@conference{4608,
  author = {S. Kwok and K. Volk and Bruce Hrivnak},
  title = {Candidates for bipolar proto-planetary nebulae},
  year = {1991},
  publisher = {San Francisco: ASP},
  url = {http://adsabs.harvard.edu/full/1991ASPC...14..155K},
  note = {JILA Pub. 4238},
}