EDP Sciences
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Volume 385, Number 3, April III 2002
Page(s) 1008 - 1013
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20020031

A&A 385, 1008-1013 (2002)
DOI: 10.1051/0004-6361:20020031

A possible observational measure of evolution in bipolar nebulae

J. P. Phillips

Instituto de Astronomia y Meteorologia, Avenida Vallarta No. 2602, Col. Arcos Vallarta, C.P. 44130 Guadalajara, Jalisco, Mexico

(Received 30 November 2001 / Accepted 4 January 2002)

Bipolar planetary nebulae (BPNe) possess a broad range of shapes, ranging from narrow-waisted butterfly-like structures, through to those which are more nearly cylindrical. We point out that these morphologies appear to be correlated with radio surface brightness $T_{\rm b}$, in the sense that higher values of $T_{\rm b}$ are associated with envelopes having narrower waists. If one interprets the variation in $T_{\rm b}$ as arising from shell evolution, as is usually assumed for other planetaries, this would then imply that shell morphology varies with time in a manner which appears not to be consistent with evolutionary models. It also remains possible, however, that different BPNe morphologies arise as a result of differing mechanisms of formation, and that the pre-collimation of high velocity central winds gives rise to narrower waists, and higher surface brightness nuclei. Our results, if this is true, may then imply that central winds possess a broad range of collimations.

Key words: ISM: planetary nebulae: general -- ISM: jets and outflows

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