Mutual phenomena of the Galilean satellites: an analysis of the 1991 observations from VBO

Abstract

Results of analysis of seventeen mutual events, of the Galilean satellites, observed at the Vainu Bappu Observatory (VBO) during the 1991 are presented. The light curves were fitted with theoretical models to derive the relative astrometric positions of the satellites. The dependence of te derived parameters on the various light scattering laws are investigated. Results of the analysis indicate that for Io fits using Minnaert's and Lommel-Seeliger's laws are comparable however the Lambert's law solution fails to give good fit at the centre and at the wings of the light curves. The mean value of the Minnaert's parameter for this satellite derived from the good quality occulation of light curves in the I band is 0.559 +/- 0.11. Analysis of occulation light curves of 201 events using model with albedo variations inferred from Voyager imagery lead to best fit. An average residual of -340 +/- 10 km in the position of Io along its track relative to Europa compared to the E-3 ephemiris is noticed.