The hydrodynamic evolution of circumstellar gas around massive stars .2. The impact of the time sequence O star->RSG->WR star

We investigate the interaction of a 35 M(.) star with its circumstellar medium over the entire stellar life time, combining an implicit hydrodynamic code for the calculation of the massive stellar evolution, and an explicit hydrodynamic code for the treatment of the circumstellar gas. The final supernova phase is not included. The 35 M(.) stellar model has three well defined evolutionary phases: main sequence, red supergiant and Wolf-Rayet stage. It provides a realistic test for the three-wind model of Wolf-Rayet bubbles. We find the velocity of the red supergiant wind to be a key parameter affecting the formation and detectability of a ring nebula in the Wolf-Rayet stage. We investigate systematic differences of wind shells and nebulae around post-RSG WR stars compared to those of post-LBV WR stars. The Wolf-Rayet star WR 136 is located on our evolutionary track in the HR diagram, and the computed circumstellar gas distribution at the time our stellar model hits the position of WR 136 is in good agreement with its observed nebula NGC 6888. The ring nebula Sh 308 around WR 6 can be explained when the RSG wind has higher velocity than in the case of NGC 6888. Our results support the interpretation of the H II regions Sh 303 and Sh 304 as parts of the fossil swept-up main sequence shell surrounding Sh 308, in accord with the three-wind model. Finally, we obtain constraints on the initial mass of the progenitor of the supernova remnant Cassiopeia A. We find that in order to explain the existence of quasi-stationary flocculi, the stellar progenitor should have an initial mass of similar to 30 M(.), just above the lower initial-mass limit for WR star formation.