Reference study to characterize plasma and magnetic properties of ultracool atmospheres

M. I. Rodriguez-Barrera, Ch. Helling, Craig R. Stark, A. M. Rice

Research output: Contribution to journalArticle

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Abstract

Radio and X-ray emission from brown dwarfs (BDs) suggest that an ionized gas and a magnetic field with a sufficient flux density must be present. We perform a reference study for late M-dwarfs (MD), BDs and giant gas planet to identify which ultracool objects are most susceptible to plasma and magnetic processes. Only thermal ionization is considered. We utilize the drift-phoenix model grid where the local atmospheric structure is determined by the global parameters Teff, log (g) and [M/H]. Our results show that it is not unreasonable to expect Hα or radio emission to origin from BD atmospheres as in particular the rarefied upper parts of the atmospheres can be magnetically coupled despite having low degrees of thermal gas ionization. Such ultracool atmospheres could therefore drive auroral emission without the need for a companion's wind or an outgassing moon. The minimum threshold for the magnetic flux density required for electrons and ions to be magnetized is well above typical values of the global magnetic field of a BD and a giant gas planet. Na+, K+ and Ca+ are the dominating electron donors in low-density atmospheres (low log(g), solar metallicity) independent of Teff. Mg+ and Fe+ dominate the thermal ionization in the inner parts of MD atmospheres. Molecules remain unimportant for thermal ionization. Chemical processes (e.g. cloud formation) affecting the most abundant electron donors, Mg and Fe, will have a direct impact on the state of ionization in ultracool atmospheres.
Original languageEnglish
Pages (from-to)3977-3995
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Volume454
Issue number4
DOIs
StatePublished - 27 Oct 2015

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atmospheres
atmosphere
ionization
gas
electrons
electron
gas giant planets
flux density
magnetic fields
planet
radio
magnetic field
plasma
gas ionization
Phoenix (AZ)
lower atmosphere
outgassing
ionized gases
natural satellites
radio emission

Cite this

Rodriguez-Barrera, M. I.; Helling, Ch.; Stark, Craig R.; Rice, A. M. / Reference study to characterize plasma and magnetic properties of ultracool atmospheres.

In: Monthly Notices of the Royal Astronomical Society, Vol. 454, No. 4, 27.10.2015, p. 3977-3995.

Research output: Contribution to journalArticle

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abstract = "Radio and X-ray emission from brown dwarfs (BDs) suggest that an ionized gas and a magnetic field with a sufficient flux density must be present. We perform a reference study for late M-dwarfs (MD), BDs and giant gas planet to identify which ultracool objects are most susceptible to plasma and magnetic processes. Only thermal ionization is considered. We utilize the drift-phoenix model grid where the local atmospheric structure is determined by the global parameters Teff, log (g) and [M/H]. Our results show that it is not unreasonable to expect Hα or radio emission to origin from BD atmospheres as in particular the rarefied upper parts of the atmospheres can be magnetically coupled despite having low degrees of thermal gas ionization. Such ultracool atmospheres could therefore drive auroral emission without the need for a companion's wind or an outgassing moon. The minimum threshold for the magnetic flux density required for electrons and ions to be magnetized is well above typical values of the global magnetic field of a BD and a giant gas planet. Na+, K+ and Ca+ are the dominating electron donors in low-density atmospheres (low log(g), solar metallicity) independent of Teff. Mg+ and Fe+ dominate the thermal ionization in the inner parts of MD atmospheres. Molecules remain unimportant for thermal ionization. Chemical processes (e.g. cloud formation) affecting the most abundant electron donors, Mg and Fe, will have a direct impact on the state of ionization in ultracool atmospheres.",
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Reference study to characterize plasma and magnetic properties of ultracool atmospheres. / Rodriguez-Barrera, M. I.; Helling, Ch.; Stark, Craig R.; Rice, A. M.

In: Monthly Notices of the Royal Astronomical Society, Vol. 454, No. 4, 27.10.2015, p. 3977-3995.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Reference study to characterize plasma and magnetic properties of ultracool atmospheres

AU - Rodriguez-Barrera,M. I.

AU - Helling,Ch.

AU - Stark,Craig R.

AU - Rice,A. M.

PY - 2015/10/27

Y1 - 2015/10/27

N2 - Radio and X-ray emission from brown dwarfs (BDs) suggest that an ionized gas and a magnetic field with a sufficient flux density must be present. We perform a reference study for late M-dwarfs (MD), BDs and giant gas planet to identify which ultracool objects are most susceptible to plasma and magnetic processes. Only thermal ionization is considered. We utilize the drift-phoenix model grid where the local atmospheric structure is determined by the global parameters Teff, log (g) and [M/H]. Our results show that it is not unreasonable to expect Hα or radio emission to origin from BD atmospheres as in particular the rarefied upper parts of the atmospheres can be magnetically coupled despite having low degrees of thermal gas ionization. Such ultracool atmospheres could therefore drive auroral emission without the need for a companion's wind or an outgassing moon. The minimum threshold for the magnetic flux density required for electrons and ions to be magnetized is well above typical values of the global magnetic field of a BD and a giant gas planet. Na+, K+ and Ca+ are the dominating electron donors in low-density atmospheres (low log(g), solar metallicity) independent of Teff. Mg+ and Fe+ dominate the thermal ionization in the inner parts of MD atmospheres. Molecules remain unimportant for thermal ionization. Chemical processes (e.g. cloud formation) affecting the most abundant electron donors, Mg and Fe, will have a direct impact on the state of ionization in ultracool atmospheres.

AB - Radio and X-ray emission from brown dwarfs (BDs) suggest that an ionized gas and a magnetic field with a sufficient flux density must be present. We perform a reference study for late M-dwarfs (MD), BDs and giant gas planet to identify which ultracool objects are most susceptible to plasma and magnetic processes. Only thermal ionization is considered. We utilize the drift-phoenix model grid where the local atmospheric structure is determined by the global parameters Teff, log (g) and [M/H]. Our results show that it is not unreasonable to expect Hα or radio emission to origin from BD atmospheres as in particular the rarefied upper parts of the atmospheres can be magnetically coupled despite having low degrees of thermal gas ionization. Such ultracool atmospheres could therefore drive auroral emission without the need for a companion's wind or an outgassing moon. The minimum threshold for the magnetic flux density required for electrons and ions to be magnetized is well above typical values of the global magnetic field of a BD and a giant gas planet. Na+, K+ and Ca+ are the dominating electron donors in low-density atmospheres (low log(g), solar metallicity) independent of Teff. Mg+ and Fe+ dominate the thermal ionization in the inner parts of MD atmospheres. Molecules remain unimportant for thermal ionization. Chemical processes (e.g. cloud formation) affecting the most abundant electron donors, Mg and Fe, will have a direct impact on the state of ionization in ultracool atmospheres.

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