of $-$0.5 and 0.0, respectively. The most helium-rich star, W20334 ([${\rm \log{\frac{n_{He}}{n_{H}}}}$]{}= +1.02), shows lines at $\lambda\lambda$ 4070 Å and 4650 Å, which are even stronger than predicted by a model atmosphere with a CNO abundance of ten times solar. In this case, the limitations of our two-step approach (see above) become evident. As noted above, a more accurate abundance determination for this star requires an analysis with a model grid taking carbon opacity into account for the determination of [$ {\rm T_{eff}}$]{} and [$\log {\rm g}$]{} (Lanz et al. [@labr03]).

A similar estimate of the carbon abundances for the $\omega$ Cen stars was not possible due to the poor S/N and resolution of these data. Nevertheless, the strong features found in some of the $\omega$ Cen spectra suggest an enhanced carbon abundance in some of the blue hook stars.

Discussion\[sec-discuss\]
=========================

Our analysis of blue tail and blue hook stars in NGC 2808 shows that these stars form two different groups according to their helium abundance (cf. Fig. \[gap\]): All stars brighter than the gap at V$\approx$ are helium-poor, although they cover a large temperature range (cf. Fig. \[ngc2808\_the\]). The stars fainter than the gap at V$\approx$, on the 