Spectroscopy and photometry of the least-massive Type-II globular
  clusters: NGC1261 AND NGC6934
  Recent work has revealed two classes of Globular Clusters (GCs), dubbed
Type-I and Type-II. Type-II GCs are characterized by a blue- and a red- red
giant branch composed of stars with different metallicities, often coupled with
distinct abundances in the slow-neutron capture elements (s-elements). Here we
continue the chemical tagging of Type-II GCs by adding the two least-massive
clusters of this class, NGC1261 and NGC6934. Based on both spectroscopy and
photometry, we find that red stars in NGC1261 are slightly enhanced in [Fe/H]
by ~0.1 dex and confirm that red stars of NGC 6934 are enhanced in iron by ~0.2
dex. Neither NGC1261 nor NGC6934 show internal variations in the s-elements,
which suggests a GC mass threshold for the occurrence of s-process enrichment.
We found a significant correlation between the additional Fe locked in the red
stars of Type-II GCs and the present-day mass of the cluster. Nevertheless,
most Type II GCs retained a small fraction of Fe produced by SNe II, lower than
the 2%; NGC6273, M54 and omega Centauri are remarkable exceptions. In the
appendix, we infer for the first time chemical abundances of Lanthanum, assumed
as representative of the s-elements, in M54, the GC located in the nucleus of
the Sagittarius dwarf galaxy. Red-sequence stars are marginally enhanced in
[La/Fe] by 0.10\pm0.06 dex, in contrast with the large [La/Fe] spread of most
Type II GCs. We suggest that different processes are responsible for the
enrichment in iron and s-elements in Type-II GCs.
