2019MNRAS.487L...7M

We extend predictive microlensing event searches using the Vista Variables in the Via Lactea survey and the second Gaia data release. We identify two events with maxima in 2019 that require urgent follow-up. First, we predict that the nearby M2 dwarf L 338-152 will align with a background source with a closest approach of 35⁺³⁵_–23 mas on 2019 November 16⁺²⁸_–27 d. This will cause a peak astrometric shift and photometric amplification of the background source of 2.7^+3.5_–1.5 mas and 5.6^+143.2_–5.2 mmag, respectively. This event should be astrometrically detectable by both the Hubble Space Telescope (HST) and the Spectro-Polarimetric High-contrast Exoplanet Research instrument on the Very Large Telescope. Secondly, we predict that the likely K dwarf NLTT 45128 will lens a background source with a closest approach of 105.3^+12.2_–11.7 mas on 2019 September 26⁺¹⁵_–15 d. This will produce a peak astrometric shift of 0.329^+0.065_–0.059 mas. NLTT 45128 is only 3.6 mag brighter than the background source which makes it an excellent candidate for follow-up with HST. Characterization of these signals will allow direct gravitational masses to be inferred for both L 338-152 and NLTT 45128 with an estimated precision of ∼9 and ∼13 per cent, respectively.