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Session 91 - Structure of Molecular Clouds.
Oral session, Wednesday, January 15
We study the linear evolution of small perturbations in self-gravitating fluid systems with magnetic fields in two spatial dimensions. We consider wave-like perturbations to nonuniform filamentary and sheet-like hydrostatic equilibria. Motivated by observations of molecular clouds that indicate significant nonthermal (turbulent) support, we adopt equations of state that are softer than isothermal. We numerically determine the dispersion relations and the forms of the perturbations for a wide range of parameters. The form of the dispersion relation is the same for all equations of state considered, for all magnetic field strengths, and for both geometries examined. We demonstrate the existence of a fastest growing mode for the system and study how its characteristics depend on the amount of turbulence and the strength of the magnetic field. Generally, turbulence tends to increase the rate and the length scale of fragmentation. While tending to slow the fragmentation, a uniform magnetic field has little effect on the length scale of fragmentation until reaching a threshold, above which the length scale decreases significantly. The influence of the magnetic field upon the rate and length scale of fragmentation, however, is sensitive to the configuration used for the unperturbed field. We discuss the implications of these results for star formation in molecular clouds.
Program listing for Wednesday