Chemical evolution of carbonaceous materials in the last stages of stellar evolution

Abstract

The out-of-plane bending modes of aromatic C-H bond at 11.3, 12.1, 12.4, and 13.3 mu m were detected in the ISO SWS spectra of the proto-planetary nebulae IRAS 07134+1005 and IRAS 22574+6609. In addition, unidentified emission features at 17.8, 18.9, and 19.1 mu m were detected in the SWS01 and SWS06 spectra of IRAS 07134+1005. The similar strengths of the 12.1, 12.4, and 13.3 mu m features relative to the 11.3 mu m feature, together with the presence of strong aliphatic CH bands at 3.4 and 6.9 mu m, demonstrate a lower aromaticitiy of the emitting material, compared to those at the later planetary nebulae stage. This suggests a chemical and physical evolution of the carbonaceous dust during the transition between these two phases. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands and the United Kingdom) and with participation of ISAS and NASA