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https://hdl.handle.net/2142/70671
Description
Title
Orion B--Anatomy of a Star-Forming Region
Author(s)
Barnes, Peter John
Issue Date
1988
Doctoral Committee Chair(s)
Crutcher, Richard M.
Department of Study
Astronomy
Discipline
Astronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Astronomy and Astrophysics
Abstract
The compact HII region/molecular cloud Orion B was observed with the VLA in the radio continuum and OH absorption line at a frequency of 1667 MHz, in the near-infrared continuum and H$\sb2$ emission line at a wavelength of 2 $\mu$m, and in several millimeter-wavelength molecular transitions (of HCO$\sp+$, SO, H$\sp $CN, and HC$\sp $N) with the Hat Creek Array.
The VLA continuum map has an integrated flux density of 59 $\pm$ 2 Jy, and we estimate that the total flux density is 63 $\pm$ 4 Jy at this frequency. This map reveals two spectacular filamentary loops just north of a very sharp, although resolved, ionization front (IF). In OH absorption maps, the eastern loop (EL) shows up near the velocity of the Zeeman-split OH in such a way as to suggest expansion, and a high optical depth cloud appears in the north central part of the nebula at the velocity of the main OH absorption. The infrared source IRS 2, with a strong stellar wind and a location within the EL, is deduced to be the cause of this loop. The IR observations reveal many new sources which together may supply the missing ionizing flux for the nebula. The IF is traced by the H$\sb2$ line emission.
In the dense molecular core the HCO$\sp+$ line maps show a centrally located broad line region with an elliptical velocity distribution, a long, quiescent, NS-oriented ridge, an EW ridge which exactly abuts the IF of the adjacent HII region, and a possible one-sided high density outflow to the south with an origin apparently not near any of the IR sources mentioned above. The ellipse seems to be tracing the impact of the bipolar outflow on a denser part of the cloud. HCO$\sp+$ in general is deduced to be a tracer of recent activity in dense molecular gas. The SO maps also show fine structure in the core, the main features being two relatively compact components aligned with the NS ridge of the NCO$\sp+$ and previous maps. Most notable, however, is the $\sim$1 km s$\sp{-1}$ blueshift of this line with respect to other high density tracers. The SO clumps may indicate the existence of shock chemistry in parts of the core. The H$\sp $CN maps only show features at the very center of the HCO$\sp+$ and SO emission, and in only two of the hyperfine components of the line.
These observations support and expand the previously proposed model of the HII region. An improved model and a suggested history for the HII region and the first detailed model for the molecular core are presented.
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