A&A 385, 1008-1013 (2002)
A possible observational measure of evolution in bipolar nebulaeJ. 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 , in the sense that higher values of are associated with envelopes having narrower waists. If one interprets the variation in 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
© ESO 2002