Mathematics – Logic
Scientific paper
Jan 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........22w&link_type=abstract
PhD Dissertation, California Univ. Berkeley, CA United States
Mathematics
Logic
2
Millimeter Waves, Star Formation, Cn Emission, Interstellar Chemistry, Interstellar Matter, Molecular Gases, Imaging Techniques, Orion Constellation, Methyl Compounds, Cyanides, Abundance, Synthetic Apertures, Formyl Ions, H Ii Regions
Scientific paper
This thesis consists of a series of observational investigations into three, bright, prototypical regions of high mass star formation, exploiting a variety of carefully selected millimeter wave probes and improved observing techniques to elucidate small scale structure and dynamics. (1) The first high resolution images of CH3CN emission are presented. These observations focus on the Orion-KL region, the only region with sufficient complementary data to evaluate the utility of this promising symmetric top molecule. Methyl cyanide emission is found associated with all of the previously recognized source substructures, including the hot core, CS1 condensation, compact ridge, western clump, extended ridge, and northwest filament. Statistical equilibrium calculations constrain the temperatures and heating mechanisms in these regions. The methyl cyanide abundance is enhanced by two orders of magnitude in the hot core, presumably due to grain chemistry. (2) Maps of HCO(+) emission reveal the structure of the S140 core, a source where previous observations failed to uncover the details of the molecular distribution because of excitation effects, molecular depletion, and unsampled low spatial frequencies. The brightest emission in the HCO(+) maps arises from the periphery of the bipolar flow, suggesting the limb brightened edges of a cavity. The images provide a spur for (a) the derivation of expressions to quantify the effects of holes in aperture plane sampling, (b) a discussion of the short spacing problem in millimeter interferometry, and (c) a demonstration of the homogeneous array concept as a solution. (3) An extensive study of nine transitions in five species mapped toward the G5.89-0.39 ultracompact H II region provides the first high resolution look at the neutral environment of this source, one of the closest, brightest, and most morphologically simple of the known ultracompact H II regions. HCO(+) observations provide evidence for both infall and outflow. Two redshifted HCO(+) J = 1-0 absorption systems are detected against the continuum, one attributed to a diffuse foreground cloud, and the other to an overall collapse of the dense core. Detailed radiative transfer models of accelerating infall match the data in both position and velocity. The maps localize the high velocity bipolar outflow to the ultracompact H II region, indicating an origin within the ionized gas. High resolution maps of the H41 alpha recombination line show a systematic approximately 10 km/s gradient across the source aligned with the flow traced by CO emission, bright knots of 2 micron H2 v = 1-0 S(1) line emission, and faint extensions of the ionized region in the radio continuum, suggesting a champagne flow along oppositely directed paths where the fast protostellar wind has disrupted the surrounding material. An additional molecular peak especially prominent in high excitation CH3CN lines is found at the ultracompact H II region boundary where the ionization front appears to encounter an obstacle.
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