SIMBAD references

We report detailed analyses of deep, high-resolution spectra of three Galactic planetary nebulae (PNe) with high abundance discrepancy factors (ADFs), Hf 2-2, M 1-42, and NGC 6153, obtained with the Ultraviolet and Visual Echelle Spectrograph on the 8.2 m Very Large Telescope. These spectra were carefully reduced, including rigorous absolute flux calibration, yielding a detection of ∼410-800 emission lines in each PN. Plasma diagnostics and abundance calculations were performed using nebular lines. In all three PNe, the electron temperatures derived using the collisionally excited lines (CELs) are higher than that yielded by the H I Balmer and Paschen jumps, while the temperatures yielded by the O II and N II optical recombination lines (ORLs) are very low, ≲2000 K, indicating that the heavy-element ORLs probe cold nebular regions. The ORL abundances of N, O, and Ne are systematically higher than the corresponding CEL values, confirming high ADFs in the three objects. Position-velocity diagrams were created, and spatiokinematical studies show that CELs come from the outer nebular regions, while the ORL-emitting regions are close to the nebular center. Additionally, the velocity indicated by CEL line-splitting decreases with ionization potential, which was not obvious in ORLs. These spatial and kinematic differences support two distinct components of ionized gas: a cold, metal-rich component and a warmer component with normal metallicity. Heavy elements are strongly enriched in the cold gas, while its H⁺ fraction is low but still produces significant H I emission, affecting CEL abundance estimates.