MUTUAL PHENOMENA OF THE GALILEAN SATELLITES - AN ANALYSIS OF THE 1991OBSERVATIONS FROM VBO

Results of analysis of seventeen mutual events, of the Galilean satell ites, observed at the Vainu Bappu Observatory (VBO) during 1991 are pr esented. The light curves were fitted with theoretical models to deriv e the relative astrometric positions of the satellites. The dependence of the derived parameters on the various light scattering laws are in vestigated. Results of the analysis indicate that for Io fits using Mi nnaert'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 th is satellite derived from the good quality occultation of light curves in the I band is 0.559 +/- .011. Analysis of occultation light curves of 201 events using model with albedo variations inferred from Voyage r 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 ephemeris is noticed.