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Session 106 - HII Regions and Ultracompact HII Regions.
Display session, Thursday, January 16
The NGC 7538 region contains a number of massive, young stellar objects, including the embedded infrared sources IRS 1, IRS 2, and IRS 3. We have obtained high-resolution images of the area surrounding these sources in the 2.12 \mum (v=1-0 s) line of molecular hydrogen, and in the 1.64 \mum line of [FeII].
A shell-like structure of shocked material is observed surrounding the compact HII region associated with IRS 2. The [FeII] and H_2 emission are resolved from one another, even along bright ridges one would normally associate with shock fronts. We discuss three scenarios under which the observed excitation might occur: (1) expansion of the HII region into its parent cloud, (2) collision of a high- velocity stellar wind with the dense material bounding the HII region, and (3) the passing of a fast, dissociative shock succeeded in time by expansion of the HII region. We assess the validity of each scenario in light of observed emission line strengths, with emphasis on necessary gas temperatures and gas-phase iron abundance.
Our observations were made using the University of Rochester 3rd Generation Infrared Camera and the Naval Research Laboratory/National Air and Space Museum Fabry-Perot Interferometer at the Wyoming Infrared Observatory 2.3 m telescope.
Program listing for Thursday