Wilson, A.D., Dobbs-Dixon, I., Diver, D.A. and Stark, C.R. (2019) Critical velocity ionization in substellar atmospheres. Astrophysical Journal, 887(2), 138. (doi: 10.3847/1538-4357/ab5800)
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Abstract
The observation of radio, X-ray, and H α emission from substellar objects indicates the presence of plasma regions and associated high-energy processes in their surrounding envelopes. This paper numerically simulates and characterizes critical velocity ionization (CVI), a potential ionization process, that can efficiently generate plasma as a result of neutral gas flows interacting with seed magnetized plasmas. By coupling a gas–magnetohydrodynamic (MHD) interactions code (to simulate the ionization mechanism) with a substellar global circulation model (to provide the required gas flows), we quantify the spatial extent of the resulting plasma regions, their degree of ionization, and their lifetime for a typical substellar atmosphere. It is found that the typical average ionization fraction reached at equilibrium (where the ionization and recombination rates are equal and opposite) ranges from 10−5 to 10−8, at pressures between 10−1 and 10−3 bar, with a trend of increasing ionization fraction with decreasing atmospheric pressure. The ionization fractions reached as a result of CVI are sufficient to allow magnetic fields to couple to gas flows in the atmosphere.
Item Type: | Articles |
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Status: | Published |
Refereed: | Yes |
Glasgow Author(s) Enlighten ID: | Diver, Professor Declan and Wilson, Dr Alasdair and Stark, Mr Craig |
Authors: | Wilson, A.D., Dobbs-Dixon, I., Diver, D.A., and Stark, C.R. |
College/School: | College of Science and Engineering > School of Physics and Astronomy |
Journal Name: | Astrophysical Journal |
Publisher: | American Astronomical Society |
ISSN: | 0004-637X |
ISSN (Online): | 1538-4357 |
Published Online: | 17 December 2019 |
Copyright Holders: | Copyright © 2019 The American Astronomical Society |
First Published: | First published in Astrophysical Journal 887(2): 138 |
Publisher Policy: | Reproduced under a Creative Commons License |
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