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arXiv · 1406.1259

The VMC Survey. XI. Radial Stellar Population Gradients in the Galactic Globular Cluster 47 Tucanae

Chengyuan Li·Richard de Grijs·Licai Deng·Stefano Rubele·Chuchu Wang·Kenji Bekki·Maria-Rosa L. Cioni·Gisella Clementini·Jim Emerson·Bi-Qing For·Leo Girardi·Martin A. T. Groenewegen·Roald Guandalini·Marco Gullieuszik·Marcella Marconi·Andrés E. Piatti·Vincenzo Ripepi·Jacco Th. van Loon
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Abstract

We present a deep near-infrared color--magnitude diagram of the Galactic globular cluster 47 Tucanae, obtained with the Visible and Infrared Survey Telescope for Astronomy (VISTA) as part of the VISTA near-infrared Y, J, K_s survey of the Magellanic System (VMC). The cluster stars comprising both the subgiant and red-giant branches exhibit apparent, continuous variations in color--magnitude space as a function of radius. Subgiant-branch stars at larger radii are systematically brighter than their counterparts closer to the cluster core; similarly, red-giant-branch stars in the cluster's periphery are bluer than their more centrally located cousins. The observations can very well be described by adopting an age spread of ~0.5 Gyr as well as radial gradients in both the cluster's helium abundance (Y) and metallicity (Z), which change gradually from Y = 0.28, Z = 0.005 in the cluster core to Y = 0.25, Z = 0.003 in its periphery. We conclude that the cluster's inner regions host a significant fraction of second-generation stars, which decreases with increasing radius; the stellar population in the 47 Tuc periphery is well approximated by a simple stellar population.

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Chengyuan Li, Richard de Grijs, Licai Deng, Stefano Rubele, Chuchu Wang, Kenji Bekki, Maria-Rosa L. Cioni, Gisella Clementini, Jim Emerson, Bi-Qing For, Leo Girardi, Martin A. T. Groenewegen, Roald Guandalini, Marco Gullieuszik, Marcella Marconi, Andrés E. Piatti, Vincenzo Ripepi, Jacco Th. van Loon. 2014-06-05. The VMC Survey. XI. Radial Stellar Population Gradients in the Galactic Globular Cluster 47 Tucanae. https://doi.org/10.1088/0004-637x%2F790%2F1%2F35

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