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R. A. Benjamin (University of Wisconsin-Madison), B. Benson (Stanford University), D. P. Cox (University of Wisconsin-Madison)
Radiative cooling is an important ingredient in hydrodynamical models involving evolution of high temperature plasmas. Unfortunately, calculating an accurate cooling coefficient generally requires the solution of over a hundred differential equations to follow the ionization. We present here a simple 2-parameter approximation for the cooling coefficient due to elements heavier than H and He, for the temperature range T= 104-108K. This method successfully tracks the ionization level in severe dynamical environments, and accurately approximates the non-equilibrium cooling coefficient of the trace elements, usually to within 10% in all cases for which cooling is actually important. The error is large only when the temperature is dropping so rapidly due to expansion that radiative cooling is negligible. Even in this situation, the ionization level is followed sufficiently accurately. We expect this method to be very useful for hydrodynamic simulations which currently use pre-computed cooling curves. The current approximation is fully implemented in publicly available FORTRAN code. We also discuss general approaches to approximation methods of this type, other realizations which could be even more accurate, and the potential for extension to calculations of non-equilibrium X-ray spectra.This work was supported by NASA Astrophysical Theory Grant Program NAG5-8417.
The author(s) of this abstract have provided an email address for comments about the abstract: benjamin@physics.wisc.edu