The Radial Distribution of the Two Stellar Populations in NGC 1851

TL;DR

This study investigates the spatial distribution of multiple stellar populations in NGC 1851, revealing consistent ratios of different star types from the core to the outer regions, indicating a uniform distribution.

Contribution

It provides the first detailed analysis of the radial distribution of the double sub-giant branch and HB populations in NGC 1851 using multi-source data.

Findings

The SGB split is observable from the center to at least 8 arcmin.

The ratio of bright to faint SGB stars shows no significant radial variation.

The ratio of blue HB plus RR Lyrae to red HB stars remains constant across the cluster.

Abstract

We have analyzed ACS/WFC and WFPC2 images from HST, as well as ground-based data to study the radial distribution of the double sub-giant branch (SGB) recently discovered in the Galactic globular cluster NGC 1851. We found that the SGB split can be followed all the way from the cluster center out to at least 8\arcmin from the center. Beyond this distance out to the tidal radius at $\sim 11.7$ arcmin, there are simply too few SGB stars to dentify the sequences. The number ratio of the bright SGB to the faint SGB stars shows no significant radial trend. Furthermore, we have found that the ratio of blue horizontal-branch (HB) stars plus RR Lyrae to the red HB stars also remains constant from the cluster center to the outer envelope.