The Uranus Occultation of 10 June 1979. I. The Rings

Abstract

Observations and analysis of a stellar occultation by the rings of Uranus on 10 June 1979 are presented. Occultations by rings 4, ɑ, β, y, δ, and є are identified, and radii and azimuths of the occulting segments in the plane of the rings calculated. Results for rings y and δ are consistent with the hypothesis (Elliot et al. 1978; Nicholson et ɑl. 1978) that these two rings are circular and coplanar, and an approximate upper limit of 8 X 10^(-5) is placed on the eccentricity of either ring. Coplanar elliptical models are presented for rings ɑ and β, with eccentricities of (6.0±0.3) x 10^(-4) and (4.9±0.5) x 10^(-4), respectively. For ring 4 two possible elliptical models are obtained, with eccentricities of (1.2±0.4) x 10^(-3) and (6.0±0.3) x 10^(-4), the former being preferred. The width-radius relation established previously for the є ring is confirmed, and the elliptical model for this ring is slightly revised. An improved estimate for Uranus's J_2 of (3.390 ± 0.005) x 10^(-3), based on the apsidal precession of the є ring, and an upper limit for │J_4│ of ~1 x 10^(-4), based on the precession of rings 4 and β, are obtained.

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