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V. V. Dwarkadas (University of Chicago), R. Sahai (NASA JPL/Caltech), D. G. York (University of Chicago), J. Thorburn (University of Chicago/Yerkes), C.-F. Lee (CfA, Harvard)
Pre-planetary nebulae (PPNs) are objects representing the crucial evolutionary phase between the completion of the AGB phase and the planetary nebula (PN) phase. PNs are formed from PPNs when the central stars becomes hot enough to ionize the circumstellar medium. We have started a project to study, both observationally and theoretically, the nature of these objects. In this poster we report on early results from our studies. On the observational side we show results from echelle spectroscopy of two extended PPNs, IRAS 20068+4051 and IRAS 09371+1212 (Frosty Leo). The spectra allow us to determine the spectral type and properties of the central star. The extended nature of the objects permits an evaluation of the expansion properties of the nebula, using appropriate approximations. These properties can be used to provide constraints on the theoretical models, which are intended to investigate the formation and evolution of outflows around these stars expanding into the surrounding dense AGB wind. High-resolution numerical simulations of collimated outflow expansion have been carried out using the Zeus-3D finite-difference hydrodynamics code. In particular we have investigated the scenario when the outflow is turned off after a finite time. First results from these calculations are presented.
This work is partially supported by NASA through grant number HST-AR-10317 awarded by the Space Science Telescope Institute to RS and VVD. VVD's research is also supported by NSF award AST 0319261.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.