The Ionization Structure of Planetary Nebulae--VIII: Models of the Nebulae NGC 7662 and IC 418

Open Access
Publisher Website
Google Scholar
Abstract
Using computer programs which are based on the. theory developed in the previous papers in this series a number of models of the planetary nebulae NGC 7662 and IC 418 have been computed. An essential feature of the models is the inclusion of stellar atmosphere fluxes calculated by Hummer & Mihalas (private communication) which fit the observational data for the central stars of these two nebulae. A detailed comparison is made between observed and calculated forbidden line intensities and values derived for the abundances of nitrogen, oxygen and neon relative to hydrogen in the nebulae. The value of particularly the neon abundance is found to be substantially less than the mean values for B-stars and for planetary nebulae given by Aller (1961 and 1964 respectively). It is shown that the intensity of the collisionally excited C IV λ 1549 resonance doublet relative to the He II λ4686 recombination line is insensitive to the physical parameters of the model but sensitive to the probability of re-absorption of He II Ly α photons produced in the nebula. Measurement of the intensity of the λ1549 1ine (from above the Earth's atmosphere) for a few high-excitation planetary nebulae would, therefore, be important to the understanding of the He II Ly α transfer problem.

This publication has 0 references indexed in Scilit: