Deep uVI photometry of NGC2419

Focusing on the RGB stars in the magnitude range 19.8<=V<=22.0, we find that (i) the u-V, u-I and the V-I spreads about the RGB ridge line are significantly larger than that expected from observational errors, accurately quantified by means of extensive artificial stars experiments, (ii) the intrinsic colour spreads in u-V and u-I are larger than in V-I, and (iii) the stars lying to the blue of the RGB ridge line in u-V and u-I are significantly more concentrated towards the cluster centre than those lying to the red of that line.

All the above observational facts can be interpreted in a scenario where a sizable fraction of cluster stars belong to a second generation heavily enriched in helium. Finally, we find that bright RGB stars (17.5<V<19.0) having [Mg/Fe]<0.0 lie preferentially on the red side of the cluster RGB, while those having [Mg/Fe]>0.0 lie preferentially on the blue side.