A Study of Bistable Behavior and Parameter Variation in Dark Molecular Clouds

A study of Bistable Behavior and Parameter Variation in Dark Molecular Clouds investigates the phenomenon of bistability and its relation to phase transitions, derives an analytical model of fractional ionization and does a parameter study. Specifically, this investigation focuses on several different types of phenomena that are associated with the modeling of giant and dark molecular clouds. The chemical model of a molecular cloud consists of a set of stiff coupled differential equations. Each differential equation represents the rate of change of the abundance of a chemical species in the molecular cloud. Analytical approximations to the fractional ionization are presented. The models are found to have bistable solutions for a range of temperatures and densities. The range over which the bistable solutions exist are shown to dependent on; cosmic-ray ionization rate, elemental abundances, grain population and chemical reaction rate coefficients. A parameter study over a range of temperatures and densities which have been inferred for the interstellar medium. The results of this study are compared to observed chemical abundances in the Taurus Molecular Cloud 1, L134, the Orion Ridge and Sagittarius B2. We examine the study for trace species which are particularly good indicators of temperature and density. For example, H_2O is a useful probe for determining temperature and OH is a useful problem for determining density. In addition we have mapped out the water, molecular oxygen, atomic carbon and carbon monoxide abundances that will be compared to observations made by the Submillimeter Wave Astronomy Satellite (SWAS).