Prominent Cu lines in the observation (gray line) of RE 0503−289, labeled with their wavelengths from Tables A.13, A.14, and A.15. Cu VI λλ 1060.890, 1100.307Å, and Cu IV λ 1410.531Å are indicated with an additional ion label, all other lines stem from Cu V. For the identification of other lines that are visible in the spectrum, please visit http://astro.uni-tuebingen.de/~TVIS/objects/RE0503-289, our Tübingen VISualization Tool (TVIS). The thick red spectrum is calculated from our best model with a Cu mass fraction of 9.3 × 10⁻⁵. The dashed green line shows a synthetic spectrum calculated without Cu. The vertical bar indicates 10% of the continuum flux.