Improved Parameters and New Lensed Features for Q0957+561 from WFPC2 Imaging

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Abstract
New Hubble Space Telescope WFPC2 observations of the lensed double QSO 0957+561 will allow stronger constraints on the lens mass distribution and hence will refine the derived value of H0. 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 (see the recent work of Grogin and Narayan) is excluded by these data and must be reevaluated. Several new resolved features are found within 10'' of G1, including an apparent fold arc with two bright knots. Several other small galaxies are detected, including two that may be multiple images of each other. We present positions and crude photometry of these objects.
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