Prediction of Astrometric Microlensing Events during the Gaia Mission

TL;DR

This paper identifies and verifies candidate stars for astrometric microlensing during Gaia's mission, highlighting the potential for precise stellar mass measurements and the challenges posed by erroneous proper motion data.

Contribution

It constructs a catalog of 43 confirmed astrometric microlensing candidates for Gaia, improving candidate verification and prediction methods.

Findings

96% of high proper motions were erroneous

43 confirmed candidates for Gaia microlensing

Potential to measure centroid shifts between 100 and 4000 microarcsec

Abstract

We identify stars with large proper motions that are potential candidates for the astrometric microlensing effect during the Gaia mission i.e. between 2012 and 2019. The effect allows a precise measurement of the mass of a single star that is acting as a lens. We construct a candidate list by combining information from several input catalogs including PPMXL, LSPM, PPMX, OGLEBG, and UCAC3. The selection of the microlensing candidates includes the verification of their proper motions as well as the calculation of the centroid shift of the source resulting from the astrometric microlensing effect. The assembled microlensing catalog comprises 1118 candidates for the years 2012 to 2019. Our analysis demonstrates that 96% of the (high) proper motions of these candidates are erroneous. We are thus left with 43 confirmed candidates for astrometric microlensing during the expected Gaia mission. For most of them the light centroid shift is below ~100 microarcsec (assuming a dark lens) or the astrometric deviation is considerably reduced by the brightness of the lens. Due to this the astrometric microlensing effect can potentially be measured for 9 candidates that have a centroid shift between 100 and 4000 microarcsec. For 2 of these astrometric microlensing candidates we predict a strong centroid shift of about 1000 and 4000 microarcsec, respectively, that should be observable over a period of a few months up to a few years with the Gaia mission.