Old stellar systems in UV: resolved and integrated properties

The UV properties of old stellar populations have been subject of intense scrutiny from the late sixties, when the UV-upturn in early type galaxies was first discovered. Because of their proximity and relative simplicity, Galactic globular clusters (GGCs) are ideal local templates to understand how the integrated UV light is driven by hot stellar populations, primarily horizontal branch stars and their progeny. Our understanding of such stars is still plagued by theoretical uncertainties, which are partly due to the absence of an accurate, comprehensive, statistically representative homogeneous data-set. To move a step forward on this subject, we have combined the HST and GALEX capabilities and collected the largest data-base ever obtained for GGCs in UV. This data-base is best suited to provide insights on the HB second parameter problem and on the first stages of GCs formation and chemical evolution and to understand how they are linked to the observed properties of extragalactic systems.