Extended main sequence turn-offs in low mass intermediate-age clusters^⋆

¹ Observatorio Astronómico, Universidad Nacional de Córdoba, Laprida 854, 5000 Córdoba, Argentina ;
e-mail: andres@oac.unc.edu.ar
² Consejo Nacional de Investigaciones Científicas y Técnicas, Av. Rivadavia 1917, C1033 AAJ Buenos Aires, Argentina
³ Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF, UK

Received: 18 February 2016
Accepted: 22 March 2016

Abstract

We present an imaging analysis of four low mass stellar clusters (≲5000 M_⊙) in the outer regions of the LMC in order to shed light on the extended main sequence turn-off (eMSTO) phenomenon observed in high mass clusters. The four clusters have ages between 1−2 Gyr and two of them appear to host eMTSOs. The discovery of eMSTOs in such low mass clusters – more than 5 times less massive than the eMSTO clusters previously studied – suggests that mass is not the controlling factor in whether clusters host eMSTOs. Additionally, the narrow extent of the eMSTO in the two older clusters (~2 Gyr) is in agreement with predictions of the stellar rotation scenario, as lower mass stars are expected to be magnetically braked, meaning that their colour magnitude diagrams should be better reproduced by canonical simple stellar populations. We also performed a structural analysis on all the clusters and found that a large core radius is not a requisite for a cluster to exhibit an eMSTO.