manage to lose nearly all of their envelope mass and still undergo the helium core flash, as indicated by the long blue tails in a number of globular clusters (e.g., NGC 6752, Moehler et al. [@mosw00]). The globular cluster NGC 2808 represents a good template cluster, since it has an extremely long blue tail extending to very high temperatures and correspondingly low envelope masses.

NGC 2808 has been the subject of four recent deep ground-based and Hubble Space Telescope (HST) photometric studies (Sosin et al. [@sosi97], Walker [@walk99], Bedin et al.[@bepi00], Brown et al. [@brsw01]). The ground-based studies have shown that the blue tail of NGC 2808 extends to extremely faint magnitudes ($M_V \approx$ ), with gaps at $M_V
\approx$ and . These gaps can be seen at V $\approx {\mbox{$\rm 18\hspace{-0.25em}\stackrel{m}{.}
      \hspace{-1.0mm}5$}}$ and ${\mbox{$\rm 20\hspace{-0.25em}\stackrel{m}{.}
      \hspace{-1.0mm}0$}}$ in Fig. \[cmd\]. The brighter gap is thus at a similar position as the underpopulated region in the colour-magnitude diagram of NGC 6752, which separates the EHB stars from the classical blue HB stars (Moehler et al. [@mohe97b], [@mosw00]; Momany et al. [@mopi02]), while the fainter gap coincides with the hot end of the blue tail in NGC 6752. The blue tail in 