He和CNONa丰度增加对球状星团相对年龄测定方法的影响
The impact of enhanced He and CNONa abundances on globular cluster relative age-dating methods
摘要：
研究了银河系球状星团化学模式中未被认识到的差异对它们相对年龄测定的影响。两个最广泛使用的相对年龄测定方法，水平和垂直，以及最近的相对MS拟合方法，仔细分析了纯理论的基础上。采用BaSTI库进行本分析。我们发现，相对年龄的水平和垂直方法在很大程度上取决于初始He含量和重元素分布。未被识别的星团间化学丰度差异可能导致推导出的相对年龄误差高达~0.5 Gyr（或~6 Gyr，如果采用12.8 Gyr的年龄进行归一化），在某些极端情况下甚至更大。结果表明，相对MS拟合方法是迄今为止的年龄测定技术，其中未检测到的集群到集群的差异，他丰富的影响较小。目前的结果是为了构成限制的基础上的估计-从文献中-的银河系球状星团的相对年龄分散的各种相对年龄测定技术的最大可能的传播，他和CNONa元素丰度。最后，它表明，年龄-金属丰度关系发现年轻的银河系球状星团的GC国库计划是一个真正的年龄序列，不能产生的变化，他和/或重元素分布。
英文摘要：
The impact that unrecognised differences in the chemical patterns of Galactic globular clusters have on their relative age determinations is studied. The two most widely used relative age-dating methods, horizontal and vertical, together with the more recent relative MS-fitting method, were carefully analyzed on a purely theoretical basis. The BaSTI library was adopted to perform the present analysis. We find that relative ages derived using the horizontal and vertical methods are largely dependent on the initial He content and heavy element distribution. Unrecognized cluster-to-cluster chemical abundance differences can lead to an error in the derived relative ages as large as ~0.5 (or ~6 Gyr if an age of 12.8 Gyr is adopted for normalization), and even larger for some extreme cases. It is shown that the relative MS-fitting method is by far the age-dating technique for which undetected cluster-to-cluster differences in the He abundance have less impact. Present results are used in order to pose constraints on the maximum possible spread in the He and CNONa elements abundances on the basis of the estimates - taken from the literature - of the Galactic globular clusters relative age dispersion obtained with the various relative age-dating techniques. Finally, it is shown that the age-metallicity relation found for young Galactic globular clusters by the GC Treasury program is a real age sequence and cannot be produced by variations in the He and/or heavy element distribution.
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