SIMBAD references

We show that computation of the behavior of circumstellar gas provides a powerful tool for the investigation of stellar mass loss history. Our computations allow us to add a new dimension to the Hertzsprung-Russell diagram by including the existence and size of circumstellar nebulae as an additional diagnostic of stellar evolution. As a first example, we follow the dynamics of the interaction of a 60M_☉ star (Langer et al. 1994) with its circumstellar medium over its entire lifetime. We use an implicit hydrodynamic code for massive stellar evolution to provide the inner boundary conditions for an explicit hydrodynamic code to model the circumstellar gas dynamics. The final supernova phase is not included. Our computations predict short-lived (τ≃10⁴yr) observable nebulae during the luminous blue variable (LBV) stage and the onset of the Wolf-Rayet stage. Small scale features of ring nebulae can also give insight into the preceding stellar wind evolution. We find that variations in the stellar wind drive an instability that produces radial filaments in ring nebulae. The filaments maintain an almost steady angular spacing, but grow radially. This may explain the short angular spacing and comet-like tails of clumps observed in ring nebulae surrounding massive stars such as RCW 58 or AG Carinae. This instability may also explain the clumps observed in several planetary nebulae such as the Helix nebula and NGC 2392. Furthermore, the double shell structure found in our computations resembles that observed in η Carinae. Finally, we obtain a fragmented circumstellar nebula in our model for the LBV phase corresponding to P Cygni.