Pile-up of the Stokes Q (left), U (center) and I (right) profiles over the whole time series. For illustrative purposes, every observation has been made to span 15 days on the vertical direction. The blue and red vertical lines mark the maximum plasma velocity V_p and the radial velocity of the center of mass of the star V_* respectively (see main text for definitions). Velocities are measured in the heliocentric reference system.