The Formation and Growth of Carbon Particles in the Atmospheres of Mira Variables

In light of recent evidence that the oxygen to carbon ratio in Mira variables may be only slightly greater than 1.0, molecular dissociative equilibrium calculations are made using an O/C ratio of 1.03, O/H ratio of 10 ^–4 and Si/H ratio of $$4 \times 10^{-5}$$ to determine the region of the P, T plane in which carbon is super-saturated and particle formation is possible. A system of equations describing the formation and growth of carbon particles throughout the temperature cycle of a variable star is solved for a gas undergoing temperature variations characteristic of those occurring in the atmospheres of Mira variables. The results show that a large number of extremely small particles will form and that the extinction due to these particles is several orders of magnitude greater than the expected atomic and molecular extinction.