Inhomogeneous cloud coverage through the Coulomb explosion of dust in substellar atmospheres
Inhomogeneous cloud coverage through the Coulomb explosion of dust in substellar atmospheres
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星际大气中尘埃库仑爆炸造成的不均匀云层覆盖
DOI：
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
D. Diver
中科院分区：
文献类型：
--
作者：
C. Stark;Ch. Helling;D. Diver
上下文。最近对褐矮星红外光谱可变性的观测推断出斑状云层的存在。目标。本文提出了大气等离子体区尘埃库仑爆炸导致云粒子耗尽而产生不均匀云层的机制。当带电尘埃颗粒的静电应力超过其机械拉应力时，带电尘埃颗粒就会发生库仑爆炸，这会导致颗粒在临界半径a<；以下破碎。方法：研究方法。这项工作概述了尘埃云在星下大气中库仑爆炸所需的判据，对尘埃粒子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。结果表明，对于电子温度为Te=10 eV(≈105 K)的大气等离子体区，粒子的临界半径从10−7到10−4 cm变化，这取决于粒子的抗拉强度。对于更高的电子温度，可以获得更高的临界半径，最高可达10−3 cm。我们发现，这个过程产生了由稳定的纳米级种子颗粒和具有≥的尘埃颗粒组成的双峰粒度分布，中间的颗粒尺寸定义了一个没有尘埃的区域。结果，尘埃数量减少，云层在0.110μm的波长范围内变得非常薄，随着更多亚微米粒子的破坏，特征峰值向更高的波长移动。结论。在等离子体体积分布密集的大气中，这将产生辐射特性不同的区域，从而形成不均匀云覆盖的来源。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。
Context. Recent observations of brown dwarf spectroscopic variability in the infrared infer the presence of patchy cloud cover. Aims. 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 Coul being broken up. Methods. 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. Results. Our results show that for an atmospheric plasma region with an electron temperature of Te = 10 eV (≈10 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 ≥ a Coul , 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 μm, with a characteristic peak that shifts to higher wavelengths as more sub-micrometer particles are destroyed. Conclusions. 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.
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