A MONITORING CAMPAIGN FOR LUHMAN 16AB. I. DETECTION OF RESOLVED NEAR-INFRARED SPECTROSCOPIC VARIABILITY
A MONITORING CAMPAIGN FOR LUHMAN 16AB. I. DETECTION OF RESOLVED NEAR-INFRARED SPECTROSCOPIC VARIABILITY
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DOI：
10.1088/0004-637x/785/1/48
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发表时间：
2014-02
期刊：
影响因子：
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通讯作者：
A. Burgasser;M. Gillon;J. Faherty;Jacqueline Radigan;A. Triaud;A. Triaud;P. Plavchan;R. Street;E. Jehin;L. Delrez;C. Opitom
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文献类型：
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作者：
A. Burgasser;M. Gillon;J. Faherty;Jacqueline Radigan;A. Triaud;A. Triaud;P. Plavchan;R. Street;E. Jehin;L. Delrez;C. Opitom
我们报告了对附近L矮/T矮双星WISE J104915.57−531906.1AB（Luhman 16 AB）的近红外光谱监测，作为更广泛的运动的一部分，以表征该系统的光谱能量分布和时间变化。利用ESO/TRAPPIST进行组合光光度测量，获得了连续45分钟的低分辨率IRTF/SpeX数据，范围为0.8-2.4 μm。我们的光谱观测证实了这个二进制的通量反转，我们检测到的两个组件的相对光谱通量与组合光的光学亮度的系统在观察过程中的下降相一致的波长依赖性下降。这些数据被成功地模拟为T0.5 Luhman 16 B中的消色差（亮度）和彩色（颜色）变化的组合，与整体云不透明度的变化一致;在L7.5 Luhman 16 A中没有发现显著的变化，与最近解决的光度监测一致。我们估计在1.25 μm处的全光变曲线上的峰-峰振幅为13.5%。利用Luhman 16 B的两点亮温模型，我们推断出一个平均的冷覆盖率为30%-55%，在一个旋转周期内变化15%-30%，假设热区和冷区之间的温差为200-400 K。我们将这些变化解释为高云层覆盖率的变化和相应的“洞”，暴露更深，更热的云层，虽然其他物理解释是可能的。莱茵尺度解释了Luhman 16 B和T矮星SIMP 0136+0933和2 MASS J2139+0220的周期和振幅之间的明显相关性，并预测了Luhman 16 B相对较快的风（1-3 km s−1），与平流时间尺度（1-3个旋转周期）上的光变曲线演化一致。在这个通量反转的棕矮星对中观察到的强变率支持了矿物质云层的斑块状破裂作为L矮星/T矮星过渡的普遍特征的模型。
We report resolved near-infrared spectroscopic monitoring of the nearby L dwarf/T dwarf binary WISE J104915.57−531906.1AB (Luhman 16AB), as part of a broader campaign to characterize the spectral energy distribution and temporal variability of this system. A continuous 45 minute sequence of low-resolution IRTF/SpeX data spanning 0.8–2.4 μm were obtained, concurrent with combined-light optical photometry with ESO/TRAPPIST. Our spectral observations confirm the flux reversal of this binary, and we detect a wavelength-dependent decline in the relative spectral fluxes of the two components coincident with a decline in the combined-light optical brightness of the system over the course of the observation. These data are successfully modeled as a combination of achromatic (brightness) and chromatic (color) variability in the T0.5 Luhman 16B, consistent with variations in overall cloud opacity; and no significant variability was found in L7.5 Luhman 16A, consistent with recent resolved photometric monitoring. We estimate a peak-to-peak amplitude of 13.5% at 1.25 μm over the full light curve. Using a simple two-spot brightness temperature model for Luhman 16B, we infer an average cold covering fraction of ≈30%–55%, varying by 15%–30% over a rotation period assuming a ≈200–400 K difference between hot and cold regions. We interpret these variations as changes in the covering fraction of a high cloud deck and corresponding “holes” which expose deeper, hotter cloud layers, although other physical interpretations are possible. A Rhines scale interpretation for the size of the variable features explains an apparent correlation between period and amplitude for Luhman 16B and the variable T dwarfs SIMP 0136+0933 and 2MASS J2139+0220, and predicts relatively fast winds (1–3 km s−1) for Luhman 16B consistent with light curve evolution on an advective time scale (1–3 rotation periods). The strong variability observed in this flux reversal brown dwarf pair supports the model of a patchy disruption of the mineral cloud layer as a universal feature of the L dwarf/T dwarf transition.