CHARACTERIZING EXOPLANETARY ATMOSPHERES THROUGH INFRARED POLARIMETRY
CHARACTERIZING EXOPLANETARY ATMOSPHERES THROUGH INFRARED POLARIMETRY
复制标题
通过红外偏振测量来表征系外行星大气
DOI：
10.1088/0004-637x/741/1/59
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
T. Karalidi
中科院分区：
文献类型：
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作者：
R. Kok;D. Stam;T. Karalidi
行星可以发射偏振热辐射，就像褐矮星一样。我们使用先进的辐射传输代码呈现来自热系外行星的计算热偏振信号，该代码完全包括气体分子和云粒子的所有散射阶次。该代码在空间上解析了行星的圆盘，允许模拟水平不均匀的行星。我们的结果表明，系外行星热辐射的线性偏振度 P 预计在行星边缘附近最高，并且该 P 取决于温度及其梯度、散射特性以及云粒子的分布。在球对称行星的圆盘上积分，热辐射的 P 为零。然而，对于呈现球形不对称的行星，例如由于平坦化、大气中的云带或斑点、白天和黑夜的差异和/或模糊环，P 通常大于 0.1%，在有利的情况下甚至在近红外波长处达到几个百分点。热极化信号的检测可以获取否则难以获得的行星参数：它立即确认云的存在，然后 P 可以限制大气的不均匀性和由于行星自转速率而导致的扁平化。对于区域对称的行星，偏振角将产生与视线垂直的行星自转轴的分量。最后，我们的模拟表明，P 通常对多云行星大气层的变化比热通量更敏感，因此可以更好地揭示某些动力学过程。
Planets can emit polarized thermal radiation, just like brown dwarfs. We present calculated thermal polarization signals from hot exoplanets, using an advanced radiative transfer code that fully includes all orders of scattering by gaseous molecules and cloud particles. The code spatially resolves the disk of the planet, allowing simulations for horizontally inhomogeneous planets. Our results show that the degree of linear polarization, P, of an exoplanet's thermal radiation is expected to be highest near the planet's limb and that this P depends on the temperature and its gradient, the scattering properties, and the distribution of the cloud particles. Integrated over the disk of a spherically symmetric planet, P of the thermal radiation equals zero. However, for planets that appear spherically asymmetric, e.g., due to flattening, cloud bands or spots in their atmosphere, differences in their day and night sides, and/or obscuring rings, P is often larger than 0.1%, in favorable cases even reaching several percent at near-infrared wavelengths. Detection of thermal polarization signals can give access to planetary parameters that are otherwise hard to obtain: it immediately confirms the presence of clouds, and P can then constrain atmospheric inhomogeneities and the flattening due to the planet's rotation rate. For zonally symmetric planets, the angle of polarization will yield the components of the planet's spin axis normal to the line of sight. Finally, our simulations show that P is generally more sensitive to variability in a cloudy planet's atmosphere than the thermal flux is, and could hence better reveal certain dynamical processes.