L.B.F.M. Waters & F.J. Molster
Astronomical Institute 'Anton Pannekoek' University of Amsterdam Kruislaan 403 NL-1098 SJ Amsterdam
The ISO-SWS and LWS spectra of circumstellar dust shells of oxygen-rich stars (both young and evolved) show a very rich harvest of new solid state bands. These bands are identified with crystalline silicates. Comparison with laboratory data indicates the presence of olivines and pyroxenes, probably Mg-rich and Fe-poor. These discoveries have implications for our understanding of grain formation and mass loss in evolved cool stars: the crystalline silicates for the frist time allow a detailed inventory of the kind of silicates that condense in the outflows of AGB stars and Red Supergiants, and they give information about the thermal and chemical processing of the grains after formation. The new emission bands also give important new clues to the mass loss history and chemical evolution of objects as diverse as AGB stars and the most massive stars in galaxies, Luminous Blue Variables.