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B. J. Hrivnak (Valparaiso University), K. Volk, S. Kwok (U. Calgary)
In a previous paper (Hrivnak, Volk, & Kwok 1999, BAAS, 31, 846; 1999, ApJ, accepted), we presented spectra from 2-45 \mum of seven carbon-rich proto-planetary nebulae (PPN), based upon our ISO SWS observations. We have extended this study to include three more carbon-rich PPN, IRAS 22272+5435, 23304+6147, and 19500-1709, based upon archival ISO spectra. All three possess the "21 \mum" and "30 \mum" features. In IRAS 22272+5435 and 19500-1709, we also find the new "26 \mum" feature, seen in many of the carbon-rich PPN discussed in our previous study. PAH features are also present.
We have fitted their spectral energy distributions using a dust, radiative-transfer model, assuming the underlying continuum is due to amorphous carbon grains. From this we find the size of the circumstellar shells, the dust temperatures, and the mass loss rates. We also calculate the strength of the various emission features.