6 Comparing level populations

Level populations (the n_j of Sect. 5.1) were presented in B94 at densities $\log\,N_{\rm e}=8,9,10,11,12$and temperatures $\log\,T=6.0,6.2,6.4$, and we compare their results with the CH97 and SMY99 models in Table 8 at $\log\,N_{\rm e}=8,10,12$ and $\log\,T=6.2$ for the most important Fexiv levels. Using the original thermally averaged collision strengths rather than the spline fitted values changes these level populations by less than 1% over the temperature range of validity (see Sect. 5.2).

Although the populations of the two ground levels are very similar for the three different models, the other levels show differences of up to a factor 5. The differences with the CH97 model are due to the substantial cascading taking place from the higher levels, while the differences between the SMY99 and B94 models can be accounted for by the more accurate radiative data and the important resonance effects incorporated here (see Sect. 4).