Mathematics – Logic
Scientific paper
Jun 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002phdt.........5f&link_type=abstract
Thesis (PhD). UNIVERSITY OF CALIFORNIA, BERKELEY, Source DAI-B 64/02, p. 762, Aug 2003, 198 pages.
Mathematics
Logic
18
Scientific paper
We begin in part 1 with a brief review of observational evidence of star formation, along with theoretical mechanisms for multiple star formation. In part 2, we detail our numerical methodology. We solve the equations of coupled radiative, self-gravitating hydrodynamics in the grey approximation, in three dimensions. Since dust provides the opacity under typical conditions in molecular clouds, it plays a crucial role in the energy budget within the cloud, and determines which regions become optically thick, heat up, and thereby arrest collapse. We discuss our dust model in some detail, along with its implicit assumptions and inherent limitations. Next, we detail a new methodology used to solve Poisson's equation in parallel on an adaptive mesh. We couple gravity to hydrodynamics on an adaptive mesh in a self-consistent, fully asynchronous fashion: finer grid levels with smaller grid spacing are advanced with a smaller timestep than coarser overlying grids with larger grid spacing, while taking into account possible mismatches occurring on different grid levels. In part three, we present the initial conditions for our models of turbulent molecular cloud cores for isolated star formation. Our models consist of centrally condensed Bonnor-Ebert spheres perturbed with a turbulent velocity field. Unlike the bulk of models of molecular cloud cores studied to date, in the absence of an applied perturbation, our cores are in exact mechanical equilibrium. The turbulent velocity field is generated as a realization of an n = -4 Gaussian field, which is consistent with observed linewidth-size relations. We discuss the similarities and differences between our turbulent velocity perturbations and Gaussian density perturbations used in studies of large scale cosmological structure. Lastly, in part four, we present the results of the time evolution of the turbulent molecular cloud core models described in part three for several cores with varying degrees of turbulence. In order to assess the effect of radiative transfer, we also examine one model both with radiative transfer and with the barotropic approximation. We discuss a novel method of translating an adaptive mesh dataset to an irregularly gridded dataset, which allows us to analyze our data using a wide variety of existing numerical methods. We present an algorithm for finding gravitationally bound structures within a dataset. We discuss the transition from single to multiple star formation in our models, and its relation to observations of molecular cloud core linewidths. (Abstract shortened by UMI.)
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