Statistical Analysis of Hubble/WFC3 Transit Spectroscopy of Extrasolar Planets
Statistical Analysis of Hubble/WFC3 Transit Spectroscopy of Extrasolar Planets
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DOI：
10.3847/2041-8213/aa8e40
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发表时间：
2017-10-01
影响因子：
7.9
通讯作者：
Fraine, Jonathan
中科院分区：
文献类型：
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作者：
Fu, Guangwei;Deming, Drake;Fraine, Jonathan
透射光谱学为研究系外行星大气提供了一个窗口，但这个窗口被云层和薄雾所遮蔽。云和雾引入了气体吸收特征的强度和行星物理参数（例如丰度）之间的简并性。打破这种退化的一种方法是通过统计研究。我们收集了所有已发表的 1.1-1.65 μm 水蒸气吸收的 HST/WFC3 传输光谱，并对水吸收特征和行星参数之间的潜在相关性进行了统计研究。我们将观测到的光谱与使用 Exo 传输代码为每个行星计算的模板进行拟合。我们用刻度高度来表示吸水率的大小，从而消除了已知的对温度、表面重力和平均分子量的依赖性。我们发现尺度高度的吸收与行星平衡温度具有正基线相关性；我们的假设是，随着温度的升高，云凝结的减少是造成基线斜率的原因。然而，从平衡温度与行星质量相关的意义上来说，观察到的样本本质上也是简并的。我们编译了尺度高度的吸收分布，我们发现该分布比高斯分布更接近对数正态分布。然而，我们还发现观测到的行星的平衡温度分布类似地呈对数正态分布。这表明吸收值受到观测偏差的影响，观测者尚未瞄准最热行星的足够样本。
Transmission spectroscopy provides a window to study exoplanetary atmospheres, but that window is fogged by clouds and hazes. Clouds and haze introduce a degeneracy between the strength of gaseous absorption features and planetary physical parameters such as abundances. One way to break that degeneracy is via statistical studies. We collect all published HST/WFC3 transit spectra for 1.1-1.65 mu m water vapor absorption and perform a statistical study on potential correlations between the water absorption feature and planetary parameters. We fit the observed spectra with a template calculated for each planet using the Exo-transmit code. We express the magnitude of the water absorption in scale heights, thereby removing the known dependence on temperature, surface gravity, and mean molecular weight. We find that the absorption in scale heights has a positive baseline correlation with planetary equilibrium temperature; our hypothesis is that decreasing cloud condensation with increasing temperature is responsible for this baseline slope. However, the observed sample is also intrinsically degenerate in the sense that equilibrium temperature correlates with planetary mass. We compile the distribution of absorption in scale heights, and we find that this distribution is closer to log-normal than Gaussian. However, we also find that the distribution of equilibrium temperatures for the observed planets is similarly log-normal. This indicates that the absorption values are affected by observational bias, whereby observers have not yet targeted a sufficient sample of the hottest planets.