GRAVITATIONAL MICROLENSING OF THE GALACTIC BULGE STARS

We estimate the optical depth to gravitational microlensing due to known stellar populations to be approximately 8.5 x 10(-7) for the Galactic bulge stars in the Baade Window. The contribution of the bulge and disk stars to the optical depth is approximately 60% and approximately 40%, respectively, all numbers being uncertain. If the stellar mass function is approximated as N(M) approximately M-2 for 0.1 less-than-or-equal-to M/M. less-than-or-equal-to 1.0 then the expected frequency of events with amplitude larger than A = 1.34 is GAMMA(bulge) almost-equal-to 10 and GAMMA(disk) almost-equal-to 2 events per year per 10(6) stars. If the bulge is elongated along the line of sight then the rate GAMMA(bulge) may be still higher. The overall distribution of event timescales is expected to peak at t0 = r(E)/v almost-equal-to 10 days.