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Session 15 - Planetary Nebulae and White Dwarfs.
Display session, Wednesday, January 07
A planetary nebula forms when a dying star begins to dissociate and ionize a surrounding dense envelope of the predominantly neutral and molecular material. This stellar ejecta is the result of heavy mass loss during the asymptotic giant branch phase. We report initial results from an HST/NICMOS program to study the distribution of hot neutral (molecular hydrogen) and ionized circumstellar material in young planetary nebulae and post-asymptotic giant branch objects. NICMOS provides very high spatial resolution imaging in line and continuum emission, and the stability and large dynamic range needed for investigating detailed structures in the circumstellar material. We present dramatic new images of NGC 7027 that have provided a new understanding of the structure in this important planetary nebula. Several other objects at various evolutionary states are being investigated, and some of our early results will be presented. This work is part of a detailed study into the evolution of circumstellar material exposed to strong and time-variable ultraviolet radiation fields.
Program listing for Wednesday