QUADRUPOLAR PLANETARY-NEBULAE - A NEW MORPHOLOGICAL CLASS

In the context of the Institute de Astrofisica de Canarias (IAC) morph ological survey of Galactic planetary nebulae (PNs), a new morphologic al class has been found, and we define their members as quadrupolar PN s. We have found five quadrupolar objects whose lobes are, in pairs, s ymmetric with respect to two different axes. Among these PNs, three (M 2-46, K3-24, and M1-75) have well-defined pairs of lobes; another two (M3-28 and M4-14) are irregular and very possibly quadrupolar. For M2- 46, we have measured the extension and the angle between the lobes, an d the expansion velocities of the lobes by means of spectroscopic anal ysis. We propose that these nebulae have been formed by precession of the rotation axis of the central stars, possibly in the presence of a binary companion, associated with multiple shell ejection at the asymp totic giant branch. A simple binary mechanism not associated with prec ession cannot produce such a morphology.