Different Sodium enhancements among multiple populations of Milky Way
  globular clusters
  We searched for trails to understand the different Na abundances measured in
first and second generation stars of ancient Milky Way globular clusters. For
that purpose, we gathered from the recent literature the aforementioned Na
abundances, orbital parameters, structural and internal dynamical properties
and ages in an homogeneous scale of 28 globular clusters. We found that the
intra-cluster Na enrichment, measured by the difference of Na abundances
between first and second generation stars, exhibits a trend as a function of
the Na abundances of first generation stars, in the sense that the more Na-poor
the first generation stars, the larger the Na enrichment. By using the
inclinations of the globular clusters' orbits, the analyzed Na enrichments also
hinted at a boundary at ~0.3 dex to differentiate globular clusters with an
accreted or in situ origin, the accreted globular clusters having larger Na
enrichments. Because relatively larger intra-cluster Na enhancements are seen
in accreted globular clusters, and small Na enhancements are observed in
globular clusters formed in situ (although not exclusively), we speculate with
the possibility that the amplitude of the Na enrichment could be linked with
the building block paradigm. Globular clusters at the time of formation of
first and second generation stars would seem to keep memory of this
hierarchical galaxy formation process.
