# OGLE-2018-BLG-0022: First Prediction of an Astrometric Microlensing Signal from a Photometric Microlensing Event

## TL;DR

This paper analyzes a binary microlensing event using combined ground and space observations, accurately determining lens masses and predicting an astrometric signal that can be tested with future Gaia data.

## Contribution

It presents the first prediction of an astrometric microlensing signal from a photometric event, enabled by precise mass and parallax measurements.

## Key findings

- Determined lens masses with high precision.
- Predicted the astrometric offset observable by Gaia.
- Demonstrated the potential for future astrometric verification.

## Abstract

In this work, we present the analysis of the binary microlensing event OGLE-2018-BLG-0022 that is detected toward the Galactic bulge field. The dense and continuous coverage with the high-quality photometry data from ground-based observations combined with the space-based {\it Spitzer} observations of this long time-scale event enables us to uniquely determine the masses $M_1=0.40 \pm 0.05~M_\odot$ and $M_2=0.13\pm 0.01~M_\odot$ of the individual lens components. Because the lens-source relative parallax and the vector lens-source relative proper motion are unambiguously determined, we can likewise unambiguously predict the astrometric offset between the light centroid of the magnified images (as observed by the {\it Gaia} satellite) and the true position of the source. This prediction can be tested when the individual-epoch {\it Gaia} astrometric measurements are released.