Comparison of the Two Follow‐up Observation Strategies for Gravitational Microlensing Planet Searches

There are two different strategies of followup observations for the detectionof planets by using microlensing. One is detecting the light curve anomaliesaffected by the planetary caustic from continuous monitoring of all eventsdetected by microlensing survey programs (type I strategy) and the other isdetecting anomalies near the peak amplification affected by the central causticfrom intensive monitoring of high amplification events (type II strategy). Itwas shown by Griest & Safizadeh that the type II strategy yields high planetdetection efficiency per event. However, it is not known the planet detectionrate by this strategy can make up a substantial fraction of the total rate. Inthis paper, we estimate the relative planet detection rates expected under thetwo followup observation strategies. From this estimation, we find that therate under the type II strategy is substantial and will comprise $\sim 1/4$ --1/2 of the total rate. We also find that compared to the type I strategy thetype II strategy is more efficient in detecting planets located outside of thelensing zone. We determine the optimal monitoring frequency of the type IIstrategy to be $\sim 20$ times/night, which can be easily achieved by thecurrent microlensing followup programs even with a single telescope.Comment: total 5 pages, including 3 figures and 1 table, ApJ, submitte