论文标题
年轻大型群集NGC 1569-B的化学组成
Chemical composition of the young massive cluster NGC 1569-B
论文作者
论文摘要
我们提供了年轻大型簇（YMC）NGC 1569-B的详细化学丰度分析。主机银河系NGC〜1569是一个矮人的不规则的Starburst Galaxy，距离为3.36 $ \ pm $ 0.20 mpc。我们通过对Keck I望远镜上的招聘型Echelle光谱仪获得的NGC 1569-B的光学整合光谱的分析确定了丰度比。我们考虑了不同的红色与蓝色超级巨大比率，即：从理论等同质获得的比率，从YMC的分辨彩色磁性图获得的比率，以及将$χ^2 $比较在将我们的模型光谱与观测值进行比较时最小化的比率。我们采用了后一个比率来产生的化学丰度。派生的铁丰度是亚磨性的，[fe/h] = $ -0.74 \ pm0.05 $。关于缩放的太阳能组成，我们发现增强的$α$元素丰度，$ \ text {[[<mg，si，ca，ca，ti>/fe>/ti>/fe>/fe>/fe>/fe> +0.25 \ pm $ 0.11， +0.49 $ \ pm $ 0.05。其他超值元素包括$ \ text {[[cr/fe]} =+0.50 \ pm $ 0.11，$ \ text {[[sc/fe]} =+0.78 \ pm $ 0.20和$ \ text {[ba/fe]} =+1.28 （$ \ text {[mn/fe]} = - 0.22 \ pm $ 0.12和$ \ text {[ni/fe]} =+0.13 \ pm $ 0.11）。 NGC 1569-B的组成类似于YMC NGC 1705-1的恒星种群，位于蓝色紧凑型矮人星系中。这两个YMC与$α$元素和大多数Fe-peak元素相同，除SC和BA外，它们在NGC〜1569-B中是极高的，并且比到目前为止所研究的任何YMC中都高。年轻人口的光谱的蓝色部分仍然是一个非常有挑战性的波长区域，可以使用IL光谱研究来分析。这是由于对蓝色超级恒星的光的不确定贡献，即使可以使用分辨的光度法，也可能很难从关闭恒星中脱离恒星。
We present a detailed chemical abundance analysis of the young massive cluster (YMC) NGC 1569-B. The host galaxy, NGC~1569, is a dwarf irregular starburst galaxy at a distance of 3.36$\pm$0.20 Mpc. We determined the abundance ratios from the analysis of an optical integrated-light spectrum of NGC 1569-B, obtained with the HIRES echelle spectrograph on the Keck I telescope. We considered different red-to-blue supergiant ratios, namely: the ratio obtained from a theoretical isochrone, the ratio obtained from a resolved colour-magnitude diagram of the YMC, and the ratio that minimises the $χ^2$ when comparing our model spectra with the observations. We adopted the latter ratio for our resulting chemical abundances. The derived iron abundance is sub-solar with [Fe/H] = $-0.74\pm0.05$. In relation to the scaled solar composition, we find enhanced $α$-element abundances, $\text{[<Mg,Si,Ca,Ti>/Fe]}=+0.25\pm$0.11, with a particularly high Ti abundance of +0.49$\pm$0.05. Other super-solar elements include $\text{[Cr/Fe]}=+0.50\pm$0.11, $\text{[Sc/Fe]}=+0.78\pm$0.20, and $\text{[Ba/Fe]}=+1.28\pm$0.14, while other Fe-peak elements are close to scaled solar abundances: ($\text{[Mn/Fe]}=-0.22\pm$0.12 and $\text{[Ni/Fe]}=+0.13\pm$0.11). The composition of NGC 1569-B resembles the stellar populations of the YMC NGC 1705-1, located in a blue compact dwarf galaxy. The two YMCs agree with regard to $α$-elements and the majority of the Fe-peak elements, except for Sc and Ba, which are extremely super-solar in NGC~1569-B -- and higher than in any YMC studied so far. The blue part of the optical spectrum of a young population is still a very challenging wavelength region to analyse using IL spectroscopic studies. This is due to the uncertain contribution to the light from blue supergiant stars, which can be difficult to disentangle from turn-off stars, even when resolved photometry is available.
