STScI Preprint #1257
Recent abundance determinations based on recombination lines in several emission-line nebulae yield ionic abundances several times larger than those derived from forbidden lines. These results cast uncertainty over all abundance determinations in such objects. One possible explanation for these discrepancies frequently cited in the literature is the presence of chemical inhomogeneities. We have run a series of photoionization models to examine what effect such inhomogeneities will have on the resulting temperature structure of nebulae. We then derive abundances from these models, utilizing Peimbert's t2 formalism. Our results suggest that although chemical inhomogeneities may produce non-negliglible biases in abundance determinations in a small number of objects, it is highly unlikely that they can resolve the observed discrepancy for most nebulae. We also stress the importance of continued high-spatial-resolution observations in nebulae to clarify the presence or absence of inhomogeneities in gaseous nebulae.
1)Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
2)Dept. of Physics, Astronomy University of Kentucky Lexington, KY 40506