Infrared Space Observatory Observations of the Unidentified 30 Micron Feature in Proto-Planetary Nebulae

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The intrinsic emission profile of the unidentified broad 30 mum emission feature is derived from Infrared Space Observatory (ISO) spectra of proto-planetary nebulae (PPNs). The feature is resolved into two components: a narrower feature at 26 mum and a broader feature at 33 mum. The intrinsic profiles of these two features and their varying strengths in PPNs are determined. The chemical origin of these features and the processes responsible for their changing strengths from asymptotic giant branch (AGB) stars to PPNs to planetary nebulae are discussed.