NGC 2808 thus extends to hotter temperatures than that of NGC 6752. That in itself would not be a problem, but the spectroscopic analyses of Moehler et al. ([@mohe97b], [@mosw00]) show that the blue tail stars in NGC 6752 already populate the EHB to the hot end predicted by canonical HB models.

[psfile=0505\_1.ps hscale=45 vscale=45 hoffset=-20 voffset=-65 angle=0]{}

Observations of NGC 2808 in the far- and near-UV (Brown et al. [@brsw01], their Fig. 3) show that the stars below the faint gap form a hook-like feature that extends up to below the hot end of the zero-age HB (ZAHB). Such “blue hook” stars are so far known in only three other globular clusters: $\omega$ Cen (D’Cruz et al. [@dcoc00], Moehler et al. [@mosw02]), NGC 6388 and possibly NGC 6441 (Busso et al. [@bupi03]), all of which are very massive. Within the framework of canonical HB theory there is no way to populate this region of the UV colour-magnitude diagram without requiring an implausibly large decrease in the helium-core mass. Thus canonical theory fails to explain both the faint UV luminosities and expected high temperatures of the blue hook stars.

Brown et al. ([@brsw01]) have proposed a scenario to explain the 