Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The VLT-FLAMES Tarantula Survey: XXVIII. Nitrogen abundances for
  apparently single dwarf and giant B-type stars with small projected
  rotational velocities   Previous analyses of the spectra of OB-type stars in the Magellanic Clouds
have identified targets with low projected rotational velocities and relatively
high nitrogen abundances. The VFTS obtained spectroscopy for B-type 434 stars.
We have estimated atmospheric parameters and nitrogen abundances using TLUSTY
model atmospheres for 54 B-type targets that appear to be single, have
projected rotational velocities <80 \kms and were not classified as
supergiants. In addition, nitrogen abundances for 34 similar stars from a
previous survey have been re-evaluated. Approximately 75-80% of the targets
have nitrogen enhancements of less than 0.3 dex, consistent with them having
experienced only small amounts of mixing. However, stars with low projected
rotational velocities <40 \kms and significant nitrogen enrichments are found
in both our samples and simulations imply that these cannot all be rapidly
rotating objects observed near pole-on. Adopting an enhancement threshold of
0.6 dex, we observed five stars, yet stellar evolution models with rotation
predict only 1.25$\pm$1.11 for random stellar viewing inclinations. The excess
of such objects is estimated to be 20-30% of all stars with current rotational
velocities of less than 40 \kms and 2-4% of the total single B-type sample.
These estimates constitute lower limits for stars that appear inconsistent with
current grids of stellar evolutionary models. Including targets with smaller
nitrogen enhancements of greater than 0.2 dex implies larger percentages of
targets that are inconsistent with current evolutionary models, viz. 70% of the
stars with rotational velocities less than 40 \kms and 6-8% of the total single
stellar population. We consider possible explanations of which the most
promising would appear to be breaking due to magnetic fields or stellar mergers
with subsequent magnetic braking.

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The categories of this paper are: alg-geom
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-th
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The categories of this paper are: stat
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The categories of this paper are: cs
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The categories of this paper are: acc-phys
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The categories of this paper are: hep-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: q-fin
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The categories of this paper are: nucl-ex
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The categories of this paper are: chem-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: supr-con
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The categories of this paper are: chao-dyn
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The categories of this paper are: physics
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The categories of this paper are: math