Unveiling cloudy exoplanets: the influence of cloud model choices on retrieval solutions
Unveiling cloudy exoplanets: the influence of cloud model choices on retrieval solutions
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DOI：
10.1093/mnras/staa2219
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发表时间：
2020-10-01
影响因子：
4.8
通讯作者：
Barstow, Joanna K.
中科院分区：
文献类型：
--
作者：
Barstow, Joanna K.
近年来，很明显，相当一部分过境的系外行星在其大气层中存在某种形式的气溶胶。凌日光谱学--主要是热彗星的光谱学，也有一些小行星的光谱学--提供了证据，在光谱的光学部分，从蓝色到红色的陡峭下降斜率，以及整个过程中柔和的气体吸收特征。因此，试图限制系外行星大气组成的检索研究必须考虑气溶胶的存在。然而，云和霾是复杂的物理现象，目前可用的过境光谱允许我们限制它们的一些属性。因此，在检索模型中的气溶胶的表示要求他们只描述了几个参数，这已经在文献中以各种方式完成。在这里，我调查了一系列参数化的系外行星气溶胶和他们的影响，从热彗星HD 189733 b和HD 209458 b的透射光谱检索。我发现，结果定性同意云/霾本身，无论使用的参数化，并确实使用多种方法提供了一个更全面的图片;检索丰富的H2O也是非常强大的气溶胶的假设。我还发现了强有力的证据，证明HD 209458 b上的气溶胶覆盖了不到一半的终结者区域，而HD 189733 b的图像则不那么清晰。
In recent years, it has become clear that a substantial fraction of transiting exoplanets have some form of aerosol present in their atmospheres. Transit spectroscopy - mostly of hot Jupiters, but also of some smaller planets - has provided evidence for this, in the form of steep downward slopes from blue to red in the optical part of the spectrum, and muted gas absorption features throughout. Retrieval studies seeking to constrain the composition of exoplanet atmospheres must therefore account for the presence of aerosols. However, clouds and hazes are complex physical phenomena, and the transit spectra that are currently available allow us to constrain only some of their properties. Therefore, representation of aerosols in retrieval models requires that they are described by only a few parameters, and this has been done in a variety of ways within the literature. Here, I investigate a range of parametrizations for exoplanet aerosol and their effects on retrievals from transmission spectra of hot Jupiters HD 189733b and HD 209458b. I find that results qualitatively agree for the cloud/haze itself regardless of the parametrization used, and indeed using multiple approaches provides a more holistic picture; the retrieved abundance of H2O is also very robust to assumptions about aerosols. I also find strong evidence that aerosol on HD 209458b covers less than half of the terminator region, whilst the picture is less clear for HD 189733b.