  During some gravitational lensing events, the lens transits the face of the
star. This causes a shift in the apparent radial velocity of the star which is
proportional to its rotation speed. It also changes the magnification relative
to what would be expected for a point source. By measuring both effects, one
can determine the rotation parameter $v\sin i$. The method is especially useful
for K giant stars because these have turbulent velocities that are typically
large compared with their rotation speed. By making a series of radial velocity
measurements, one can typically determine $v\sin i$ to the same accuracy as the
individual radial velocity measurements. There are approximately 10
microlensing transit events per year which would be suitable to make these
measurements.
