  We present metallicity measurements of 25 stars in the blue horizontal branch
of the Galactic globular cluster NGC 2808. Our measurements are based on
moderate-resolution spectra taken with the multi-object fiber facility
FLAMES-UVES, mounted on Kueyen at the Very Large Telescope. We confirm that
stars hotter than a threshold temperature have super-solar abundance, while the
cooler ones respect the nominal metallicity of the cluster, i.e. [Fe/H] ~ -1.1.
The threshold temperature is estimated to be about 12000 K, corresponding to
the so called u-jump, and coincides with the sudden departure of the cluster
horizontal branch from the models. The metallicity increases with temperature
for star hotter than the jump, confirming the hypothesis that the process
responsible for this abrupt metallic enhancement is the levitation due to the
strong radiation field in absence of a significative convective envelope. A
metallicity dependence of the abundance enhancement is also suggested, with
more metal poor clusters having a higher increase in metal content. The slope
in the temperature vs. abundance diagram is higher than the errors involved,
and the metal content of the cluster plays possibly a role in determining the
amplitude of the jump (more metal poor clusters show more enhancement after the
jump), although other parameters, such as clusters' characteristics and even
the atomic species involved, may also someway contribute.
