Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spatially extended K I 7699 emission in the nebula of VY CMa: Kinematics
  and geometry   Long-slit echelle spectra reveal bright extended emission from the K I
lambda7699 resonance line in the reflection nebula surrounding the extreme red
supergiant VY Canis Majoris. The central star has long been known for its
unusually-bright K I emission lines, but this is the first report of intrinsic
emission from K I in the nebula. The extended emission is not just a reflected
spectrum of the star, but is due to resonant scattering by K atoms in the outer
nebula itself, and is therefore a valuable probe of the kinematics and geometry
of VY CMa's circumstellar environment. Dramatic velocity structure is seen in
the long-slit spectra, and most lines of sight intersect multiple distinct
velocity components. A faint ``halo'' at large distances from the star does
appear to show a reflected spectrum, however, and suggests a systemic velocity
of +40 km/s with respect to the Sun. The most striking feature is blueshifted
emission from the filled interior of a large shell seen in images; the
kinematic structure is reminiscent of a Hubble flow, and provides strong
evidence for asymmetric and episodic mass loss due to localized eruptions on
the star's surface.

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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: math-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: cmp-lg
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The categories of this paper are: econ
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The categories of this paper are: patt-sol
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The categories of this paper are: supr-con
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The categories of this paper are: dg-ga
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The categories of this paper are: funct-an
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The categories of this paper are: cond-mat
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The categories of this paper are: cs
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The categories of this paper are: stat
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The categories of this paper are: nucl-ex