Bibcode
                                    
                            DOI
                                    
                            Guerrero, M. A.; Vázquez, R.; López, J. A.
    Bibliographical reference
                                    The Astronomical Journal, Volume 117, Issue 2, pp. 967-973.
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                        2
            
                        1999
            
  Citations
                                    36
                            Refereed citations
                                    19
                            Description
                                    Four planetary nebulae (PNe) with conspicuous point-symmetric morphology
are studied in this paper through high-quality imagery and long-slit
echelle spectroscopy. Point symmetry is also found in the velocity
space, and this is related to particular forms of bipolar collimated
outflows. Morphology and kinematics together reveal the presence of
collimated bipolar ejections in an episodic way with indications of
rotation or displacement of the symmetry axis of the outflow. Point
symmetry is currently known to occur in a wide variety of PNe and the
convenience of a reevaluation of point-symmetric PNe as a main
morphological class is pointed out.