The Use of High‐Magnification Microlensing Events in Discovering Extrasolar Planets

Hundreds of gravitational microlensing events have now been detected towardsthe Galactic bulge, with many more to come. The detection of fine structure inthese events has been theorized to be an excellent way to discover extra-solarplanetary systems along the line-of-sight to the Galactic center. We show thatby focusing on high magnification events the probability of detecting planetsof Jupiter mass or greater in the lensing zone (.6 -1.6 $R_E$) is nearly 100%,with the probability remaining high down to Saturn masses and substantial evenat 10 Earth masses. This high probability allows a nearly definitive statementto made about the existence of lensing zone planets in each such system thatundergoes high magnification. One might expect lightcurve deviations caused bythe source passing near the small primary lens caustic to be small due to thelarge distance of the perturbing planet, but this effect is overcome by thehigh magnification. High magnification events are relatively rare (e.g. $\sim1/20$th of events have peak magnifications greater than 20), but they occurregularly and the peak can be predicted in advance, allowing extra-solar planetdetection with a relatively small use of resources over a relatively smallamount of time.Comment: 17 pages includes 10 postscript figures, AAS Latex, submitted to Ap