# Criteria in the Selection of Target Events for Planetary Microlensing Follow-Up Observation

## TL;DR

This paper establishes criteria for selecting target events in planetary microlensing follow-up observations, highlighting the importance of magnification and source brightness in increasing detection probability, especially for moderate magnifications and bright sources.

## Contribution

It provides new insights into how magnification and source brightness influence planetary signal detection probability, guiding optimal target selection in microlensing surveys.

## Key findings

- Probability increases with magnification, especially around A≈20.
- Brighter source stars have higher detection probabilities at lower magnifications.
- Detection of low mass ratio planets is difficult at very high magnifications with giant stars.

## Abstract

To provide criteria in the selection of target events preferable for planetary lensing follow-up observations, we investigate the variation of the probability of detecting planetary signals depending on the observables of the lensing magnification and source brightness. In estimating the probability, we consider variation of the photometric precision by using a quantity defined as the ratio of the fractional deviation of the planetary perturbation to the photometric precision. From this investigation, we find consistent result from previous studies that the probability increases with the increase of the magnification. The increase rate is boosted at a certain magnification at which perturbations caused by central caustic begin to occur. We find this boost occurs at moderate magnifications of $A\lesssim 20$, implying that probability can be high even for events with moderate magnifications. The probability increases as the source brightness increases. We find that the probability of events associated with stars brighter than clump giants is not negligible even at magnifications as low as $A\sim 5$. In the absence of rare the prime target of very high-magnification events, we, therefore, recommend to observe events with brightest source stars and highest magnifications among the alerted events. Due to the increase of the source size with the increase of the brightness, however, the probability rapidly drops off beyond a certain magnification, causing detections of low mass ratio planets ($q\lesssim 10^{-4}$) difficult from the observations of events involved with giant stars with magnifications $A\gtrsim 70$.