2011ApJ...729..121S

A sample of 90 Galactic S stars observed by the Spitzer Space Telescope includes two sources with unusual low-contrast spectral structure between 7 and 14 µm. The most likely estimate of the spectral continuum leads to the identification of molecular emission features from SiS at 7 and 13-14 µm. The spectra also show what is best described as featureless excess emission, most likely from iron dust but possibly from amorphous carbon, as well as an emission feature from amorphous alumina dust peaking at 11-12 µm. The spectra show long-wavelength excesses from cool dust grains in an extended envelope and additional emission features of unknown origin.