ESO 452-SC11: the lowest mass globular cluster with a potential chemical inhomogeneity

Abstract

We present the largest spectroscopic investigation of one of the faintest and least studied stellar clusters of the Milky Way, ESO 452-SC11. Using the Anglo-Australian Telescope AAOmega and Keck High Resolution Echelle Spectrometer spectrographs we have identified 11 members of the cluster and found indications of star-to-star light element abundance variation, primarily using the blue cyanogen absorption features. From a stellar density profile, we estimate a total cluster mass of (6.8 ± 3.4) × 10³ M_⊙. This would make ESO 452-SC11 the lowest mass cluster with evidence for multiple populations. These data were also used to measure the radial velocity of the cluster (16.7 ± 0.3 km s^-1) and confirm that ESO 452-SC11 is relatively metal rich for a globular cluster ([Fe/H] = -0.81 ± 0.13). All known massive clusters studied in detail show multiple populations of stars each with a different chemical composition, but many low-mass globular clusters appear to be chemically homogeneous. ESO 452-SC11 sets a lower mass limit for the multiple stellar population phenomenon.