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Fig. 2

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Spectra of He-weak stars for which hydrogen is dominant and helium lines of only one ionization state may be visible. Metallic lines are very weak or absent. Note that PG1708+602 fits this definition even though the helium class is much higher than those of the other stars. The lines marked are H + HeII λλ 4101, 4340, 4861; and HeII λλ 4200, 4541, 4686.

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