Kavli Affiliate: Michael Fausnaugh
| First 5 Authors: Zhecheng Hu, Wei Zhu, Andrew Gould, Andrzej Udalski, Takahiro Sumi
| Summary:
We present the analysis of the microlensing event OGLE-2015-BLG-0845, which
was affected by both the microlensing parallax and xallarap effects. The former
was detected via the simultaneous observations from the ground and Spitzer, and
the latter was caused by the orbital motion of the source star in a relatively
close binary. The combination of these two effects led to a direct mass
measurement of the lens object, revealing a low-mass ($0.14 pm 0.05
M_{odot}$) M-dwarf at the bulge distance ($7.6 pm 1.0$ kpc). The source
binary consists of a late F-type subgiant and a K-type dwarf of $sim1.2
M_{odot}$ and $sim 0.9 M_{odot}$, respectively, and the orbital period is
$70 pm 10$ days. OGLE-2015-BLG-0845 is the first single-lens event in which
the lens mass is measured via the binarity of the source. Given the abundance
of binary systems as potential microlensing sources, the xallarap effect may
not be a rare phenomenon. Our work thus highlights the application of the
xallarap effect in the mass determination of microlenses, and the same method
can be used to identify isolated dark lenses.
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