The VMC survey - XI: Radial Stellar Population Gradients in the Galactic Globular Cluster 47 Tucanae

Li Chengyan, R. de Grijs, Licai Deng, S. Rubele, Chuchu Wang, K. Bekki, M-R.L. Cioni, G. Clementini, J.P. Emerson, Bi-Qing For, L. Girardi, M.A.T. Groenewegen, Roald Guandalini, M. Gullieuszik, M. Marconi, Andres Piatti, V. Ripepi, J. 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, Ks 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.
Original languageEnglish
Article number35
Number of pages14
JournalThe Astrophysical Journal
Volume790
Issue number1
DOIs
Publication statusPublished - Jul 2014

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