Critical velocity ionisation in substellar atmospheres

A. D. Wilson*, I. Dobbs-Dixon, D. A. Diver, C. R. Stark

*Corresponding author for this work

Research output: Contribution to journalArticle

1 Downloads (Pure)

Abstract

The observation of radio, X-ray and Hα emission from substellar objects indicates the presence of plasma regions and associated high-energy processes in their surrounding envelopes. This paper numerically simulates and characterises Critical Velocity Ionisation, a potential ionisation process, that can efficiently generate plasma as a result of neutral gas flows interacting with seed magnetized plasmas. By coupling a Gas-MHD interactions code (to simulate the ionisation 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 ionisation and their lifetime for a typical substellar atmosphere. It is found that the typical average ionisation fraction reached at equilibrium (where the ionisation 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 ionisation fraction with decreasing atmospheric pressure. The ionisation fractions reached as a result of Critical Velocity Ionisation are sufficient to allow magnetic fields to couple to gas flows in the atmosphere.
Original languageEnglish
Article number138
Number of pages8
JournalAstrophysical Journal
Volume887
Issue number2
Early online date17 Dec 2019
DOIs
Publication statusE-pub ahead of print - 17 Dec 2019

Fingerprint

critical velocity
ionization
atmospheres
atmosphere
gas flow
plasma
neutral gases
ionization potentials
seeds
atmospheric pressure
recombination
envelopes
trends
life (durability)
radio
magnetic field
seed
gases
magnetic fields

Cite this

Wilson, A. D. ; Dobbs-Dixon, I. ; Diver, D. A. ; Stark, C. R. / Critical velocity ionisation in substellar atmospheres. In: Astrophysical Journal. 2019 ; Vol. 887, No. 2.
@article{5d7dc81a7a63491eb3bc516de8b5988b,
title = "Critical velocity ionisation in substellar atmospheres",
abstract = "The observation of radio, X-ray and Hα emission from substellar objects indicates the presence of plasma regions and associated high-energy processes in their surrounding envelopes. This paper numerically simulates and characterises Critical Velocity Ionisation, a potential ionisation process, that can efficiently generate plasma as a result of neutral gas flows interacting with seed magnetized plasmas. By coupling a Gas-MHD interactions code (to simulate the ionisation 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 ionisation and their lifetime for a typical substellar atmosphere. It is found that the typical average ionisation fraction reached at equilibrium (where the ionisation 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 ionisation fraction with decreasing atmospheric pressure. The ionisation fractions reached as a result of Critical Velocity Ionisation are sufficient to allow magnetic fields to couple to gas flows in the atmosphere.",
author = "Wilson, {A. D.} and I. Dobbs-Dixon and Diver, {D. A.} and Stark, {C. R.}",
year = "2019",
month = "12",
day = "17",
doi = "10.3847/1538-4357/ab5800",
language = "English",
volume = "887",
journal = "Astrophysical Journal",
issn = "0004-637X",
publisher = "IOP Publishing Ltd.",
number = "2",

}

Critical velocity ionisation in substellar atmospheres. / Wilson, A. D.; Dobbs-Dixon, I.; Diver, D. A.; Stark, C. R.

In: Astrophysical Journal, Vol. 887, No. 2, 138, 17.12.2019.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Critical velocity ionisation in substellar atmospheres

AU - Wilson, A. D.

AU - Dobbs-Dixon, I.

AU - Diver, D. A.

AU - Stark, C. R.

PY - 2019/12/17

Y1 - 2019/12/17

N2 - The observation of radio, X-ray and Hα emission from substellar objects indicates the presence of plasma regions and associated high-energy processes in their surrounding envelopes. This paper numerically simulates and characterises Critical Velocity Ionisation, a potential ionisation process, that can efficiently generate plasma as a result of neutral gas flows interacting with seed magnetized plasmas. By coupling a Gas-MHD interactions code (to simulate the ionisation 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 ionisation and their lifetime for a typical substellar atmosphere. It is found that the typical average ionisation fraction reached at equilibrium (where the ionisation 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 ionisation fraction with decreasing atmospheric pressure. The ionisation fractions reached as a result of Critical Velocity Ionisation are sufficient to allow magnetic fields to couple to gas flows in the atmosphere.

AB - The observation of radio, X-ray and Hα emission from substellar objects indicates the presence of plasma regions and associated high-energy processes in their surrounding envelopes. This paper numerically simulates and characterises Critical Velocity Ionisation, a potential ionisation process, that can efficiently generate plasma as a result of neutral gas flows interacting with seed magnetized plasmas. By coupling a Gas-MHD interactions code (to simulate the ionisation 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 ionisation and their lifetime for a typical substellar atmosphere. It is found that the typical average ionisation fraction reached at equilibrium (where the ionisation 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 ionisation fraction with decreasing atmospheric pressure. The ionisation fractions reached as a result of Critical Velocity Ionisation are sufficient to allow magnetic fields to couple to gas flows in the atmosphere.

U2 - 10.3847/1538-4357/ab5800

DO - 10.3847/1538-4357/ab5800

M3 - Article

VL - 887

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 2

M1 - 138

ER -