  Gravitational microlensing events produced by lenses composed of binary
masses are important because they provide a major channel to determine physical
parameters of lenses. In this work, we analyze the light curves of two
binary-lens events OGLE-2006-BLG-277 and OGLE-2012-BLG-0031 for which the light
curves exhibit strong deviations from standard models. From modeling
considering various second-order effects, we find that the deviations are
mostly explained by the effect of the lens orbital motion. We also find that
lens parallax effects can mimic orbital effects to some extent. This implies
that modeling light curves of binary-lens events not considering orbital
effects can result in lens parallaxes that are substantially different from
actual values and thus wrong determinations of physical lens parameters. This
demonstrates the importance of routine consideration of orbital effects in
interpreting light curves of binary-lens events. It is found that the lens of
OGLE-2006-BLG-277 is a binary composed of a low-mass star and a brown dwarf
companion.
