CAREER: A Comprehensive Study of Proto--Planetary Nebulae Dust Shells and the Development of Experimental Astronomy Programs at the University of Illinois

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9733697 Meixner Dr. Margaret Meixner, of the University of Illinois, is investigating proto-planetary nebulae dust shells around dying stars and developing experimental astronomy programs for graduate and undergraduate students. The research program, which focuses on the late stages of stellar evolution of intermediate mass stars (0.8 to 8 Solar masses), addresses two long standing problems in stellar astrophysics: What physical mechanism drives the asymptotic giant branch star mass loss? What is the nature of the circumstellar dust created by the asymptotic giant branch star during mass loss? The history of asymptotic giant branch star mass loss is imprinted in the circumstellar dustshells of proto-planetary nebulae (objects in transition between the stellar asymptotic giant branch and planetary nebula phases). To discern the final part of this history, Dr. Meixner is collecting infrared data on approximately 100 proto-planetary nebulae dustshells. Ground-based, mid-infrared (0.8-2.5 micrometers wavelength), images of these proto-planetary nebulae show the spatial distribution of the warm (about 300 degree K) dust in the inner regions. The spatial distribution of the scattered starlight is imaged in these proto-planetary nebulae using the Near-InfraRed IMager (NIRIM) on a laser-guided adaptive optics system. A computer program, which models the radiative transfer in the central star and dustshell system, will be used to quantitatively derive the 3D geometries of these dustshells and their inner radii. The information from the infrared data and Hubble Space Telescope images will be used in making the computer models. The 3D models of the geometries will provide insight into the geometry of mass loss during the star's final death throes. A preliminary investigation of several proto-planetary nebulae by Dr. Meixner et al showed that the geometries had an axial symmetry and this indicated that the star's loss mass at a higher rate in the equatorial plane than in the polar region. The data from the observations of the dustshell inner radii are used to estimate the dynamical ages for the proto-planetary nebulae. These ages will be used to test the theoretical timescales of stellar evolution predicted by other scientists. These theoretical timescales are uncertain because the mass loss processes which dominate this stage of stellar evolution are poorly understood. These data will be used to constrain the models of the characteristics of circumstellar dust, including the grain sizes, the composition, and the optical properties of the dust. The circumstellar dust created during the asymptotic giant branch mass loss process in stars is the single most important contribution to the dust observed in our Galaxy. The next generation of stars in our Galaxy are born from this dust enriched interstellar medium. Hence, the new understanding about this dust composition will improve our understanding of galactic evolution. Concurrent with this research program, two educational experimental astronomy programs are being developed. The infrared astronomy program will be expanded by involving graduate and undergraduate students in research on proto-planetary nebulae. These students will learn the latest in infrared observing techniques. A new introductory astronomy laboratory course, entitled Observing the Sky, will be created. This will be used for the large introductory courses that are populated by non-science majors. In this course, the students will learn about astronomical observations by doing observations in a supervised, small-group environment.