arXiv 2011.140222020-11astro-ph.EP

热木星 HD 189733b 大气中光化学霾的三维模拟

3D simulations of photochemical hazes in the atmosphere of hot Jupiter HD 189733b

Maria E Steinrueck, Adam P. Showman, Panayotis Lavvas, Tommi Koskinen, Xianyu Tan, Xi Zhang

备注：: This version incorporates the corrected versions of equations (7) and (8), as described in the correction published in July 2024, available at \url{https://academic.oup.com/mnras/article/531/3/3444/7691150}
发表信息：: Monthly Notices of the Royal Astronomical Society, Volume 504, Issue 2, June 2021, Pages 2783-2799
DOI：: 10.1093/mnras/stab1053

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AI总结：

本文通过三维模拟研究热木星 HD 189733b 大气中光化学霾的输送与分布，揭示小粒子在晨侧明暗线聚集、大粒子在昏侧聚集的规律，并指出模型光谱与观测短波陡坡不匹配的可能原因。

摘要：

光化学霾已被认为是许多热木星透射光谱中观测到的高空气溶胶的候选来源。我们展示了对热木星 HD 189733b 的三维模拟，以研究光化学霾如何被大气环流输送。模型包含球形、恒定尺寸的霾粒子，这些粒子受重力沉降并作为被动示踪物被风输送，粒子半径范围从 1 nm 到 300 μm。我们根据粒子尺寸识别出两种一般类型的霾分布：在小粒子区间（<30 nm），重力沉降不重要，霾在两个以夜面为中心、跨越晨侧明暗线的中纬度大涡旋中累积。因此，小霾粒子在晨侧明暗线比在昏侧明暗线更集中。在大粒子区间（>30 nm），霾在夜面迅速沉降，导致昏侧明暗线处有更多霾。对于小粒子，分别考虑霾质量混合比和温度的明暗线差异，可以在明暗线的透射光谱中产生显著差异。然而，当对 HD 189733b 将两种效应结合时，它们在很大程度上相互抵消，导致光谱中的明暗线差异非常小。基于 GCM 导出的霾分布的透射光谱无法重现当前 HD 189733b 透射观测中短波长的陡峭光谱斜率。霾的不同光学性质、由于霾加热导致的低压处更高温度、增强的次网格尺度混合或恒星黑子可能解释模型与观测之间的不匹配。

英文摘要：

Photochemical hazes have been suggested as candidate for the high-altitude aerosols observed in the transmission spectra of many hot Jupiters. We present 3D simulations of the hot Jupiter HD 189733b to study how photochemical hazes are transported by atmospheric circulation. The model includes spherical, constant-size hazes particles that gravitationally settle and are transported by the winds as passive tracers, with particle radii ranging from 1 nm to 300 $μ$m. We identify two general types of haze distribution based on particle size: In the small-particle regime (<30 nm), gravitational settling is unimportant, and hazes accumulate in two large mid-latitude vortices centered on the night side that extend across the morning terminator. Therefore, small hazes are more concentrated at the morning terminator than at the evening terminator. In the large-particle regime (>30 nm), hazes settle out quickly on the nightside, resulting in more hazes at the evening terminator. For small particles, terminator differences in haze mass mixing ratio and temperature considered individually can result in significant differences in the transit spectra of the terminators. When combining both effects for HD189733b, however, they largely cancel out each other, resulting in very small terminator differences in the spectra. Transit spectra based on the GCM-derived haze distribution fail to reproduce the steep spectral slope at short wavelengths in the current transit observations of HD 189733b. Differing optical properties of hazes, hotter temperatures at low pressures because of heating by hazes, enhanced sub-grid-scale mixing, or star spots might explain the mismatch between the model and observations.

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