Modeling Polarization Signals from Cloudy Brown Dwarfs Luhman 16 A and B in Three Dimensions
Modeling Polarization Signals from Cloudy Brown Dwarfs Luhman 16 A and B in Three Dimensions
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DOI：
10.3847/1538-4357/ac2d92
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发表时间：
2021-10
期刊：
影响因子：
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通讯作者：
S. Mukherjee;J. Fortney;R. Jensen-Clem;Xianyu Tan;M. Marley;N. Batalha
中科院分区：
文献类型：
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作者：
S. Mukherjee;J. Fortney;R. Jensen-Clem;Xianyu Tan;M. Marley;N. Batalha
从Luhman 16 A和B在H波段的圆盘积分偏振的检测，以及随后的建模，已被解释在这些机构的纬向云带的框架。最近，Tan和Showman用大气环流模型（GCM）研究了褐矮星的3D大气环流和云结构，他们的模拟产生了复杂的云分布，显示了纬向喷流的某些方面，但也有复杂的涡旋，不能用简单的模型来捕捉。在这里，我们使用这些三维GCM特定于Luhman 16 A和B，沿着与三维蒙特卡罗辐射传输代码阿尔特斯，计算它们的偏振信号。我们采用的三维温压和云廓线从GCM作为我们的输入大气结构。我们在1.6 μm处的偏振计算结果与Luhman 16 A和B的线偏振度测量值吻合得很好。我们的计算再现了两个物体的测量偏振与云粒子大小之间的0.5和1 μm的Luhman 16 A和5 μm的Luhman 16 B。我们发现，在一个旋转周期的过程中，线性偏振的程度可以在一个小时的时间尺度上变化。我们还表明，模型与方位角对称带状云的几何形状，通常用于解释偏振观测的棕矮星，过度预测的偏振信号，如果云的模式不包括复杂的漩涡在这些波段。这一探索性的工作表明，GCM是有希望的建模和解释棕矮星的偏振信号。
The detection of disk-integrated polarization from Luhman 16 A and B in the H band, and subsequent modeling, has been interpreted in the framework of zonal cloud bands on these bodies. Recently, Tan and Showman investigated the 3D atmospheric circulation and cloud structures of brown dwarfs with general circulation models (GCMs), and their simulations yielded complex cloud distributions showing some aspects of zonal jets, but also complex vortices that cannot be captured by a simple model. Here we use these 3D GCMs specific to Luhman 16 A and B, along with the 3D Monte Carlo radiative transfer code ARTES, to calculate their polarization signals. We adopt the 3D temperature–pressure and cloud profiles from the GCMs as our input atmospheric structures. Our polarization calculations at 1.6 μm agree well with the measured degree of linear polarization from both Luhman 16 A and B. Our calculations reproduce the measured polarization for both objects with cloud particle sizes between 0.5 and 1 μm for Luhman 16 A and of 5 μm for Luhman 16 B. We find that the degree of linear polarization can vary on hour-long timescales over the course of a rotation period. We also show that models with azimuthally symmetric band-like cloud geometries, typically used for interpreting polarimetry observations of brown dwarfs, overpredict the polarization signal if the cloud patterns do not include complex vortices within these bands. This exploratory work shows that GCMs are promising for modeling and interpreting polarization signals of brown dwarfs.