STOKESS THEOREM APPLIED TO MICROLENSING OF FINITE SOURCES

The computation of the magnification of a finite source by an arbitrar y gravitational lens can be reduced from a two-dimensional to a one-di mensional integral using a generalization of Stokes's thereom. For a l arge source lensed by a planetary system whose planet lies at the posi tion where one of the two images would be in the absence of a planet, the integral can be done analytically. If the planet lies at the posit ion of the major (unperturbed) images, the excess flux is the same as it would be for an isolated planet. If the planet lies at the minor im age, there is no excess flux.