Luhman 16 AB褐矮星的自转周期和天体测量运动的高分辨率幸运成像监测
Rotation periods and astrometric motions of the Luhman 16AB brown dwarfs by high-resolution lucky-imaging monitoring
摘要：
上下文对棕矮星的光度变化进行监测可以提供有关其冷大气中云结构的有用信息。褐矮星双星系统Luhman 16 AB是此类研究的一个有趣目标，因为它的组成部分位于L/T过渡区，并显示出高水平的可变性。Luhman 16 AB也是第三个离太阳系最近的系统，允许使用地面设施进行精确的天体测量调查。目标。这项工作的目的是估计旋转周期和研究天体测量运动的两个组成部分。方法.我们已经用安装在拉西拉的丹麦1.54米望远镜上的幸运成像相机对Luhman 16 AB进行了两年的监测，通过一个特殊的i+z长通滤波器，这使我们能够清楚地将两颗褐矮星分解为单个物体。在16个晚上对靶标进行了密集监测，其中我们观察到Luhman 16 A和16 B的峰间变异性分别为0.20 \pm 0.02 mag和0.34 \pm 0.02 mag。结果我们使用16夜的时间序列数据来估计这两个分量的旋转周期。我们发现Luhman 16 B的自转周期为5.1 \pm 0.1 hr，与以前的测量结果非常吻合。对于Luhman 16 A，我们报告说，它的旋转速度比它的同伴慢，即使我们不能得到一个强大的决心，我们的数据表明旋转周期约为8小时。这意味着这两个组件的旋转轴很好地对齐，并建议一个场景中，这两个对象经历了相同的吸积过程。利用2年的完整数据集研究了Luhman 16 AB的天体测量运动。我们预测该系统的运动与之前基于两个月监测的估计不一致，但无法证实或反驳该系统中存在其他行星质量的天体。
英文摘要：
Context. Photometric monitoring of the variability of brown dwarfs can provide useful information about the structure of clouds in their cold atmospheres. The brown-dwarf binary system Luhman 16AB is an interesting target for such a study, as its components stand at the L/T transition and show high levels of variability. Luhman 16AB is also the third closest system to the Solar system, allowing precise astrometric investigations with ground-based facilities. Aims. The aim of the work is to estimate the rotation period and study the astrometric motion of both components. Methods. We have monitored Luhman 16AB over a period of two years with the lucky-imaging camera mounted on the Danish 1.54m telescope at La Silla, through a special i+z long-pass filter, which allowed us to clearly resolve the two brown dwarfs into single objects. An intense monitoring of the target was also performed over 16 nights, in which we observed a peak-to-peak variability of 0.20 \pm 0.02 mag and 0.34 \pm 0.02 mag for Luhman 16A and 16B, respectively. Results. We used the 16-night time-series data to estimate the rotation period of the two components. We found that Luhman 16B rotates with a period of 5.1 \pm 0.1 hr, in very good agreement with previous measurements. For Luhman 16A, we report that it rotates slower than its companion and, even though we were not able to get a robust determination, our data indicate a rotation period of roughly 8 hr. This implies that the rotation axes of the two components are well aligned and suggests a scenario in which the two objects underwent the same accretion process. The 2-year complete dataset was used to study the astrometric motion of Luhman 16AB. We predict a motion of the system that is not consistent with a previous estimate based on two months of monitoring, but cannot confirm or refute the presence of additional planetary-mass bodies in the system.
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