Cloud busting: enstatite and quartz clouds in the atmosphere of 2M2224-0158
Cloud busting: enstatite and quartz clouds in the atmosphere of 2M2224-0158
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DOI：
10.1093/mnras/stab1361
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发表时间：
2021-05
影响因子：
4.8
通讯作者：
B. Burningham;J. Faherty;Eileen C. Gonzales;M. Marley;C. Visscher;R. Lupu;Josefine Gaarn;
中科院分区：
文献类型：
--
作者：
B. Burningham;J. Faherty;Eileen C. Gonzales;M. Marley;C. Visscher;R. Lupu;Josefine Gaarn;
我们介绍了迄今为止最详细的由数据驱动的对恒星下天体中云不透明度的探索。我们使用布鲁斯特反演框架对异常红色L4.5矮星2MASSWJ2224438-015852的档案1-15μm光谱进行了60多种云组成和结构、粒子尺寸分布、散射模式和气相组成假设的测试。我们发现，在我们的框架内，包括浅压力下的顽火辉石云层和石英云层，以及深层铁云甲板的模型最符合数据。该模型假定每个云的粒子大小和Mie散射均为Hansen分布。测得辉石、石英和铁的颗粒有效半径分别为-1.41、-0.44和-0.77。如果没有镁或硅的其他汇，我们推断的云柱密度=0.69^{+0.06}_{-0.08}$。将镁橄榄岩包括在这些云物种旁边或替代这些云物种的模型强烈反对上述组合。我们估计的半径为0.75±0.02RJup，这比光度为2M2224-0158的场龄天体的演化模型所预测的要小得多。假设气体分数垂直恒定的模型总是比假设热化学平衡的模型更受欢迎。从我们恢复的气体馏分，我们推算出${Rm[M/H]}=+0.38^{+0.07}_{-0.06}$和${\RmC/O}=0.83^{+0.06}_{-0.07}$。这两个值都接近太阳附近恒星分布的上端，并且在这方面是相互一致的。接近局部分布极端的成分与这个目标是超冷矮星种群中的异常值是一致的。
We present the most detailed data-driven exploration of cloud opacity in a substellar object to-date. We have tested over 60 combinations of cloud composition and structure, particle-size distribution, scattering model, and gas phase composition assumptions against archival 1–15 μm spectroscopy for the unusually red L4.5 dwarf 2MASSW J2224438-015852 using the Brewster retrieval framework. We find that, within our framework, a model that includes enstatite and quartz cloud layers at shallow pressures, combined with a deep iron cloud deck fits the data best. This model assumes a Hansen distribution for particle sizes for each cloud, and Mie scattering. We retrieved particle effective radii of $\log _{10} a {\rm (\mu m)} = -1.41^{+0.18}_{-0.17}$ for enstatite, $-0.44^{+0.04}_{-0.20}$ for quartz, and $-0.77^{+0.05}_{-0.06}$ for iron. Our inferred cloud column densities suggest ${\rm (Mg/Si)} = 0.69^{+0.06}_{-0.08}$ if there are no other sinks for magnesium or silicon. Models that include forsterite alongside, or in place of, these cloud species are strongly rejected in favour of the above combination. We estimate a radius of 0.75 ± 0.02 RJup, which is considerably smaller than predicted by evolutionary models for a field age object with the luminosity of 2M2224-0158. Models which assume vertically constant gas fractions are consistently preferred over models that assume thermochemical equilibrium. From our retrieved gas fractions, we infer ${\rm [M/H]} = +0.38^{+0.07}_{-0.06}$ and ${\rm C/O} = 0.83^{+0.06}_{-0.07}$. Both these values are towards the upper end of the stellar distribution in the Solar neighbourhood, and are mutually consistent in this context. A composition towards the extremes of the local distribution is consistent with this target being an outlier in the ultracool dwarf population.