Evolutionary tracks of the stars on the HR diagram. Panel a: for the 10 M_⊙ stars with Z = 0.014 but with different initial rotational velocities, v_ini = 0 km s⁻¹, 120 km s⁻¹, 250 km s⁻¹, 350 km s⁻¹. Panel b: for the 10 M_⊙ stars with Z = 0.0008 but with the corresponding different initial rotational velocities. The instability strip and observational data are from Bono et al. (2000), Turner & Burke (2002), Tammann et al. (2003). Point A in both panels corresponds to the position of the ZAMS and point B corresponds to the start of the overall contraction phase near the end of the main sequence (i.e. the central hydrogen mass fraction X_c ≈ 0.03). Point C corresponds to the exhaustion of hydrogen in the centre and the disappearance of the convective core and point D in the left panel implies the bottom of the Hayashi line. Point E indicates the ignition of the core helium and point F denotes the starting point of the blue loop. Point G implies the bluest location of the blue loop and point H illustrates the terminal of the blue loop.