论文标题
在不断发展的阶段，多个恒星种群：NGC 1978年主要序列矮人之间的化学变化检测
Multiple stellar populations at less evolved stages: detection of chemical variations among main-sequence dwarfs in NGC 1978
论文作者
论文摘要
具有不同化学成分的多个恒星种群（MPS）不是旧GC的独家特征（超过10 GYR）。实际上，最近的研究表明，麦芽素云中的年轻簇（$ \ sim $ 2--6 Gyr-Over）也表现出不断发展的恒星之间的星际明星化学变化。但是，在这些中年龄群体中不太进化的矮人中是否存在MPS仍不清楚。在这项工作中，我们在$ \ sim $ \ sim $ 2 Gyr-Old Cluster NGC 1978中搜索GK型矮人之间的化学变化，这是MPS最年轻的群集。我们从哈勃太空望远镜中利用深层紫外线和视觉观测，以限制MS恒星之间的氮（N）和氧（O）变化。为此，我们将对N和O敏感的适当光度图与简单恒星种群和MPS的合成图进行了比较。我们得出的结论是，NGC \，1978年主机MPS中的G-和K型MS星。我们的统计分析表明，富含N的恒星的比例从$ \ sim $ 40 \％到$ \ sim $ 80 \％，具体取决于氮和氧的详细分布。
Multiple stellar populations (MPs) with different chemical compositions are not exclusive features of old GCs (older than 10 Gyr). Indeed, recent studies reveal that younger clusters ($\sim$2--6 Gyr-old) in the Magellanic Clouds also exhibit star-to-star chemical variations among evolved stars. However, whether MPs are present among less evolved dwarfs of these intermediate-age clusters is still unclear. In this work, we search for chemical variations among GK-type dwarfs in the $\sim$2 Gyr-old cluster NGC 1978, which is the youngest cluster with MPs. We exploit deep ultraviolet and visual observations from the Hubble Space Telescope to constrain the nitrogen (N) and oxygen (O) variations among MS stars. To do this, we compare appropriate photometric diagrams that are sensitive to N and O with synthetic diagrams of simple stellar populations and MPs. We conclude that the G- and K-type MS stars in NGC\,1978 host MPs. Our statistical analysis shows that the fraction of N-rich stars ranges from $\sim$40\% to $\sim$80\%, depending on the detailed distributions of nitrogen and oxygen.
