MOCASSIN 2.02 manual
Analytical and Monte Carlo line fluxes
The total luminosity of the nebula in various emission lines longward of the Lyman limit can be obtained by using two methods. The first method, which is only available to Monte Carlo codes, consists of summing up the number of energy packets in the given line over all the grid cells. From this, the power emitted in that line can be readily obtained (see e.g. Ercolano et al., 2003). The second method consists of using the values of the local electron temperatures and ionic abundances given by the final model solution to obtain the line emissivities for each grid cell. The luminosity of the nebula in any given line can then be calculated easily by integrating the emissivity of the required line over the volume of the nebula.
A comparison of the results obtained using the two methods described above, provides an indication of the level of statistical accuracy achieved during the simulation, as the two methods will give consistent results only if enough energy packets are used in order to yield good statistics for every line. However, in general, the second method (formal solution) yields the most accurate results, particularly for weak lines, which only emit a few photons.
Calculation of the line emissivities using the first method, although straightforward, requires extra book-keeping which can be expensive for larger simulations. For this reason, this calculation will only be carried out when the keyword debug is included in the input file, otherwise the more speedy (and accurate) formal solution will only be employed.