INDUCED NUCLEATION OF CARBON DUST IN RED GIANT STARS

This study quantitatively tests the proposed model of induced nucleati on of carbonaceous grains in carbon-rich red giant stars. Induced nucl eation is the process of grain growth initiated by the presence of rea ctive surfaces provided by seed particles. The numerical study was per formed using a detailed chemical kinetic model of carbon deposition, g rain coagulation, and homogeneous nucleation of polycyclic aromatic hy drocarbons (PAHs). The model uses a method of moments to keep track of developing grain population in the forming dust shell. We test the ef ficiency of grain formation for large ranges of dust shell parameters typical for carbon stars. Our model is capable of producing a range of optically thick and thin dust shells in carbon stars. Results are in accord with IRAS spectral classes of carbon stars. The resulting compo site grains produced are consistent with those recently found in ancie nt meteorites. This model also provides a realistic explanation for hi gh abundances of polycyclic aromatic hydrocarbons (PAHs) in the inters tellar medium and some planetary nebulae.