Dispersion curves for the torsional wave for various density contrasts. The equilibrium twist is equal to zero and the equilibrium rotation ℛ is equal to 0.1 for all three sets. The black curves are for a density contrast of 4.6, the blue curves for a density contrast of 5.6, and the red curves for a density contrast of 5.9. The solid curves are obtained numerically from Eq. (14), while the dashed curves are plotted from the explicit expression of Eq. (22). The phase speeds are normalised by the internal Alfvén speed.