Luhman 16 AB褐矮星系统的TESS观测：旋转周期、光变曲线演化和纬向环流
TESS Observations of the Luhman 16AB Brown Dwarf System: Rotational Periods, Lightcurve Evolution, and Zonal Circulation
摘要：
最近发现棕矮星显示旋转调制，通常归因于不同厚度的云层，可能是由行星尺度波调制的。然而，长期的，连续的，高精度的监测数据，以检验这一假设的更多的对象是缺乏的。通过将我们新的光度测量方法应用于TESS数据，我们提取了最近的棕矮星的高精度光变曲线，这些棕矮星形成了Luhman 16 AB双星系统。我们的观测，涵盖了大约100个旋转的Luhman 16 B，显示连续的光变曲线演化。周期图分析表明，在光变曲线中占主导地位的分量的转动周期为5.28小时。我们还发现了2.5 h、6.94 h和90.8 h周期的证据。我们发现，2.5小时和5.28小时的周期出现在Luhman 16 B，它们包括多个，略有移动的峰值，揭示了高速射流和纬向环流在这个对象的存在。我们发现，光变曲线的演变是很好的符合行星尺度波模型，进一步支持这一解释。我们认为，6.94小时的峰值可能是Luhman 16 A的旋转周期。通过比较旋转周期与观测到的vsin（i）测量值，我们发现这两颗棕矮星是在接近赤道面的角度观察的。我们还描述了一个长周期（P~91小时）的光变曲线的演变，我们建议出现从涡旋占主导地位的极地地区。我们的研究为通过周期图分析直接比较全球环流模型的预测与观测铺平了道路。
英文摘要：
Brown dwarfs were recently found to display rotational modulations, commonly attributed to cloud cover of varying thickness, possibly modulated by planetary-scale waves. However, the long-term, continuous, high-precision monitoring data to test this hypothesis for more objects is lacking. By applying our novel photometric approach to TESS data, we extract a high-precision lightcurve of the closest brown dwarfs, which form the binary system Luhman 16AB. Our observations, that cover about 100 rotations of Luhman 16B, display continuous lightcurve evolution. The periodogram analysis shows that the rotational period of the component that dominates the lightcurve is 5.28 h. We also find evidence for periods of 2.5 h, 6.94 h, and 90.8 h. We show that the 2.5 h and 5.28 h periods emerge from Luhman 16B and that they consist of multiple, slightly shifted peaks, revealing the presence of high-speed jets and zonal circulation in this object. We find that the lightcurve evolution is well fit by the planetary-scale waves model, further supporting this interpretation. We argue that the 6.94 h peak is likely the rotation period of Luhman 16A. By comparing the rotational periods to observed v sin(i) measurements, we show that the two brown dwarfs are viewed at angles close to their equatorial planes. We also describe a long-period (P~91 h) evolution in the lightcurve, which we propose emerges from the vortex-dominated polar regions. Our study paves the way toward direct comparisons of the predictions of global circulation models to observations via periodogram analysis.
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