The two-point-mass lens - Detailed investigation of a special asymmetric gravitational lens

The authors consider here as a specific nonsymmetric lens model a system of two point masses which is just easy enough to study some generic properties of lenses analytically in some detail. The geometry of critical curves is determined and, for the limiting case of large distance between the two point masses, compared to the geometry of Chang and Refsdal (1979, 1984) lenses. Starting from special solutions of the lens equation, a simple method to obtain the general solution is described, which is also applicable to more general lens models. It is shown that the specific model is of some relevance for double stars and close pairs of galaxies.