Investigation of MgO as a candidate for the primary nucleating dust species around M stars

The possibility of magnesium oxide being the first species to nucleate in the cooling outflows around M stars has been investigated. By treating the formation of the seed nuclei as a homogeneous nucleation problem and using molecular dynamics data obtained with the ‘compressible ion potential’ for MgO, free energy calculations are performed to obtain an estimate of the population densities of MgO clusters of various sizes. It is found that a free energy barrier of at least hundreds of kBT would need to be climbed in order for MgO to nucleate in significant amount in typical circumstellar shells, hence ruling out MgO as a realistic candidate for the primary nucleating dust species. This is in agreement with a similar conclusion reached in earlier studies, although the present calculations are based on a much more robust potential model for MgO.