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

CH. LI; A.E. PIATTI; ET AL. (16 COAUTORES)

ASTROPHYSICAL JOURNAL

IOP PUBLISHING LTD

Año: 2014 vol. 790 p. 1 - 14

0004-637X

   We present a deep near-infrared color?magnitude diagram of the Galacticglobular cluster 47 Tucanae, obtained with the Visible and Infrared Survey Tele-scope for Astronomy (VISTA) as part of the VISTA near-infrared Y, J, Ks surveyof the Magellanic System (VMC). The cluster stars comprising both the sub-giant and red-giant branches exhibit apparent, continuous variations in color?magnitude space as a function of radius. Subgiant-branch stars at larger radiiare systematically brighter than their counterparts closer to the cluster core;similarly, red-giant-branch stars in the cluster?s periphery are bluer than theirmore centrally located cousins. The observations can very well be described byadopting an age spread of ∼ 0.5 Gyr as well as radial gradients in both the clus-ter?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 pe-riphery. We conclude that the cluster?s inner regions host a significant fractionof second-generation stars, which decreases with increasing radius; the stellarpopulation in the 47 Tuc periphery is well approximated by a simplestellar population.