Abundances of the planetary nebula IC 4997

In this study, we have determined the physical conditions and chemical abundances of this object using the collisionally excited lines (CELs) and optical recombination lines (ORLs) measured from the medium-resolution spectra taken in 2014 July with the FIbre-fed Echelle Spectrograph on the Nordic Optical Telescope at La Palma Observatory.

We derived electron densities of ~>3x10^4^cm^-3^ and electron temperatures of ~>14000K from CELs, whereas cooler temperatures of ~11000 and ~7000K were obtained from helium and heavy element ORLs, respectively. The elemental abundances deduced from CELs point to a metal-poor progenitor with [O/H]<~-0.75, whereas the ORL abundances are slightly above the solar metallicity, [O/H]~0.15. Our abundance analysis indicates that the abundance discrepancy factors (ADFs=ORLs/CELs) of this PN are relatively large: ADF(O2+)>~8 and ADF(N2+)>~7.