Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: [Fe IV] emission in ionized nebulae   This paper presents an analysis of [Fe IV] emission based on new
identifications and previous measurements of [Fe IV] lines in 30 Doradus, IC
4846, M42, SMC N88A, and SBS 0335-052. The Fe abundances obtained by adding the
abundances of the relevant Fe ions (mainly Fe^{++} and Fe^{3+}) are found to be
lower, by factors in the range 2.6-5.9, than the Fe abundances implied by [Fe
III] emission and an ionization correction factor derived from ionization
models. The most likely explanation of this discrepancy is that either the
collision strengths for [Fe IV] or the Fe ionization fractions predicted by
models are unreliable. The available data neither allow one to distinguish
between these two possibilities nor to exclude another possible explanation:
that the discrepancy implies the presence of a gradient in the Fe abundance
within the ionized gas. Further measurements of [Fe IV] lines and checks on the
Fe^{3+} atomic data and ionization models are needed to reach a definitive
conclusion. The discrepancy introduces an uncertainty in the determination of
Fe abundances in ionized nebulae. This uncertainty has implications for our
understanding of both the evolution of dust in ionized nebulae and the chemical
history of low metallicity galaxies.

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The categories of this paper are: nlin
22
The categories of this paper are: chao-dyn
36
The categories of this paper are: cmp-lg
31
The categories of this paper are: ao-sci
7
The categories of this paper are: hep-th
0
The categories of this paper are: hep-ph
32
The categories of this paper are: atom-ph
35
The categories of this paper are: mtrl-th
18
The categories of this paper are: econ
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The categories of this paper are: q-fin
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The categories of this paper are: gr-qc
4
The categories of this paper are: cond-mat
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The categories of this paper are: adap-org
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The categories of this paper are: acc-phys
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The categories of this paper are: comp-gas
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The categories of this paper are: quant-ph