AAS 201st Meeting, January, 2003
Session 112. The ISM: Clouds and Regions
Poster, Thursday, January 9, 2003, 9:20am-4:00pm, Exhibit Hall AB

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[112.01] Morphologies and Physical Parameters of a Large Sample UCHII Regions

C. G. De Pree, L. E. Davis, A. Mercer (Agnes Scott College), D. Wilner (Center for Astrophysics)

We have observed the massive star forming regions W49A and Sgr B2 with the Very Large Array (VLA) at resolutions as high as 0.04 arcseconds, corresponding to a physical scale of a few hundred AU. We have assigned a morphological type to each of the 90+ compact and ultracompact (UC) HII regions in these regions using the classification scheme first defined by Wood & Churchwell (1989). In their survey of 75 Galactic HII regions, Wood & Churchwell found that 20 the UCHII regions observed were cometary, 4 shell-like, and the remainder were irregular, spherical/unresolved or core-halo sources. A number of recent observations, including those of Sgr B2 and W49A, have motivated modifications to the original classification scheme. In this work, we describe the proposed modified scheme, the criteria used in the classification of sources, and the percentage of each morphology found in Sgr B2 and W49A. The morphological types are: (1) Asymmetrically Bright Shell (ASB), (2) Bipolar, (3) Cometary, (4) Core-Halo, (5) Irregular, and (6) Spherical or Unresolved. We find that about 19 and the remainder core-halo, irregular, and spherical or unresolved. We examine the relationship between source morphologies and physical parameters, including measured radio recombination line widths, and we describe how this work forms a starting point for planned hydrodynamic simulations of the evolution of UCHII regions in high density environments.

This research is supported by a grant from the National Science Foundation (AST-0206103).

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