Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Improved Parameters and New Lensed Features for Q0957+561 from WFPC2
  Imaging   New HST WFPC2 observations of the lensed double QSO 0957+561 will allow
improved constraints on the lens mass distribution and hence will improve the
derived value of H$_0$. We first present improved optical positions and
photometry for the known components of this lens. The optical separation
between the A and B quasar images agrees with VLBI data at the 10 mas level,
and the optical center of the primary lensing galaxy G1 coincides with the VLBI
source G' to within 10 mas. The best previous model for this lens (Grogin and
Narayan 1996) is excluded by these data and must be reevaluated.
  Several new resolved features are found within 10\arcsec of G1, including an
apparent fold arc with two bright knots. Several other small galaxies are
detected, including two which may be multiple images of each other. We present
positions and crude photometry of these objects.

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The categories of this paper are: plasm-ph
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The categories of this paper are: stat
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: hep-ex
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The categories of this paper are: nucl-ex
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The categories of this paper are: bayes-an
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The categories of this paper are: eess
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The categories of this paper are: nucl-th
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The categories of this paper are: q-fin
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The categories of this paper are: solv-int
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The categories of this paper are: physics
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The categories of this paper are: q-bio
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The categories of this paper are: quant-ph
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The categories of this paper are: funct-an
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The categories of this paper are: math-ph