2016MNRAS.455.3263J

We present new optical spectra of the nearby, bright, planetary nebula NGC 6778. The nebula has been known to emit strong recombination lines for more than 40 years but this is the first detailed study of its abundances. Heavy element abundances derived from recombination lines are found to exceed those from collisionally excited lines by a factor of ∼ 20 in an integrated spectrum of the nebula, which is among the largest known abundance discrepancy factors. Spatial analysis of the spectra shows that the abundance discrepancy factor is strongly, centrally peaked, reaching ∼ 40 close to the central star. The central star of NGC 6778 is known to be a short-period binary, further strengthening the link between high nebular abundance discrepancy factors and central star binarity.