Co-Existence And Switching Between Fast And Omega-Slow Wind Solutions In Rapidly Rotating Massive Stars

Most radiatively-driven massive star winds can be modelled with m-CAK theory\nresulting in so called fast solution. However, those most rapidly rotating\namong them, especially when the stellar rotational speed is higher than $\\sim\n75\\%$ of the critical rotational speed, can adopt a different solution called\n$\\Omega$-slow solution characterized by a dense and slow wind. Here, in this\nwork we study the transition region of the solutions where the fast solution\nchanges to the $\\Omega$-slow. Using both time-steady and time-dependent\nnumerical codes, we study this transition region for different equatorial\nmodels of B-type stars. In all the cases, at certain range of rotational\nspeeds, we found a region where the fast and $\\Omega$-slow solution can\nco-exist. We find that the type of solution obtained in this co-existence\nregion depends heavily on the initial conditions of our models. We also test\nthe stability of the solutions within the co-existence region by performing\nbase density perturbations in the wind. We find that under certain conditions,\nthe fast solution can switch to a $\\Omega$-slow solution, or vice versa. Such\nsolution switching may be a possible contributor of material injected into the\ncircumstellar environment of Be stars, without requiring rotational speeds near\ncritical values.\n