LUMINOSITY VARIATION IN (DE)FOCUSING MICROLENSING

The luminosity variation of a stellar source due to the gravitational microlensing effect can be considered also if the light rays are defoc used (instead of focused) toward the observer. In this case, we should detect a gap instead of a peak in the light curve of the source. Actu ally, we describe how the phenomenon depends on the relative position of source and lens with respect to the observer: if the lens is betwee n, we have focusing, if the lens is behind, we have defocusing. It is shown that the number of events with predicted gaps is equal to the nu mber of events with peaks in the light curves.