On the Cool Side: Modeling the Atmospheres of Brown Dwarfs and Giant Planets

Marley, Mark S.; Robinson, Tyler D.

doi:10.1146/annurev-astro-082214-122522

Cited by 208 publications

(189 citation statements)

References 200 publications

(226 reference statements)

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“…However, as the atmosphere cools and becomes more neutral, the ability of the atmosphere to sustain these magnetic features becomes less clear. Concurrently, the low temperature of the atmospheres allows for the formation of dust condensates and clouds that influence the emergent stellar flux (e.g., Marley & Robinson 2015). Thus, in UCD atmospheres, there is some ambiguity with regard to the dominant processes generating photometric variability, especially at the M/ L transition, whether magnetic spots or clouds (Gizis et al 2015).…”

Section: Photometric Variabilitymentioning

confidence: 99%

A Panchromatic View of Brown Dwarf Aurorae

Pineda

Hallinan

Kao

2017

ApJ

118

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Stellar coronal activity has been shown to persist into the low-mass star regime, down to late M-dwarf spectral types. However, there is now an accumulation of evidence suggesting that at the end of the main sequence, there is a transition in the nature of the magnetic activity from chromospheric and coronal to planet-like and auroral, from local impulsive heating via flares and MHD wave dissipation to energy dissipation from strong large-scale magnetospheric current systems. We examine this transition and the prevalence of auroral activity in brown dwarfs through a compilation of multiwavelength surveys of magnetic activity, including radio, X-ray, and optical. We compile the results of those surveys and place their conclusions in the context of auroral emission as a consequence of large-scale magnetospheric current systems that accelerate energetic electron beams and drive the particles to impact the cool atmospheric gas. We explore the different manifestations of auroral phenomena, like Hα, in brown dwarf atmospheres and define their distinguishing characteristics. We conclude that large-amplitude photometric variability in the near-infrared is most likely a consequence of clouds in brown dwarf atmospheres, but that auroral activity may be responsible for long-lived stable surface features. We report a connection between auroral Hα emission and quiescent radio emission in electron cyclotron maser instability pulsing brown dwarfs, suggesting a potential underlying physical connection between quiescent and auroral emissions. We also discuss the electrodynamic engines powering brown dwarf aurorae and the possible role of satellites around these systems both to power the aurorae and seed the magnetosphere with plasma.

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Section: Photometric Variabilitymentioning

confidence: 99%

A Panchromatic View of Brown Dwarf Aurorae

Pineda

Hallinan

Kao

2017

ApJ

118

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“…The evolution of brown dwarfs and the substellar boundary itself are largely understood based on theoretical work over the last two decades (e.g., Saumon et al 1994;Baraffe et al 1995;Burrows et al 1997;Chabrier & Baraffe 1997;Lodders 1999;Chabrier et al 2000;Burrows et al 2001;Baraffe et al 2003;Saumon & Marley 2008;MacDonald & Mullan 2009;Baraffe et al 2015). Broadly speaking, the interior physics of evolutionary models over this time has remained the same, while the treatment of the surface boundary conditions has advanced greatly due to improved molecular line lists, chemistry, and cloud modeling (see a recent review by Marley & Robinson 2015). Clouds in particular have long thought to be the key to explaining major variations in the emergent flux of brown dwarfs, especially in the change from L to T spectral types (the L/T transition).…”

Section: Introductionmentioning

confidence: 99%

Individual Dynamical Masses of Ultracool Dwarfs* ^† ^‡

Dupuy

Liu

2017

ApJS

189

216

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We present the full results of our decade-long astrometric monitoring programs targeting 31 ultracool binaries with component spectral types M7-T5. Joint analysis of resolved imaging from Keck Observatory and Hubble Space Telescope and unresolved astrometry from CFHT/WIRCam yields parallactic distances for all systems, robust orbit determinations for 23 systems, and photocenter orbits for 19 systems. As a result, we measure 38 precise individual masses spanning 30-115 M Jup . We determine a modelindependent substellar boundary that is ≈70 M Jup in mass (≈L4 in spectral type), and we validate Baraffe et al. (2015) evolutionary model predictions for the lithium-depletion boundary (60 M Jup at field ages). Assuming each binary is coeval, we test models of the substellar mass-luminosity relation and that find in the L/T transition, only the Saumon & Marley (2008) "hybrid" models accounting for cloud clearing match our data. We derive a precise, mass-calibrated spectral type-effective temperature relation covering 1100-2800 K. Our masses enable a novel direct determination of the age distribution of field brown dwarfs spanning L4-T5 and 30-70 M Jup . We determine a median age of 1.3 Gyr, and our population synthesis modeling indicates our sample is consistent with a constant star formation history modulated by dynamical heating in the Galactic disk. We discover two triple-brown-dwarf systems, the first with directly measured masses and eccentricities. We examine the eccentricity distribution, carefully considering biases and completeness, and find that low-eccentricity orbits are significantly more common among ultracool binaries than solar-type binaries, possibly indicating the early influence of long-lived dissipative gas disks. Overall, this work represents a major advance in the empirical view of very low-mass stars and brown dwarfs.

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“…gas and cloud opacities, gas-phase chemistry (kinetic or LTE), hydrodynamics (HD), magnetohydrodynamics (MHD), and cloud formation. The radiative transfer problem and the gas-phase chemical abundances have achieved rather high standards as core problems of atmosphere modelling and data analysis (see review by Marley & Robinson 2015, also Benneke 2015. HD and MHD have a long standing tradition in meteorology and in solar physics, respectively.…”

Section: Introductionmentioning

confidence: 99%

The mineral clouds on HD 209458b and HD 189733b

Helling

Lee

Dobbs-Dixon

et al. 2016

Monthly Notices of the Royal Astronomical Society

123

107

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ABSTRACT3D atmosphere model results are used to comparatively study the kinetic, nonequilibrium cloud formation in the atmospheres of two example planets guided by the giant gas planets HD 209 458b and HD 189 733b. Rather independently of hydrodynamic model differences, our cloud modelling suggests that both planets are covered in mineral clouds throughout the entire modelling domain. Both planets harbour chemically complex clouds that are made of mineral particles that have a height-dependent material composition and size. The remaining gas-phase element abundances strongly effects the molecular abundances of the atmosphere in the cloud forming regions. Hydrocarbon and cyanopolyyne molecules can be rather abundant in the inner, dense part of the atmospheres of HD 189 733b and HD 209 458b. No one value for metallicity and the C/O ratio can be used to describe an extrasolar planet. Our results concerning the presence and location of water in relation to the clouds explain some of the observed differences between the two planets. In HD 189 733b, strong water features have been reported while such features are less strong for HD 209 458b. By considering the location of the clouds in the two atmospheres, we see that obscuring clouds exist high in the atmosphere of HD 209 458b, but much deeper in HD 189 733b. We further conclude that the (self-imposed) degeneracy of cloud parameters in retrieval methods can only be lifted if the cloud formation processes are accurately modelled in contrast to prescribing them by independent parameters.

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On the Cool Side: Modeling the Atmospheres of Brown Dwarfs and Giant Planets

Cited by 208 publications

References 200 publications

A Panchromatic View of Brown Dwarf Aurorae

A Panchromatic View of Brown Dwarf Aurorae

Individual Dynamical Masses of Ultracool Dwarfs* ^† ^‡

The mineral clouds on HD 209458b and HD 189733b

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On the Cool Side: Modeling the Atmospheres of Brown Dwarfs and Giant Planets

Cited by 208 publications

References 200 publications

A Panchromatic View of Brown Dwarf Aurorae

A Panchromatic View of Brown Dwarf Aurorae

Individual Dynamical Masses of Ultracool Dwarfs* † ‡

The mineral clouds on HD 209458b and HD 189733b

Contact Info

Product

Resources

About

Individual Dynamical Masses of Ultracool Dwarfs* ^† ^‡