HST/COS spectrum of the white dwarf in Tol 26 (gray) compared to a photospheric model spectrum (red; T_eff = 85 000 K, log g = 7.4) with abundances as given in Sect. 3.4. The blue graph is the photospheric model attenuated by interstellar lines. Prominent photospheric lines are identified. Absorption profiles of the C IV resonance doublet and He II λ1640 Å (except for the far wings) are masked by nebular emission lines.