Growth rate of the toroidal mode as a function of M_a. The four panels refer to different values of the pitch parameter P_c (Top left: P_c = 10; Top right: P_c = 1; Bottom left: P_c = 0.1; Bottom right: P_c = 0.01). The solid curves are for α = 1, dashed curves are for α = 0.2, curves with different colours refer to different values of γ_c = 1.01, 2, 5, 10 as indicated in the legend of each panel. The black lines represent the growth rate calculated with non-relativistic ideal MHD equations at zero thermal pressure and the same pitch and α in the respective panel. If the dashed curve is absent in any panel, this means that the equilibrium with α = 0.2 is not possible for that pair of P_c and γ_c associated with this panel. The wavenumber is k = 0.01 in all the cases, although the growth rate is essentially independent of this value.