Magnesium isotopes: a tool to understand self-enrichment in Globular
  Clusters
  A critical issue in the asymptotic giant branch (AGB) self-enrichment
scenario for the formation of multiple populations in Globular Clusters (GCs)
is the inability to reproduce the magnesium isotopic ratios, despite the model
in principle can account for the depletion of magnesium. In this work we
analyze how the uncertainties on the various p-capture cross sections affect
the results related to the magnesium content of the ejecta of AGB stars. The
observed distribution of the magnesium isotopes and of the overall Mg-Al trend
in M13 and NGC 6752 are successfully reproduced when the proton-capture rate by
25Mg at the temperatures 100 MK, in particular the 25Mg(p, gamma)26Alm channel,
is enhanced by a factor 3 with respect to the most recent experimental
determinations. This assumption also allows to reproduce the full extent of the
Mg spread and the Mg-Si anticorrelation observed in NGC 2419. The uncertainties
in the rate of the 25Mg(p,gamma)26Alm reaction at the temperatures of interest
here leave space for our assumption and we suggest that new experimental
measurements are needed to settle this problem. We also discuss the competitive
model based on the super massive star nucleosynthesis.
