Published online by Cambridge University Press: 04 August 2017
The existence of circumstellar dust in late-type stars is connected with stellar pulsations since periodic shocks accompanying pulsations seem to be the most probable mechanism of the gas density increase needed for condensation of dust particles in outer layers of the stellar atmosphere. Most abundant solid materials formed in O-rich stars are forsterite (or enstatite), silicon monoxide and iron, whereas in C-rich stars these are carbon, silicon carbide, magnesium sulphur and iron. Application of the homogeneous nucleation theory shows that condensation proceeds at extremely high departures from thermal equilibrium due to a very long time between collisions of condensable monomers. The most efficient mechanism of destruction of dust grains is thermal evaporation caused by variations of the stellar effective temperature.