Evolution of the stellar surface-rotation rate (top panel), stellar Rossby number (middle panel) and X-ray luminosity (bottom panel), under the impact of planetary inward migration. In this case, we fix the initial mass of the planet (3 M_J), the initial surface rotation rate of the host star (Ω_in = 3.2 Ω_⊙), while we vary the initial orbital distance (a_in = 0.02, 0.025, 0.03, 0.035, 0.04, 0.06, 0.08, 0.1 AU). The meaning of the other quantities is the same as in Fig. 3.