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M. F. Campbell, D. M. Clark (Colby C.), P. M. Harvey, D. F. Lester (U. Texas)
The complex of radio sources G34.3+0.2 A, B, C (the "cometary'' UC HII region), and D are associated with one of the brightest IRAS sources, IRAS 18507+1110. The IRAS PSC position is offset 26 \arcsec SE of component C, towards component D. In contrast, we have observed peaks at 47 and 95 \mum from the KAO which are consistent with the position of C, within their accuracy. IRAS HIRES images show that the 12 and 25 \mum peaks are centered on D, while the 60 and 100 \mum peaks are on centered C, with extended emission covering D. Our KAO maps at 47 and 95 \mum show sharp central peaks with extended emission surrounding them. The extended emission at 47 \mum is similiar in extent to that at 95 \mum, which is unusual.
A mid-ir spectrum from the ISO Archive in a 24 \arcsec beam centered on the PSC position shows PAH features. In contrast, Faison et al. (1998) presented a spectrum in a 9 \arcsec beam centered on C which shows very deep silicate absorption. Campbell et al. (2000) modeled mid-ir emission in narrowband images from C as due to hot dust surrounded by a cooler silicate absorbing cloud. We propose that the IRAS 12 and 25 \mum emissions, and part of the IRAS 60 \mum emission are due to PAHs and small grains. The sharp emission peaks at 47 and 95 \mum are due to silicate dust grains, perhaps the same grains which are seen in absorption in the models of Campbell et al. for mid-ir emission from component C. The nature of the extended emission seen on the KAO at 47 and 95 \mum is unclear.
This work was supported by NASA Grants 2-67 and 2-546 and by Colby College.
Campbell, M.F. et al. 2000, ApJ, 536, 816 Faison, M. et al. 1998, ApJ, 500, 280
The author(s) of this abstract have provided an email address for comments about the abstract: mfcampbe@colby.edu