of core-mantle grains with a MgS mantle are calculated to demonstrate that such grains reproduce the structure of the observed 30 $μ$m feature. These considerations are complemented by model calculations of circumstellar dust shells around carbon stars. It is argued that MgS is formed via precipitation on silicon carbide grains. This formation mechanism explains some of the basic observed features of MgS condensation in dust shells around carbon stars. A weak secondary peak at about 33 ... 36 $μ$m is shown to exist in certain cases if MgS forms a coating on SiC.
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