Title: The VMC Survey. XII. Radial Stellar Population Gradients in the Galactic Globular Cluster 47 Tucanae

Speaker: Chengyuan LI (DoA/KIAA-PKU)

Time: Friday, March 7, 3pm-5pm

Place: A408, NAOC 

Abstract: We present a deep near-infrared color–magnitude diagram of the Galactic globular 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 survey of the Magellanic System (VMC). The cluster stars comprising both the subgiant and red giant branches exhibit distinct, continuous variations in color–magnitude space as a function of radius. Subgiant-branch stars at larger radii are systemati- cally 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 radial gradients in both the cluster’s helium abundance (Y) and metallicity (Z), which gradually change from (Y = 0.28, Z = 0.009) 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.