Radius (top panel) and spin (bottom panel) evolution of a 0.1   M_⊙ and a 1   M_⊙ star. In the bottom panel, the full and dashed dotted blue lines represent, respectively, the evolution of the rotation period of an initially fast rotating star and an initially slow rotating star with no planet. As in the top panel, the blue curves correspond to the 0.1   M_⊙ star and the black curves to the solar-mass star. The blue diamonds in the bottom panel correspond to the values of the spin at 5 Gyr for the two extreme trends of Irwin et al. (2011). The vertical dashed lines represent t₀ for the two stellar masses.