系外行星和褐矮星上的矿物雪花：{ \sc HyLandS }云粒子的凝聚和碎裂
Mineral Snowflakes on Exoplanets and Brown Dwarfs: Coagulation and Fragmentation of Cloud Particles with {\sc HyLandS}
摘要：
褐矮星和系外行星提供了独特的大气机制，这些机制包含了它们形成路线和演化状态的信息。模拟矿物云粒子的形成是为CRIRES+、JWST和ARIEL等任务和仪器以及{ \sc PolStar}等可能的偏振测量任务做准备的关键。其目的是支持更详细的观测，需要更好地了解微物理云过程。我们扩展我们的动力学云形成模型，处理成核，冷凝，蒸发和沉淀的混合材料云粒子一致的模型云粒子-粒子碰撞。新的混合代码，{ \sc HyLandS}，被应用到{ \sc Drift-Phoenix}（T，p）-profiles的网格。利用有效介质理论和米氏理论研究了该材料的光学性质。湍流是碰撞的主要驱动过程，碰撞成为云底（$p>10^{-4}\,{\rm bar}$）的主导过程。碰撞产生三种结果之一：碎裂大气层（$\log_{10}(g)=3$），分裂大气层（$\log_{10}(g)=5$，$T_{\rm eff} \leq 1800\, {\rm K}$）和凝聚生长主导大气层（$\log_{10}(g\,)=5$，$T_{\rm eff} > 1800\, {\rm K}$）。云粒子不透明度斜率在光学波长（HST）的增加与碎片，是硅酸盐功能在中红外波长。混合矩箱法{ \sc HyLandS}证明了在保证单元守恒的同时将矩箱法结合起来的可行性。它为捕捉粒子碰撞的一般趋势提供了一个强大而快速的工具，与其他微物理过程保持一致。碰撞在系外行星和褐矮星大气中很重要，但不能假设只是碰撞。碰撞的光谱效应使得从观测数据推断云的颗粒大小和物质组成变得复杂。
英文摘要：
Brown dwarfs and exoplanets provide unique atmospheric regimes that hold information about their formation routes and evolutionary states. Modelling mineral cloud particle formation is key to prepare for missions and instruments like CRIRES+, JWST and ARIEL as well as possible polarimetry missions like {\sc PolStar}. The aim is to support more detailed observations that demand greater understanding of microphysical cloud processes. We extend our kinetic cloud formation model that treats nucleation, condensation, evaporation and settling of mixed material cloud particles to consistently model cloud particle-particle collisions. The new hybrid code, {\sc HyLandS}, is applied to a grid of {\sc Drift-Phoenix} (T, p)-profiles. Effective medium theory and Mie theory are used to investigate the optical properties. Turbulence is the main driving process of collisions, with collisions becoming the dominant process at the cloud base ($p>10^{-4}\,{\rm bar}$). Collisions produce one of three outcomes: fragmenting atmospheres ($\log_{10}(g)=3$), coagulating atmospheres ($\log_{10}(g)=5$, $T_{\rm eff} \leq 1800\, {\rm K}$) and condensational growth dominated atmospheres ($\log_{10}(g\,)=5$, $T_{\rm eff} > 1800\, {\rm K}$). Cloud particle opacity slope at optical wavelengths (HST) is increased with fragmentation, as are the silicate features at mid-infrared wavelengths. The hybrid moment-bin method {\sc HyLandS} demonstrates the feasibility of combining a moment and a bin method whilst assuring element conservation. It provides a powerful and fast tool for capturing general trends of particle collisions, consistently with other microphysical processes. Collisions are important in exoplanet and brown dwarf atmospheres but cannot be assumed to be hit-and-stick only. The spectral effects of collisions complicates inferences of cloud particle size and material composition from observational data.
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