Radio continuum interferometry of dark clouds. II. A study of the physical properties of local newly formed H II regions
A radio continuum survey of dark clouds )Gilmore (Astron. J. 85, 894 (1980), preceding paper)) revealed only a few new regions of star formation. The observations of these individual regions are presented and discussed in this paper. The regions include S140 IR, S156, and Mon R2, as well as the dark cloud complexes in Perseus, Taurus, Orion, and Ophiuchus. The H II regions detected in the radio continuum have associated visible nebulosity and are excited by early B stars. However, five infrared sources thought to have the luminosity of early B stars were not detected in the radio continuum. These five sources showed high correlation with the presence of CO self-absorption, CO emission over a wide range of velocities, and type I OH masers, but an absence of coincident visible nebulosity and detectable radio continuum emission. Therefore, it is suggested that they represent an earlier evolutionary stage than those H II regions detected in the radio continuum. This first evolutionary state marks the presence of ''pre-emergent'' (with respect to the molecular cloud) cocoon stars. H II regions in the second evolutionary state are marked by the presence of detectable radio continuum emission, i.e., they are stronger than 10 mJy at 2695 MHz. They have associated visible nebulosity, are relatively large, and appear to be located at the edges of molecular clouds. We designate these as ''emergent edge'' H II regions. The fact that many young H II regions are edge H II regions implies that massive stars may be born near the edges of clouds, a phenomenon previously suggested by several other investigators. Comparison of the results of this survey with other investigators of H II regions and newly formed massive stars indicates that the radio continuum detectability of H II regions surrounding young massive cocoon stars is a function of the age and mass of the star.
- Research Organization:
- Astronomy Department, University of Maryland, College Park, Maryland 20742
- OSTI ID:
- 5209067
- Journal Information:
- Astron. J.; (United States), Journal Name: Astron. J.; (United States) Vol. 85:7; ISSN ANJOA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
Radio
& X-Ray Sources-- (-1987)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COSMIC RADIO SOURCES
ELECTROMAGNETIC RADIATION
GALAXIES
H2 REGIONS
INFRARED RADIATION
INTERFEROMETRY
MAIN SEQUENCE STARS
MILKY WAY
NEBULAE
PHYSICAL PROPERTIES
RADIATIONS
RADIOWAVE RADIATION
STAR EVOLUTION
STARS