The evolution of circumstellar medium around rotating massive stars

Abstract

A rotating 12Mȯ star, after its main-sequence evolution, becomes a redsupergiant when it starts core He burning. During core helium burning, as consequence of a variation of the hydrogen shell burning efficiency, the star undergoes a so called ``blue loop'', i.e. it evolves into a blue supergiant stage, where it finishes core helium burning and becomes a redsupergiant again, before exploding as a supernova. We try to explain the structures in Sher5 and in SN987A through wind asymmetry caused by rotation. We use a stellar evolution model to provide us with the time dependent stellar wind parameters such as wind velocity and mass-loss rate. These parameters serve as an input for hydrodynamical simulation of the circumstellar medium. The blue loop causes a very aspherical structure due to rotation, while the main sequence and redsupergiant phases are basically spherical. We can conclude that the asymmetry of Sher 25 can be explained through stellar rotation.