2003ApJ...582L..43C

The core helium flash in low-mass stars with extreme mass loss occurs after the tip of the red giant branch, when the H-rich envelope is very thin. The low efficiency of the H-shell source enables the He flash-driven convective zone to penetrate H-rich layers and trigger a thermonuclear runaway, resulting in a subsequent surface enrichment with He and C. In this Letter, we present the first full computations of Population II low-mass stellar models through this phase. Models experiencing this dredge-up event are significantly hotter than their counterparts with H-rich envelopes, which makes them promising candidates for explaining the existence of stars observed beyond the canonical blue end of the horizontal branch (``blue hook stars''). Moreover, this temperature difference could explain the observed gap in M_Vbetween extreme blue horizontal-branch and blue hook stars. A first comparison with spectroscopic observations of blue hook stars in the globular cluster ω Cen is also presented.