Left panel: variation of the angular velocity as a function of the Lagrangian mass inside a 1.5 M_⊙ model along the red giant branch just before (blue continuous line) and after the engulfment (red dashed line) of a 15 M_J mass planet at an initial distance of 0.5 au from the star. Right panel: evolution of the ratio between the angular velocity of the core and surface angular velocity as a function of the surface gravity along the red giant branch for the same models as in the left panel.