A two orbits proposal to solve the age spread dilemma in young Magellanic Clouds clusters


This is a two-orbits proposal to explore pre-main sequence (pre-MS) stars in Large Magellanic Cloud young clusters to assess, once and for all, if multiple bursts of star formation can be supported by these systems. The discovery that nearly all star clusters younger than 2Gyr in both Magellanic Clouds exhibit double/extended main-sequence turn offs (eMSTOs) has been one of the major advances made by HST in stellar astrophysics. Despite a huge effort has been undertaken to understand these observations, the mechanism responsible for the eMSTO is still controversial. It has been suggested that the eMSTO is due to coeval stellar populations with different rotation, but it seems that rotation alone is not able to reproduce the eMSTOs. On the other hand, the eMSTO could be due to a spread in age, so that these clusters would be the younger counterparts of old globular clusters with multiple populations. We propose a novel approach to disentangle between age and rotation by using the Turn-On (TOn), where the pre-MS reaches the main sequence in the color-magnitude diagram (CMD). The most remarkable feature introduced by different ages on this region of the CMD would be the appearance of multiple or broaden TOn peaks in the luminosity function. Specifically a single narrow peak is expected in the case of a single generation, whereas multiple/broaden TOn peaks would imply multiple stellar generations. The proposed observations will allow us, to understand, whether the age spread contributes to eMSTO in young clusters or not, and will be surely seminal for future investigation of the still-eluding multiple stellar populations phenomenon.

HST proposal