Atomic data and the density structures of planetary nebulae

Abstract

We study the density structures of planetary nebulae implied by four diagnostics that sample different regions within the nebulae: [S II] $\lambda 6716/\lambda 6731$, [O II] $\lambda 3726/\lambda 3729$, [Cl III] $\lambda 5518/\lambda 5538$, and [Ar IV] $\lambda 4711/\lambda 4740$. We use a sample of 46 objects with deep spectra that allow the calculation of the electron density from these four diagnostics, and explore the impact that different atomic data have on the results. We compare the observational results with those obtained from photoionization models characterized by three different density structures. We conclude that the atomic data used in the calculations of electron density fully determine the density structures that are derived for the objects. We illustrate this by selecting three combinations of atomic data that lead to observational results that are compatible with each of the three different density structures explored with the models.

arXiv comment9 pages, 6 figures, 2 table. Accepted for publication in MNRAS

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• The homogeneity of chemical abundances in H II regions of the Magellanic Clouds
• Atomic Data Assessment with PyNeb: Radiative and Electron Impact Excitation Rates for [Fe II] and [Fe III]