M30与M92的比较研究：M92是一个具有大幅氦增丰的并合遗迹
A Comparative Study Between M30 and M92 : M92 Is A Merger Remnant With A Large Helium Enhancement
AI总结：
本文比较M30与M92的化学丰度和星族特征，发现M92具有双峰金属丰度、ΔY约0.05的氦增丰及不同[Eu/Fe]，主张其为两个球状星团的并合遗迹。
摘要：
我们对异位第二参数对球状星团（GC）M30和M92开展了比较研究，二者具有相似的金属丰度，但水平分支形态不同。我们得到两个星团相似的平均原初碳丰度。然而，M92因更延展的C-N反相关而表现出较大的碳弥散，而M30表现出更高的原初氮丰度，表明它们具有不同的化学增丰历史。我们的新结果证实了此前的结论：M92是一个金属丰度复杂的GC，呈现双峰金属丰度分布。我们还发现，根据红巨星支凸起（RGBB）的V星等，M92中的富金属恒星群表现出高达ΔY～0.05的氦增丰，这也得到以下证据支持：（i）缺少明亮的RGB恒星，（ii）合成演化HB星族模型，以及（iii）由于较低质量恒星扩散过程程度不同而导致的更延展空间分布。我们重新解释了他人的[Eu/Fe]测量结果，发现M92中两个金属丰度恒星群具有显著不同的[Eu/Fe]丰度且弥散很小。这强烈表明它们是在不同环境中由充分混合的星际介质独立形成的。我们认为M92是一个比普通GC更复杂的系统，最有可能是两个GC的并合遗迹，甚至是更复杂的系统。在附录中，我们讨论了近期建立的色-温关系以及在星族标记中使用宽带测光所存在的问题。
英文摘要：
We perform a comparative study of the ex--situ second--parameter pair globular clusters (GCs) M30 and M92, having similar metallicities but different horizontal branch morphologies. We obtain the similar mean primordial carbon abundances for both clusters. However, M92 shows a large dispersion in carbon due to a more extended C--N anticorrelation, while M30 exhibits a higher primordial nitrogen abundance, suggesting that they have different chemical enrichment histories. Our new results confirm our previous result that M92 is a metal--complex GC showing a bimodal metallicity distribution. We also find that the metal--rich group of stars in M92 shows a helium enhancement as large as $ΔY$ $\sim$ 0.05 from the red giant branch bump (RGBB) $V$ magnitudes, which can also be supported by (i) a lack of bright RGB stars, (ii) synthetic evolutionary HB population models and (iii) the more extended spatial distribution due to different degree of the diffusion process from their lower masses. We reinterpret the [Eu/Fe] measurements by other, finding that the two metallicity groups of stars in M92 have significantly different [Eu/Fe] abundances with small scatters. This strongly suggests that they formed independently out of well mixed interstellar media in different environments. We suggest that M92 is a more complex system than a normal GC, most likely a merger remnant of two GCs or a even more complex system. In Appendix, we address the problems with the recently developed color--temperature relations and the usage of broadband photometry in the populational taggings.
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