SIMBAD references

We have studied the chemical composition of the silicates around the two massive protostellar objects RAFGL 7009S (IRAS 18316-0602) and IRAS 19110+1045. The silicate features of both sources are similar. The position and shape of the 9.6 and 18µm silicate bands coincide with those of amorphous pyroxene-type silicates. We find that the silicate features cannot be reproduced with compact pyroxene grains containing magnesium and iron. An admixture of iron, aluminium and some degree of porosity is necessary to reproduce respectively the red wing of the 18µm band, the plateau between the two silicate bands and the widths of the bands. The iron is to be found in the form of Fe-rich pyroxenes, also containing small amounts of calcium, and in iron-oxides. Better fits are obtained with aluminium incorporated into the silicate structure (in aluminosilicates) than for aluminium in oxides such as Al₂O₃. The compositions we propose are in agreement with cosmic elemental abundance constraints. No crystalline material is observed in either source and we find that at most 1-2% of the silicate mass could be crystalline in these sources.