The VISCACHA survey : XIII. The extended main-sequence turnoff in intermediate-age low-mass clusters

Abstract

The extended main-sequence turnoff (eMSTO), a significant broadening of the MSTO region, is a well-known feature observed in young and intermediate-age star clusters. Although prolonged star formation and stellar rotation have been proposed as possible explanations for this extension, 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 the HST. Our analysis confirms that the eMSTO phenomenon is also present in low-mass clusters and follows the known age– and mass–MSTO width relations. In particular, the least massive cluster in our sample does not show an eMSTO; this is further evidence in support of the proposed link between the eMSTO and the escape velocity of the cluster and provides a new lower limit to the age spread of 88 ± 40 Myr for the presence of an eMSTO. The consistent MSTO width measurements of 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 for investigations of the eMSTO phenomenon.