The effects of resolved sources and blending on the detection of planets via gravitational microlensing

It has been shown that gravitational microlensing events towards the Galactic Bulge are sensitive to the presence of a planet orbiting the lensing star. The probability of planet detection is calculated here as a function of the binary geometry for mass ratios of q 10(-3)-10(-5), taking the effects of resolving the source and the inclusion of unlensed light (blending) into account. Source radii up to R-S = 0.3 theta (E) are considered, at which point the detection probability becomes negligible. Small (q < 10(-4)) mass ratio planets become undetectable at source radii of R-S = 0.08 (E). Blending has a slight adverse effect on planet detection. It is worst when the unblended detection probability is small and causes planets to become undetectable at smaller source radii than would be the case in the absence of blending. An alternative to current gravitational microlensing follow-up observations is investigated, where only the peaks of high amplification events are followed. Such a strategy promises to be at least twice as efficient at detecting planets as current observations, but requires a large number of high amplification events.