Lithium in M 67: From the main sequence to the red giant branch
Lithium in M 67: From the main sequence to the red giant branch
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DOI：
10.1051/0004-6361/201117704
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发表时间：
2012-03
影响因子：
6.5
通讯作者：
G. Pace;M. Castro;J. Meléndez;S. Théado;J. D. Nascimento
中科院分区：
文献类型：
--
作者：
G. Pace;M. Castro;J. Meléndez;S. Théado;J. D. Nascimento
开放星团中的锂丰度是混合过程的一个非常有效的探针，它们的研究可以帮助理解太阳中锂的大量耗尽。由于它的年龄和金属丰度，疏散星团M67在这方面特别有趣。许多关于M67中锂丰度的研究已经进行了，但是对从次太阳到最大质量成员的恒星中的锂进行均匀的全球分析，从未完成基于高质量光谱的大样本。我们测试了我们的非标准模型，这些模型是用太阳的观测数据校准的。我们收集了文献数据，第一次以均匀的方式跟踪M67中所有观测到的质量大于0.9太阳质量的单星的NLTE锂丰度。我们的进化模型网格是在金属丰度[Fe/H] = 0.01的非标准混合条件下，使用Toulouse-Geneva进化代码计算的。分析从ZAMS的入口开始。除了少数例外，M67中的锂是质量比太阳大的恒星的紧密函数。在关闭恒星中观察到锂丰度的平稳期。无论是质量较小的恒星还是质量较大的恒星，都比高原上的恒星消耗得更多。对于小于M <= 1.1太阳质量的任何给定质量，锂丰度存在显著的散射。我们的模型定性地再现了上述大部分特征，尽管预测的锂耗损比高原地区观测到的低0.45个指数，即在1.1到1.28个太阳质量之间。显然，需要做更多的工作来完全匹配观察结果。尽管有迹象表明色球活动和旋转在锂耗尽中起作用，但根据目前可用的数据还不能得出确切的结论。
Lithium abundances in open clusters are a very effective probe of mixing processes, and their study can help to understand the large depletion of lithium in the Sun. Due to its age and metallicity, the open cluster M67 is especially interesting on this regard. Many studies on lithium abundances in M67 have already been performed, but a homogeneous global analysis of lithium in stars from subsolar up to the most massive members, was never accomplished for a large sample based on high-quality spectra. We tested our non-standard models, which were calibrated using the Sun with observational data. We collected literature data to follow, for the first time in a homogeneous way, NLTE lithium abundances of all observed single stars in M67 more massive than about 0.9 solar masses. Our grid of evolutionary models were computed with non-standard mixing at metallicity [Fe/H] = 0.01, using the Toulouse-Geneva evolution code. The analysis is started from the entrance in the ZAMS. Lithium in M67 is a tight function of mass for stars more massive than the Sun, apart of a few outliers. A plateau in lithium abundances is observed for turn-off stars. Both less massive and more massive stars are more depleted than those in the plateau. There is a significant scatter in lithium abundances for any given mass lower than M <= 1.1 solar masses. Our models qualitatively reproduce most of the features described above, although the predicted depletion of lithium is 0.45 dex smaller than observed for masses in the plateau region, i.e. between 1.1 and 1.28 solar masses. Clearly, more work is needed to throughly match the observations. Despite hints that chromospheric activity and rotation play a role in lithium depletion, no firm conclusion can be drawn with the presently available data.