A Spitzer/Infrared Spectrograph Spectral Study of a Sample of Galactic Carbon-Rich Proto-Planetary Nebulae

Document Type


Publication Date



Recent infrared spectroscopic observations have shown that proto-planetary nebulae (PPNs) are sites of active synthesis of organic compounds in the late stages of stellar evolution. This paper presents a study of Spitzer/Infrared Spectrograph spectra for a sample of carbon-rich PPNs, all except one of which show the unidentified 21 mu m emission feature. The strengths of the aromatic infrared band, 21 mu m, and 30 mu m features are obtained by decomposition of the spectra. The observed variations in the strengths and peak wavelengths of the features support the model that the newly synthesized organic compounds gradually change from aliphatic to aromatic characteristics as stars evolve from PPNs to planetary nebulae.