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 explain the basic shape of the rotational light curves of Europa, Ganymede and Callisto. In case of Io the albedo map from USGS along with global values of scattering parameters work 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 R.M.S 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 R.M.S. 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 disk (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 is consistent with the shift of the light center from the geometric center. Results using Model 1, which intrinsically takes into account the intensity distribution show no such bias.