Inhomogeneous cloud coverage through the Coulomb explosion of dust in substellar atmospheres


Autoria(s): Stark, Craig R.; Helling, Ch.; Diver, D. A.
Contribuinte(s)

Abertay University. School of Arts Media & Computer Games

UK Science and Technology Funding Council

European Community under the FP7 by an ERC starting grant

Data(s)

19/05/2016

19/05/2016

01/07/2015

27/04/2015

Resumo

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 crit 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 (≈105 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 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 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.

Identificador

Stark, Craig R., Helling, Ch., and Diver D. A. 2015. Inhomogeneous cloud coverage through the Coulomb explosion of dust in substellar atmospheres. Astronomy and Astrophysics. 579. doi: 10.1051/0004-6361/201526045

0004-6361 (print)

1432-0746 (online)

http://hdl.handle.net/10373/2334

257431

ST/I001808/1

https://dx.doi.org/10.1051/0004-6361/201526045

Idioma(s)

en

Publicador

EDP Sciences

Relação

Astronomy and Astrophysics, 579

Direitos

© ESO 2015. Article published by EDP Sciences and available at http://www.edpsciences.org/aa

Palavras-Chave #Stars: atmospheres #Brown dwarfs #Stars: low mass #Plasmas #Stars: atmospheres #Brown dwarfs
Tipo

Journal Article

published

peer-reviewed

n/a