A Dynamical Signature of Multiple Stellar Populations in 47 Tucanae

TL;DR

This study investigates multiple stellar populations in 47 Tucanae by analyzing their proper-motion anisotropies and spatial distributions, revealing differences linked to their chemical compositions and providing insights into cluster formation.

Contribution

The paper introduces a method of dividing 47 Tuc's main sequence into four color groups and analyzes their kinematic properties, uncovering distinct anisotropies and spatial concentrations.

Findings

Bluest stars show the largest proper-motion anisotropy.

Bluest stars are more centrally concentrated.

SMC stars do not exhibit similar anisotropy.

Abstract

Based on the width of its main sequence, and an actual observed split when viewed through particular filters, it is widely accepted that 47 Tucanae contains multiple stellar populations. In this contribution, we divide the main-sequence of 47 Tuc into four color groups, which presumably represent stars of various chemical compositions. The kinematic properties of each of these groups is explored via proper-motions, and a strong signal emerges of differing proper-motion anisotropies with differing main-sequence color; the bluest main-sequence stars exhibit the largest proper-motion anisotropy which becomes undetectable for the reddest stars. In addition, the bluest stars are also the most centrally concentrated. A simiilar analysis for SMC stars, which are located in the background of 47 Tuc on our frames, yields none of the anisotropy exhibited by the 47 Tuc stars. We discuss implications of these results for possible formation scenarios of the various populations.