The morphologies and physical properties of ultracompact H II regions

Details The morphologies and physical properties of ultracompact H II regions The morphologies and physical properties of ultracompact H II regions

Apr 1989

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989apjs...69..831w&link_type=abstract

Astrophysical Journal Supplement Series (ISSN 0067-0049), vol. 69, April 1989, p. 831-895.

Astronomy and Astrophysics

Astronomy

633

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

Scientific paper

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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