Notes. Line identifications were primarily from the Atomic Line List (van Hoof 2018), supplemented by the extensive line lists for NGC 7009 (Fang & Liu 2011) and NGC 7027 (Zhang et al. 2007). If a line is identified, then the rest wavelength is listed; if no identification was found, the wavelength is the observed value, corrected for the systemic heliocentric radial velocity (+10 km s⁻¹). Observed Hβ normalising flux: 1.66 ×10⁻¹¹ ± 6.88×10⁻¹⁶ erg cm⁻² s⁻¹. Dereddened Hβ normalising flux: 2.09×10⁻¹¹ ± 4.82×10⁻¹³ erg cm⁻² s⁻¹. Extinction c = 0.10 ± 0.01 calculated with T_e = 17 000 K; N_e = 1500 cm⁻³. Only the first ten entries of this table are shown; the full table is available at the CDS.