DENSITY INHOMOGENEITIES AND THE DEDUCED CHEMICAL COMPOSITION OF PLANETARY NEBULAE

Abstract

ABSTRACT In this paper the effects of density and temperature inhomogeneities on the emission-line spectra of planetary nebulae are studied. Model calculations are performed with various density inhomogeneities: three filling factor densities are examined as well as a more realistic sine-wave density variation. In the latter case temperature fluctuations occur in response to changes in the density. Carbon abundances are determined using both the optical recombination lines and the ultraviolet collisionally excited lines although the well-known discrepancy between the two is not reproduced. Peimbert's (1967) temperature fluctuation parameter is found to be justified, although the value which typifies the presented model is often smaller than his preferred value. Since the models and analysis use a consistent set of atomic data, errors normally introduced by uncertainties in the atomic data base do not plague the analysis. It is found that most methods of determining abundance ratios give systematic errors of 0.3 dex.