Late-type MS stars
display optical variability on different time scales due to the presence of photospheric
brightness inhomogeneities produced by surface magnetic fields, analogous to cool spots
and bright faculae observed in the Sun. We are developing methods
to model the optical variability of main-sequence late-type stars
to understand the impact of solar-like activity on the detection
of planetary transits and to significantly improve the detection
efficiency. Our techniques will also allow to map
the longitude distribution of active regions
on stars that harbor planets and to look for a possible connection
between stellar activity and the presence of planets around a star.