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| Paper: |
Strange-Mode Instabilities |
| Volume: |
135, A Half Century of Stellar Pulsation Interpretations: a Tribute to Arthur N. Cox |
| Page: |
89 |
| Authors: |
Glatzel, W. |
| Abstract: |
Based on a review of the properties of strange - mode instabilities meanwhile identified in a variety of models for luminous stars (massive main sequence stars, LBVs, Wolf - Rayet stars, central stars of Planetary Nebulae) and having growth rates in the dynamical range an intuitive model for the underlying physical mechanism is presented. It is argued that the existence of strange modes and an instability apparently oft en associated with them in general do not have a common physical origin. With respect to the instability mechanism we prove that Carnot - type processes, in particular the classical k- and e- mechanisms cannot be responsible for this type of instability at least in those common cases, where instability persists even in the limit of vanishing specific heat (NAR approximation). Rather the instability is of nonthermal origin and may be interpreted in terms of mechanical quantities only. It occurs for small ratios of the thermal and dynamical timescales at intermediate wavenumbers, if radiation pressure dominates. The range of unstable wavenumbers is then proportional to the ratio of total pressure to gas pressure. Possible extensions and tests of the model are commented on. |
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