Analysis of mutual events of Galilean satellites observed from VBO during 2014-2015

Abstract

Results of analysis of 23 events of the 2014–2015 mutual event series from the Vainu Bappu Observatory are presented. Our intensity distribution model for the eclipsed/occulted satellite is based on the criterion that it simulates a rotational light curve that matches the ground-based light curve. Dichotomy in the scattering characteristics of the leading and trailing sides explains the basic shape of the rotational light curves of Europa, Ganymede and Callisto. In the case of Io, the albedo map (courtesy United States Geological Survey) along with global values of scattering parameters works well. Mean values of residuals in (O − C) along and perpendicular to the track are found to be −3.3 and −3.4 mas, respectively, compared to ‘L2’ theory for the seven 2E1/2O1 events. The corresponding rms values are 8.7 and 7.8 mas, respectively. For the five 1E3/1O3 events, the along and perpendicular to the track mean residuals are 5.6 and 3.2 mas, respectively. The corresponding rms residuals are 6.8 and 10.5 mas, respectively. We compare the results using the chosen model (Model 1) with a uniform but limb-darkened disc (Model 2). The residuals with Model 2 of the 2E1/2O1 and 1E3/1O3 events indicate a bias along the satellite track. The extent and direction of bias are consistent with the shift of the light centre from the geometric centre. Results using Model 1, which intrinsically takes into account the intensity distribution, show no such bias.