Condensation Calculations in Circumstellar Shells for Different C/O Ratios

Abstract

We have performed some equilibrium calculations using a modified form of the computer code SOLGASMIX to calculate the abundances of a number of important gas phase and condensed phase species at temperatures below 2000K which are relevant to very cool stellar atmospheres and circumstellar shells. Calculations have been done for a number of different C/O ratios from oxygen rich to carbon rich, and the condensation of grains can significantly alter the C/O ratio of the gas phase, which can have a large effect on a number of molecular species. It was found that for some moderately oxygen rich mixtures the condensation of silicates can substantially enhance the abundance of gas phase species like HCN which was looked at in some detail.