Photometric, Astrometric and Polarimetric observations of gravitational
  microlensing events
  The gravitational microlensing as a unique astrophysical tool can be used for
studying the atmosphere of stars thousands of parsec far from us. This
capability results from the bending of light rays in the gravitational field of
a lens which can magnify the light of a background source star during the
lensing. Moreover, one of properties of this light bending is that the circular
symmetry of the source is broken by producing distorted images at either side
of the lens position. This property makes the possibility of the observation of
the polarization and the light centroid shift of images. Assigning vectors for
these two parameters, they are perpendicular to each other in the simple and
binary microlensing events, except in the fold singularities. In this work, we
investigate the advantages of polarimetric and astrometric observations during
microlensing events for (i) studying the surface of the source star and spots
on it and (ii) determining the trajectory of source stars with respect to the
lens. Finally we analyze the largest sample of microlensing events from the
OGLE catalog and show that for almost ~ 4.3 per cent of events in the direction
of the Galactic bulge, the polarization signals with large telescopes would be
observable.
