A DISTRIBUTION FUNCTION CALCULATION OF THE H-ALPHA PROFILES OF HIGH-VELOCITY SHOCKS

Models of multifluid shocks propagating into media of very high pre-shock ionization introduce difficulties in the use of standard hydrodynamic continuity equations to describe the neutral gas and hence reproduce the Ha profiles of these shocks. The problems arise from the lack of thermal contact between the atoms in the neutral component of the shock structure, the model of this component as an ideal gas in thermal equilibrium therefore being inaccurate. We have overcome this problem by explicitly solving a transport equation to obtain the velocity distribution function of the neutral gas. Numerical solutions to this equation, under the physical conditions of a shock transition, are used to follow the evolution of the distribution function. The effect on the neutral distribution function of atomic interactions with the other components of the shock structure can be calculated, and the emitted Ha line profiles can then be obtained. Predicted Ha profiles of shocks with pre-ionization fractions that are so high that the neutral gas makes no significant dynamical contribution to the shock structure are presented for shock velocities between 313 and 2500 km s(-1) These profiles show the two-component structure seen in several observations of filamentary structures in supernova remnants.