Year: 1997
Type: article
Abstract: The errors inherent to the use of the standard ``ionization correction factor'' (``iCF'') method of calculating nebular conditions and relative abundances of H, He, N, O, Ne, S, and Ar in emission line nebulae have been investigated under conditions typical for planetary nebulae. The photoionization code Cloudy was used to construct a series of model nebulae with properties spanning the range typical of PNe. Its radial ``profiles'' of bright, frequently observed optical emission lines were then summed over a variety of ``apertures'' to generate sets of emission line measurements. These resulting line ratios were processed using the iCF method to ``derive'' nebular conditions and abundances. We find that for lines which are summed over the entire nebula the iCF-derived abundances differ from the input abundances by <= 5% for He and O up to <= 25% or more for Ne, S, and Ar. For resolved observations, however, the discrepancies are often much larger and are systematically variable with radius. This effect is especially pronounced in low-ionization zones where nitrogen and oxygen are neutral or once-ionized such as in FLIERs, ansae and ionization fronts. We argue that the reports of stellar-enriched N in the FLIERs of several PNe are probably specious.
Source: The Astronomical Journal
DOI: 10.1086/118505
Authors: Jason Alexander, Bruce Balick
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2142607336