16255

Studies of massive stellar clusters in the Large and Small Magellanic Clouds comma spanning a wide range of ages from 100 Myr to 11 Gyr comma have potentially pinpointed the onset of the multiple populations (MPs) phenomenon. Focusing on clusters with similar mass (virgul10elev5 Msun) comma all systems with ages above 2 Gyr were found to host MPs while clusters below this limit do not. Such a relation with age is not expected in any scenario for the origin of MPs comma and constitutes one of the most important findings in the field in recent years. One potential explanation for the observations is that MPs do exist within the young clusters comma but only below a certain stellar mass limit. We propose to obtain deeper imaging of NGC 1783 comma a 1.7 Gyr cluster that does not show MPs on its RGB (virgul1.6 Msun) comma in order to search for splitting along main sequence stars (virgul1 Msun and below) caused by the chemical anomalies. Based on stellar isochrones with MPs abundance variations comma we expect to observe main sequence splitting with an additional 10 orbits of exposure using our unique optical-UV filter combination. Determining if a stellar mass limit exists for MPs would consistute a major step forward in the search for the origin of the multiple populations phenomenon.

针对大麦哲伦云（Large Magellanic Clouds）与小麦哲伦云（Small Magellanic Clouds）中的大质量恒星团开展的研究，覆盖了从100百万年（100 Myr）至110亿年（11 Gyr）的宽泛年龄范围，该研究已精准锁定多星族（multiple populations, MPs）现象的起始临界条件。聚焦质量相近（~10^5 太阳质量（M☉））的恒星团，研究发现所有年龄大于20亿年的恒星团均拥有多星族结构，而年龄低于该阈值的恒星团则未观测到此现象。这种与年龄相关的关联在现有多星族起源的各类理论框架中均未被预期到，堪称近年该领域最重要的研究成果之一。针对该观测结果的一种潜在解释为：年轻恒星团内部确实存在多星族结构，但仅存在于低于特定恒星质量极限的恒星中。我们计划对NGC 1783开展更深层次的成像观测——这是一个年龄为17亿年的恒星团，其红巨星分支（Red Giant Branch, RGB，~1.6 M☉）上未观测到多星族现象——以期搜寻由化学异常引发的主序星（≤1 M☉及以下）分裂特征。基于包含多星族丰度变化的恒星等时线（stellar isochrones）模型，我们预计通过独特的光学-紫外滤光片组合并新增10轨曝光后，可观测到主序星分裂现象。明确多星族是否存在恒星质量极限，将是探寻多星族现象起源过程中的重大突破。