热海王星GJ 436 b昼侧大气中的高金属丰度和非平衡化学
High Metallicity and Non-equilibrium Chemistry in the Dayside Atmosphere of hot-Neptune GJ 436b
摘要：
我们提出了一个详细的分析，热海王星GJ~ 436 b的昼侧大气，根据最近的斯皮策观测。我们报告的统计约束的热和化学性质的行星大气，研究各种分子物种之间的相关性，并讨论方案的平衡和非平衡化学在GJ 436 b。我们用一维逐线辐射转移程序模拟大气，参数化了分子丰度和温度结构。我们使用马尔可夫链蒙特卡罗方法探索了10^6个模型的模型参数空间。我们的研究结果包括以前的研究结果，表明甲烷的缺乏，过剩的CO和CO2，和H2O的略有不足，相比，与太阳能金属丰度的平衡化学。各物种的浓度高度相关。我们的最佳拟合和最合理的约束条件要求CH 4混合比为1.0E-7至1.0E-6，CO >= 1.0E-3，CO2 ~ 1.0E-6至1.0E-4，H2O <= 1.0E-4;较高的CH 4需要更高的CO和CO2。基于平衡和非平衡化学的计算，我们发现观测到的丰度可以用高金属丰度（~ 10倍太阳）和Kzz ~ 10^6 - 10^7 cm ^2/s的垂直混合的组合来解释。推断的金属丰度比已知与太阳金属丰度一致的宿主恒星的金属丰度更高。我们的限制排除了GJ 436 b的昼侧逆温。我们强调，在这项工作中报告的限制，关键取决于在两个斯皮策通道在3.6微米和4.5微米的观察。未来用温暖的斯皮策和詹姆斯韦伯太空望远镜进行的观测对于改善目前对GJ 436 b昼侧大气中碳物种丰度的限制将是极其重要的。
英文摘要：
We present a detailed analysis of the dayside atmosphere of the hot-Neptune GJ~436b, based on recent Spitzer observations. We report statistical constraints on the thermal and chemical properties of the planetary atmosphere, study correlations between the various molecular species, and discuss scenarios of equilibrium and non-equilibrium chemistry in GJ 436b. We model the atmosphere with a one-dimensional line-by-line radiative transfer code with parameterized molecular abundances and temperature structure. We explore the model parameter space with 10^6 models, using a Markov chain Monte Carlo scheme. Our results encompass previous findings, indicating a paucity of methane, an overabundance of CO and CO2, and a slight underabundance of H2O, as compared to equilibrium chemistry with solar metallicity. The concentrations of the species are highly correlated. Our best-fit, and most plausible, constraints require a CH4 mixing ratio of 1.0E-7 to 1.0E-6, with CO >= 1.0E-3, CO2 ~ 1.0E-6 to 1.0E-4, and H2O <= 1.0E-4; higher CH4 would require much higher CO and CO2. Based on calculations of equilibrium and non-equilibrium chemistry, we find that the observed abundances can potentially be explained by a combination of high metallicity (~ 10 x solar) and vertical mixing with Kzz ~ 10^6 - 10^7 cm^2/s. The inferred metallicity is enhanced over that of the host star which is known to be consistent with solar metallicity. Our constraints rule out a dayside thermal inversion in GJ 436b. We emphasize that the constraints reported in this work depend crucially on the observations in the two Spitzer channels at 3.6 micron and 4.5 micron. Future observations with warm Spitzer and with the James Webb Space Telescope will be extremely important to improve upon the present constraints on the abundances of carbon species in the dayside atmosphere of GJ 436b.
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