Two-fluid models for stationary dust driven winds: II. The grain size distribution in consideration of drift

D. Krüger and E. Sedlmayr

Astronomy & Astrophysics, 321, 557-567 (1997)

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Abstract:

A multicomponent method for the description of the evolution of the grain size distribution in consideration of a size dependent grain drift and growth rate is applied in order to model dust driven winds around cool C-stars.

Grain drift introduces several modifications concerning dust growth: On the one hand the residence time in the region of efficient growth is reduced, on the other hand the growth efficiency is higher due to an increased collisional rate. For carbon grains the surface density of radical sites is increased, but on the other hand there is a reduction of the sticking efficiency of the growth species for drift velocities larger than sim 5 km s^{-1}. Furthermore, nonthermal sputtering may become relevant for high drift velocities.

It is found that the consideration of drift results in a considerable distortion of the size distribution as compared to the case of zero drift velocity. Generally, there are less, but larger grains if drift is included.

Keywords:

stars: mass loss - circumstellar matter - stars: AGB - stars: carbon - hydrodynamics