论文标题
大型麦哲伦云集群NGC1971中的HBETA发射线星星的多个种群
Multiple populations of Hbeta emission line stars in the Large Magellanic Cloud cluster NGC1971
论文作者
论文摘要
我们重新审视了年轻的大型麦哲伦云星团NGC1971，目的是为我们对其观察到的扩展主序列转口（EMSTO）的理解提供更多线索，这是年轻星团簇中常见的特征，最近被认为是由类似于群集年龄（〜160 Myr）的真实年龄差异引起的。我们结合了高成员概率星的精确华盛顿和Stromgren光度法，以探索这种emsto的性质。从不同的临时定义的伪颜色中，我们发现在整个Emsto中分布的蓝色和红色星星都没有显示出轻度和重型元素丰度的任何不均匀性。这些“蓝色”和“红色”星星只有在使用华盛顿$ m $ $ $的幅度时分为两个明显不同的群体，这将划分了负责Emsto出现的光谱特征的数量。我们推测是恒星填充了NGC1971的emsto，因为：i）hbeta有助于M Passband； ii）HBETA排放是恒星的常见特征； iii）华盛顿M和T1幅度显示紧密相关；后者测量了恒星中观察到的HALPHA发射线的贡献，这又与HBETA排放相关。据我们所知，这是指出HBETA排放的第一个观察结果，这是年轻恒星簇中观察到的EMSTO的起源。存在结果肯定会打开从具有恒星中通常看到的特征的通带的光度法系统中研究EMSTO的新可能性。
We revisited the young Large Magellanic Cloud star cluster NGC1971 with the aim of providing additional clues to our understanding of its observed extended Main Sequence turnoff (eMSTO), a feature common seen in young stars clusters, which was recently argued to be caused by a real age spread similar to the cluster age (~160 Myr). We combined accurate Washington and Stromgren photometry of high membership probability stars to explore the nature of such an eMSTO. From different ad hoc defined pseudo colors we found that bluer and redder stars distributed throughout the eMSTO do not show any inhomogeneities of light and heavy-element abundances. These 'blue' and 'red' stars split into two clearly different groups only when the Washington $M$ magnitudes are employed, which delimites the number of spectral features responsible for the appearance of the eMSTO. We speculate that Be stars populate the eMSTO of NGC1971 because: i) Hbeta contributes to the M passband; ii) Hbeta emissions are common features of Be stars and; iii) Washington M and T1 magnitudes show a tight correlation; the latter measuring the observed contribution of Halpha emission line in Be stars, which in turn correlates with Hbeta emissions. As far as we are aware, this is the first observational result pointing to Hbeta emissions as the origin of eMSTOs observed in young star clusters. The presence outcome will certainly open new possibilities of studying eMSTO from photometric systems with passbands centered at features commonly seen in Be stars.
