WFCAM凌日巡天中的一个高度不等质量食M矮星双星
A highly unequal-mass eclipsing M-dwarf binary in the WFCAM Transit Survey
摘要：
在本文中，我们提出了一个高度不等质量的食M-矮双星的发现，提供了一个独特的约束双星形成理论和低质量双星的演化模型。该双星是使用WFCAM凌日巡天（WTS）的高精度红外线曲线发现的，轨道周期为2. 44 d。我们发现恒星质量M1 = 0.53（0.02）Msun和M2 = 0.143（0.006）Msun（质量比0.27），半径R1 = 0.51（0.01）Rsun和R2 = 0.174（0.006）Rsun。这使得伴星处于一个非常稀疏的采样和重要的晚期M矮星质量状态。由于这两颗恒星的年龄和金属丰度相同，并且跨越了完全对流和部分对流恒星内部之间的理论边界，因此可以使用相同的模型等时线对大范围M矮星质量的模型预测进行比较。与1 Gyr模型预测的质量相比，这两颗恒星的半径似乎略有膨胀，但未来的工作需要适当考虑恒星斑点对光曲曲线解的影响。一个显着的，次同步，~2.56 d的信号与~2%的峰到峰的幅度检测WFCAM光变曲线，我们归因于冷星斑的旋转调制。我们建议，次同步旋转是由于一个稳定的星点复杂的高纬度（磁活性）的主要（即差分旋转），或额外的磁制动，或相互作用的二进制与第三个机构或circumbinary磁盘在其前主序阶段。
英文摘要：
In this paper we present the discovery of a highly unequal-mass eclipsing M-dwarf binary, providing a unique constraint on binary star formation theory and on evolutionary models for low-mass binary stars. The binary is discovered using high- precision infrared light curves from the WFCAM Transit Survey (WTS) and has an orbital period of 2.44 d. We find stellar masses of M1 = 0.53 (0.02) Msun and M2 = 0.143 (0.006) Msun (mass ratio 0.27), and radii of R1 = 0.51 (0.01) Rsun and R2 = 0.174 (0.006) Rsun. This puts the companion in a very sparsely sampled and important late M-dwarf mass-regime. Since both stars share the same age and metallicity and straddle the theoretical boundary between fully and partially convective stellar interiors, a comparison can be made to model predictions over a large range of M-dwarf masses using the same model isochrone. Both stars appear to have a slightly inflated radius compared to 1 Gyr model predictions for their masses, but future work is needed to properly account for the effects of star spots on the light curve solution. A significant, subsynchronous, ~2.56 d signal with ~2% peak-to-peak amplitude is detected in the WFCAM light curve, which we attribute to rotational modulation of cool star spots. We propose that the subsynchronous rotation is either due to a stable star-spot complex at high latitude on the (magnetically active) primary (i.e. differential rotation), or to additional magnetic braking, or to interaction of the binary with a third body or circumbinary disk during its pre-main-sequence phase.
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