Heavy elements and chemical enrichment in globular clusters

High resolution (Rgreater than or similar to40000) and high S/N spectra have been acquired with UVES on the VLT-Kueyen (Paranal Observatory, ESO Chile) for several main sequence turnoff stars (Vsimilar to17 mag) and subgiants at the base of the Red Giant Branch (Vsimilar to16 mag) in three globular clusters (NGC 6397, NGC 6752 and 47 Tuc/NGC 104) at different metallicities (respectively [Fe/H]similar or equal to-2.0; -1.5; -0.7). Spectra for a sample of 25 field halo subdwarves have also been taken with equal resolution, but higher S/N. These data have been used to determine the abundances of several neutron-capture elements in these three clusters: strontium, yttrium, barium and europium. This is the first abundance determination of these heavy elements for such unevolved stars in these three globular clusters. These values, together with the [Ba/Eu] and [Sr/Ba] abundance ratios, have been used to test the self-enrichment scenario. A comparison is done with field halo stars and other well known Galactic globular clusters in which heavy elements have already been measured in the past, at least in bright giants (Vgreater than or similar to11-12 mag). Our results show clearly that globular clusters have been uniformly enriched by r- and s-process syntheses, and that most of them seem to follow exactly the same abundance patterns as field halo stars, which discards the classical self-enrichment scenario for the origin of metallicities and heavy elements in globular clusters.