Observations of Pluto-Charon Mutual Events. II.

The planned 'Pluto-Charon Mutual Eclipse Season Campaign' observed one mutual event at ESO Observatory (La Silla, Chile) on March 19, 1987 and three mutual events at the Serra La Nave stellar station of Catania Astrophysical Observatory on April 8, May 13, and July 16, 1988. The measurements and the data reduction were carried out following the same strategy reported in Blanco et al. (1989). From the light curves of total events a greater slope of the B light losses appears, if compared with the V one. This behavior is consistent with the spectrophotometric data from which the color of Pluto appears redder with respect to that of Charon, a phenomenon attributed to a lack of volatile methane frost over Charon's surface.