Na-O Anticorrelation and HB. VIII. Proton-capture elements and
  metallicities in 17 globular clusters from UVES spectra
  We present homogeneous abundances for Fe and some of the elements involved in
the proton-capture reactions (O, Na, Mg, Al, and Si) for 202 red giants in 17
Galactic globular clusters (GCs) from the analysis of high resolution UVES
spectra obtained with FLAMES@ESO-VLT2. Our programme clusters span almost the
whole range in metallicity of GCs and were selected to sample the widest range
of global parameters (HB morphology, masses, concentration, etc). Here we focus
on the discussion of the Na-O and Mg-Al anticorrelations and related issues.
Our study finds clear Na and O star-to-star abundance variations in all GCs.
Variations in Al are present in all but a few GCs. Finally, a spread in
abundances of Mg and Si are also present in a few clusters. Mg is slightly less
overabundant and Si slightly more overabundant in the most Al-rich stars. The
correlation between Si and Al abundances is a signature of production of 28Si
leaking from the Mg-Al cycle in a few clusters. The cross sections required for
the proper reactions to take over in the cycle point to temperatures in excess
of about 65 MK for the favoured site of production. We used a dilution model to
infer the total range of Al abundances starting from the Al abundances in the
UVES spectra, and the Na abundance distributions found from analysis of the
much larger set of stars for which GIRAFFE spectra were available. We found
that the maximum amount of additional Al produced by first generation polluters
contributing to the composition of the second generation stars in each cluster
is closely correlated with the same combination of metallicity and cluster
luminosity that reproduced the minimum O abundances found from GIRAFFE spectra.
We then suggest that the high temperatures required for the Mg-Al cycle are
only reached in the most massive and most metal-poor polluters.
