On the growth of carbonaceous grains in circumstellar envelopes

D. Krüger, A.B.C.D. Patzer and E. Sedlmayr

Astronomy & Astrophysics, 313, 891-896 (1996)

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Abstract:

We present a phenomenological description of relevant aspects of the grain surface chemistry on pre-existing carbonaceous seed particles. The production of radical surface sites is calculated by means of modified analogous gas-phase thermodynamic and reaction kinetic data. Our results suggest that surface growth processes mainly take place at sp^3 bonded carbon atoms rather than at the edges of graphitic plates or polycyclic aromatic hydrocarbons and that the resulting grain material will be amorphous diamond-like carbon. Furthermore, we argue that the sticking efficiency of the key growth species C_2H_2 at radical sites is high even for significant grain drift velocities. The dust growth rate will generally be proportional to the radical surface coverage.

Keywords:

dust growth - circumstellar matter - stars: carbon - stars: AGB - stars: mass loss