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S. Kwok, K. Volk (University of Calgary), B. Hrivnak (Valparaiso University)
One of the most interesting current unsolved problems in astrochemistry is the identification of the strong 21 \mum emission feature found in carbon-rich proto-planetary nebulae (Kwok, Volk, and Hrivnak, 1989, ApJ, 345, L51). As of 2001, 12 such sources have been discovered (Kwok 1999, IAU Symp.~191, p. 297). The 21-\mum feature is often accompanied by aromatic emission features at 3.3, 6.2, 7.7, and 11.3 \mum, as well as aliphatic emission features at 3.4 and 6.9 \mum (Hrivnak, Volk, and Kwok 2000, ApJ, 535, 275). These associations suggest that the 21 \mum feature may also originate from a carbonaceous material. Since the aromatic/aliphatic compounds and the 21-\mum feature bearing materials are all produced in the circumstellar envelope, it would be interesting to compare the spatial distributio ns of these emission features.
With the OSCIR instrument on the Gemini North telescope, we obtained mid-infrared images of two 21-\mum sources IRAS 07134+1005 and IRAS Z02229+6208 at four narrow band filters (10.3, 11.7, 12.7, 18.0, and 20.8 \mum). The emission shell (approximatel y 2 arcsec in size) is clearly resolved in IRAS 07134+1005 and marginally resolved in Z02229+6208. The relationship between the distribution of the aromatic and the 21-\mum emitting material is discussed.