The shaping of aging planetary nebulae

Deep narrow-band CCD imaging is used to investigate the mechanism responsible for the present shaping of nine faint, nearby planetary nebulae (PNe) of large angular extent. Despite the variety in their shapes revealed in great detail for the first time by our deep, wide-field imaging, common features are identified to characterize this sample of aging PNe. Severely disturbed emission distributions, dominated mainly by distinct low-ionization features associated with extremely low expansion velocities and turbulent media, as well as huge (approximate to 1 pc diameter) faint halos asymmetrically engulfing the nebular relies, suggest that the mechanism primarily influencing the shaping of aging PNe is the interaction at an early or advanced stage between the nebular material and the ambient interstellar medium (ISM). Clear evidence for such a process is presented here, increasing substantially the number of cases where a PN-ISM interaction has been identified.