NGC 6522: a typical globular cluster in the Galactic bulge without signatures of rapidly rotating Population III stars

Abstract

We present an abundance analysis of eight potential member stars of the old Galactic bulge globular cluster NGC 6522. The same stars have previously been studied by Chiappini et al., who found very high abundances of the slow neutron capture elements compared with other clusters and field stars of similar metallicity, which they interpreted as reflecting nucleosynthesis in rapidly rotating, massive Population III stars. In contrast to their analysis, we do not find any unusual enhancements of the neutron capture elements Sr, Y, Ba and Eu and conclude that previous claims result mainly from not properly accounting for blending lines. Instead, we find NGC 6522 to be an unremarkable globular cluster with comparable abundance trends to other Galactic globular clusters at the same metallicity ([Fe/H] = −1.15 ± 0.16). The stars are also chemically similar to halo and bulge field stars at the same metallicity, spanning a small range in [Y/Ba] and with normal α-element abundances. We thus find no observational evidence for any chemical signatures of rapidly rotating Population III stars in NGC 6522.