CORDONI, GiacomoGiacomoCORDONIMilone, Antonino P.Antonino P.MiloneMARINO, AnnaAnnaMARINOCignoni, MicheleMicheleCignoniLagioia, Edoardo P.Edoardo P.LagioiaTAILO, MarcoMarcoTAILOCarlos, MaríliaMaríliaCarlosDONDOGLIO, EmanueleEmanueleDONDOGLIOJang, SoheeSoheeJangMohandasan, AnjanaAnjanaMohandasanLegnardi, Maria V.Maria V.Legnardi2023-07-252023-07-2520222041-1723http://hdl.handle.net/20.500.12386/34334The origin of young star clusters represents a major challenge for modern stellar astrophysics. While stellar rotation partially explains the colour spread observed along main-sequence turn-offs, i.e. where stars leave the main-sequence after the exhaustion of hydrogen in their core, and the multiple main sequences in the colour-magnitude diagrams of stellar systems younger than approximately 2 Gyr, it appears that an age difference may still be required to fulfill the observational constraints. Here we introduce an alternative approach that exploits the main-sequence turn-on, i.e. the point alongside the colour-magnitude diagram where pre-main-sequence stars join the main-sequence, to disentangle between the effects of stellar rotation and age to assess the presence, or lack thereof, of prolonged star formation in the approximately 40-Myr-old cluster NGC1818. Our results provide evidence for a fast star formation, confined within 8 Myr, thus excluding age differences as responsible for the extended main-sequence turn-offs, and leading the way to alternative observational perspectives in the exploration of stellar populations in young clusters.ELETTRONICOenArticle10.1038/s41467-022-31977-y2-s2.0-85134744849https://www.nature.com/articles/s41467-022-31977-yFIS/05 - ASTRONOMIA E ASTROFISICA