Differential rotators. a) Iso-density surfaces in model stars of M = 15   M_⊙ in the ZAMS having the internal rotation law (61), whose parameters Ω_o/Ω_cr and β are indicated. Ω_cr is for the critical rigid rotation. The iso-density surfaces are labeled with the corresponding density ratios ρ/ρ_c, which are the same as in Fig. 6 and for all panels of this figure. b) Iso-density surfaces in model stars of M = 15   M_⊙ in the TAMS having the internal rotation law (61), whose parameters Ω_o/Ω_cr and β are indicated. In each panel, the ordinates are in the same scale as the abscissas, but they differ from one to the other panel.