Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Photometric observations of distant active comets   We present CCD VR_C observations of 6 distant comets located at heliocentric
distances of 3.4--7.2 AU. Time-series data were obtained on three nights in
July, 2000 covering 16 hours. Each comet was observed after the perihelion,
when a lower activity was expected. Contrary to expectation, we found
well-defined circular comae and extended tails visible out to a few (3-5)
arcminutes. We detected a quasi-cyclic light variation of C/1999 J2, while
C/1999 N4 showed some hints of a more complex variation. C/2000 K1 was constant
to +/-0.04 mag during the observing run. The standard V and R_C data were used
to estimate nuclear diameters, while the colour indices implied a slighly
reddish (V-R=0.68, C/2000 K1), a neutral (V-R=0.47, C/1999 N4) and a slightly
bluish (V-R=0.25, C/1999 J2) coma. Simple fits of the surface brightness
distributions are also presented enabling order of magnitude estimates of
nuclear radii. Beside the time-series observations, further single-shot
observations of three faint comets are briefly described.

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The categories of this paper are: nlin
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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: hep-ex
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The categories of this paper are: adap-org
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The categories of this paper are: hep-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: math
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The categories of this paper are: q-alg
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The categories of this paper are: patt-sol
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The categories of this paper are: stat
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The categories of this paper are: cmp-lg
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The categories of this paper are: math-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: q-bio
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The categories of this paper are: hep-ph