Modelling of oxygen-rich envelopes using corundum and silicate grains

A set of 31 oxygen-rich stars has been modelled using corundum and silicate grains. These stars were selected according to their dust-envelope class, as suggested by Little-Marenin and Little in 1990. Then 16 stars classified as Sil were modelled using silicate grains; 10 Broad class stars using corundum (Al₂O₃) grains; and 5 ' Intermediate ' class stars using two kinds of grain simultaneously: corundum and silicate. The temperature of the central stars and some characteristics of their circumstellar envelopes such as their extinction opacities and extensions were determined by fitting the flux curves. The corundum/silicate ratios as well as the energy distributions and temperature laws have been obtained. Based on the authors' results they suggest the existence of chemical and structural evolution of the modelled circumstellar dust shells. The temperature of the central stars and the temperature of the hottest grains decrease from Broad to Intermediate to Sil classes, while the inner radii and optical depths increase in this sequence.