We determined abundances for ionic species of N, O, Ne, S and Ar from CELs. To deduce ionic abundances, we solve the statistical equilibrium equations for each ion using EQUIB code, giving level population and line sensitivities for specified cm and K adopted according to our photoionization modelling. Once the equations for the population numbers are solved, the ionic abundances, X/H, can be derived from the observed line intensities of CELs as follows:
Total elemental and ionic abundances of nitrogen, oxygen, neon, sulphur and argon from CELs are presented in Table 7. Total elemental abundances are derived from ionic abundances using the ionization correction factors () formulas given by Kingsburgh & Barlow (1994). The total O/H abundance ratio is obtained by simply taking the sum of the O/H derived from [O II] 3726,3729 doublet, and the O/H derived from [O III] 4959,5007 doublet, since HeII 4686 is not present, so O/H is negligible. The total N/H abundance ratio was calculated from the N/H ratio derived from the [N II] 6548,6584 doublet, correcting for the unseen N/H using,
Fig.4 shows the spatial distribution of ionic abundance ratio He/H, N/H, O/H and S/H derived for given K and cm. We notice that both O/H and He/H are very high over the shell, whereas N/H and S/H are seen at the edges of the shell. It shows obvious results of the ionization sequence from the highly inner ionized zones to the outer low ionized regions.