The Hubble Space Telescope UV Legacy Survey of Galactic Globular Clusters. X. The radial distribution of stellar populations in NGC 2808

TL;DR

This study uses Hubble Space Telescope data to analyze the radial distribution of different stellar populations in NGC 2808, revealing that helium-enhanced populations are more centrally concentrated, supporting multiple-population formation models.

Contribution

It provides the first detailed radial distribution analysis of multiple stellar populations in NGC 2808 using high-precision HST photometry.

Findings

Blue and middle MS populations are more centrally concentrated than the red MS.

The radial distributions support models predicting centrally concentrated helium-enhanced populations.

The differences in distribution are statistically significant above 3 sigma.

Abstract

Due to their extreme helium abundance, the multiple stellar populations of the globular cluster NGC 2808 have been widely investigated from a photometric, spectroscopic, and kinematic perspective. The most striking feature of the color-magnitude diagram of NGC 2808 is the triple main sequence (MS), with the red MS corresponding to a stellar population with primordial helium, and the middle and the blue MS being enhanced in helium up to Y$\sim$0.32 and $\sim$0.38, respectively. A recent study has revealed that this massive cluster hosts at least five distinct stellar populations (A, B, C, D, and E). Among them populations A, B, and C correspond to the red MS, while populations C and D are connected to the middle and the blue MS. In this paper we exploit Hubble-Space-Telescope photometry to investigate the radial distribution of the red, the middle and the blue MS from the cluster center out to about 8.5 arcmin. Our analysis shows that the radial distribution of each of the three MSs is different. In particular, as predicted from multiple-population formation models, both the blue MS and the middle MS appears to be more concentrated than the red MS with a significance level for this result wich is above 3{\sigma}.