SIMBAD references

We present high resolution images and high dispersion spectra of the planetary nebula IC 4593. Benefiting from superb seeing (0"4), the narrowband images reveal the existence of a complex system of collimated knots in the inner 15" of the nebula. The knots, which morphologically resemble outward facing bow-shocks, are located at different position angles and distances from the centre, present very low radial velocities, extended tails pointing toward the central star, as well as peculiar extensions in the outer regions of the nebula. Some of these properties seem to indicate that the observed structures are multiple collimated outflows propagating from the central star throughout the nebula along very different directions. This is a mass loss scenario, however, that is not predicted or reproduced by any theoretical model for AGB and post-AGB stars. The origin of the inner knots remains therefore enigmatic. The isolated, outermost condensations of the nebula previously detected by various authors are found to be part of a very faint and large asymmetrical halo.