Equivalent widths of 18 subgiant of {omega} Cen

We measure abundances of Al, Ba, Ca, Fe, Ni, Si, and Ti and we find that these stars have <[Fe/H]>=-0.73+/-0.14dex, similarly to the corresponding red giant branch population (the RGB-a). We also measure <[alpha/Fe]>=+0.40+/-0.16dex, and <[Ba/Fe]>=+0.87+/-0.23dex, in general agreement with past studies.

It is very interesting to note that we found a uniform Al abundance, <[Al/Fe]>=+0.32+/-0.14dex, for all the 18 SGB-a stars analysed here, thus supporting past evidence that the usual (anti-)correlations are not present in this population, and suggesting a non globular cluster-like origin of this particular population. In the dwarf galaxy hypothesis for the formation of omega Cen, this population might be the best candidate for the field population of its putative parent galaxy, although some of its properties appear contradictory.