Abstract
For the solution of the hydrodynamic equations in differentially moving media the calculation of the radiation fiux, the gradient of the radiation pressure, and the energy balance is required. After a brief discussion of the shortcomings of the approximations which are frequently made, we suggest a fast method for the accurate calculation of these quantities by means of three mean opacity coefficients which replace the Rosseland mean of the static case. This method allows a consistent inclusion of the important contribution of spectral lines to the radiation field. Key words: ACCRETION - OPACITIES - STARS: NOVAE - STARS: SUPERNOVAE
