Small molecular carbide clusters as precursors of dust particles in extended atmospheres of AGB stars

A. Beate C. Patzer, Ch. Chang, S. Gebauer & D. Suelzle

Zentrum fuer Astronomie und Astrophysik, Germany

In circumstellar environments around cool, late-type stars on the asymptotic giant branch (AGB) dust particles are effectively formed via the formation and subsequent growth of small molecular clusters in the gas phase. The details of the dust formation process and the nature of the condensed material depend decisively on the chemical composition as determined by the elemental mixtures of the circumstellar envelopes. As verified by many studies of pre-solar carbide grains enclosed in meteorites dust grains formed in circumstellar outflows of carbon-rich AGB stars are a mixture of several chemical elements such as silicon or titanium in addition to the main component carbon. In this contribution we focus on the investigation of the properties of small molecular carbide clusters, which have been estimated within density functional theory (DFT) approaches. The molecular properties, thus obtained, are necessary prerequisites for the study of dust nucleation in circumstellar environments of AGB stars to determine the required data of the mircophysical processes involved. Implications regarding the formation of dust particles especially under carbon-rich conditions are discussed.

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