  We discuss a possible method for detection of dark companions of galactic
objects of stellar mass. Such binary systems are likely to occur in the
galactic disk and possibly also in the halo. The high incidence of binary and
higher-multiplicity systems in the solar neighborhood, if indicative of the
galactic disk at large, implies that current searches for the gravitational
microlensing signature of massive compact objects in our galaxy would yield a
significant fraction of binary systems. Our calculations suggest that 40% of
the lightcurves that will be obtained in such searches may be sufficiently
perturbed to reveal, if sufficiently well-sampled, the presence of a compact
dark companion of Jovian mass orbiting a primary. The likelihood of occurrence
of perturbed lightcurves must also be taken into account by systematic search
programs, to improve their event detection efficiency. The statistics of
perturbed lensing events, if carefully interpreted, could yield estimates of
the incidence of binary systems with low mass ratios, including that of systems
with planets.

Astrophysics