The 20 March 1980 occultation by the Uranian rings

Abstract

On March 20, 1980, observations of occultations by rings alpha, beta, gamma, delta, and epsilon were observed from Cerro Tololo and Sutherland. A model ring profile was fit to the data to obtain the midtimes of the occultations and the widths of the profiles. A 14-parameter kinematic model, including J sub 2, J sub 4, and some of the orbital elements for rings 4, alpha, beta, and epsilon as free parameters, was fit to these data and previous ring occultation timings. The results yield J sub 2 = (3.396 + or - 0.020) x 10 to the -3 and a 2 sigma upper limit, absolute value of J sub 4 less than 7 x 10 to the -5th. Uniform precession models for rings alpha, beta are established and the dispersion in the values of semimajor axes and eccentricities for rings alpha, beta, and epsilon have been obtained. If self-gravity is the cause of the uniform precession, the mass of the beta ring is estimated at approximately 4 x 10 to the 16th g; the mass of the alpha ring probably is also near this value.