Emission features in IRAS low-resolution spectra of MS, S and SC stars

The authors find a progression of emission features due to dust grains in the 8 - 22 μm region of IRAS low-resolution spectra of MS, S, and SC stars that parallels their increasing C:O ratio and s-process enhancement. Strong S stars usually show a 9 - 14 μm emission feature which peaks around 10.8 μm, whereas mild S or MS stars show a variety of features ranging from the typical 10 μm silicate emission to a three-component feature, to the 10.8 μm S star feature. SC stars show either the S star feature or the SiC feature. The infrared excesses in the 8 - 22 μm region correlate very strongly with the period of Mira S, MS, and SC variables. The excesses also correlate with mass loss rate for these stars.