Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Trigonometric Parallaxes of Four Star-forming Regions in the Distant
  Inner Galaxy   We have measured trigonometric parallaxes for four water masers associated
with distant massive young stars in the inner regions of the Galaxy using the
VLBA as part of the BeSSeL Survey. G026.50$+$0.28. is located at the near end
of the Galactic bar, perhaps at the origin of the Norma spiral arm.
G020.77$-$0.05 is in the Galactic Center region and is likely associated with a
far-side extension of the Scutum arm. G019.60$-$0.23 and G020.08$-$0.13 are
likely associated and lie well past the Galactic Center. These sources appear
to be in the Sagittarius spiral arm, but an association with the Perseus arm
cannot be ruled out.

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The categories of this paper are: adap-org
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The categories of this paper are: alg-geom
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The categories of this paper are: solv-int
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The categories of this paper are: econ
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The categories of this paper are: hep-lat
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The categories of this paper are: gr-qc
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The categories of this paper are: nlin
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The categories of this paper are: chem-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: cs
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The categories of this paper are: q-bio
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The categories of this paper are: math-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: cmp-lg
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The categories of this paper are: eess
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The categories of this paper are: chao-dyn