Computer Science
Scientific paper
Jan 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........14c&link_type=abstract
Thesis (PH.D.)--THE UNIVERSITY OF TEXAS AT AUSTIN, 1995.Source: Dissertation Abstracts International, Volume: 56-10, Section: B,
Computer Science
1
Protostellar Collapse, Bipolar Outflow
Scientific paper
Star formation is a dynamic and complex activity. In this thesis, we will study characteristic activities in star formation regions: protostellar collapse, bipolar outflow, and large scale rotation. In Chapter 1, we study a protostellar collapse in a low-mass star formation region. A dark cloud core, B335, is modeled as an inside-out collapse. The radiative transfer code uses the Monte Carlo method. Line profiles for several transitions of CS and rm H_2CO are computed and they agreed with the observations very well. In Chapter 2, we investigate kinematic structures in a high-mass star formation region. Monoceros R2 dense core region was observed with molecular lines. We suggest that the main part can be explained as a parsec scale toroid around the H scII region with its symmetry axis parallel to the CO outflow and the magnetic field. The Omega~ r^{-1} rotation profile indicates that rotation alone cannot support the dense core. We modeled the toroid with a 2-dimensional radiative transfer code. Our simple model can reproduce the intensities and profiles of observed CS transitions very well. In Chapter 3, extremely high velocity (EHV) wings are studied with CO lines. The results of our survey suggest that EHV wings are common around infrared sources of moderate to high luminosity in dense regions. Line ratios imply that the EHV gas is usually optically thin and warm. Characteristic velocities range from 20 to 40 km rm s^ {-1}, yielding timescales of 1600-4200 yr. Since most sources in this study are producing some ionizing photons, these short timescales suggest that neutral winds coexist with ionizing photons. We examined two possible sources for the extremely high velocity CO emission: a neutral stellar wind; and swept-up or entrained molecular gas. Neither can be ruled out. In Chapter 4, molecular outflows associated with GL 2591 and W28 A2 were studied with the (C scI) line. Upper limits are set on the (C scI) emission in the EHV line wings. These limits are discussed in terms of wind-driven and jet-driven models of molecular outflows.
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