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Session 44 - The Local Diffuse ISM.
Display session, Tuesday, June 11
The relative amounts of cold, warm and hot phases in the Galactic ISM continues to be the focus of intense observational and theoretical studies. The production and fate of hot gas primarily from supernova explosions requires numerical simulations of increasing sophistication. We have embarked on a systematic program to incorporate magnetic fields, heat conduction, radiative cooling, cosmic rays, and turbulent motions into multidimensional models of supernova remnant and superbubble evolution. Here we present results of 2D numerical MHD simulations of the late (> 5 Myr) evolution of an isolated supernova remnant in a warm diffuse medium threaded by a uniform magnetic field. We follow the complete evolution of the remnant through collapse of the hot bubble as it radiates away its thermal energy. The effects of heat conduction are included through the incorporation of a new implicit algorithm in the ZEUS-2D code which we describe. The parameters adopted are identical to those used by Slavin and Cox (ApJ, 392, 131, 1992): E_o=5 \times 10^50 erg, n_o=0.2 cm^-3, T_o=10^4 K, B_o=5 \mu G. Our results generalize the spherically symmetric models of Slavin and Cox (1992) to 2D axisymmetry. Magnetic stresses collimate the hot bubble into a prolate ``hot sausage" aligned with the magnetic field by 1 Myr. Thereafter the axis ratio of the sausage increases superlinearly with time as the bubble collapses radially but continues to expand axially with approximately the ambient magnetosonic speed. Magnetic pressure prevents the shell from collapsing due to radiative losses everywhere except at the polar caps. We compute the four-volume of the hot bubble for various choices of heat conduction and compare these results with the spherically symmetric models.
Program listing for Tuesday