Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Ground-based Optical and SPITZER Infrared Imaging Observations of Comet
  21P/Giacobini-Zinner   We present ground-based optical and Spitzer Space Telescope infrared imaging
observations of the ecliptic (Jupiter-family) comet 21P/Giacobini-Zinner, the
parent body of the Draconid meteor stream, during its 2005 apparition. Onset of
nucleus activity occurred at a pre-perihelion heliocentric distance, < 3.80 AU,
while post-perihelion 21P was dusty (peak Afrho = 131 cm^{-1}) and active out
to heliocentric distances > 3.3 AU following a logarithmic slope with
heliocentric distance -2.04. Coma colors, (V-R) = 0.524 +/- 0.003, (R-I) =
0.487 +/- 0.004 are redder than solar, yet comparable to colors derived for
other Jupiter-family comets. A nucleus radius of 1.82 +/- 0.05 km is derived
from photometry at quiescence. Spitzer images post-perihelion exhibit an
extensive coma with a prominent dust tail, where excess emission (over the dust
continuum) in the 4.5 micron IRAC image arises from volatile gaseous CO and/or
CO2. No dust trail was detected (3-sigma surface brightness upper-limit of 0.3
MJy/sr/pixel) along the projected velocity vector of comet 21P in the MIPS 24
micron image suggesting that the number density of trail particles is < 7 x
10^{-11} m^{-3}. The bolometric albedo of 21P derived from the contemporaneous
optical and Spitzer observations is A(theta = 22 degr.) = 0.11, slightly lower
than values derived for other comets at the same phase angle.

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The categories of this paper are: acc-phys
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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: funct-an
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-ex
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The categories of this paper are: plasm-ph
13
The categories of this paper are: quant-ph
9
The categories of this paper are: nlin
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The categories of this paper are: dg-ga
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The categories of this paper are: atom-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: physics
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The categories of this paper are: nucl-ex
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The categories of this paper are: stat
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The categories of this paper are: econ