  Despite astrophysical importance of binary star systems, detections are
limited to those located in small ranges of separations, distances, and masses
and thus it is necessary to use a variety of observational techniques for a
complete view of stellar multiplicity across a broad range of physical
parameters. In this paper, we report the detections and measurements of 2
binaries discovered from observations of microlensing events MOA-2011-BLG-090
and OGLE-2011-BLG-0417. Determinations of the binary masses are possible by
simultaneously measuring the Einstein radius and the lens parallax. The
measured masses of the binary components are 0.43 $M_{\odot}$ and 0.39
$M_{\odot}$ for MOA-2011-BLG-090 and 0.57 $M_{\odot}$ and 0.17 $M_{\odot}$ for
OGLE-2011-BLG-0417 and thus both lens components of MOA-2011-BLG-090 and one
component of OGLE-2011-BLG-0417 are M dwarfs, demonstrating the usefulness of
microlensing in detecting binaries composed of low-mass components. From
modeling of the light curves considering full Keplerian motion of the lens, we
also measure the orbital parameters of the binaries. The blended light of
OGLE-2011-BLG-0417 comes very likely from the lens itself, making it possible
to check the microlensing orbital solution by follow-up radial-velocity
observation. For both events, the caustic-crossing parts of the light curves,
which are critical for determining the physical lens parameters, were resolved
by high-cadence survey observations and thus it is expected that the number of
microlensing binaries with measured physical parameters will increase in the
future.
