论文标题
云的作用在辐照系超球星的传输光谱中甲烷耗尽和水优势的作用
The role of clouds on the depletion of methane and water dominance in the transmission spectra of irradiated exoplanets
论文作者
论文摘要
观察结果表明，大多数观察到的超球星大气中的水和甲烷的稀少。我们隔离大气过程的效果以研究可能的原因。以前，我们研究了有效温度，表面重力，金属性，碳与氧气比和恒星类型的效果，假设无云的热化学平衡和不平衡化学性质。但是，在这些假设下，甲烷在特定参数空间（甲烷谷）上的透射光谱中仍然是持续的光谱特征。在这项工作中，我们研究了云在该领域的作用，我们发现云通过两种直接的方式改变了甲烷的光谱外观：1）通过加热冷行星的光球，以及2）通过掩盖分子特征。云的存在还间接影响甲烷的特征：1）云加热会导致冷凝水的更多蒸发，因此释放出额外的氧气，导致较冷的碳贫困型系外植物的水光谱，以及2）HCN/CO的产生，这些分子抑制了这些分子抑制甲烷特征的抑制作用。 HCN/CO和缺乏甲烷的存在可能表明热系外星上云形成。云加热也会耗尽氨。因此，甲烷和氨的同时耗竭并不是光化学过程所独有的。我们建议，甲烷检测的最佳靶标可能是巨大的，但是较小的行星，温度约为1450 K，绕着恒星旋转。我们还构建了Spitzer合成色图，并发现云可以解释IRAC的1和2的一些高对比度观测值。
Observations suggest an abundance of water and paucity of methane in the majority of observed exoplanetary atmospheres. We isolate the effect of atmospheric processes to investigate possible causes. Previously, we studied the effect of effective temperature, surface gravity, metallicity, carbon-to-oxygen ratio, and stellar type assuming cloud-free thermochemical equilibrium and disequilibrium chemistry. However, under these assumptions, methane remains a persisting spectral feature in the transmission spectra of exoplanets over a certain parameter space, the Methane Valley. In this work we investigate the role of clouds on this domain and we find that clouds change the spectral appearance of methane in two direct ways: 1) by heating-up the photosphere of colder planets, and 2) by obscuring molecular features. The presence of clouds also affects methane features indirectly: 1) cloud heating results in more evaporation of condensates and hence releases additional oxygen, causing water dominated spectra of colder carbon-poor exoplanets, and 2) HCN/CO production results in a suppression of depleted methane features by these molecules. The presence of HCN/CO and a lack of methane could be an indication of cloud formation on hot exoplanets. Cloud heating can also deplete ammonia. Therefore, a simultaneous depletion of methane and ammonia is not unique to photochemical processes. We propose that the best targets for methane detection are likely to be massive but smaller planets with a temperature around 1450 K orbiting colder stars. We also construct Spitzer synthetic color-maps and find that clouds can explain some of the high contrast observations by IRAC's channel 1 and 2.
