4 Results for the coronal equilibrium

In Table 2 we give the ionization fraction $X_{\rm i}$, for the 28 elements. In these calculations we included only the collisional processes in the low-density case. We compared our ionic abundances fractions with those given by AR85 (AR for the iron). We found a very good agreement or differences less then 10% for all the atoms and ions of H, He, N, Ne, Na, Mg, Si. For C II, C III, O III, O IV, O V we found differences up to 50% near the peaks of maximum ionic abundance, but good agreement for the other ions of these elements.

  

Figure 1: Upper panel: Ionic fraction vs. temperature for Al ions, from Al V to Al X. Solid curves: present work; dashed curves: AR85. Lower panel: percent variations in the ionic abundance fractions in the present work with respect to that of AR85. For each ion, the percent variations are evaluated only for a range of temperatures in which the respective ionic fractions are > 10-1

  

Figure 2: Same as Fig. 1 but for Ar ions, from Ar VII to Ar XVI

  

Figure 3: Same as Fig. 1 but for Ca ions, from Ca V to Ca XI

  

Figure 4: Same as Fig. 1 but for Ca ions, from Ca XII to Ca XVIII

  

Figure 5: Upper panel: Ionic fraction vs. temperature for Fe ions, from Fe XVII to Fe XXI. Solid curves: present work; dashed curves: AR. Lower panel: percent variations in the ionic abundance fractions in present work with respect to AR. For each ion the percent variations are evaluated only for a range of temperatures in which the respective ionic fractions are > 10-1

  

Figure 6: Same as Fig. 1 but for Ni ions, from Ni IV to Ni IX

  

Figure 7: Same as Fig. 1 but for Ni ions, from Ni X to Ni XV

  

Figure 8: Same as Fig. 1 but for Ni ions, from Ni XVI to Ni XXI

  

Figure 9: Same as Fig. 1 but for Ni ions, from Ni XXII to Ni XXVII

  

Figure 10: Ionic fraction vs. temperature Cr ions, from Cr XVIII to Cr XXVI. Solid curves: present work; dashed curves: Landini & Monsignori Fossi(1991)

In Fig. 1 we compare our ionic fraction for the less ionized ions of Al with those of AR85. In the same figure we report, for each ion, also the percent variation near the peak of maximum ionic abundance. We can note that our ionic abundance fraction at $T\approx 2\ 10^{5}$ K is a factor of 2 greater than those of AR85. In Figs. 2 to 4 we report the comparisons for some Ar and Ca ions. In those cases we found, depending on the temperature and on the ions considered, differences up to 400%. The curves obtained for the iron ions are both or the same or in very good agreement with those of AR except for the ions from Fe XVII to Fe XXI due to the updating of Fe XIX dielectronic recombination rate, as shown by Fig. 5, where we still have small variations. In Figs. 6 to 9 we compare the curves for some Ni ions and we found substantially differences with respect to AR85. If we fix the temperature at which the ion abundance curves reach their maxima, we can see that generally the big differences found are due to a shift, depending on the considered ion, to higher or lower temperature with respect to the other considered case.

We compered, also, our ionic abundance curves for the less abundant astrophysical elements with those of Landini & Monsignori Fossi(1991) and found again significant differences, depending on the temperature and ion considered. In Fig. 10, as an example, we show the comparison of our ionic fraction curves for the most ionized ions of Cr with those of Landini & Monsignori Fossi(1991) and we can observe that our curves are shifted to higher temperatures.