**AAS 198th Meeting, June 2001**

*Session 59. Galactic ISM*

Display, Wednesday, June 6, 2001, 10:00am-7:00pm, Exhibit Hall
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## [59.10] A Useful Approximation to the Cooling Coefficient of Trace Elements

*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= 10^{4}-10^{8}K. 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

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