Ongoing astrometric microlensing events from VVV and Gaia. (arXiv:1905.08270v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+McGill_P/0/1/0/all/0/1">Peter McGill</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Smith_L/0/1/0/all/0/1">Leigh C. Smith</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Evans_N/0/1/0/all/0/1">N. Wyn Evans</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Belokurov_V/0/1/0/all/0/1">Vasily Belokurov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lucas_P/0/1/0/all/0/1">Philip W. Lucas</a>
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 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 magnitudes brighter than the background source which makes it an
excellent candidate for follow-up with HST. Characterisation of these signals
will allow direct gravitational masses to be inferred for both L 338-152 and
NLTT 45128 with an estimated precision of $sim9$ and $sim13$ per cent
respectively.
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 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 magnitudes brighter than the background source which makes it an
excellent candidate for follow-up with HST. Characterisation of these signals
will allow direct gravitational masses to be inferred for both L 338-152 and
NLTT 45128 with an estimated precision of $sim9$ and $sim13$ per cent
respectively.
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