Reversed radial distribution trend of subpopulations in the globular clusters NGC 362 and NGC 6723

TL;DR

This study reveals a reversed radial distribution of stellar subpopulations in the globular clusters NGC 362 and NGC 6723, challenging existing formation models and suggesting mass segregation as a potential explanation.

Contribution

It provides the first evidence of reversed radial trends in subpopulations within these clusters, using combined photometry and spectroscopy.

Findings

Reversed radial distribution of subpopulations in NGC 362 and NGC 6723.

Confirmation of multiple populations with bimodal CN and CN-CH anti-correlation.

Mass segregation may explain the reversed trends.

Abstract

Most globular clusters (GCs) are now known to host multiple stellar populations with different light element abundances. Here we use narrow-band photometry and low-resolution spectroscopy for NGC 362 and NGC 6723 to investigate their chemical properties and radial distributions of subpopulations. We confirm that NGC 362 and NGC 6723 are among the GCs with multiple populations showing bimodal CN distribution and CN-CH anti-correlation without a significant spread in calcium abundance. These two GCs show more centrally concentrated CN-weak earlier generation stars compared to the later generation CN-strong stars. These trends are reversed with respect to those found in previous studies for many other GCs. Our findings, therefore, seem contradictory to the current scenario for the formation of multiple stellar populations, but mass segregation acting on the two subpopulations might be a possible solution to explain this reversed radial trend.