USE OF MULTIPLY NESTED GRIDS FOR THE SOLUTION OF FLUX-LIMITED RADIATION DIFFUSION AND HYDRODYNAMICS

Local grid refinement techniques allow improved spatial resolution for a large class of astrophysical problems involving radiation hydrodyna mics. We describe here the implementation of multiply nested grids in a 2D radiation hydrodynamic code. The basic hydrodynamic code is expli cit (except for the equation of energy conservation), spatially second -order, invokes artificial viscosity for the treatment of shocks, and through the use of operator-splitting is greater than first-order accu rate in time. Radiation transfer is treated in the flux-limited diffus ion approximation and solved implicitly in a separate substep. Tests a nd the following astrophysical applications are presented and briefly discussed: (a) expansion of a blast wave through several nested grids; (b) protostellar collapse with the formation of a circumstellar disk around a central source; (c) the interaction of circumstellar disk wit h a hot, hydrogen-ionizing star with a stellar wind.