Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Post-AGB stars in the SMC as tracers of stellar evolution: the extreme
  s-process enrichment of the 21 micrometer star J004441.04-732136.4   By virtue of their spectral types, favourable bolometric corrections as well
as their constrained distances, post-AGB stars in external galaxies offer
unprecedented tests to AGB nucleosynthesis and dredge-up predictions. We focus
here on one object J004441.04-732136.4, which is the only known 21 micrometer
source of the SMC. Spectral abundance results reveal J004441.04-732136.4 to be
one of the most s-process enriched objects found up to date, while the
photospheric C/O ratio of 1.9 +- 0.7, shows the star is only modestly C-rich.
J004441.04-732136.4 also displays a low [Fe/H] = -1.34 +- 0.32, which is
significantly lower than the mean metallicity of the SMC. From the SED, a
luminosity of 7600 +- 200 solar luminosities is found, together with E(B-V) =
0.64 +- 0.02. According to evolutionary post-AGB tracks, the initial mass
should be approximately 1.3 solar masses. The photometric variability shows a
clear period of 97.6 +- 0.3 days. The detected C/O as well as the high
s-process overabundances (e.g. [Y/Fe] = 2.15, [La/Fe] = 2.84) are hard to
reconcile with the predictions. The chemical models also predict a high Pb
abundance, which is not compatible with the detected spectrum, and a very high
12C/13C, which is not yet constrained by observations. The predictions are only
marginally dependent on the evolution codes used. We show that our theoretical
predictions match the s-process distribution, but fail in reproducing the
detected high overabundances and predict a high Pb abundance which is not
detected. Additionally, there remain serious problems in explaining the
observed pulsational properties of this source.

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The categories of this paper are: funct-an
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The categories of this paper are: q-alg
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The categories of this paper are: atom-ph
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The categories of this paper are: eess
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The categories of this paper are: solv-int
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The categories of this paper are: q-fin
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The categories of this paper are: ao-sci
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The categories of this paper are: nucl-th
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The categories of this paper are: nlin
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The categories of this paper are: cond-mat
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The categories of this paper are: acc-phys
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The categories of this paper are: cs
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The categories of this paper are: hep-ex
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The categories of this paper are: nucl-ex
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The categories of this paper are: alg-geom
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The categories of this paper are: patt-sol