Brunt–Väisälä frequency profiles as a function of the distance to the center of the star, normalized to the radius of its radiative zone, at 30 Myr (top panel), 900 Myr (middle panel), and 5 Gyr (bottom panel). The dotted profiles are situated in the PMS, the plain lines in the MS, and the dash-dotted lines in the post-MS phase. The colors correspond to the same stellar masses as in Fig. 4. The dashed lines correspond to the tangents to the N² profiles at the interface. The triangles indicate the position of the maximum Brunt–Väisälä frequency.