红巨星铍丰度的光谱研究
Spectroscopic Study on the Beryllium Abundances of Red Giant Stars
摘要：
对200颗红巨星（主要是晚G型和早K型）的铍丰度进行了广泛的光谱研究，这些红巨星是根据Subaru/HDS获得的高色散光谱从近紫外Be II 3131.066线确定的，目的是调查这些演化巨星表面Be含量的性质;例如，依赖于恒星的参数，随着其起源和建立时间的特殊程度。我们发现Be在这些演化巨星的光球层中相对于初始丰度有1-3 dex（或更多）的显著不足（从恒星到恒星的程度相差很大）。虽然Be丰度（A（Be））对T_eff、log g、[Fe/H]、M、年龄和v_sin i的依赖性很弱，但这可能是由于A（Be）的金属丰度依赖性以及这些恒星参数之间的相互关联，因为这种趋势在金属丰度标度的Be丰度（[Be/Fe]）中几乎消失。通过比较Be丰度（以及它们与Li和C的相关性）和最近基于复杂恒星演化计算的理论预测，我们得出结论，如此大范围/多样性的Be亏损很难仅仅用红巨星包层中的第一次挖掘的标准理论来解释，一些额外的混合过程（如旋转或热盐混合）必须负责，这大概已经开始在主序阶段运行。这一观点得到了这样一个事实的支持，即在靠近主序星的演化程度较低的中等质量B-A型恒星中可以看到明显的Be耗尽。
英文摘要：
An extensive spectroscopic study was carried out for the beryllium abundances of 200 red giants (mostly of late G and early K type), which were determined from the near-UV Be II 3131.066 line based on high-dispersion spectra obtained by Subaru/HDS, with an aim of investigating the nature of surface Be contents in these evolved giants; e.g., dependence upon stellar parameters, degree of peculiarity along with its origin and build-up timing. We found that Be is considerably deficient (to widely different degree from star to star) in the photosphere of these evolved giants by ~1-3 dex (or more) compared to the initial abundance. While the resulting Be abundances (A(Be)) appear to weakly depend upon T_eff, log g, [Fe/H], M, age, and v_sin i, this may be attributed to the metallicity dependence of A(Be) coupled with the mutual correlation between these stellar parameters, since such tendencies almost disappear in the metallicity-scaled Be abundance ([Be/Fe]). By comparing the Be abundances (as well as their correlations with Li and C) to the recent theoretical predictions based on sophisticated stellar evolution calculations, we concluded that such a considerable extent/diversity of Be deficit is difficult to explain only by the standard theory of first dredge-up in the envelope of red giants, and that some extra mixing process (such as rotational or thermohaline mixing) must be responsible, which presumably starts to operate already in the main-sequence phase. This view is supported by the fact that appreciable Be depletion is seen in less evolved intermediate-mass B-A type stars near to the main sequence.
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