The Hollywood Strategy for Microlensing Detection of Planets

TL;DR

This paper reviews microlensing detection methods for exoplanets, emphasizing follow-up observations of giant-star events to measure key parameters and resolve degeneracies, thereby advancing understanding of planetary systems and galactic structure.

Contribution

It introduces a simple analytic model for parameter degeneracy in microlensing and discusses observational strategies to break this degeneracy effectively.

Findings

Monitoring giant-star microlensing events enables measurement of planet/star parameters.

Accurate photometry can break degeneracies between key parameters.

Giant-star events provide insights into the structure of the inner Galaxy.

Abstract

Follow the big stars! I review the theory of detection and parameter measurement of planetary systems by follow-up observations of ongoing microlensing events. Two parameters can generically be measured from the event itself: the planet/star mass ratio, $q$, and the planet/star separation in units of the Einstein ring. I emphasize the advantages of monitoring events with giant-star sources which are brighter (thus easier to monitor) and bigger (thus offering the prospect of measuring an additional parameter from finite-source effects: the proper motion $\mu$). There is potentially a strong degeneracy between $q$ and $\mu$. I present a simple analytic representation of this degeneracy. I then describe how it can be broken using accurate single-band photometry from observatories around the world, or optical/infrared photometry from a single site, or preferably both. Both types of observations are underway or will be soon. Monitoring of giant-star events seen toward the bulge is also the best way to determine the content and structure of the inner Galaxy.