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arXiv 1603.08809astro-ph.SR
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疏散星团锂丰度演化的质量效应：Hyades，NGC 752和M67

Mass effect on the lithium abundance evolution of open clusters: Hyades, NGC 752, and M67

Matthieu Castro, Tharcísyo Duarte, Giancarlo Pace, José Dias do Nascimento

备注：
13 pages, 9 figures, 2 tables
发表信息：
A&A 590, A94 (2016)
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摘要：

疏散星团中的锂丰度提供了一种探测太阳型恒星内部混合过程的有效方法，对流并不是唯一的混合机制。为了了解低质量恒星中发生的混合机制，我们测试了非标准模型，这些模型是用太阳校准的，并观测了三个不同年龄的疏散星团，毕宿星团，NGC 752和M67。我们收集了所有可用的数据，并为疏散星团NGC 752，我们重新确定了等效宽度和锂丰度。两套进化模型进行了计算，一个网格的微观扩散和旋转诱导混合，只有标准模型，在金属丰度[Fe/H] = 0.13，0.0和0.01德克斯，分别使用图卢兹-日内瓦进化代码。我们比较观察模型中的颜色星等图为每个集群推断集群年龄和每个集群成员的恒星质量。然后，对于每个星团，我们分析每个恒星的锂丰度作为质量的函数。疏散星团毕星团、NGC 752和M67的数据与锂丰度是这些星团中恒星的年龄和质量的函数相一致。我们的模型与日冕循环定性再现锂丰度演化的一般趋势，在所有三个集群的恒星质量的函数。这项研究指出了在锂丰度随年龄变化的过程中质量依赖性的重要性。有和没有旋转引起的混合模型之间的比较表明，包括双质体循环是必不可少的，以占低质量恒星的锂耗尽。然而，我们的研究结果表明，其他机制应包括解释锂浸和锂分散在低质量的恒星。

英文摘要：

Lithium abundances in open clusters provide an effective way of probing mixing processes in the interior of solar-type stars and convection is not the only mixing mechanism at work. To understand which mixing mechanisms are occurring in low-mass stars, we test non-standard models, which were calibrated using the Sun, with observations of three open clusters of different ages, the Hyades, NGC 752, and M67. We collected all available data, and for the open cluster NGC 752, we redetermine the equivalent widths and the lithium abundances. Two sets of evolutionary models were computed, one grid of only standard models with microscopic diffusion and one grid with rotation-induced mixing, at metallicity [Fe/H] = 0.13, 0.0, and 0.01 dex, respectively, using the Toulouse-Geneva evolution code. We compare observations with models in a color-magnitude diagram for each cluster to infer a cluster age and a stellar mass for each cluster member. Then, for each cluster we analyze the lithium abundance of each star as a function of mass. The data for the open clusters Hyades, NGC 752, and M67, are compatible with lithium abundance being a function of both age and mass for stars in these clusters. Our models with meridional circulation qualitatively reproduce the general trend of lithium abundance evolution as a function of stellar mass in all three clusters. This study points out the importance of mass dependence in the evolution of lithium abundance as a function of age. Comparison between models with and without rotation-induced mixing shows that the inclusion of meridional circulation is essential to account for lithium depletion in low-mass stars. However, our results suggest that other mechanisms should be included to explain the Li-dip and the lithium dispersion in low-mass stars.

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