arXiv 1706.030842017-06-09astro-ph.SRastro-ph.EP

K2在Praesepe发现的新的低质量食双星系统

New low-mass eclipsing binary systems in Praesepe discovered by K2

Edward Gillen, Lynne A. Hillenbrand, Trevor J. David, Suzanne Aigrain, Luisa Rebull, John Stauffer, Ann Marie Cody, Didier Queloz

备注：: 28 pages, 22 figures, 6 tables. Accepted for publication in ApJ
DOI：: 10.3847/1538-4357/aa84b3

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摘要：

利用Kepler/K2时间序列光度学和Keck/HIRES光谱学在亚回旋古老的Praesepe疏散星团中发现了四个低质量（$M<0.6$ $M_\odot$）食双星系统。我们提出了一个新的高斯过程食双星模型，GP-EBOP，以及同时确定有效的温度和距离的EBs的方法。三个报告的系统（AD 3814，AD 2615和AD 1508）是分离和双线的，前两个的精确解决方案。我们确定的质量和半径，AD 3814的精度为1-3%，AD 2615的精度为5-6%。结合$\sim$ 50 K精度的有效温度，我们测试了PARSEC v1.2和BHAC 15恒星演化模型。我们的EB参数与PARSEC模型更一致，主要是因为BHAC 15温标比我们在中M矮星质量范围内探测的数据更热。AD 3814和2615的轨道周期分别为6.0和11.6天，它们都是环形的，但并不同步。这表明，无论是同步进行更慢的完全对流恒星比理论的平衡潮汐预测或磁制动目前正在发挥更重要的作用比潮汐力在这些双星的自旋演化。第四个系统（AD 3116）由一颗褐矮星经过一颗中M矮星组成，这是在次回旋疏散星团中发现的第一个这样的系统。最后，这些新的发现增加了20%（40%）低于$M<1.5$ $M_{\odot}$（$M<0.6$ $M_{\odot}$）的亚Gyr疏散星团的特征EB的数量。

英文摘要：

We present the discovery of four low-mass ($M<0.6$ $M_\odot$) eclipsing binary (EB) systems in the sub-Gyr old Praesepe open cluster using Kepler/K2 time-series photometry and Keck/HIRES spectroscopy. We present a new Gaussian process eclipsing binary model, GP-EBOP, as well as a method of simultaneously determining effective temperatures and distances for EBs. Three of the reported systems (AD 3814, AD 2615 and AD 1508) are detached and double-lined, and precise solutions are presented for the first two. We determine masses and radii to 1-3% precision for AD 3814 and to 5-6% for AD 2615. Together with effective temperatures determined to $\sim$50 K precision, we test the PARSEC v1.2 and BHAC15 stellar evolution models. Our EB parameters are more consistent with the PARSEC models, primarily because the BHAC15 temperature scale is hotter than our data over the mid M-dwarf mass range probed. Both ADs 3814 and 2615, which have orbital periods of 6.0 and 11.6 days, are circularized but not synchronized. This suggests that either synchronization proceeds more slowly in fully convective stars than the theory of equilibrium tides predicts or magnetic braking is currently playing a more important role than tidal forces in the spin evolution of these binaries. The fourth system (AD 3116) comprises a brown dwarf transiting a mid M-dwarf, which is the first such system discovered in a sub-Gyr open cluster. Finally, these new discoveries increase the number of characterized EBs in sub-Gyr open clusters by 20% (40%) below $M<1.5$ $M_{\odot}$ ($M<0.6$ $M_{\odot}$).

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