Predicted microlensing events from analysis of Gaia Data Release 2

Astrometric microlensing can be used to make precise measurements of the masses of lens stars that are independent of their assumed internal physics. Such direct mass measurements, obtained purely by observing the gravitational effects of the stars on external objects, are crucial for validating theoretical stellar models. Specifically, astrometric microlensing provides a channel to direct mass measurements of single stars for which so few measurements exist. To use the astrometric solutions and photometric measurements of ~1.7 billion stars from Gaia Data Release 2 to predict microlensing events during the nominal Gaia mission and beyond. This will enable astronomers to observe the entirety of each event with appropriate observing resources. The data will allow precise lens mass measurements for white dwarfs and low-mass main sequence stars helping to constrain stellar evolutionary models. I search for source-lens pairs in GDR2 that could lead to events between 25/07/2014 and 25/07/2026. I estimate lens masses using GDR2 photometry and parallaxes, and appropriate model isochrones. Combined with source and lens parallax measurements from GDR2, this allows the Einstein radius to be computed for each pair. By considering the paths on the sky, I calculate the microlensing signals that are to be expected. I present a list of 76 predicted microlensing events. 9 and 5 astrometric events will be caused by LAWD37 and Stein2051B. 9 events will exhibit detectable photometric and astrometric signatures. Of the remaining events, ten will exhibit astrometric signals with amplitudes above 0.5 mas, while the rest are low-amplitude astrometric events with amplitudes between 0.131 and 0.5 mas. 5 and 2 events will reach their peaks during 2018 and 2019. 5 of the photometric events have the potential to evolve into high-magnification events, which may also probe for planetary companions to the lenses.