Bayesian Approach for Determining Microlens System Properties with High-Angular-Resolution Follow-up Imaging

TL;DR

This paper develops a Bayesian analysis method to determine properties of microlensing systems using high-resolution follow-up imaging, addressing uncertainties in excess flux attribution and improving lens mass estimates.

Contribution

The paper introduces a Bayesian approach for analyzing microlensing events with excess flux, incorporating prior distributions and applying it to multiple planetary events with high-resolution data.

Findings

Lens mass estimates are more uncertain for small Einstein radii events.

Predictions align with recent Keck and HST observations for some events.

Identifying the lens star via proper motion is crucial for accurate characterization.

Abstract

We present the details of the Bayesian analysis on the planetary microlensing event MOA-2016-BLG-227, whose excess flux is likely due to a source/lens companion or an unrelated ambient star, as well as of the assumed prior distributions. Furthermore, we apply this method to four reported planetary events, MOA-2008-BLG-310, MOA-2011-BLG-293, OGLE-2012-BLG-0527, and OGLE-2012-BLG-0950, where adaptive optics observations have detected excess flux at the source star positions. For events with small angular Einstein radii, our lens mass estimates are more uncertain than those of previous analyses who assumed that the excess was due to the lens. Our predictions for MOA-2008-BLG-310 and OGLE-2012-BLG-0950 are consistent with recent results on these events obtained via Keck and Hubble Space Telescope observations when the source star is resolvable from the lens star. For events with small angular Einstein radii, we find that it is generally difficult to conclude whether the excess flux comes from the host star. Therefore, it is necessary to identify the lens star by measuring its proper motion relative to the source star to determine whether the excess flux comes from the lens star. Even without such measurements, our method can be used to statistically test the dependence of the planet-hosting probability on the stellar mass.