U.S.-Netherlands Cooperative Research on Hydrodynamic Modelsof the Shaping of Planetary Nebulae

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This award will enable Professor Bruce Balick of the University of Washington to collaborate with Professor Vincent Icke of the University of Leiden, The Netherlands, in a study of planetary nebulae, which are hot, ionized clouds of gas associated with the final stages of stellar life. Their collaboration will involve obtaining improved observational descriptions of planetary nebulae and developing improved models to explain the causes of the intricate and symmetrical shapes of the nebulae. Professor Balick has an extensive observational data base on planetary nebulae and he has experience in testing model predictions by detailed observations. Professor Icke is an expert in theoretical nebular hydrodynamics, and has developed a very sophisticated computer simulation program that has been successfully adapted for modelling other stellar objects such as supernovae remnants. Collaboration with Dr. Balick will facilitate access to a U.S. supercomputer to run the complex programs needed to model nebular dynamics. Planetary nebulae are gaseous shells ejected by aging stars. The ejection is thought to occur in two stages, first as a rather slow "wind" containing the outer layers of the star (over a period of thousands of years), then a much faster expulsion of deeper layers in only a few centuries. Theoretical models and recent observations suggest that the nebulae acquire their shapes as this fast wind overtakes and interacts with the outer layers ejected earlier. A recent survey of 50 planetary nebulae shows that the concept of wind shaping is generally valid, but that the models developed to explain the phenomenon are much too simplistic. The goal of this project is to develop and test more complex models to explain the shapes and evolutions of planetary nebulae. Three-dimensional hydrodynamic models require years to develop and can only reasonably be tested with the aid of a supercomputer. Development of the enhanced models needed to explain nebular shapes will be greatly facilitated by the combination of Dr. Balick's observational data and model testing skills with Dr. Icke's theoretical insights and ability to modify the computer code he has already developed. Ultimately, their collaboration should contribute to resolving some longstanding questions about the shapes and evolution of planetary nebulae.