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V. T. Dinh (Inst. of Astronomy & Astrophysics, Academia Sinica (Taipei, Taiwan))
In this talk I will summarize recent results of our program using the Sub-millimeter Array (SMA) to study the structure and dynamics of circumstellar envelopes around AGB (asymptotic giant branch) and post-AGB stars. It's commonly believed that the envelopes around AGB stars are spherically symmetric and asymmetric structures appear later during the short transition phase (proto-planetary nebula or PPN) as the stars evolve rapidly toward higher temperatures and eventually emerge as planetary nebulae (PNs). The SMA with its unique capabilities allows us to probe at high angular resolution the morphological changes of the envelopes at different evolutionary stages. Our detection and imaging of an expanding equatorial disk and collimated high velocity outflow in S star \pi Gru suggest that asymmetric structures already exist in envelopes around normal AGB stars. The envelope around supergiant VY CMa is also imaged and resolved into a massive high velocity outflow and an elongated disk-like structure. The expanding molecular torus around the well-known PPN IRAS 07134+1005 and the detached envelope around supergiant IRC+10420 are also imaged at high angular resolution, allowing for the first time a detailed comparison with mid-IR and optical images. By modelling the CO emission using a multi-dimensional radiation transfer code, we are able to constrain the geometry and mass loss history of the observed envelopes.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.