Close binary central stars and the abundance discrepancy - new extreme
  objects
  Recent work (Corradi et al. 2015, Jones et al. 2016) has shown that the
phenomenon of extreme abundance discrepancies, where recombination line
abundances exceed collisionally excited line abundances by factors of 10 or
more, seem to be strongly associated with planetary nebulae with close binary
central stars. To further investigate, we have obtained spectra of a sample of
nebulae with known close binary central stars, using FORS2 on the VLT, and we
have discovered several new extreme abundance discrepancy objects. We did not
find any non-extreme discrepancies, suggesting that a very high fraction of
nebulae with close binary central stars also have an extreme abundance
discrepancy.
