From the diagrams in Figure 2 we obtain the following results. H ratios are strongly dependent on the ionization parameter U . H depend only weakly on the density and U . H , we computed models with metallicities half-solar and three and five times solar. These models, together with the solar abundance model and the data points, are plotted in Figures 3a-d .
H is equivalent to the effect of a higher density.
It can be seen that the data on this diagram are compatible with a higher metallicity in the nuclear gas. H ratios presented by the data. Same diagrams as Figures 2 and 3 for model with simultaneous variation of sulfur and nitrogen abundances from 0.5 to 5 times solar. The other elements have solar abundance. The next step we have tried was to vary only the abundances of nitrogen and sulfur, keeping the abundance of the other elements at the solar value.