The VISCACHA Survey: XIII. The extended main-sequence turn-off in intermediate-age low-mass clusters

TL;DR

This study confirms the presence of extended main-sequence turn-offs in low-mass star clusters in the Magellanic Clouds, linking the phenomenon to cluster escape velocity and demonstrating the effectiveness of ground-based observations.

Contribution

It extends the analysis of eMSTO phenomena to low-mass clusters and validates a method for measuring age spreads using ground-based data.

Findings

eMSTO is present in low-mass clusters, following known relations.

The less massive cluster does not show eMSTO, supporting the link with escape velocity.

Ground-based photometry reliably measures MSTO width, independent of photometric system.

Abstract

The extended main-sequence turn-off (eMSTO) is a well-known feature observed in young and intermediate-age star clusters, characterized by a significant broadening of the main-sequence turn-off region. Although prolonged star formation and stellar rotation have been proposed as possible explanations, no consensus has yet been reached. Most previous studies have focused on high-mass clusters. In this work, we extend the analysis to the less-explored low-mass regime by investigating star clusters in the Magellanic Clouds using data from the VISCACHA survey. We employed a widely used method to quantify the MSTO width in terms of age spread. Additionally, to validate our approach, we used a cluster also observed with HST. Our analysis confirms that the eMSTO phenomenon is also present in low-mass clusters, following the known age/mass-MSTO width relations. In particular, the less massive cluster in our sample does not show an eMSTO, supporting the proposed link between the eMSTO and the escape velocity of the cluster, providing a new lower limit to the age spread of $88\pm40$ Myr for the presence of the eMSTO. The consistent MSTO width measurements between the VISCACHA and HST photometries confirm the robustness of our method and demonstrate that the age spread determination is independent of the photometric system, showing also the power of ground-based observations to investigate the eMSTO phenomenon.