关于疏散星团中巨星的钠过剩：毕星团的情况
On the sodium overabundance of giants in open clusters: The case of the Hyades
摘要：
钠的丰度已经在大量的疏散星团巨星系中被测定，但却发现了相互矛盾的结果，从太阳值到高达五个数量级的过量，这种分歧的原因还没有很好的理解。由于这些钠的过量可能是深混合的结果，对它们的正确理解对恒星演化的模型有重要意义。正如文献中所讨论的，这种分歧的一部分来自于对非LTE效应采用不同的校正，以及对同一组谱线使用不同的原子数据。然而，仍然缺少对巨人中Na行为的清晰描述。为了在这个方向上做出贡献，这项工作提出了一个仔细的重新确定的Na丰度的毕星团巨星，最近的测量其角直径的动机。在NLTE中，平均[Na/Fe] =+0.30，这可以用高初旋转速度的流体动力学模型来解释。这一结果，以及在以前的工作中发现的Na随着恒星质量增加而增加的趋势，表明没有强有力的证据表明红巨星中的Na过量超过了超过2 Msun的恒星演化模型所预期的值。
英文摘要：
Sodium abundances have been determined in a large number of giants of open clusters but conflicting results, ranging from solar values to overabundances of up to five orders of magnitude, have been found. The reasons for this disagreement are not well-understood. As these Na overabundances can be the result of deep mixing, their proper understanding has consequences for models of stellar evolution. As discussed in the literature, part of this disagreement comes from the adoption of different corrections for non-LTE effects and from the use of different atomic data for the same set of lines. However, a clear picture of the Na behaviour in giants is still missing. To contribute in this direction, this work presents a careful redetermination of the Na abundances of the Hyades giants, motivated by the recent measurement of their angular diameters. An average of [Na/Fe] = +0.30, in NLTE, has been found. This overabundance can be explained by hydrodynamical models with high initial rotation velocities. This result, and a trend of increasing Na with increasing stellar mass found in a previous work, suggests that there is no strong evidence of Na overabundances in red giants beyond those values expected by evolutionary models of stars with more than ~ 2 Msun.
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