Mean rotation velocity profiles on the equatorial plane for the selected critical second-order rigidly rotating models with Ψ = 1,2,...,10 (from left to right). The mean velocity increases linearly with radius because the rotation is rigid (see Eq. (18); note the logarithmic scale of the horizontal axis). The values of the termination points of the curves depend on the value of χ_cr (which decreases as Ψ increases, see Fig. 2) and on the extension of the models on the equatorial plane (which increases as Ψ increases, see Fig. 4).