The Sonora Substellar Atmosphere Models. IV. Elf Owl: Atmospheric Mixing and Chemical Disequilibrium with Varying Metallicity and C/O Ratios

S. Mukherjee, J. Fortney, C. Morley, N. Batalha, M. Marley, T. Karalidi, C. Visscher, Roxana Lupu, R. Freedman, E. Gharib-Nezhad
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Abstract

Disequilibrium chemistry due to vertical mixing in the atmospheres of many brown dwarfs and giant exoplanets is well established. Atmosphere models for these objects typically parameterize mixing with the highly uncertain K zz diffusion parameter. The role of mixing in altering the abundances of C-N-O-bearing molecules has mostly been explored for atmospheres with a solar composition. However, atmospheric metallicity and the C/O ratio also impact atmospheric chemistry. Therefore, we present the Sonora Elf Owl grid of self-consistent cloud-free 1D radiative-convective equilibrium model atmospheres for JWST observations, which includes a variation in K zz across several orders of magnitude and also encompasses subsolar to supersolar metallicities and C/O ratios. We find that the impact of K zz on the T(P) profile and spectra is a strong function of both T eff and metallicity. For metal-poor objects, K zz has large impacts on the atmosphere at significantly higher T eff than in metal-rich atmospheres, where the impact of K zz is seen to occur at lower T eff. We identify significant spectral degeneracies between varying K zz and metallicity in multiple wavelength windows, in particular, at 3–5 μm. We use the Sonora Elf Owl atmospheric grid to fit the observed spectra of a sample of nine early to late T-type objects from T eff = 550–1150 K. We find evidence for very inefficient vertical mixing in these objects, with inferred K zz values lying in the range between ∼101 and 104 cm2 s−1. Using self-consistent models, we find that this slow vertical mixing is due to the observations, which probe mixing in the deep detached radiative zone in these atmospheres.
索诺拉亚恒星大气模型。IV.精灵猫头鹰:大气混合和化学失衡与不同的金属性和 C/O 比率
在许多褐矮星和巨型系外行星的大气层中,由于垂直混合而产生的非平衡化学反应已经得到公认。这些天体的大气模型通常用高度不确定的 K zz 扩散参数对混合进行参数化。混合在改变含 C-N-O 分子丰度方面的作用主要是针对太阳成分的大气层进行探索的。然而,大气金属性和 C/O 比率也会影响大气化学。因此,我们提出了用于 JWST 观测的自洽无云一维辐射对流平衡模型大气的 Sonora Elf Owl 网格,其中包括 K zz 在几个数量级上的变化,还包括从太阳系下到太阳系上的金属性和 C/O 比率。我们发现,K zz对T(P)剖面和光谱的影响是T eff和金属性的强烈函数。与富含金属的大气相比,K zz对贫金属天体大气的巨大影响发生在更高的T eff上,而在富含金属的大气中,K zz的影响发生在更低的T eff上。我们发现在多个波长窗口,特别是在 3-5 μm 波长窗口,K zz 的变化与金属性之间存在明显的光谱退行性。我们利用索诺拉精灵猫头鹰大气网格拟合了九个早期到晚期T型天体的观测光谱样本(T eff = 550-1150 K)。我们发现这些天体的垂直混合效率非常低,推断的K zz值介于 ∼101 和 104 cm2 s-1 之间。利用自洽模型,我们发现这种缓慢的垂直混合是由观测结果造成的,观测结果探测了这些大气层中深脱离辐射区的混合情况。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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