Ni and Fe abundances, assuming Ni/H = Ni⁺/H⁺and Fe/H = Fe⁺/H⁺, respectively. All the abundances were calculated for T_e = 10 000 K and n_e = 1000 cm⁻³ and Chianty v10.1 atomic data for nickel. The dashed pink and brown horizontal lines correspond to the solar abundance of nickel and iron, respectively. Green and purple dots correspond to nickel abundance, with the last ones accounting for fluorescence. Blue and orange dots corresponds to iron abundance utilizing B15 and TZ18 atomic data, respectively.