通过亚恒星大气中尘埃库仑爆炸的不均匀云覆盖
Inhomogeneous cloud coverage through the Coulomb explosion of dust in substellar atmospheres
摘要：
最近对褐矮星红外光谱变化的观测推断了斑片状云层的存在。本文提出了大气等离子体区尘埃库仑爆炸引起云粒子损耗而产生不均匀云覆盖的一种机制。当颗粒的静电应力超过其机械张应力时，带电尘埃颗粒库仑爆炸，这导致低于临界半径$a<a^{\rm Coul}_{\rm crit}$的颗粒破碎。这项工作概述了亚恒星大气中的尘埃云库仑爆炸所需的标准，对尘埃颗粒尺寸分布函数的影响，以及由此产生的大气区域的辐射特性。结果表明，对于电子温度为$T_{e}=10$ ~eV（$\approx10^{5}$ ~K）的大气等离子体区，临界晶粒半径随晶粒抗拉强度的变化而变化，范围为$10^{-7}$ ~ $10^{-4}$ ~cm。对于更高的电子温度，可获得高达$10^{-3}$ ~cm的更高临界半径。我们发现，该过程产生的双峰粒径分布组成的稳定的纳米级种子颗粒和灰尘颗粒与$a\geq a^{\rm Coul}_{\rm crit}$，与介入的粒径定义的区域没有灰尘。结果，尘埃数量减少，云层在$0.1-10~μ$ m波长范围内变得光学薄，随着更多的亚微米颗粒被破坏，特征峰向更高的波长移动。在充满等离子体体积分布的大气中，这将产生辐射特性对比鲜明的区域，从而产生不均匀的云覆盖源。这里给出的结果也可能与超新星遗迹和原行星盘中的尘埃有关。
英文摘要：
Recent observations of brown dwarf spectroscopic variability in the infrared infer the presence of patchy cloud cover. This paper proposes a mechanism for producing inhomogeneous cloud coverage due to the depletion of cloud particles through the Coulomb explosion of dust in atmospheric plasma regions. Charged dust grains Coulomb-explode when the electrostatic stress of the grain exceeds its mechanical tensile stress, which results in grains below a critical radius $a<a^{\rm Coul}_{\rm crit}$ being broken up. This work outlines the criteria required for the Coulomb explosion of dust clouds in substellar atmospheres, the effect on the dust particle size distribution function, and the resulting radiative properties of the atmospheric regions. Our results show that for an atmospheric plasma region with an electron temperature of $T_{e}=10$~eV ($\approx10^{5}$~K), the critical grain radius varies from $10^{-7}$ to $10^{-4}$~cm, depending on the grains' tensile strength. Higher critical radii up to $10^{-3}$~cm are attainable for higher electron temperatures. We find that the process produces a bimodal particle size distribution composed of stable nanoscale seed particles and dust particles with $a\geq a^{\rm Coul}_{\rm crit}$, with the intervening particle sizes defining a region devoid of dust. As a result, the dust population is depleted, and the clouds become optically thin in the wavelength range $0.1-10~μ$m, with a characteristic peak that shifts to higher wavelengths as more sub-micrometer particles are destroyed. In an atmosphere populated with a distribution of plasma volumes, this will yield regions of contrasting radiative properties, thereby giving a source of inhomogeneous cloud coverage. The results presented here may also be relevant for dust in supernova remnants and protoplanetary disks.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
