Observed spectra (black) around two lines of the He II Pickering series compared with synthetic spectra (red). From top to bottom: WD 0111+002 with three models (Teff = 58 000 K and log g = 7.6, 7.7, 7.8), PG 0109+111 with model 70 000/7.5, PG 1707+427 with model 85 000/7.5. The observations of PG 0109+111 and PG 1707+427 were smoothed with a low-pass filter (Savitzky & Golay 1964).
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