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S. Kwok (University of Calgary)
In addition to the main nebular shells, planetary nebulae (PNe) are now known to possess secondary shell structures called crowns and haloes. These structures can be satisfactorily explained by coupled dynamical and stellar evolutionary models based on the interacting winds scenario. By introducing time-variability in the fast wind, these models also have some success in accounting for other microsctructures such as jets and FLIERs.
A more surprising development has been the discovery of multipolar structures in PNe. A number of bipolar nebulae have been found to have 2 or 3 bipolar axes, sometimes superimposed with multiple 2-dimensional rings and concentric circular arcs. The existence of these features suggests that the fast wind may be changing in direction in addition to varying in magnitude. In this paper, we will summarize the current observations of multipolar nebulae and discuss their possible origins.
This work is supported by the Natural Sciences and Engineering Research Council of Canada, and by a Killam Fellowship from the Canada Council for the Arts.
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The author(s) of this abstract have provided an email address for comments about the abstract: kwok@iras.ucalgary.ca
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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.