PHOTOMETRIC-STUDY OF MUTUAL PHENOMENA OF GALILEAN SATELLITES

By use of Kaare Aksnes’revised predictions,six events including two of mutual occultation and four of mutual eclipse have been observed photoelectrically.The equipment used consists of a photoelectric photometer mounted on a 60cm Cassegrain reflector and a GGll filter. Part 1.Mutual Occultation Various criteria and formulae for the occulted area S and the occulted bright- ness I_j corresponding to various occultation configurations illustrated in Fig A-F are given in(2)—(20). The brightness distribution over the apparent disk of the occulted satellite f(R) can be solved from the integral equations involving I_j. It is shown from Tab.4 and Tab.5 that the occulted satellite J2 has a basically uniform disk with some limb brightening.It could be interpreted that the occulted J2 has no atmosphere or has only such a thin atmospheric layer that no limb-dark- ening is caused.Its brightness distribution over the apparent disk is caused by its surface feature.One may imagine that a concave area exists near the center of the surface confronting the observers. The actual measure shows that the drop △V in visual magnitude for the two satellites combined is by far larger than the predicted value.(See Tab.2).The observations also show that Harris values of albedoes for Jovian satellites are ques- tionable. A comparison is made between the observed and the theoretical light curves(Tab. 6 and Tab.7). Part 2.Mutual Eclipse Link's photometric theory of eclipse is generalized. The simplifying method of computing i_N is described in Section 5.Three theore- tical light curves computed by this simplifying method and their comparison with observed light curves are shown in Fig.11—13. In the final part of this paper,the integral equations(90)and(91)of reduced curves are derived and the methods of solving these equations are discussed. The radius of J2 is computed by iterative process from equation(1)′—(5)′. The observational materials of 1973.8.9.102P are used in the computation.