Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Progenitors of Planetary Nebulae in Dwarf Irregular Galaxies   We present chemical abundances for planetary nebulae and H II regions in the
Local Group dwarf irregular galaxy NGC 6822 based upon spectroscopy obtained at
the Canada-France-Hawaii Telescope using the Multi-Object Spectrograph. From
these and similar data compiled from the literature for planetary nebulae in
the Magellanic Clouds, Sextans A, Sextans B, and Leo A, we consider the origin
and evolution of the stellar progenitors of bright planetary nebulae in dwarf
irregular galaxies. On average, the oxygen abundance observed in the bright
planetary nebulae in these galaxies coincides with that measured in the
interstellar medium, indicating that, in general, the bright planetary nebulae
in dwarf irregulars descend primarily, though not exclusively, from stars
formed in the relatively recent past. We also find that the ratio of neon to
oxygen abundances in these bright planetary nebulae is identical to that
measured in the interstellar medium, indicating that neither abundance is
significantly altered as a result of the evolution of their stellar
progenitors. We do find two planetary nebulae, that in Sextans A and S33 in NGC
6822, where oxygen appears to have been dredged up, but these are the exception
rather than the rule. In fact, we find that even nitrogen is not always dredged
up, so it appears that the dredge-up of oxygen is uncommon for the abundance
range of the sample.

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The categories of this paper are: mtrl-th
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: eess
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The categories of this paper are: hep-th
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The categories of this paper are: cs
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The categories of this paper are: physics
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The categories of this paper are: bayes-an
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The categories of this paper are: math
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The categories of this paper are: gr-qc
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The categories of this paper are: stat
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The categories of this paper are: patt-sol
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The categories of this paper are: hep-lat
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The categories of this paper are: dg-ga
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The categories of this paper are: ao-sci