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Title:
The morphologies and physical properties of ultracompact H II regions
Authors:
Wood, Douglas O. S.; Churchwell, Ed
Affiliation:
AA(Washburn Observatory, Madison, WI), AB(Washburn Observatory, Madison, WI)
Publication:
Astrophysical Journal Supplement Series (ISSN 0067-0049), vol. 69, April 1989, p. 831-895. (ApJS Homepage)
Publication Date:
04/1989
Category:
Astrophysics
Origin:
STI
NASA/STI Keywords:
H Ii Regions, Radio Sources (Astronomy), Stellar Mass, Very Large Array (Vla), Cartesian Coordinates, Data Reduction, Infrared Astronomy Satellite, Infrared Radiation, Molecular Clouds, Morphology, Physical Properties, Radio Astronomy
DOI:
10.1086/191329
Bibliographic Code:
1989ApJS...69..831W

Abstract

Seventy-five ultracompact (UC) H II regions are observed 0.4 arcsec resolution at 2 and 6 cm using the Very Large Array, and their radio continuum brightness distributions are presented in the form of contour plots. H-76 alpha recombination line profiles are obtained for six sources using a 4.4 arcsec beam. It is shown that these UC H II regions have electron densities of at least approximately 10,000 per cubic cm, emission measures of at least approximately 10 to the 7th pc cm to the -6th, and diameters no more than approximately 0.1 pc, consistent with their being small photoionized nebulae produced by O and B stars embedded in clouds of molecular gas and dust. At high angular resolution five different morphologies of the ionized gas are seen: spherical or unresolved (43 percent), cometary (20 percent), core-halo (16 percent), shell (4 percent), and irregular or multiply peaked (17 percent). Evidence is presented that the UC H II region phase of a massive star must last for a significant fraction of its main-sequence lifetime.

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