## 5. Radiative quantities in the diffusion limit
We now turn to the description of the expressions for the flux and the
radiative acceleration in a differentially moving medium with
velocities and gradients
The monochromatic flux in the diffusion limit for a linearized source function (Eq. 39) now reads In order to emphasize the effects of the motions we write the flux in the form and hence the monochromatic acceleration as where and
are the static quantities (18) and
(22), respectively. According to Eq. (41), the " Analogously to the monochromatic expressions, we give the
corresponding with and being the corresponding integrated static quantities. Then with We may now introduce a Note that comprises, for , the conventional Rosseland mean . According to Eq. (45) the generalized Rosseland mean is then given by When applying one should keep in
mind that it has been defined specifically for expressing total
fluxes. However, it is We note that our formulae which express the radiative quantities in
terms of their static values can - in a straightforward manner - be
applied only to © European Southern Observatory (ESO) 2000 Online publication: July 7, 2000 |