THE INFLUENCE OF NONUNIFORM CLOUD COVER ON TRANSIT TRANSMISSION SPECTRA
THE INFLUENCE OF NONUNIFORM CLOUD COVER ON TRANSIT TRANSMISSION SPECTRA
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不均匀云层对凌日传输频谱的影响
DOI：
10.3847/0004-637x/820/1/78
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
V. Parmentier
中科院分区：
文献类型：
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作者：
M. Line;V. Parmentier
我们模拟了不均匀云层对传输透射光谱的影响。几乎每个太阳系大气层、褐矮星和凌日系外行星中都存在斑驳的云。我们的主要发现表明，部分云覆盖可以准确地模拟高平均分子量大气，反之亦然，在某些波长区域，特别是在哈勃太空望远镜（HST）广角相机3（WFC3）带通（1.1-1.7μm）上。我们还发现，斑驳的云覆盖表现出与均匀的全球云不同的特征。此外，我们分析解释了为什么存在“斑片云-高平均分子量”简并性。我们还探索了合成行星和真实行星大气反演中不均匀云覆盖的简并性。我们通过对具有斑片云的合成太阳成分热木星和无云高平均分子量温暖海王星的反演发现，无云高平均分子量大气和部分多云大气都可以同样很好地解释数据。另一个重要发现是，两个观测良好的物体（热木星 HD 189733b 和温暖的海王星 HAT-P-11b）的 HST WFC3 凌日透射光谱可以通过具有斑片云的太阳成分大气来很好地解释，而无需调用高平均分子量或全球云。高分子量和太阳成分部分多云大气之间的简并性可以通过观察两者之间的分子瑞利散射差异来打破。此外，如果凌日时间已知为秒，则部分多云边缘的特征也会在凌日光曲线的入口和出口中显示为约 100 ppm 的残留。
We model the impact of nonuniform cloud cover on transit transmission spectra. Patchy clouds exist in nearly every solar system atmosphere, brown dwarfs, and transiting exoplanets. Our major findings suggest that fractional cloud coverage can exactly mimic high mean molecular weight atmospheres and vice versa over certain wavelength regions, in particular, over the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) bandpass (1.1–1.7 μm). We also find that patchy cloud coverage exhibits a signature that is different from uniform global clouds. Furthermore, we explain analytically why the “patchy cloud-high mean molecular weight” degeneracy exists. We also explore the degeneracy of nonuniform cloud coverage in atmospheric retrievals on both synthetic and real planets. We find from retrievals on a synthetic solar composition hot Jupiter with patchy clouds and a cloud-free high mean molecular weight warm Neptune that both cloud-free high mean molecular weight atmospheres and partially cloudy atmospheres can explain the data equally well. Another key finding is that the HST WFC3 transit transmission spectra of two well-observed objects, the hot Jupiter HD 189733b and the warm Neptune HAT-P-11b, can be explained well by solar composition atmospheres with patchy clouds without the need to invoke high mean molecular weight or global clouds. The degeneracy between high molecular weight and solar composition partially cloudy atmospheres can be broken by observing the molecular Rayleigh scattering differences between the two. Furthermore, the signature of partially cloudy limbs also appears as a ∼100 ppm residual in the ingress and egress of the transit light curves, provided that the transit timing is known to seconds.