The Gradients in the 47 Tuc Red Giant Branch Bump and Horizontal Branch are Consistent With a Centrally-Concentrated, Helium-Enriched Second Stellar Generation

Understand

We combine ground and space-based photometry of the Galactic globular cluster 47 Tuc to measure four independent lines of evidence for a helium gradient in the cluster, whereby stars in the cluster outskirts would have a lower initial helium abundance than stars in and near the cluster core.

• First and second, we show that the red giant branch bump (RGBB) stars exhibit gradients in their number counts and brightness.
• With increased separation from the cluster center, they become more numerous relative to the other red giant (RG) stars.
• They also become fainter.