MULTIPLE COLLIMATED OUTFLOWS IN A PLANETARY-NEBULA

We present high resolution images and high dispersion spectra of the p lanetary nebula IC 4593. Benefiting from superb seeing (0 ''.4), the n arrowband images reveal the existence of a complex system of collimate d knots in the inner 15 '' of the nebula. The knots, which morphologic ally resemble outward facing bow-shocks, are located at different posi tion angles and distances from the centre, present very low radial vel ocities, extended tails pointing toward the central star, as well as p eculiar extensions in the outer regions of the nebula. Some of these p roperties seem to indicate that the observed structures are multiple c ollimated outflows propagating from the central star throughout the ne bula along very different directions. This is a mass loss scenario, ho wever, that is not predicted or reproduced by any theoretical model fo r AGB and post-AGB stars. The origin of the inner knots remains theref ore enigmatic. The isolated, outermost condensations of the nebula pre viously detected by various authors are found to be part of a very fai nt and large asymmetrical halo. (C) 1997 Elsevier Science B.V.