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 ] \simeq -1.1 .
The threshold temperature is estimated to be about 12 000 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 .