Session 19 - Solar & Planetary Systems.
Display session, Monday, January 13
Metropolitan Ballroom,

## [19.08] The Probability of Microlensing Detections of Planetary Systems

R. A. Scalzo (U. Virginia), R. Di Stefano (Harvard College Obs.)

The microlensing monitoring programs have detected lensing by binaries. It would seem to be only a matter of time before planets are also detected. Most calculations of the probability of detecting planets, however, have focused on the case in which a single planet is located at a distance, a \sim R_E, from the central star. In this so-called ``resonant" case, the signature of the planet's presence is a spike in a light curve whose basic shape is governed by the lensing associated with the central star. The spike is typically sharp and short-lived.

We point out that it is also possible for the microlensing monitoring programs to find evidence of planets with a > 1.5 R_E. The signal of the planets' presence is a multiply-peaked event. Finite source-size effects are less problematic in this ``wide" orbit case. We compute the probability of the detection of planets in wide orbits. Since it seems likely that most planetary systems contain multiple planets, we explicitly consider systems with N planets, and include orbital inclination and finite orbital velocity effects. We obtain numerical results for different lensing geometries and solar systems by analytic approximations to the resulting nonlinear equations. Finally, we use a Monte Carlo model to generate several sample light curves. We find that, if planets are typically found in planetary systems, then the discovery of planets in wide (as opposed to resonant) orbits seems promising.