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K.Y.L. Su, K. Volk, S. Kwok (Univ. of Calgary)
Recent HST observations of Proto-Planetary Nebulae (PPN) and young planetary nebulae (PN) have found evidence that the shaping of PN morphology occurs early in PN evolution (Kwok et al. 1998, ApJ, 501, L117; Su et al. 1998, ApJ, 509, in press; Sahai & Trauger 1998, AJ, 116, 1357). Many interesting structures, including bipolar lobes, searchlight beams, colliminated jets, and concentric arcs, have been discovered. The bipolar nebulosities and the searchlight beams are believed to be created by scattered light from a polar cavity cleared by stellar winds or collimated jets.
Results from a 2-D radiation transfer program created to model the morphologies of PPN are presented. Using the observed spectral energy distributions, flux ratios between the two reflection lobes, and the separation angles of the searchlight beams as constraints, the mass, sizes, and sky orientations of the circumstellar dust envelopes can be derived. Simulated images at different wavelengths are calculated and compared with the observed HST WFPC2 and NICMOS images.
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