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A.S. Bosh, C.B. Olkin (Lowell Obs.), R.G. French (Wellesley), P.D. Nicholson (Cornell)
We observed the 1995 occultation of GSC5249-01240 by Saturn's rings with the Faint Object Spectrometer on the Hubble Space Telescope. These data provide spectrally-resolved chords across the narrow F ring, at wavelengths from 3540 to 7075 {Å}. The F ring's equivalent depth is found to have no significant dependence on wavelength, indicating the presence of a population of ring particles larger in size than approximately 10 microns. This contrasts with the results from a previous analysis of Voyager images at various phase angles (Showalter et al. 1992, Icarus 100, 394), in which the particles were determined to be predominantly sub-micron in size. The difference may be due to temporal or longitudinal variability within the ring.
When combined with other occultation data, we determine the orbital parameters for the F ring (Bosh et al. Icarus, submitted): a = 140223.7 ±1.7 km, e = 0.00253 ±0.00005, longitude of pericenter = 24.3 ± 1.3 deg, pericenter precession rate = 2.7001 ±0.0003 deg day-1, i = 0.0067 ±0.0012 deg, longitude of ascending node = 16.0 ±3.0 deg, node regression rate = -2.6877 deg day-1. The reference time is the J2000 epoch. Our inclined F ring orbit model explains an abrupt decrease in flux at the west ansa of the ring that was observed during the November 1995 ring-plane crossing (Nicholson et al. 1996, Science 272, 509) as well as the non-detection of 1995 S5 during one set of observations (Roddier et al. 2000, Icarus 143, 299).
This research was supported in part by NASA Grant NAG5-6826.