The problem now arises how to treat the above singularities when integrating. The eigenvalue problem is able to be solved only by means of numerical calculations. It occurred that for all involved in calculations, so the jet seems to be stable with respect to helicoidal perturbations too. We are only sure that our model jet is stable with respect to perturbations having wavelength long enough, i.e. for perturbations with limited values of , and radial wavenumber. The dependence of the real part of . , .
Straight lines are and .
Following the procedure outlined we have calculated the dispersion curves . The first three branches of them for and are shown in Figure 1 . In Figure 2 we show the dependence of the real part of for . Those having can be obtained by the reflection of Figure 1 and Figure 2 with respect to the coordinates origin. The remarkable feature of the dependencies is that they have a minimum at some and .