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LibraryG.C. Sloan (NASA Ames), T.L. Hayward (Cornell), J.D. Bregman, L.J. Allamandola (NASA Ames)
1996, BAAS, 28, 1417
We present long-slit spectroscopy of the Orion Bar at 8-13 µm, obtained 1996 September 28-30 at the 5-m Hale telescope of Palomar Observatory, using Spectro-Cam 10. The Bar is a photo-dissociation region viewed edge-on, so the layering produced from the attenuation of the UV radiation field is easily distinguishable to the observer. We oriented the spectrometer slit perpendicular to the Bar in order to trace the behavior of the PAH emission features at 8.6, 11.2, and 12.7 µm and their dependence on the UV field. The slit position used is identical with the 3 µm data published by Sloan et al. (1997, ApJ, 474, in press), allowing us to directly compare the behavior of the PAH features in these two spectral regions.
The 11.2 µm emission band dominates the mid-infrared spectrum, just as the 3.29 µm band dominates the 3 µm spectrum. Both are produced from aromatic C-H bonds, but the intensity of the 11.2 µm band decreases more slowly into the neutral region. Its behavior resembles that of the 3.40 and 3.51 µm bands and the 3 µm PAH plateau, suggesting a common carrier for all of these bands. This finding is consistent with the hypotheses that larger PAHs emit more strongly at 11.2 µm and that they also produce the 3 µm PAH plateau. Compared to the 8.6 µm feature, the 11.2 µm feature survives further into the ionized region. This finding is inconsistent with suggestions that ionized PAHs will show an enhancement at 8.6 µm relative to 11.2 µm.
Last modified 27 May, 2008. © Gregory C. Sloan and others.