论文标题
温带亚北极k2-18b的1D大气研究
1D atmospheric study of the temperate sub-Neptune K2-18b
论文作者
论文摘要
对质量在2到10 m $ _ \ oplus $之间的大气成分知之甚少。在这方面，受地球样恒星辐射的次数K2-18b为这种大气的表征提供了宝贵的机会。先前使用检索算法和前向模型的开普勒，哈勃（HST）和Spitzer太空望远镜数据的传输频谱进行了分析，这表明存在H $ _2 $ O和A h $ _2 $ - 他的气氛，但没有检测到其他气体，例如其他气体，例如CH $ _4 $。 我们使用巨大的大气参数网格来推断其化学成分的约束，使用exo-rem（我们的自谐辐射平衡模型）对K2-18 B的大气进行了模拟。 我们表明，我们的模拟有利于大气金属含量在太阳能40到500倍之间，在某些情况下表明h $ _2 $ o-et云的形成，但不是液体H $ _2 $ o clouds。我们还确认了我们先前研究的发现，该研究表明，CH $ _4 $吸收特征名义上主导了HST光谱范围内的传输光谱。我们将我们的结果与检索算法的结果进行了比较，发现H $ _2 $ O O-O-O-O-O-O-O-O-O-O-O-O频谱解释要么是由于省略了CH $ _4 $吸收或强烈的数据过度拟合。最后，我们调查了不同的情况，这些情况将允许$ _4 $ $ $ $ $ $ $ $ $。我们能够将数据拟合到这些情况下，发现K2-18B的内部温度极不可能。低c/o比率（$ \ $ \ $ 0.01--0.1）允许H $ _2 $ O O来控制传输频谱并可以适合数据，但是到目前为止，此设置缺乏物理解释。 C/O比率$ <$ 0.01的仿真无法令人满意地拟合数据。
The atmospheric composition of exoplanets with masses between 2 and 10 M$_\oplus$ is poorly understood. In that regard, the sub-Neptune K2-18b, which is subject to Earth-like stellar irradiation, offers a valuable opportunity for the characterisation of such atmospheres. Previous analyses of its transmission spectrum from the Kepler, Hubble (HST), and Spitzer space telescopes data using both retrieval algorithms and forward-modelling suggest the presence of H$_2$O and an H$_2$--He atmosphere, but have not detected other gases, such as CH$_4$. We present simulations of the atmosphere of K2-18 b using Exo-REM, our self-consistent 1D radiative-equilibrium model, using a large grid of atmospheric parameters to infer constraints on its chemical composition. We show that our simulations favour atmospheric metallicities between 40 and 500 times solar and indicate, in some cases, the formation of H$_2$O-ice clouds, but not liquid H$_2$O clouds. We also confirm the findings of our previous study, which showed that CH$_4$ absorption features nominally dominate the transmission spectrum in the HST spectral range. We compare our results with results from retrieval algorithms and find that the H$_2$O-dominated spectrum interpretation is either due to the omission of CH$_4$ absorptions or a strong overfitting of the data. Finally, we investigated different scenarios that would allow for a CH$_4$-depleted atmosphere. We were able to fit the data to those scenarios, finding, however, that it is very unlikely for K2-18b to have a high internal temperature. A low C/O ratio ($\approx$ 0.01--0.1) allows for H$_2$O to dominate the transmission spectrum and can fit the data but so far, this set-up lacks a physical explanation. Simulations with a C/O ratio $<$ 0.01 are not able to fit the data satisfactorily.
