Transit is the passage of the planet in front of its star. During one of these transits, the planet may occult a spot on the photosphere of the star, causing small variations in its light curve. By detecting the same spot in a later transit, it is possible to estimate the stellar rotation period. The comparison between the rotation period of star at the equator and the planets orbital period showed the existence of resonances between these periods. Two types of mechanisms are proposed in the literature: electromagnetic interaction between the stellar and planetary fields and gravitational interaction. Our results have shown that for planets CoRoT-2b, CoRoT-5b and CoRoT-8b, tidal effects seem to dominate, whereas for planets CoRoT-4b and CoRoT-6b electromagnetic interaction dominates over tidal effects. A distinct characteristic of these last two systems is that the orbital period is larger than the rotation period of the star.
