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J.H. Kastner (Carlson Center for Imaging Science, Rochester Institute of Technology)
Since its discovery 25 years ago, the Egg Nebula (AFGL 2688) generally has been regarded as a classical example of a bipolar nebula shed by an intermediate-mass star that is evolving toward the planetary nebula stage. Recent optical, infrared, and radio observations at high spatial and spectral resolution have revealed a surprising degree of complexity in this object, however. Some of the new results --- for example, polarimetric evidence for a widely separated companion to the central star (Sahai et al. 1998, ApJ, 492, L163; Weintraub et al. 2000, ApJ, 531, 401) --- may provide clues to the processes that shape bipolar planetary nebulae. On the other hand, observations suggesting the presence of multiple axes of symmetry (Cox et al. 2000, A&A, 353, L25; Jura et al. 2000, ApJ, 528, L105) appear to cast doubt on the very interpretation of the Egg as a bipolar planetary nebula in formation. I briefly review these and other recent observational results for the Egg and summarize the challenges posed to our understanding of the structure, formation, and evolution of evolved bipolar nebulae.
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The author(s) of this abstract have provided an email address for comments about the abstract: jhk@cis.rit.edu