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The K2 M67 Study: Precise Mass for a Turnoff Star in the Old Open Cluster M67
The Astronomical Journal ( IF 5.3 ) Pub Date : 2021-01-11 , DOI: 10.3847/1538-3881/abca8d Eric L. Sandquist 1 , David W. Latham 2 , Robert D. Mathieu 3 , Emily Leiner 3, 4 , Andrew Vanderburg 5 , Dennis Stello 6, 7, 8 , Jerome A. Orosz 1 , Luigi R. Bedin 9 , Mattia Libralato 9, 10, 11 , Luca Malavolta 9, 11 , Domenico Nardiello 9, 12
The Astronomical Journal ( IF 5.3 ) Pub Date : 2021-01-11 , DOI: 10.3847/1538-3881/abca8d Eric L. Sandquist 1 , David W. Latham 2 , Robert D. Mathieu 3 , Emily Leiner 3, 4 , Andrew Vanderburg 5 , Dennis Stello 6, 7, 8 , Jerome A. Orosz 1 , Luigi R. Bedin 9 , Mattia Libralato 9, 10, 11 , Luca Malavolta 9, 11 , Domenico Nardiello 9, 12
Affiliation
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: $M_A = 1.222\pm0.006 M_\odot$ and $M_B = 0.909\pm0.004 M_\odot$. 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 temperature, before the so-called hook at the end of 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.
中文翻译:
K2 M67 研究:老疏散星团 M67 中一颗关闭星的精确质量
我们对疏散星团 M67 中明亮分离的食主序双星 WOCS 11028 (Sanders 617) 进行了研究。尽管双星每个轨道周期只有一次日食,但我们表明,由于轨道倾角的强约束,可以非常精确地推导出恒星的质量:$M_A = 1.222\pm0.006 M_\odot$ 和 $M_B = 0.909\pm0.004 M_\dot$。我们使用光谱能量分布拟合方法来推导组成恒星的特征,而不是通常从双食双星得出的精确半径。SED 的解卷积表明,双星中较亮的部分位于星团的微弱转折点——一个明显的演化点,发生在对流核心建立之后,而恒星正处于向低处运动的中间表面温度,在主序末端的所谓钩之前。这些测量结果与太阳金属丰度的演化模型存在明显分歧:需要更高的金属丰度来重现 WOCS 11028 A 的特征。我们讨论了可能需要对模型物理进行更改以解决这些差异。最明确的结论是,为了使 M67 恒星的光谱丰度与更高金属丰度模型的需要相协调,扩散可能是必要的,并且这种强度降低的对流超调正在关闭处发生在恒星上。在超太阳大块金属丰度下,各种指标一致认为星团年龄在 3.5 到 4.0 Gyr 之间。
更新日期:2021-01-11
中文翻译:
K2 M67 研究:老疏散星团 M67 中一颗关闭星的精确质量
我们对疏散星团 M67 中明亮分离的食主序双星 WOCS 11028 (Sanders 617) 进行了研究。尽管双星每个轨道周期只有一次日食,但我们表明,由于轨道倾角的强约束,可以非常精确地推导出恒星的质量:$M_A = 1.222\pm0.006 M_\odot$ 和 $M_B = 0.909\pm0.004 M_\dot$。我们使用光谱能量分布拟合方法来推导组成恒星的特征,而不是通常从双食双星得出的精确半径。SED 的解卷积表明,双星中较亮的部分位于星团的微弱转折点——一个明显的演化点,发生在对流核心建立之后,而恒星正处于向低处运动的中间表面温度,在主序末端的所谓钩之前。这些测量结果与太阳金属丰度的演化模型存在明显分歧:需要更高的金属丰度来重现 WOCS 11028 A 的特征。我们讨论了可能需要对模型物理进行更改以解决这些差异。最明确的结论是,为了使 M67 恒星的光谱丰度与更高金属丰度模型的需要相协调,扩散可能是必要的,并且这种强度降低的对流超调正在关闭处发生在恒星上。在超太阳大块金属丰度下,各种指标一致认为星团年龄在 3.5 到 4.0 Gyr 之间。