C Munoz Poster

The Origin and Chemical Evolution of the Exotic Globular Cluster NGC 3201
 
C. Munoz (Universidad de Concepcion), D. Geisler, and S. Villanova

NGC3201 is a globular cluster (GC) which shows very peculiar kinematic characteristics including an extreme radial velocity and a highly retrograde orbit, strongly suggesting an extragalactic origin. Every Galactic GC (GGC) studied in detail spectroscopically up to now shows multiple stellar populations (MPs) that are the result of the primordial evolution of the cluster, when a second generation of stars formed from material polluted by evolved stars of the first generation. Several candidate polluters have been proposed, including AGB stars, fast-rotating massive stars, and massive binaries, each leaving its own chemical fingerprint.

Our aims are to study NGC3201 in the context of MPs, hoping to constrain possible candidates for the self-enrichment by studying the chemical abundance pattern, as well as adding insight into the origin of this intriguing cluster. If it is an extragalactic object, did it pass through a similar chemical evolution as other GCs?

We present a detailed chemical abundance analysis of eight red giant branch (RGB) stars using high resolution spectroscopy. The data were obtained from the Magellan Clay telescope at LCO using the MIKE echelle spectrograph with a wide spectral coverage and with good S/N. We measured the following elements: light (C, N, O, Na, Mg, Al), alpha (Si,Ca,Ti), iron-peak (Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) and neutron capture (Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, Dy, Pb).

We found [Fe/H]=-1.53 ± 0.01 with no intrinsic spread (Sigma obs= 0.04) and an alpha-enhancement typical of halo GCs. Significant spreads are observed in the abundances of all light elements except for Mg. We confirm the presence of an extended Na-O anticorrelation, albeit with an initial Na/O abundance which is rather unique for Galactic globulars. n-capture elements generally are dominated by the r-process, in good agreement with the bulk of Galactic GCs. The total (C+N+O) abundance is slightly supersolar and requires a small downward correction to the isochrone age, yielding 11.4 Gyr. Kinematically, NGC3201 appears likely to have had an extragalactic origin but its chemical evolution is similar to most other, presumably native, Galactic GCs.