Two-dimensional parameter space of differentially rotating models (Ψ,χ); the remaining parameters are fixed at values . The upper solid line marks the maximum admitted values of χ, as in Fig. 9. The lower solid line marks the values of χ at which the models start to exhibit a central toroidal structure; the dashed line marks the upper limit of the condition for the existence of the central toroidal structure (see Eq. (51)).