The triple-shell structure and collimated outflows of the planetary nebulaNGC 6891

Narrow-band H alpha and [N-II] images and high-dispersion spatially resolve d echelle spectroscopy of the planetary nebula NGC 6891 are presented. Thes e observations show a great wealth of structures. The bright central nebula is surrounded by an attached shell and a detached outer halo. Both the inn er and intermediate shells can be described as ellipsoids with similar majo r to minor axial ratios, but different spatial orientations. The kinematica l ages of the intermediate shell and halo are 4800 and 28 000 yr, respectiv ely. The intershell time lapse is in good agreement with the evolutionary i nterpulse time lapse. A highly collimated outflow is observed to protrude f rom the tips of the major axis of the inner nebula and impact on the outer edge of the intermediate shell. Kinematics and excitation of this outflow p rovide conclusive evidence that it is deflected during the interaction with the outer edge of the intermediate shell. At the same time, both the kinem atics and the morphology of the intermediate shell appear to be affected by this interaction.