Normalized growth rate η (Stellingwerf 1978) vs. frequency for l = 0–4 modes in nine pairs of coeval models with masses 12.0 and 10.6 M_⊙ calculated with OP opacities for X = 0.7374, Z = 0.0134 and V_rot = 0. The observed frequencies of β Cen (Table 3) are shown as vertical dash-dotted (f₁) and dashed (f₂ to f₁₈) lines. To separate the models substantially, an offset of 1.5 is introduced between the consecutive pairs. The inset explains symbols used for unstable modes with different l in models of primary (Pr.) and secondary (Sec.). Stable modes (η< 0) are shown in light gray with the same symbols as the unstable (η> 0) modes. Pairs of models are labeled with model numbers and age. The first number corresponds to the evolutionary track of the primary, the other to that of the secondary.