Surprisingly different star-spot distributions on the near equal-mass equal-rotation-rate stars in the M dwarf binary GJ 65 AB
Surprisingly different star-spot distributions on the near equal-mass equal-rotation-rate stars in the M dwarf binary GJ 65 AB
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DOI：
10.1093/mnras/stx1482
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发表时间：
2017-06
影响因子：
4.8
通讯作者：
John R. Barnes;S. Jeffers;C. Haswell;H. Jones;D. Shulyak;Ya. V. Pavlenko;James S. Jenkins
中科院分区：
文献类型：
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作者：
John R. Barnes;S. Jeffers;C. Haswell;H. Jones;D. Shulyak;Ya. V. Pavlenko;James S. Jenkins
我们的目标是了解质量和自转等恒星参数如何影响恒星表面上的星斑分布。为此，我们利用多普勒成像重建了三颗自转速度相近的全对流M矮星的表面亮度分布。我们获得了5.5Au分离双星GJ65的高阶谱时间序列观测，该双星由GJ65A(M5.5V，Prot=0.24d)和GJ65B(M6V，Prot=0.23d)组成。我们还给出了GJ 791.2a(M4.5V，Prot=0.31d)的新观测结果。用UVES对每颗恒星进行了两个晚上的观测，覆盖的波长范围从0.64-1.03μm。时间序列光谱显示了多重线扭曲，我们将其解释为凉爽的星斑，这种扭曲在两个夜晚都持续存在，表明在3d的时间尺度上是稳定的。GJ 791.2a的全球黑子分布与一年前的观测结果相似。在GJ 791.2A和GJ 65A上也可以看到类似的高纬度和绕极黑子结构。然而，令人惊讶的是，它们在GJ 65B上没有出现，相反，GJ 65B显示出更广泛、更大的黑子，集中在中纬度。这三颗恒星都表现出与固体自转一致的小幅度纬度相关的自转。我们将我们对差动旋转的测量与以前的多普勒成像研究进行比较，并在其他观测估计和最近的理论预测的更广泛的背景下讨论结果。
We aim to understand how stellar parameters such as mass and rotation impact the distribution of star-spots on the stellar surface. To this purpose, we have used Doppler imaging to reconstruct the surface brightness distributions of three fully convective M dwarfs with similar rotation rates. We secured high cadence spectral time series observations of the 5.5 au separation binary GJ 65, comprising GJ 65A (M5.5V, Prot = 0.24 d) and GJ 65B (M6V, Prot = 0.23 d). We also present new observations of GJ 791.2A (M4.5V, Prot = 0.31 d). Observations of each star were made on two nights with UVES, covering a wavelength range from 0.64 - 1.03μm. The time series spectra reveal multiple line distortions that we interpret as cool star-spots and which are persistent on both nights suggesting stability on the time-scale of 3 d. Spots are recovered with resolutions down to 8.3° at the equator. The global spot distributions for GJ 791.2A are similar to observations made a year earlier. Similar high latitude and circumpolar spot structure is seen on GJ 791.2A and GJ 65A. However, they are surprisingly absent on GJ 65B, which instead reveals more extensive, larger, spots concentrated at intermediate latitudes. All three stars show small amplitude latitude-dependent rotation that is consistent with solid body rotation. We compare our measurements of differential rotation with previous Doppler imaging studies and discuss the results in the wider context of other observational estimates and recent theoretical predictions.