arXiv 1710.024272017-10-06astro-ph.EP

热土星质量行星WASP-49 b大气的气溶胶约束

Aerosol Constraints on the Atmosphere of the Hot Saturn-mass planet WASP-49b

Patricio Cubillos, Luca Fossati, Nikolai Erkaev, Matej Malik, Tetsuya Tokano, Monika Lendl, Colin Johnstone, Helmut Lammer, Aurelien Wyttenbach

备注：: Accepted for publication in ApJ
DOI：: 10.3847/1538-4357/aa9019

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摘要：

气溶胶强烈的、几乎与波长无关的吸收截面产生了无特征的系外行星透射光谱，限制了我们描述其大气的能力。在这里，我们表明，即使在无特征光谱的存在下，我们仍然可以表征某些大气特性。具体来说，我们约束气溶胶层的上，下压力边界，并提出合理的组成候选人。我们研究了膨胀的土星质量行星WASP-49 b的情况，近红外观测揭示了0.7和1.0 { \microns }之间的平坦透射光谱。首先，我们使用一个流体动力学上层大气代码来估计电离恒星高能光子在$10^{-8}$巴达到的压力，设置气溶胶可能存在的压力上限。然后，我们结合HELIOS和Pyrat湾辐射传输模型来约束大气气溶胶的温度和光球压力，在贝叶斯框架。对于WASP-49 b，我们将透射光球（因此，气溶胶甲板边界）限制为高于$10^{-5}$ bar（100 $\times$太阳金属丰度）、$10^{-4}$ bar（太阳）和$10^{-3}$ bar（0.1 $\times$太阳）的压力作为下边界，低于$10^{-7}$ bar作为上边界。最后，我们将气溶胶化合物的凝结曲线与地球的压力-温度曲线进行比较，以确定负责吸收的合理凝结物。在这些情况下，我们发现作为候选人：钠$_{2}$ S（在100 $\times$太阳金属丰度）;铬和MnS（在太阳和0.1 $\times$太阳）;和镁橄榄石，顽火辉石和alabandite（在0.1 $\times$太阳）。

英文摘要：

The strong, nearly wavelength-independent absorption cross section of aerosols produces featureless exoplanet transmission spectra, limiting our ability to characterize their atmospheres. Here we show that even in the presence of featureless spectra, we can still characterize certain atmospheric properties. Specifically, we constrain the upper and lower pressure boundaries of aerosol layers, and present plausible composition candidates. We study the case of the bloated Saturn-mass planet WASP-49b, where near-infrared observations reveal a flat transmission spectrum between 0.7 and 1.0 {\microns}. First, we use a hydrodynamic upper-atmosphere code to estimate the pressure reached by the ionizing stellar high-energy photons at $10^{-8}$ bar, setting the upper pressure boundary where aerosols could exist. Then, we combine HELIOS and Pyrat Bay radiative-transfer models to constrain the temperature and photospheric pressure of atmospheric aerosols, in a Bayesian framework. For WASP-49b, we constrain the transmission photosphere (hence, the aerosol deck boundaries) to pressures above $10^{-5}$ bar (100$\times$ solar metallicity), $10^{-4}$ bar (solar), and $10^{-3}$ bar (0.1$\times$ solar) as lower boundary, and below $10^{-7}$ bar as upper boundary. Lastly, we compare condensation curves of aerosol compounds with the planet's pressure-temperature profile to identify plausible condensates responsible for the absorption. Under these circumstances, we find as candidates: Na$_{2}$S (at 100$\times$ solar metallicity); Cr and MnS (at solar and 0.1$\times$ solar); and forsterite, enstatite, and alabandite (at 0.1$\times$ solar).

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