THE DETECTABILITY OF PLANETARY COMPANIONS OF COMPACT GALACTIC OBJECTSFROM THEIR EFFECTS ON MICROLENSED LIGHT CURVES OF DISTANT STARS

We discuss a possible method for detection of dark companions of Galac tic objects of stellar mass. Such binary systems are likely to occur i n the Galactic disk and possibly also in the halo. The high incidence of binary and higher-multiplicity systems in the solar neighborhood, i f indicative of the Galactic disk at large, implies that current searc hes for the gravitational microlensing signature of massive compact ob jects in our Galaxy would yield a significant fraction of binary syste ms. Our calculations suggest that 40% of the light curves that will be obtained in such searches may be sufficiently perturbed to reveal, if sufficiently well sampled, the presence of a compact dark companion o f Jovian mass orbiting a primary. The likelihood of occurrence of pert urbed light curves must also be taken into account by systematic searc h programs, to improve their event detection efficiency. The statistic s of perturbed lensing events, if carefully interpreted, could yield e stimates of the incidence of binary systems with low mass ratios, incl uding that of systems with planets.