Nonlinear Stellar Pulsations

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Quite possibly all stars pulsate, though in most stars the pulsations are so small and the stars are so distant that the pulsations are very difficult to detect. For example, in the case of the sun, pulsations have been detected only recently with newly developed instrumentation, giving rise to the science of "helioseismology." Ther are, however, stars that pulsate rather strongly. These stars grow visibly brighter and dimmer, and they expand and contract. Some do so with rather regular periods, as for example the Cepeheid and RR Lyra stars; others are quite erratic in their pulsations, such as the RV Tauri stars. The Principal Investigator (PI) proposes to continue with his current NSF funded theoretical and numerical study of pulsating stars of all types, from Cepeheids and RR Lyra stars to Semi- Regulars and the RV Tauri stars. The computing method will consist of a "judicious mixture of semi-analytical amplitude equation formalism and of numerical hydrodynamics." The goal will be to develop one-parameter families of pulsating star models, rather than to study specific observed stars. In support of this study, the PI proposes to expand his current computer codes to make them more realistic and to interpret stellar pulsation in terms of chaos theory.