Evolution of a 0.55 M_⊙ model. Top: Kippenhahn diagram. Radius of interfaces in solar unit as a function of the model’s age. Convective zones (resp. radiative zones) are represented as dark (resp. light) gray areas. Middle: Aspect ratio (left axis) and density contrast (right axis). The inner radius, r_i, is the bottom radius of the convective envelope, while the outer radius, r_o, is 90% of the photospheric radius. Bottom: Kelvin-Helmholtz (blue) and convection (green) timescales and surface rotation period (red). The shaded areas correspond to the classical T Tauri phase (CTTS; light green), which coincides in our case with the disk-locking phase and weak T Tauri phase (WTTS; green).