Aerosols are not spherical cows: using discrete dipole approximation to model the properties of fractal particles
Aerosols are not spherical cows: using discrete dipole approximation to model the properties of fractal particles
复制标题
气溶胶不是球形牛：使用离散偶极近似来模拟分形粒子的属性
DOI：
10.1093/mnras/stad3743
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发表时间：
2024
影响因子：
4.8
通讯作者：
Lodge M
中科院分区：
文献类型：
--
作者：
Lodge M
采用三种不同的模型：米氏理论、修正平均场（MMF）理论和离散偶极近似（DDA），比较了系外行星和褐矮星大气环境下颗粒物气溶胶的光学特性。先前的研究结果表明，分形雾粒（MMF和DDA）吸收的长波辐射比它们的球形粒子（Mie）要少得多，然而，如果使用更不同的折射率曲线，情况也可能相反。此外，还证明了如果使用Mie理论，吸收/散射截面和不对称参数会被低估。虽然DDA可以用来获得更准确的结果，但它的计算量要大得多；为了避免这种情况，研究人员探索了使用低分辨率气溶胶模型，这可以大大加快在一定参数空间内获得精确光学截面计算的过程。对于系外行星和褐矮星大气中气溶胶观测的兴趣波长(m)，探索了DDA的有效性。最后，提出了新的代码来比较Mie， MMF和DDA理论的结果（珊瑚：辐射分析的比较），并相应地增加和减少DDA形状文件的分辨率（球化）。除了系外行星大气，这两种代码都可以应用于一系列其他有趣的天体物理环境，例如原行星盘中的尘埃颗粒。
The optical properties of particulate-matter aerosols, within the context of exoplanet and brown dwarf atmospheres, are compared using three different models: Mie theory, modified mean field (MMF) theory, and discrete dipole approximation (DDA). Previous results have demonstrated that fractal haze particles (MMF and DDA) absorb much less long-wavelength radiation than their spherical counterparts (Mie), however it is shown here that the opposite can also be true if a more varying refractive index profile is used. Additionally, it is demonstrated that absorption/scattering cross-sections, and the asymmetry parameter, are underestimated if Mie theory is used. Although DDA can be used to obtain more accurate results, it is known to be much more computationally intensive; to avoid this, the use of low-resolution aerosol models is explored, which could dramatically speed up the process of obtaining accurate computations of optical cross-sections within a certain parameter space. The validity of DDA is probed for wavelengths of interest for observations of aerosols within exoplanet and brown dwarf atmospheres (m). Finally, novel code is presented to compare the results of Mie, MMF, and DDA theories (coral: Comparison Of Radiative AnaLyses), as well as to increase and decrease the resolution of DDA shape files accordingly (spherify). Both codes can be applied to a range of other interesting astrophysical environments in addition to exoplanet atmospheres, for example dust grains within protoplanetary discs.