Detectability of Orbital Motion in Stellar Binary and Planetary
  Microlenses
  A standard binary microlensing event lightcurve allows just two parameters of
the lensing system to be measured: the mass ratio of the companion to its host,
and the projected separation of the components in units of the Einstein radius.
However, other exotic effects can provide more information about the lensing
system. Orbital motion in the lens is one such effect, which if detected, can
be used to constrain the physical properties of the lens. To determine the
fraction of binary lens lightcurves affected by orbital motion (the detection
efficiency) we simulate lightcurves of orbiting binary star and star-planet
(planetary) lenses and simulate the continuous, high-cadence photometric
monitoring that will be conducted by the next generation of microlensing
surveys that are beginning to enter operation. The effect of orbital motion is
measured by fitting simulated lightcurve data with standard static binary
microlensing models; lightcurves that are poorly fit by these models are
considered to be detections of orbital motion. We correct for systematic false
positive detections by also fitting the lightcurves of static binary lenses.
For a continuous monitoring survey without intensive follow-up of high
magnification events, we find the orbital motion detection efficiency for
planetary events with caustic crossings to be 0.061+-0.010, consistent with
observational results, and 0.0130+-0.0055 for events without caustic crossings
(smooth events). Similarly for stellar binaries, the orbital motion detection
efficiency is 0.098+-0.011 for events with caustic crossings and is
0.048+-0.006 for smooth events. These result in combined (caustic crossing and
smooth) orbital motion detection efficiencies of 0.029+-0.005 for planetary
lenses and 0.070+-0.006 for stellar binary lenses. We also investigate how
various microlensing parameters affect the orbital motion detectability.
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