年轻恒星系统色星等图和造父变星的多星族后效
Multipopulation aftereffects on the color-magnitude diagram and Cepheid variables of young stellar systems
摘要：
内容：银河系球状星团中多星群的证据提出了几个关于两代（或更多代）恒星形成和演化的问题。这些人群在年龄和化学成分上存在差异。这些差异存在于本星系群中的年老和中等年龄的星团中.对年轻恒星系统的观测预计将呈现多个恒星星族的足迹。目的：这项理论工作旨在成为探索多星群观测指标空间的一个具体步骤，但不包括可能有助于在星团或星系中形成多代恒星的所有参数组合。我们的目标是阐明可能的观测功能，预期核心氦燃烧的恒星，属于两个恒星星族具有不同的原始氦含量和年龄。方法：采用恒星星族合成方法。我们使用新的恒星和脉动模型来构建一个均匀和一致的框架。在几个光度波段计算了年轻和中等年龄恒星系统（从2000万年到1Gyr）的合成色星等图（CMD），以获得在观测到的CMD和造父变星脉动特性中双种群的可能指标。结果如下：我们预测，在VIK波段的红/蓝团块的形态可以用来光度指示两个恒星星族在一个丰富的恒星组合，如果有一个显着的差异，在其原始的He含量。此外，造父变星的周期分布似乎受到恒星系统内同时代多代恒星的广泛影响。我们表明，韦森关系可能会受到造父变星的氦含量。
英文摘要：
Context: The evidence of a multipopulation scenario in Galactic globular clusters raises several questions about the formation and evolution of the two (or more) generations of stars. These populations show differences in their age and chemical composition. These differences are found in old- and intermediate- age stellar clusters in the Local Group. The observations of young stellar systems are expected to present footprints of multiple stellar populations. Aims: This theoretical work intends to be a specific step in exploring the space of the observational indicators of multipopulations, without covering all the combinations of parameters that may contribute to the formation of multiple generations of stars in a cluster or in galaxy. The goal is to shed light on the possible observational features expected by core He-burning stars that belong to two stellar populations with different original He content and ages. Methods: The tool adopted was the stellar population synthesis. We used new stellar and pulsation models to construct a homogeneous and consistent framework. Synthetic color-magnitude diagrams (CMDs) of young- and intermediate-age stellar systems (from 20 Myr up to 1 Gyr) were computed in several photometric bands to derive possible indicators of double populations both in the observed CMDs and in the pulsation properties of the Cepheids. Results: We predict that the morphology of the red/blue clump in VIK bands can be used to photometrically indicate the two stellar populations in a rich assembly of stars if there is a significant difference in their original He content. Moreover, the period distribution of the Cepheids appears to be widely affected by the coeval multiple generations of stars within stellar systems. We show that the Wesenheit relations may be affected by the helium content of the Cepheids.
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