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

Abstract

There are two different strategies of follow-up observations for the detection of planets by using microlensing. One is detecting the light-curve anomalies affected by the planetary caustic from continuous monitoring of all events detected by microlensing survey programs (type I strategy), and the other is detecting anomalies near the peak amplification affected by the central caustic from intensive monitoring of high-amplification events (type II strategy). It was shown by Griest & Safizadeh that the type II strategy yields high planet detection efficiency per event. However, it is not known whether the planet detection rate by this strategy can make up a substantial fraction of the total rate. In this paper, we estimate the relative planet detection rates expected under the two follow-up observation strategies. From this estimation, we find that the rate under the type II strategy is substantial and will comprise ~- of the total rate. We also find that compared to the type I strategy the type II strategy is more efficient in detecting planets located outside of the lensing zone. We determine the optimal monitoring frequency of the type II strategy to be ~20 times per night, which can be easily achieved by the current microlensing follow-up programs even with a single telescope.