Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: High-velocity collimated outflows in planetary nebulae: NGC 6337, He
  2-186, and K 4-47   We have obtained narrow-band images and high-resolution spectra of the
planetary nebulae NGC 6337, He 2-186, and K 4-47, with the aim of investigating
the relation between their main morphological components and several
low-ionization features present in these nebulae. The data suggest that NGC
6337 is a bipolar PN seen almost pole on, with polar velocities higher than 200
km/s. The bright inner ring of the nebula is interpreted to be the "equatorial"
density enhancement. It contains a number of low-ionization knots and outward
tails that we ascribe to dynamical instabilities leading to fragmentation of
the ring or transient density enhancements due to the interaction of the
ionization front with previous density fluctuations in the ISM. The lobes show
a pronounced point-symmetric morphology and two peculiar low-ionization
filaments whose nature remains unclear. The most notable characteristic of He
2-186 is the presence of two high-velocity (higher than 135 km/s) knots from
which an S-shaped lane of emission departs toward the central star. K 4-47 is
composed of a compact core and two high-velocity, low-ionization blobs. We
interpret the substantial broadening of line emission from the blobs as a
signature of bow shocks, and using the modeling of Hartigan, Raymond, & Hartman
(1987), we derive a shock velocity of 150 km/s and a mild inclination of the
outflow on the plane of the sky. We discuss possible scenarios for the
formation of these nebulae and their low-ionization features. In particular,
the morphology of K 4-47 hardly fits into any of the usually adopted mass-loss
geometries for single AGB stars. Finally, we discuss the possibility that
point-symmetric morphologies in the lobes of NGC 6337 and the knots of He 2-186
are the result of precessing outflows from the central stars.

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The categories of this paper are: atom-ph
12
The categories of this paper are: nucl-th
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The categories of this paper are: patt-sol
7
The categories of this paper are: hep-th
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The categories of this paper are: eess
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The categories of this paper are: comp-gas
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The categories of this paper are: stat
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The categories of this paper are: chao-dyn
5
The categories of this paper are: gr-qc
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The categories of this paper are: bayes-an
3
The categories of this paper are: physics
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The categories of this paper are: q-fin
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The categories of this paper are: alg-geom
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The categories of this paper are: mtrl-th
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The categories of this paper are: chem-ph
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The categories of this paper are: math-ph