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The ten faint, inner satellites of Uranus have not been observed since their discovery in 1986 with Voyager II. Astrometric observations of these faint satellites with the Hubble Space Telescope were sought in an effort to improve their orbits for a spectroscopic follow-up and to study their dynamical resonances.
Thirty three images were taken on 14 August 1994 with WFPC2 in the BVRI filters. As expected, eight of the ten inner satellites were recovered -- only the two faintest and innermost were not detected. In addition, measurable images of Ariel and Miranda were obtained on the same CCD chip. The orbits were well covered, and a range of exposures was used to cover the nine magnitude difference between Ariel (V=14) and Bianca (V=23).
Our strategy was to use accurate Miranda/Ariel orbital predictions and measurements to reduce the measurements of the faint satellites. We will discuss in some detail our techniques of measurement and reduction, as well as our results. While measurement precision varied widely depending on signal strength, even rough pixel measurements have a precision of 0.04 arcsec in the Planetary Camera.
In addition to astrometry of the faint satellites, the four color images were used to determine magnitudes and color indexes for the brighter ones, relative to ground-based photometry of Ariel.
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