Stellar profiles for a 30 M_⊙ star. Abundances of hydrogen (blue), helium (orange), ¹²C (red), and ¹⁴N (black) as a function of the mass enclosed in a given shell. Left panels are for Z = 0.002, right for Z = 0.004. Top panels: main sequence evolution. Line styles are for different times: dotted for ZAMS, dashed for half main sequence, solid for end of the main sequence. Bottom panels: post main sequence phases. Line styles are for different times: dotted for the time corresponding to minimum temperature, dashed for log(T_eff/K)∼5, solid for log(T_eff/K)∼5.15.