Millions of stars need to be photometrically monitored to find examples of gravitational microlensing. Very large
databases are consequently formed on variable stars. For example, the database of stars in the Large Magellanic
Cloud has been used by the MOA group to study long-period red variable stars. A multiplicity in the
period-luminosity relation, shown below, was confirmed, and studied in terms of excitation mechanisms of red
pulsating variables. We found that almost all Mira stars are located on the classical period-luminocity relation in
spite of the multiplicity.
Period-luminos ity diagram of red variables in the LMC. Several sequences of
stars are apparent.
Other types of variable stars are also searched for using wide-field survey telescopes,
including the optical counterparts of gamma ray bursts and X-ray transients. The optical
counterpart of an X-ray transient is shown below.
Optical counterpart of an X-ray transient found at Mt John