Theoretical Transmission Spectra of Exoplanet Atmospheres with Hydrocarbon Haze. II. Dependence on UV Irradiation Intensity, Metallicity, C/O Ratio, Eddy Diffusion Coefficient, and Temperature
Yui Kawashima, Masahiro Ikoma
备注：
28 pages, 24 figures, accepted for publication in ApJ, title shortened
Recent transmission spectroscopy has revealed that clouds and hazes are common in the atmospheres of close-in exoplanets. In this study, using the photochemical, microphysical, and transmission spectrum models for close-in warm ($\lesssim$ 1000 K) exoplanet atmospheres that we newly developed in our preceding paper (Kawashima & Ikoma 2018), we investigate the vertical distributions of haze particles and gaseous species and the resultant transmission spectra over wide ranges of the model parameters including UV irradiation intensity, metallicity, carbon-to-oxygen ratio (C/O), eddy diffusion coefficient, and temperature. The sensitivity to metallicity is of particular interest. We find that a rise in metallicity leads basically to reducing the photodissociation rates of the hydrocarbons and therefore the haze monomer production rates. This is due to an enhanced photon-shielding effect by the major photon absorbers such as $\mathrm{H_2O}$, $\mathrm{CO}$, $\mathrm{CO_2}$, and $\mathrm{O_2}$, existing at higher altitudes than the hydrocarbons. We also find that at relatively short wavelengths ($\lesssim$ 2-3 $μ$m), the absorption features in transmission spectra are most pronounced for moderate metallicities such as 100 times the solar metallicity, whereas the lower the metallicity the stronger the absorption features at relatively long wavelengths ($\gtrsim$ 2-3 $μ$m), where the contribution of haze is small. These are because of the two competing effects of reduced haze production rate and atmospheric scale height for higher metallicities. For the other model parameters, we show that stronger absorption features appear in transmission spectra of the atmospheres with lower UV irradiation, lower C/O ratio, higher eddy diffusion coefficient, and higher temperature.
Theoretical transmission spectra of exoplanet atmospheres with hydrocarbon haze: Effect of creation, growth, and settling of haze particles. I. Model description and first results
Detectable molecular features above hydrocarbon haze via transmission spectroscopy with JWST: Case studies of GJ 1214b-, GJ 436b-, HD 97658b-, and Kepler-51b-like planets
Aerosol Composition of Hot Giant Exoplanets Dominated by Silicates and Hydrocarbon Hazes
气溶胶在不同温度、质量和年龄的系外行星的大气中很常见。这些气溶胶强烈影响了对系外行星透射、反射和发射光的观测，模糊了我们对系外行星热结构和组成的理解。了解主要的气溶胶成分将有助于解释系外行星的观测结果，并从理论上了解其大气层。已经提出了各种组合物，包括金属氧化物和硫化物、铁、铬、硫和烃。然而，这些物种对系外行星气溶胶不透明度的相对贡献是未知的。在这里，我们表明，在传输中观察到的巨型系外行星的气溶胶成分主要是由硅酸盐和碳氢化合物。通过约束气溶胶微物理模型与巨大的系外行星传输光谱的趋势，我们发现，硅酸盐占主导地位的气溶胶不透明度以上的行星平衡温度950 K由于低的成核能垒和高元素丰度，而碳氢化合物气溶胶占主导地位低于950 K由于甲烷丰度的增加。我们的结果是强大的行星重力和大气金属丰度的变化范围内的最巨大的过境系外行星。我们预测，在中红外线的凝聚硅酸盐的光谱特征是最突出的热（>1600 K），低重力（<10 m s $^{-2}$）对象。
Hydrocarbon Hazes on Temperate sub-Neptune K2-18b supported by data from the James Webb Space Telescope
University College London（伦敦大学学院）；Universite de Reims Champagne Ardenne（兰斯香槟阿登大学）；King’s College London（伦敦国王学院）；Osservatorio Astronomico di Palermo（巴勒莫天文台）
Optical Constants of Photochemical Haze Analogs in N2-CH4-CO Atmospheres from 0.4 to 28.6 μm
National Key Laboratory of Deep Space Exploration/School of Earth and Space Sciences, University of Science and Technology of China（中国科学技术大学地球与空间科学学院深空探测重点实验室）；Department of Earth and Planetary Sciences, Johns Hopkins University（约翰斯·霍普金斯大学地球与行星科学系）；Space Telescope Science Institute（太空望远镜科学研究所）
Constraints on the Microphysics of Pluto's Photochemical Haze from New Horizons Observations
新视野号飞越冥王星证实了其大气层中存在薄雾。观测到的高相亮度与低相亮度之比很大，再加上霾的蓝色，表明霾粒子是分形聚集体，类似于土卫六上的光化学霾。因此，研究冥王星的薄雾可以揭示冥王星和泰坦大气之间的相似性和差异。我们使用社区气溶胶和大气辐射模型来模拟雾霾分布，假设分布是由来自光化学的颗粒的沉降和凝聚形成的。被认为是由纯粹的球形和纯粹的分形聚集体颗粒的霾。当光化学产物的向下通量等于柱积分甲烷破坏率~1.2 $\times$ 10 $^{-14}$ g cm $^{-2}$ s $^{-1}$时，模型结果与掩星观测结果之间的一致性可通过聚集粒子获得，而对于球形粒子，质量通量必须大2-3倍。这一通量几乎与以前通过将微物理模型结果与卡西尼号观测结果进行比较而获得的土卫六的霾产生通量相同。根据前向散射测量，聚集体粒子半径对粒子带电很敏感，粒子荷径比为30 e-/μm是在冥王星表面附近产生约0.1-0.2 μm聚集体所必需的。这样的粒子荷径比以前在土卫六上获得的粒子荷径比高2-4倍。由具有相同粒子荷径比的球体组成的雾具有小4倍的粒子。这些结果进一步表明，烟雾颗粒是分形聚集体。我们还考虑了HCN和C $_{2}$ -碳氢化合物的凝结对霾颗粒的影响，这可能在形成它们的分布中起重要作用。
The Influence of Galactic Cosmic Rays on Ion-Neutral Hydrocarbon Chemistry in the Upper Atmospheres of Free-Floating Exoplanets
宇宙射线可能与形成前生物化学所必需的挥发物有关。我们探索宇宙射线在氢为主的大气中的影响，作为一个概念证明，离子中性化学可能是重要的氢为主的大气建模。为了实现这一点，我们利用Monte Carlo宇宙线输运模型的粒子能量为$10^6$ eV $< E < 10^{12}$ eV，以研究宇宙线增强的自由电子在亚恒星大气中。离子中性化学，然后应用到一个自由浮动的巨大气体行星的漂移凤凰模型。我们的研究结果表明，在高层大气中的离子中性化学的激活显着提高了各种物种的形成率，我们发现，C $_2$ H $_2$，C $_2$ H $_4$，NH $_3$，C $_6$ H PDMATHAMR和可能的C $_{10}$ H在高层大气中，因为宇宙射线增强。我们的研究结果表明，宇宙射线化学和在各种太阳系外行星的高层大气中观察到的薄雾之间存在潜在的联系。简要讨论了化学电离反应，因为它们可以提高云层中的电离度。
The SPACE Program II: No discernible spectral features in the transmission spectrum of the sub-Neptune HD 191939 b observed with HST/WFC3
Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；Department of Physics and Astronomy, Heidelberg University（海德堡大学物理与天文系）；The Johns Hopkins University Applied Physics Laboratory（约翰斯·霍普金斯大学应用物理实验室）；Jet Propulsion Laboratory, California Institute of Technology（加州理工学院喷气推进实验室）；School of Science, University of Newcastle（纽卡斯尔大学理学院）；Laboratory for Atmospheric and Space Physics, University of Colorado Boulder（科罗拉多大学博尔德分校大气与空间物理实验室）；University of Maryland, College Park（马里兰大学帕克分校）
