Atomic data and the density structures of planetary nebulae

TL;DR

This study investigates how different atomic data influence the inferred density structures of planetary nebulae by analyzing multiple diagnostics and comparing observations with photoionization models.

Contribution

It demonstrates that the choice of atomic data critically affects the derived density structures of planetary nebulae, highlighting the importance of atomic data accuracy.

Findings

Atomic data choices determine the inferred density structures.

Different atomic data lead to compatibility with different models.

Density diagnostics sample various regions within nebulae.

Abstract

We study the density structures of planetary nebulae implied by four diagnostics that sample different regions within the nebulae: [S II] $\lambda6716/\lambda6731$, [O II] $\lambda3726/\lambda3729$, [Cl III] $\lambda5518/\lambda5538$, and [Ar IV] $\lambda4711/\lambda4740$. 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.