Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Resolving the distance controversy for Sharpless 269: A possible kink in
  the outer arm   Sharpless 269 (S269) is one of a few HII regions in the outer spiral arm of
the Milky Way with strong water maser emission. Based on data from the Very
Long Baseline Interferometry (VLBI) Exploration of Radio Astrometry (VERA)
array, two parallax measurements have been published, which differ by nearly
$2\sigma$. Each distance estimate supports a different structure for the outer
arm. Moreover, given its large Galactocentric radii, S269 has special relevance
as its proper motion and parallax have been used to constrain the Galactic
rotation curve at large radii. Using recent Very Long Baseline Array (VLBA)
observations, we accurately measure the parallax and proper motion of the water
masers in S269. We interpret the position and motion of S269 in the context of
Galactic structure, and possible optical counterparts. S269's 22 GHz water
masers and two close-by quasars were observed at 16 epochs between 2015 and
2016 using the VLBA. We measure an annual parallax for S269 of 0.241 $\pm$
0.012 mas corresponding to a distance from the Sun of $4.15^{+0.22}_{-0.20}$
kpc by fitting four maser spots. The mean proper motion for S269 was estimated
as $0.16\pm0.26$ mas $\rm{yr^{-1}}$ and $-0.51\pm0.26$ mas $\rm{yr^{-1}}$ for
$\mu_{\alpha} \ cos \delta$ and $\mu_{\delta}$ respectively, which corresponds
to the motion expected for a flat Galactic rotation curve at large radius. This
distance estimate, Galactic kinematic simulations and observations of other
massive young stars in the outer region support the existence of a kink in the
outer arm at $l \approx$ 140 degrees. Additionally, we find more than 2,000
optical sources in the Gaia DR2 catalog within 125 pc radius around the 3D
position of the water maser emission; from those only three sources are likely
members of the same stellar association that contains the young massive star
responsible for the maser emission (S269 IRS 2w).

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The categories of this paper are: chao-dyn
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The categories of this paper are: nucl-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: atom-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: nlin
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The categories of this paper are: eess
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-th
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The categories of this paper are: bayes-an
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The categories of this paper are: dg-ga
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The categories of this paper are: q-alg
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The categories of this paper are: q-fin
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The categories of this paper are: hep-lat