光谱学揭示Terzan 5的复杂性质
Spectroscopy Unveils the Complex Nature of Terzan 5
摘要：
我们提出了33个红巨星的化学丰度分析属于复杂的恒星系统泰山5。我们确认发现了两个具有不同铁丰度的恒星星族（Ferraro等人，2009，Nature，462，483）：一个相对贫金属的组分，[Fe/H]=-0.25 +/- 0.07 r.m.s.，另一组分的[Fe/H]=+0.27 +/-0.04 r.m.s.，超过了任何已知的银河系球状星团。这两个种群也显示出不同的[α/Fe]丰度比。贫金属组分的平均值[α/Fe]=+0.34 +/-0.06 r.m.s.，这与核心坍缩超新星（SNe）快速富集的典型情景一致。富金属组分具有[α/Fe]=+0.03 +/-i 0.04 r.m.s.，这表明形成它的气体在较长的时间尺度上受到II型和Ia型SNe的污染。这两个群体都没有显示出[Al/Fe]超过[O/Fe]反相关的证据，这通常在银河系球状星团中观察到。由于这些化学丰度模式是独特的，我们认为泰山5不是一个真正的球状星团，而是一个恒星系统，具有更复杂的恒星形成和化学富集的历史。
英文摘要：
We present the chemical abundance analysis of 33 red giant stars belonging to the complex stellar system Terzan 5. We confirm the discovery of two stellar populations (Ferraro et al. 2009, Nature, 462,483) with distinct iron abundances: a relatively metal-poor component with [Fe/H]=-0.25 +/- 0.07 r.m.s., and another component with [Fe/H]=+0.27 +/- 0.04 r.m.s., exceeding in metallicity any known Galactic globular cluster. The two populations also show different [alpha/Fe] abundance ratios. The metal-poor component has an average [alpha/Fe]=+0.34 +/- 0.06 r.m.s., consistent with the canonical scenario for rapid enrichment by core collapse supernovae (SNe). The metal-rich component has [alpha/Fe]=+0.03 +/-i 0.04 r.m.s., suggesting that the gas from which it formed was polluted by both type II and type Ia SNe on a longer timescale. Neither of the two populations shows evidence of the [Al/Fe] over [O/Fe] anti-correlation, that is typically observed in Galactic globular clusters. Because these chemical abundance patterns are unique, we propose that Terzan 5 is not a true globular cluster, but a stellar system with a much more complex history of star formation and chemical enrichment.
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