Beryllium Abundances in F and G Dwarfs in Praesepe and Other Young Clusters from Keck HIRES Observations
Beryllium Abundances in F and G Dwarfs in Praesepe and Other Young Clusters from Keck HIRES Observations
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根据 Keck HIRES 观测，Praesepe 和其他年轻星团中 F 和 G 矮星中的铍丰度
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发表时间：
2004
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通讯作者：
J. King
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作者：
A. Boesgaard;E. Armengaud;J. King
对Be和Li的研究为恒星内部结构提供了有用的线索。特别令人感兴趣的是对疏散星团中的这些轻元素的研究，它们具有已知的年龄和金属丰度。本文报道了在Praesepe中10颗f型恒星中Be的丰度，并对其他疏散星团（Hyades、Pleiades、α Per、Coma和UMa）中Be的丰度进行了全面的讨论。我们利用凯克1号望远镜和高分辨率梯队光谱仪（HIRES）在Praesepe恒星中观测到了3130 Å附近的Be II双星。利用光谱合成方法得到了铍的丰度。我们发现有四颗恒星在Li倾角的温度范围内有明确的Be耗尽，就像我们在之前的星团研究中发现的那样，特别是在毕宿星团和后发星团中。把所有的星团放在一起，我们确认在F星的一个狭窄的温度范围内存在一个Be dip。铍的损耗在这个倾角中没有Li的损耗那么明显。对于温度较低的恒星，尽管有大量的Li消耗，但很少或根本没有Be消耗。对于很少或没有Li耗尽的恒星，A(Li)≥3.0，Li/Be的比值为75±4.6，而陨星的比值为77.6。对于温度低于~5900 K的恒星，似乎很少或没有be耗尽，平均A（be）为1.30±0.02。对于给定星团中这些较冷的恒星来说，没有证据表明a （Be）的恒星与恒星之间存在内在差异，可能只有较冷的昴宿星团的恒星例外。在Li-Be倾角的温度范围内，Li和Be之间存在很强的相关性，符合旋转诱导混合理论。此外，Li与Be相关关系的斜率随温度范围的不同而不同。对于5900 ~ 6650 K之间的42颗恒星的完整样本，斜率为0.43±0.05[其中A（Li）为横坐标]。6300 K < Teff < 6650 K坡度为0.48±0.08,5900 K < Teff < 6300 K坡度为0.30±0.05。对于Li高原恒星（较冷的子集），由于增加的表面对流区影响混合，因此相对于Be消耗更多的Li，斜率较小。不同年龄的团簇在Be耗尽方面的不同行为与主层序演化阶段与旋转有关的缓慢混合的观点是一致的。该簇的金属丰度范围仅为0.2个指数，因此很难看出金属丰度对Li-Be关系的影响；而温度较低的星（[Fe/H] = +0.13）的平均A（Be）为1.35±0.02，比彗发星（[Fe/H] = -0.09）的1.26±0.02高出0.09个指数。
The study of both Be and Li gives useful clues about stellar internal structure. Of particular interest is the study of these light elements in open clusters, which have a known age and metallicity. In this paper we present a study of Be abundances in 10 F-type stars in Praesepe and a comprehensive discussion about Be abundances in other open clusters: Hyades, Pleiades, α Per, Coma, and UMa. We have made observations of the doublet of Be II around 3130 Å in Praesepe stars, using the Keck I telescope and the High Resolution Echelle Spectrometer (HIRES). Beryllium abundances were derived from the spectra using the spectrum synthesis method. We find four stars with definite Be depletion in the temperature range of the Li dip like we found in our previous cluster studies, notably for the Hyades and Coma clusters. Putting all the clusters together, we confirm the existence of a Be dip in a narrow temperature range for F stars. Beryllium depletion in this dip is less pronounced than Li depletion. For the cooler stars there is little or no Be depletion, even though there are large depletions of Li. For stars that have little or no Li depletion, A(Li) ≥ 3.0, the ratio Li/Be is 75 ± 4.6, compared to the meteoritic ratio of 77.6. For stars cooler than ~5900 K there appears to be little or no Be depletion, and the mean A(Be) is 1.30 ± 0.02. For these cooler stars within a given cluster there is no evidence for intrinsic star-to-star differences in A(Be), with the possible exception of the cool Pleiades stars. In the temperature range of the Li-Be dip, a strong correlation exists between Li and Be, consistent with the theory of rotationally induced mixing. Moreover, the slopes of the Li versus Be correlations are different depending on the temperature range. For the full sample of 42 stars between 5900 and 6650 K the slope is 0.43 ± 0.05 [where A(Li) is the abscissa]. The slope is 0.48 ± 0.08 for 6300 K < Teff < 6650 K and 0.30 ± 0.05 for 5900 K < Teff < 6300 K. For the Li plateau stars (the cooler subset), the slope is smaller as the impact of the increasing surface convection zone affects the mixing, thus depleting more Li relative to Be. The different behavior in Be depletion for clusters of different ages is consistent with the idea of slow mixing related to rotation during the main-sequence phase of evolution. The range in metallicity in this sample of clusters is only 0.2 dex, so it is difficult to discern any influence of metallicity on the Li-Be relationship; however, the mean A(Be) in the cooler Hyades stars (with [Fe/H] = +0.13) is 1.35 ± 0.02, which is higher than that for the Coma stars (with [Fe/H] = -0.09) of 1.26 ± 0.02 by 0.09 dex.