Astronomy and Astrophysics – Astrophysics
Scientific paper
Feb 1988
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988apj...325..694w&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 325, Feb. 15, 1988, p. 694-698.
Astronomy and Astrophysics
Astrophysics
22
Emission Spectra, Flux Density, H Ii Regions, Millimeter Waves, B Stars, Interstellar Matter, Microwave Spectra, O Stars, Star Formation
Scientific paper
Three-millimeter continuum observations of 33 suspected ultracompact (UC) H II regions are reported. Twenty-eight sources were detected, about half of which had not previously been observed at 3 mm. These observations demonstrate that UC H II regions are bright at millimeter wavelengths and have very high emission measures. Because of this, and because UC H II regions are often associated with diffuse free-free emission, they are more easily detected at millimeter than at centimeter wavelengths. All the sources in the sample with distance estimates correspond to ionization by O6 stars or hotter. To obtain an unbiased sample of UC H II regions ionized by a single B0 star or hotter a detection limit of about 1 mJy is required. The fraction of stellar ionizing photons absorbed by dust is typically a 0.5 or more. Some of the sources reported here are small and bright enough to serve as flux and pointing calibrators at millimeter wavelengths.
Churchwell Edward
Salter Christopher J.
Wood Douglas O. S.
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