Investigating Unusually Extended Main Sequence Turnoff of the Galactic Open Cluster NGC 3532

TL;DR

This study investigates the extended main-sequence turnoff in the open cluster NGC 3532, revealing the roles of fast rotators, binaries, and chemically peculiar stars in creating the observed features.

Contribution

It provides a detailed case study of NGC 3532, identifying multiple stellar populations and mechanisms contributing to the extended turnoff phenomenon.

Findings

Fast rotators are significantly redder in the cluster.

Stars near the turnoff show multi-modal velocity distribution.

Binaries and chemically peculiar stars are linked to the turnoff features.

Abstract

Extended main-sequence turnoffs are observed in the color-magnitude diagrams of some young and intermediate-age star clusters. Here we report the case study of NGC 3532. Among the cluster member candidates identified using the ML-MOC algorithm on Gaia DR3 sources, we found that fast rotators are significantly redder. Stars near the main-sequence turnoff exhibit a multi-modal distribution in the Gaia broadening velocity ($v_{\rm broad}$). A comparison with relevant literature suggests binaries being typically interspersed with fast rotators, often manifesting as slow to moderate rotators. Additionally, chemically peculiar stars are predominantly located in the bluer regions of the turnoff, with those in the fast-rotator region having large values of Gaia re-normalised unit weight error, indicating plausible companions. Our analysis suggests multiple channels responsible for angular momentum loss to account for the extended turnoff.