HUBBLE-SPACE-TELESCOPE ASTROMETRIC OBSERVATIONS AND ORBITAL MEAN MOTION CORRECTIONS FOR THE INNER URANIAN SATELLITES

The 10 small inner satellites of Uranus were discovered in 1986 with V oyager 2 and not seen again until 1994, when eight were recovered with the Hubble Space Telescope Wide Field Planetary Camera 2 for astromet ric, dynamical, and photometric studies. Thirty-three exposures were t aken on 1994 August 14 with the PC1 chip in the BVRI filters. Measurab le images of Ariel and Miranda were also obtained on the same CCD fram es with those of the faint satellites. We present here the astrometric observations of these eight satellites relative to Miranda, as well a s corrected orbital mean motions for them. For the full-well images of Ariel and Miranda, the astrometric limitation was due to an inadequat e geometric distortion correction and distance from center. For the fa int inner satellites, the astrometric precision varied from 50 mas for Bianca (V = 23 mag) to 9 mas for Puck (V = 20 mag) and was due primar ily to a centroiding error caused by a low signal-to-noise ratio. The orbits of Owen & Synnott for the inner satellites were compared with t hese observations and corrections derived to their mean daily motions. While the orbits of Owen & Synnott proved to be better than their err ors indicated, the new mean motions are 2 orders of magnitude more pre cise.