INORGANIC DUST FORMATION IN ASTROPHYSICAL ENVIRONMENTS

The problem of inorganic dust formation is discussed for the condition s of cool late-type giants and supergiants having an oxygen rich eleme nt composition. Particular emphasis is put on the formation of the pri mary condensates, i.e., the first kind of grains forming from the gas phase. By explorative chemical equilibrium discussion it has been show n that titanium oxides, especially TiO2 molecules, are the most probab le candidates to nucleate first. Though SiO is by far the most abundan t reacting oxygen bearing species it can usually be ruled out at high temperatures, because effective condensation takes place only below 60 0 K under typical M star conditions. The situation regarding the nucle ation of aluminium bearing molecules to form corundum is not as clear. Though corundum has an extremely high stability the constituting alum inium oxides are much less stable at temperatures above the onset of T iO2 condensation. Therefore, it might be argued that corundum is also not likely to constitute the first condensate in the outflows of M sta rs.