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C. Covatto, P. A. Aannestad (ASU)
A model of a wind driven by radiation pressure on dust is developed. The wind is composed of gas and dust and is treated as a two component fluid. Equations of motion for the gas and dust are coupled through a collision term which accounts for the transfer of momentum between the two fluids. Amorphous carbon dust is assumed to form instantaneously near the sonic point of the flow with either a power law or log-normal size distribution. The grain size distribution may be modified in several ways. Nonthermal sputtering of grains may occur if the dust drift velocity exceeds a velocity threshold which depends upon the surface binding energy of the dust material as well as the the mass of the impinging gas atoms. Chemical sputtering of grains may also modify the dust grain size distribution if the temperature of the dust grains falls within a specific temperature range. To study the effects of nonthermal and chemical sputtering, the size distribution of dust grains is calculated at every point in the flow. Results show that nonthermal sputtering can be important when the luminosity of the central star exceeds {\rm few} \times 104 L\sun and that chemical sputtering can be important for stellar effective temperatures ~2000 K and stellar luminosities ~104 L\sun. This work was funded in part by a NASA Space Grant.