Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical appearance of the gravitational lens system B0218+35.7   We present high-resolution CCD images (FWHM=0.6"-0.7") of the compact
gravitational lens system B0218+35.7 obtained at the Nordic Optical Telescope.
Using aperture and PSF photometry we detect the two closely separated (335 mas)
components A and B as well as the lensing galaxy. In the optical B seems to be
very much brighter than A, opposite to the radio morphology. This suggests that
most of the light from A is absorbed in the lensing galaxy, possibly by a giant
molecular cloud located in the line-of-sight to component A. The lensing galaxy
appears to be a late-type galaxy at a small inclination. For future variability
studies we present calibrated photometry of the system and its immediate
surroundings, even though the relative faintness of A will make it difficult to
obtain an optical time delay even with the Hubble Space Telescope.

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The categories of this paper are: patt-sol
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The categories of this paper are: dg-ga
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The categories of this paper are: q-fin
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The categories of this paper are: mtrl-th
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The categories of this paper are: plasm-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: hep-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: bayes-an
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The categories of this paper are: econ
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The categories of this paper are: eess
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The categories of this paper are: nucl-ex
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The categories of this paper are: math
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The categories of this paper are: hep-th
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The categories of this paper are: quant-ph
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The categories of this paper are: nlin