Li, C. ; de Grijs, R. ; Deng, L. ; Rubele, S. ; Wang, C. ; Bekki, K. ; Cioni, M.-R. L. ; Clementini, G. ; Emerson, J. ; For, B.-Q. ; Girardi, L. ; Groenewegen, M. A. T. ; Guandalini, R. ; Gullieuszik, M. ; Marconi, M. ; Piatti, A. E. ; Ripepi, V. ; van Loon, J. T.

published in The Astrophysical Journal, 790, pp. 35 (2014)

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.

DOI: 10.1088/0004-637X/790/1/35
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