Evolution of the surface velocity of a 2 M_⊙ stellar model during the red giant phase as a function of the luminosity. The initial rotation of the star is 10% of the critical velocity (on the ZAMS). When evolution proceeds, the luminosity in general increases except at the bump visible in the left panel under the form of a small hook. Magenta lines indicate cases without planet engulfment, while blue, green, red, and cyan lines correspond to the engulfment of a planet with a mass equal to 1, 5, 10, and 15 M_J, respectively. The surface velocity reached just before engulfment, i.e. resulting only from tidal forces, is indicated by a small dot. Left panel: the initial semimajor axis is equal to 0.5 au. Right panel: the initial semimajor axis is equal to 1.5 au.