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A.A. McLean (Brigham Young University), M.A. Guerrero, R.A. Gruendl, Y.H. Chu (University of Illinois)
Most planetary nebulae (PNe) show aspherical morphologies or have collimated outflows associated with highly elongated nebular structures. It has been suggested that this wide range of morphologies might all result from the influence of a binary companion throughout the formation of the PN. Very few PNe, however, have known binary central stars because the central stars of PNe are very luminous and a late-type companion would be overwhelmed and difficult to detect.
If the central star of a PN has a binary companion, the evolution of the binary system with mass loss may result in a displacement of the central star from the nebular center. The detection of this offset and its correlation with the morphological characteristics of PNe may provide evidence for a connection between asphericity and binarity in PNe. We have started a program to study the detailed symmetry of the large sample of PNe observed by HST and measure the offset of their central stars from the center of symmetry. Preliminary results are reported in this poster.