Combined Effects of Binaries and Stellar Rotation on the Color-Magnitude Diagrams of Intermediate-Age Star Clusters

TL;DR

This paper demonstrates that the combined effects of stellar rotation and binary interactions can explain the complex color-magnitude diagrams observed in intermediate-age star clusters, challenging the need for prolonged star formation scenarios.

Contribution

It introduces a model combining stellar rotation and binary effects to reproduce observed CMD features, offering a unified explanation for multiple cluster phenomena.

Findings

Reproduces broad and multiple turn-offs in CMDs

Explains dual red clumps and blue stragglers

Suggests simple stellar populations can account for complex CMDs

Abstract

About seventy percent of intermediate-age star clusters in the Large Magellanic Clouds have been confirmed to have broad main sequence, multiple or extended turn-offs and dual red giant clumps. The observed result seems against the classical idea that such clusters are simple stellar populations. Although many models have been used for explaining the results via factors such as prolonged star formation history, metallicity spread, differential redenning, selection effect, observational uncertainty, stellar rotation, and binary interaction, the reason for the special color-magnitude diagrams is still uncertain. We revisit this question via the combination of stellar rotation and binary effects. As a result, it shows "golf club" color-magnitude diagrams with broad or multiple turn-offs, dual red clump, blue stragglers, red stragglers, and extended main sequences. Because both binaries and massive rotators are common, our result suggests that most color-magnitude diagrams including extended turn-off or multiple turn-offs can be explained using simple stellar populations including both binary and stellar rotation effects, or composite populations with two components.