Silicate and related dust emission in stars on the asymptotic giant branch

The Low-Resolution Spectrometer (LRS) on the Infrared Astronomical Satellite (IRAS) produced a rich set of spectra from oxygen-rich circumstellar dust shells. Little-Marenin and Little found that in addition to the classic 10 micron emission feature due to silicate dust, many oxygen-rich shells also produce components at 11 and 13 microns. Some shells exhibit only a broad, low-contrast feature which peaks longward of 11 microns and has been attributed to alumina dust. We have modified the classification method of Little-Marenin and Little, applied it to a large sample of bright oxygen-rich variables on the asymptotic giant branch, and undertaken a study of the 13 micron emission feature and the sources which produce it. We present some of the results of these studies.