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Fig. 2
Normalized spectra of early-O CSPN (see Table 1) grouped according to their spectral classification. The interstellar absorption bands (λ4428; λ5780, and λ5893) are not indicated. The most important spectral features (absorption or emission) identified are He ii λ4200, Hγ, He ii λ4541, He ii λ4686, Hβ, and He ii λ5412.
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