Ionization Correction Factors from an Extensive Grid of Photoionization Models of Planetary Nebulae

Abstract

Using a new photoionization code PAN (Yu.Malkov et al, this book) we have built a grid of 250 photoionization models for planetary nebulae (PN). The stellar evolutionary tracks for PN nuclei with M* = 0.566, 0.598,0.644 and O.8M ⨀ are taken from the computations of the Blocker (A&A, 299, 1995). On the L * — T eff diagram our grid covers whole region in which the PN nuclei are observed. The spectra of the central stars at λ ≤ 912 A corresponded to non-LTE model atmospheres (R.E.S. Clegg and D. Middlemass, MNRAS, 228, 1987), corrected for presence of the stellar wind. The nebular shell was assumed to be spherically symmetric, and the profile of the radial gas density distribution in it was taken equal to the empirical approximate expression found from the analysis of isophotal maps of real PN (V. Golovaty and Yu. Malkov, Astron. Zh., 69, 1992). Each model was calculated for three choises of M shell and each of them for two choises of shell expansion velosity - 15 and 30 km/sec respectively. The relative elemental abundances were the same for all models: H:He:C:N:O:Ne:Mg:Si:S:Ar = 10000:1200:5.0:1.0:6.0:0.8:0.3:0.3:0.15:0.04 (by number of atoms).