The K2 M67 Study: Precise Mass for a Turnoff Star in the Old Open Cluster M67
The K2 M67 Study: Precise Mass for a Turnoff Star in the Old Open Cluster M67
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DOI：
10.3847/1538-3881/abca8d
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发表时间：
2020-11
期刊：
影响因子：
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通讯作者：
E. Sandquist;D. Latham;R. Mathieu;E. Leiner;A. Vanderburg;D. Stello;J. Orosz;L. Bedin;M. Libralat
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文献类型：
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作者：
E. Sandquist;D. Latham;R. Mathieu;E. Leiner;A. Vanderburg;D. Stello;J. Orosz;L. Bedin;M. Libralat
我们对疏散星团M67中的明亮的分离食主序星WOCS 11028（Sanders 617）进行了研究。虽然该双星在每个轨道周期只有一次食，但我们证明，由于轨道倾角的强约束，可以非常精确地导出恒星的质量：M A = 1.222 ± 0.006 M，M B = 0.909 ± 0.004 M。我们使用光谱能量分布拟合的方法来代替精确的半径，通常是来自一个双重食双星的组成部分的恒星的特性。反褶积的SED显示，较亮的组成部分的二是在微弱的关闭点的集群-一个独特的进化点，发生后，对流核心已经建立，而星星是在其运动的中间向较低的表面温度，在所谓的钩在主序列结束。这些测量结果与太阳金属丰度演化模型存在明显分歧：需要更高的金属丰度才能重现WOCS 11028 A的特征。我们讨论了模型物理的变化，可能需要解决的差异。最清楚的结论是，扩散可能是必要的，以调和光谱丰度的M67恒星需要更高的金属丰度模型和强度降低对流过冲发生在恒星的转折。在超太阳体金属丰度，各种指标同意之间的集群年龄约3.5和4.0 Gyr。
We present a study of the bright detached eclipsing main-sequence binary WOCS 11028 (Sanders 617) in the open cluster M67. Although the binary has only one eclipse per orbital cycle, we show that the masses of the stars can be derived very precisely thanks to a strong constraint on the orbital inclination: M A = 1.222 ± 0.006M ⊙ and M B = 0.909 ± 0.004M ⊙. We use a spectral energy distribution fitting method to derive characteristics of the component stars in lieu of the precise radii that would normally be derived from a doubly eclipsing binary. The deconvolution of the SEDs reveals that the brighter component of the binary is at the faint turnoff point for the cluster—a distinct evolutionary point that occurs after the convective core has been established and while the star is in the middle of its movement toward lower surface temperatures, before the so-called hook at the end of the main sequence. The measurements are in distinct disagreement with evolution models at solar metallicity: higher metal abundances are needed to reproduce the characteristics of WOCS 11028 A. We discuss the changes to model physics that are likely to be needed to address the discrepancies. The clearest conclusions are that diffusion is probably necessary to reconcile spectroscopic abundances of M67 stars with the need for higher metallicity models and that reduced strength convective overshooting is occurring for stars at the turnoff. At super-solar bulk metallicity, various indicators agree on a cluster age between about 3.5 and 4.0 Gyr.