  Light curves of microlensing events involving stellar binaries and planetary
systems can provide information about the orbital elements of the system due to
orbital modulations of the caustic structure. Accurately measuring the orbit in
either the stellar or planetary case requires detailed modeling of subtle
deviations in the light curve. At the same time, the natural, Cartesian
parameterization of a microlensing binary is partially degenerate with the
microlens parallax. Hence, it is desirable to perform independent tests of the
predictions of microlens orbit models using radial velocity time series of the
lens binary system. To this end, we present 3.5 years of RV monitoring of the
binary lens system OGLE-2009-BLG-020L, for which Skowron et al. (2011)
constrained all internal parameters of the 200--700 day orbit. Our RV
measurements reveal an orbit that is consistent with the predictions of the
microlens light curve analysis, thereby providing the first confirmation of
orbital elements inferred from microlensing events.

Solar and Stellar Astrophysics;Earth and Planetary Astrophysics