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Fig. 1.
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Normalised Gemini spectra of the DAO central stars of PNe in our sample. The Balmer lines Hβ, Hγ, and Hδ, together with the He II line at 4686 Å, are indicated. The interstellar D lines of Na I at 5890 and 5896 Å are not marked, but are clearly seen in all spectra.
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