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

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 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 of Jovian mass orbiting a primary. The likelihood of occurrence of perturbed light curves 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.