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The planetary nebula (PN) IC 4997 is one of a few rapidly evolving objectswith variable brightness and nebular emission around a hydrogen-deficient star.In this study, we have determined the physical conditions and chemicalabundances of this object using the collisionally excited lines (CELs) andoptical recombination lines (ORLs) measured from the medium-resolution spectrataken in July 2014 with the FIbre-fed \'Echelle Spectrograph on the NordicOptical Telescope at La Palma Observatory. We derived electron densities of$\gtrsim 3 \times 10^4$ cm$^{-3}$ and electron temperatures of $\gtrsim 14,000$K from CELs, whereas cooler temperatures of $\sim 11,000$ and $\sim 7,000$ Kwere obtained from helium and heavy element ORLs, respectively. The elementalabundances deduced from CELs point to a metal-poor progenitor with[O/H]$\lesssim-0.75$, whereas the ORL abundances are slightly above the solarmetallicity, [O/H]$\approx 0.15$. Our abundance analysis indicates that theabundance discrepancy factors (ADFs$\equiv$ORLs/CELs) of this PN are relativelylarge: ADF(O$^{2+})\gtrsim 8$ and ADF(N$^{2+})\gtrsim 7$. Further research isneeded to find out how the ADFs and variable emissions are formed in thisobject and whether they are associated with a binary companion or a very latethermal pulse.

Physical Conditions and Chemical Abundances of the Variable Planetary Nebula IC 4997