where more flux is emitted shortward of the Lyman edge at 912 Å and less flux is emitted at ultraviolet (1500 Å) and longer wavelengths, which makes flash-mixed stars fainter than canonical EHB stars at these wavelengths.

Spectroscopic observations of blue hook stars in $\omega$ Cen by Moehler et al. ([@mosw02]) showed that these stars reach effective temperatures of more than 35,000 K, i.e., well beyond the hot end of the canonical EHB. In addition, most of them show at least solar helium abundances with the helium abundance increasing with effective temperature, in contrast to canonical EHB stars such as those studied in NGC 6752 by Moehler et al. ([@mosw00]). Contrary to the predictions of Brown et al. ([@brsw01]), however, only one star showed a helium abundance of [${\rm \log{\frac{n_{He}}{n_{H}}}}$]{} $>$ 0. These results may indicate that flash mixing is less efficient than assumed, or that some residual hydrogen survives flash mixing and then diffuses outward to the surface. It is unclear whether the lower than expected helium abundances can still reproduce the UV properties of the stars. UV data have been presented for the blue hook stars in the central region of $\omega$ Cen by D’Cruz et al. ([@dcoc00]), 