A Three Dimensional Model for Molecular Cloud Collapse and Protostellar Formation
Abstract
A three dimensional Cartesian code was developed to model molecular cloud collapse and protostellar formation. The basic Eulerian scheme employs secondorder accurate finite difference methods to advance the fluid variables in time. The hydrodynamic equations governing the collapse contain the effects of selfgravity, rotation, and radiative transfer. Poisson's equation is solved with Green's functions and Fourier transforms, and the Eddington approximation is used to handle radiative transfer. Six collapse calculations were made of initially centrally condensed molecular cloud cores. Two initial density profiles, rho alpha r^{1} and rho alpha r ^{2}, were considered. Half of the clouds began the collapse with solid body rotation, while the rest of the models were assigned a differential rotation profile consistent with conservation of angular momentum during core condensation. The results indicate that fragmentation is possible in molecular cloud cores which begin gravitational collapse with r^ {1} or r^{2} density distributions if the initial conditions also include differential rotation. Cores which collapse with initial uniform rotation, however, do not appear to produced binary fragments. Hence if molecular cloud cores are indeed centrally condensed, as suggested by observations of star forming regions and by studies of ambipolar diffusion, then differential rotation may be necessary if binary protostars are to be produced during gravitational collapse. The nonisothermal scheme employs Rosseland mean opacities throughout the collapse calculations. Two models were run to evaluate the effect of using Planck opacities, rather than Rosseland values, for the optically thin regions of the protostellar cloud. The mixed opacity scheme produced essentially the same results as the standard procedure of using strictly Rosseland mean values.
 Publication:

Ph.D. Thesis
 Pub Date:
 1991
 Bibcode:
 1991PhDT.........1M
 Keywords:

 STAR FORMATION;
 Physics: Astronomy and Astrophysics, Geophysics;
 Binary Stars;
 Finite Difference Theory;
 Gravitational Collapse;
 Hydrodynamic Equations;
 Molecular Clouds;
 Protostars;
 Rotating Bodies;
 Three Dimensional Models;
 Ambipolar Diffusion;
 Angular Momentum;
 Density Distribution;
 Green'S Functions;
 Poisson Equation;
 Radiative Transfer;
 Astrophysics