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K.C. Yu (CASA)
The thesis examines outflows from young low-mass accreting protostars. The outflow phenomenon appears to be ubiquitous to all newborn stars, and is often the first observational evidence for embedded young stars. Outflows may be crucial for removing angular momentum from the accretion disk, thereby allowing material to accrete onto the stellar core. In addition, since they can transport supersonic gas over parsec-scale distances, outflows probably contribute to changing the chemistry of the molecular cloud, adding to the cloud's overall turbulence, and may even affect the efficiency of star formation by physically disrupting the infall environments around other protostars.
New observations and interpretations are reported for two regions: the Barnard~5 cloud containing the IRS~1 flow, and the OMC-2 and OMC-3 cloud cores, containing a rich cluster of young stars and criss-crossing H2 jets. 12CO J=2--1 mapping, H2 and optical line imaging, and high resolution optical and NIR spectroscopy have revealed the locations of H2 emission; provided support for bow shock entrainment models for the acceleration of CO bearing gas; showed evidence for H2 heating by a magnetic precursor or HH-object-induced fluorescence; showed that many H2 knots can be described as bow shocks with forward and reverse shock line profiles; gave support to outflow models where both a jet and a wide angle wind emanate from the YSO or accretion disk; and revealed possible differences between how low and high mass YSOs entrain ambient gas into outflows as they evolve.