Studies Of Hydrodynamical Models And Line Emission Of Cometary Compact H Ⅱ Region

Based on previous works in dynamical models of cometary H Ⅱ regions, a full numerical method is developed to investigate the kinematics and dynamics of cometary compact HⅡ regions. Both bow shock and champagne flow models are considered in our code, and are contrasted with each other. We investigate the evolution of ionized regions. The associated photodissociation regions (PDRs) are also studied. Our code includes the hydrodynamics, the radiate transfer, the chemical reactions and the thermal processes both in ionized regions and PDRs. The line profiles from the ionized regions and PDRs are analyzed and compared for two kinds of models. The analysis presents that two kinds of models show many differences that can be useful to distinguish them. Both ionization fronts and dissociation fronts grow with time in champagne flow mod-els, but eventually will be overtaken by shock front and drop into the neutral dense shell formed by the expansion of the HⅡ region at certain ages. Emission lines from the ion-ized region present obviously the influence of acceleration along the direction toward the tail of the HⅡ region due to the pressure gradient. The kinematics of the molecular gas inside the dense shell is mainly determined by the expansion of the HⅡ region. But in bow shock models, the volumes of the H Ⅱ region and the PDR do not grow with time and will be quasi-stationary eventually. The ionized gas mainly moves at the same direction as the stellar motion if the stellar velocity is not low. The ionized gas is also accelerated by the pressure gradient toward the tail, but the acceleration is not as great as in the champagne flow models. The kinematics of the molecular gas inside the shell only reflects the motion of the dense shell with the star.