Ultracompact HII regions associated with massive star formation

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1988

OSTI ID:5151080

Wood, D O.S.

This dissertation establishes the physical properties of ultracompact (UC) HII regions and investigates their interaction with the interstellar medium. UC HII regions are small photoionized nebulae produced by massive stars embedded in clouds of molecular gas and dust. New observations have been made using the Very Large Array (VLA) at cm wavelengths and single dish telescopes at mm wavelengths. Data were also collected from the Infrared Astronomical Satellite (IRAS) and from the literature. It is shown that UC HII regions have electron densities {approx gt} 10{sup 4} cm{sup {minus}3}, emission measures {approx gt} 10{sup 7} pc cm{sup {minus}6} and diameters {approx lt} .01 pc. The VLA was used at 2 and 6 cm to identify 75 UC HII regions. Radio continuum brightness distributions with 0.4 inch resolution are presented in the form of contour plots. At high angular resolution five different morphologies were seen: spherical or unresolved (43%), cometary (20%), core-halo (16%), shell (4%) and irregular or multiply peaked (17%). Cometary UC HII regions may be produced by the bow shock of a star moving supersonically through the molecular gas. The total number of UC HII regions found is inconsistent with a UC HII region lifetime of <3 {times} 10{sup 4} years. It is shown that UC HII regions have a characteristic FIR flux density distribution that is very different from typical entries in the IRAS Point Source Catalog. A two-color selection criterion based on the known UC HII regions is developed and when applied to the entire PSC a total of 1708 embedded OB star candidates are found.

• Research Organization: Wisconsin Univ., Madison, WI (USA)
• OSTI ID: 5151080
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics &amp; Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COLOR
COSMIC DUST
COSMIC GASES
COSMIC RADIO SOURCES
DUSTS
ELECTROMAGNETIC RADIATION
ELECTRON DENSITY
FLUIDS
FLUX DENSITY
GASES
H2 REGIONS
INFRARED RADIATION
INTERACTIONS
INTERSTELLAR SPACE
MORPHOLOGY
NEBULAE
OPTICAL PROPERTIES
ORGANOLEPTIC PROPERTIES
ORIGIN
PHYSICAL PROPERTIES
RADIATIONS
RADIOWAVE RADIATION
SHOCK WAVES
SPACE
STAR EVOLUTION
STARS