Spectral line strength binning method for opacity calculations

In modern opacity calculations that employ intermediate coupling based atomic physics, it can be necessary to include the contribution of millions of spectral lines to evaluate the bound–bound part of the opacity. Unfortunately, the processing of millions of line shapes is impractical because of prohibitive computational times, therefore fast computational methods are needed. In the present work, a simple procedure is described to process line strengths and widths in finely spaced photon energy histogram bins. Line shapes are then calculated for each bin, rather than for individual spectral lines, resulting in a significant speed up of a factor of 100 or more in some cases. The method is shown to agree very well with the usual detailed line-by-line treatment for opacity calculations.