The morphologies of ultracompact HII regions in W49A and sagittarius B2: The prevalence of shells and a modified classification scheme

被引:26
作者
De Pree, CG
Wilner, DJ
Deblasio, J
Mercer, AJ
Davis, LE
机构
[1] Agnes Scott Coll, Dept Phys & Astron, Decatur, GA 30030 USA
[2] Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA
[3] Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA
[4] Univ Florida, Dept Astron, Bryant Space Sci Ctr 211, Gainesville, FL 32611 USA
关键词
HII regions; instrumentation : interferometers; ISM : individual (Sagittarius B2; W49N); techniques : interferometric;
D O I
10.1086/430738
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
We have used Very Large Array (VLA) observations of the massive star-forming regions W49A and Sgr B2, obtained with resolutions from 2.&DPRIME; 0 to 0.&DPRIME; 04, to classify the morphologies of nearly 100 ultracompact (UC) H II regions. These high-resolution, multifrequency, multiconfiguration VLA observations motivate us to make several modifications of the existing morphological classification scheme for UC H II regions. In this work, we describe the modified morphology scheme and the criteria used in source classification. In particular, we drop the "core-halo" classification, add a "bipolar" classification, and change the shell classification to "shell-like." We tally the percentage of each morphology found in the Sgr B2 and W49A regions and find broad agreement with the Galactic plane surveys in the distribution of morphologies for most types. However, we find that nearly a third of the sources in these regions are shell-like, which is a higher percentage by nearly a factor of 10 than found in the surveys of Galactic plane star-forming regions by Wood & Churchwell and Kurtz et al. This difference may be due to physical differences in the environments of these two extreme star-forming regions. Alternatively, differences in observational technique may be responsible.
引用
收藏
页码:L101 / L104
页数:4
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