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Expectations from a Microlensing Search for Planets

Expectations from a Microlensing Search for Planets

S. J. Peale
Dept. of Physics, University of California, Santa Barbara, CA

Samples of expected results from an intensive search for planets about stars acting as gravitational lenses (lens stars) of galactic bulge stars (source stars) during microlensing events are constructed. Four or five dedicated telescopes at three specific developed sites in the southern hemisphere and Hawaii in the northern hemisphere can recover about 50% of the detectable planetary perturbations of the lensing light curves. The Gould and Loeb (1992) detection probabilities are scaled to arbitrary planetary mass and mean lens distance and averaged over the lens mass function. For planetary systems that are assumed to be similar to the solar system and for an assumed data set of 3000 events obtained over perhaps an eight year period, the number of detections are sufficient to constrain the planetary mass distribution to within about a factor of three and yield a rough estimate of the distribution of semimajor axes of the planets as a function of their mass. The expected total number of planets detected depends entirely on the assumptions about the nature of the planetary systems being sought. Comparison with a calculation based on the Bennett and Rhie (1996) analysis, where the finite size of the source is accounted for, indicates that our estimates for the detection of terrestrial mass planets may not be in error by more than a factor of two for given assumptions about the nature of the planetary systems.