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Keywords:

  • stars: abundances;
  • stars: late-type;
  • globular clusters: individual: IC 4499

ABSTRACT

We present radial velocity and metallicity measurements for the far southern Galactic globular cluster IC 4499. We selected several hundred target red giant stars in and around the cluster from the 2MASS point source catalogue, and obtained spectra at the near-infrared calcium triplet using the AAOmega spectrograph. Observations of giants in globular clusters M4, M22 and M68 were taken to provide radial velocity and metallicity comparison objects. Based on velocity data we conclude that 43 of our targets are cluster members, by far the largest sample of IC 4499 giants spectroscopically studied. We determine the mean heliocentric radial velocity of the cluster to be 31.5 ± 0.4 km s−1, and find the most likely central velocity dispersion to be 2.5 ± 0.5 km s−1. This leads to a dynamical mass estimate for the cluster of 93 ± 37 × 103  M. We are sensitive to cluster rotation down to an amplitude of ≈1 km s−1, but no evidence for cluster rotation is seen. The cluster metallicity is found to be [Fe/H]=−1.52 ± 0.12 on the Carretta–Gratton scale; this is in agreement with some earlier estimates but carries significantly higher precision. The radial velocity of the cluster, previously highly uncertain, is consistent with membership in the Monoceros tidal stream as proposed by Peñarrubia and co-workers, but also with a halo origin. The horizontal branch morphology of the cluster is slightly redder than average for its metallicity, but it is likely not unusually young compared to other clusters of the halo. The new constraints on the cluster kinematics and metallicity may give insight into its extremely high specific frequency of RR Lyrae stars.