  Atmospheric parameters (effective temperature Teff, surface gravity log g),
masses and helium abundances are derived for 42 hot horizontal branch (HB)
stars in the globular cluster NGC 6752. For 19 stars we derive magnesium and
iron abundances as well and find that iron is enriched by a factor of 50 on
average with respect to the cluster abundance whereas the magnesium abundances
are consistent with the cluster abundance. Radiation pressure may levitate
heavy elements like iron to the surface of the star in a diffusive process.
Taking into account the enrichment of heavy elements in our spectroscopic
analyses we find that high iron abundances can explain part, but not all, of
the problem of anomalously low gravities along the blue HB. The blue HB stars
cooler than about 15,100 K and the sdB stars (Teff > 20,000 K) agree well with
canonical theory when analysed with metal-rich ([M/H] = +0.5) model
atmospheres, but the stars in between these two groups remain offset towards
lower gravities and masses. Deep Mixing in the red giant progenitor phase is
discussed as another mechanism that may influence the position of the blue HB
stars in the (Teff, log g)-plane but not their masses.
