Hot HB stars in globular clusters - Physical parameters and consequences for theory V. Radiative levitation versus helium mixing

Atmospheric parameters (T-eff, log g), masses and helium abundances are der ived for 42 hot horizontal branch (HB) stars in the globular cluster NGC 67 52. For 19 stars we derive magnesium and iron abundances as well and find t hat iron is enriched by a factor of 50 on average with respect to the clust er abundance whereas the magnesium abundances are consistent with the clust er abundance. Radiation pressure may levitate heavy elements like iron to t he surface of the star in a diffusive process. Taking into account the enri chment of heavy elements in our spectroscopic analyses we find that high ir on abundances can explain part, but not all, of the problem of anomalously low gravities along the blue HE. The blue HE stars cooler than about 15,100 K and the sdB stars (T-eff greater than or equal to 20,000 K) agree well w ith canonical theory when analysed with metal-rich ([M/H] = +0.5) model atm ospheres, but the stars in between these two groups remain offset towards l ower gravities and masses. Deep Mixing in the red giant progenitor phase is discussed as another mechanism that may influence the position of the blue HE stars in the (T-eff, log g)-plane but not their masses.