First Resolution of Microlensed Images of a Binary-Lens Event

Kavli Affiliate: Jinyi Shangguan

| First 5 Authors: Zexuan Wu, Subo Dong, A. Mérand, Christopher S. Kochanek, Przemek Mróz

| Summary:

We resolve the multiple images of the binary-lens microlensing event
ASASSN-22av using the GRAVITY instrument of the Very Large Telescope
Interferometer (VLTI). The light curves show weak binary-lens perturbations,
complicating the analysis, but the joint modeling with the VLTI data breaks
several degeneracies, arriving at a strongly favored solution. Thanks to
precise measurements of angular Einstein radius theta_E = 0.724 +/- 0.002 mas
and microlens parallax, we determine that the lens system consists of two M
dwarfs with masses of M_1 = 0.258 +/- 0.008 M_sun and M_2 = 0.130 +/- 0.007
M_sun, a projected separation of r_perp = 6.83 +/- 0.31 au and a distance of
D_L = 2.29 +/- 0.08 kpc. The successful VLTI observations of ASASSN-22av open
up a new path for studying intermediate-separation (i.e., a few astronomical
units) stellar-mass binaries, including those containing dark compact objects
such as neutron stars and stellar-mass black holes.

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