Computer Science
Scientific paper
Jun 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996phdt........81h&link_type=abstract
Thesis work conducted at the University of Rochester, Rochester, New York, (1996)
Computer Science
3
Scientific paper
Massive stars live short, violent lives that have a major impact on nearby star formation and the interstellar medium (ISM). To study the process of high-mass star formation and its effect on the surrounding ISM, we have observed four regions that include 10 HII regions representing ultracompact, compact, and nearly classical HII regions: Monoceros R2; K3-50; S255-2; and NS 14. Exciting stars of the 10 HII regions span a range of masses (B1 to O4 type stars). We have placed the objects in an evolutionary sequence with K3-50A, C1, and C2 representing the earliest, ultracompact HII region stage, S255-2 and NS 14 representing an intermediate compact stage, while MonR2, K3-50B and K3-50D are more evolved, representing a nearly classical HII region stage. The process of high-mass star formation does not have a well developed theoretical basis, in part, because many complete observational studies of such regions have not been made. Toward this end, we have obtained extensive infrared images of each region mentioned above with near-infrared (NIR) broadband filters and narrow band (1-2% spectral resolution) circular variable filters (CVFs). These are complemented by radio wavelength continuum and millimeter wavelength molecular aperture synthesis observations. Massive stars spend >= 10% of their lives embedded in molecular clouds and are generally enshrouded in gas and dust when they reach the main-sequence. To account for this, we have mapped dust extinction on small spatial scales and compared these maps with dense molecular gas structures. These comparisons yield mass and molecular abundance estimates. Massive toroidal clouds are found in each region and may be ubiquitous features. Such toroidal clouds may provide the collimation necessary to form jets from strong stellar winds. Bipolar ionized outflows or jets appear well correlated with evolutionary stage, with the youngest objects producing the strongest jets. The jets appear to entrain molecular material, thereby powering bipolar outflows which last > 1.5 × 105yrs. Detailed analyses of the four individual regions, including population studies of associated stellar cluster members, are made and a general picture of the process of high mass star formation is presented including: triggered formation of toroidal (proto-cluster) cloud core(s); fragmentation of the core(s) and formation of high-mass protostar(s), ultracompact HII region(s) and associated stellar cluster(s); and evolution of outflows from bipolar ionized jets to massive, extended molecular outflows.
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