**AAS Meeting #194 - Chicago, Illinois, May/June 1999**

*Session 32. Coronal Holes and Solar Wind*

Oral, Monday, May 31, 1999, 2:00-3:30pm, Continental Ballroom B
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## [32.08] A Resummed Radiative Stress Tensor

*X. Chen, E.A. Spiegel (Astronomy Department, Columbia University)*

We extend Thomas' (1930) development of the solution of the
equation of radiative transfer to include terms of third
order in photon mean free path. The sum of the calculated
higher order terms is then replaced by a Padé approximant
(or rational approximation; see Baker, 1975), to provide an
improved closure approximation for the radiative stress
tensor, as has been done for the kinetic theory of gases by
Rosenau (1993) and Slemrod (1997), and for the radiative
heat equation in a grey medium (Unno and Spiegel, 1966). The
results are uniformly valid in mean free path and so work
well for both the optically thick and thin limits. Using
simple examples, we contrast the results obtained for the
transmission of shear stresses with those found with the
conventional form for the radiative viscosity. These
illustrate how the usual form of viscous tensor fails for
transparent media and is rectified by the resummation
procedure. Similarly, we exhibit the formula obtained for
the radiative bulk viscosity and use it to extend the
calculation of the cosmological entropy to cases with long
photon mean free paths.

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