The role of convection, overshoot, and gravity waves for the transport of dust in M dwarf and brown dwarf atmospheres
TLDR
In this paper, the authors applied hydrodynamical simulations to develop an improved physical understanding of the mixing properties of macroscopic flows in M dwarf and brown dwarf atmospheres, in particular of the influence of the underlying convection zone.Abstract:
Observationally, spectra of brown dwarfs indicate the presence of dust in their atmospheres while theoretically it is not clear what prevents the dust from settling and disappearing from the regions of spectrum formation. Consequently, standard models have to rely on ad hoc assumptions about the mechanism that keeps dust grains aloft in the atmosphere. We apply hydrodynamical simulations to develop an improved physical understanding of the mixing properties of macroscopic flows in M dwarf and brown dwarf atmospheres, in particular of the influence of the underlying convection zone. We performed 2D radiation hydrodynamics simulations including a description of dust grain formation and transport with the CO5BOLD code. The simulations cover the very top of the convection zone and the photosphere including the dust layers for effective temperatures between 900K and 2800K, all with logg=5 assuming solar chemical composition. Convective overshoot occurs in the form of exponentially declining velocities with small scale heights, so that it affects only the region immediately above the almost adiabatic convective layers. From there on, mixing is provided by gravity waves that are strong enough to maintain thin dust clouds in the hotter models. With decreasing effective temperature, the amplitudes of the waves become smaller but the clouds become thicker and develop internal convective flows that are more efficient in mixing material than gravity waves. The presence of clouds leads to a highly structured appearance of the stellar surface on short temporal and small spatial scales. We identify convectively excited gravity waves as an essential mixing process in M dwarf and brown dwarf atmospheres. Under conditions of strong cloud formation, dust convection is the dominant self-sustaining mixing component.read more
Citations
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New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
TL;DR: In this paper, the authors presented new models for low-mass stars down to the hydrogen-burning limit that consistently couple atmosphere and interior structures, thereby superseding the widely used BCAH98 models.
Journal ArticleDOI
New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
TL;DR: In this paper, the authors presented new models for low-mass stars down to the hydrogen-burning limit that consistently couple atmosphere and interior structures, thereby superseding the widely used BCAH98 models.
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Models of very-low-mass stars, brown dwarfs and exoplanets
TL;DR: Recent advances in modelling the stellar to substellar transition are reviewed, and the revised solar oxygen abundances and cloud model allow the photometric and spectroscopic properties of this transition to be reproduced for the first time.
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The prevalence of dust on the exoplanet HD 189733b from Hubble and Spitzer observations
Frederic Pont,David K. Sing,Neale P. Gibson,Neale P. Gibson,Suzanne Aigrain,Gregory W. Henry,Nawal Husnoo +6 more
TL;DR: In this paper, the authors provided a new tabulation of the transmission spectrum across the entire visible and infrared range of the hot Jupiter HD 189733b from UV to infrared using the STIS, ACS and WFC3 instruments.
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Simulations of stellar convection with CO5BOLD
Bernd Freytag,Matthias Steffen,Hans-Günter Ludwig,Sven Wedemeyer-Böhm,W. Schaffenberger,Oskar Steiner +5 more
TL;DR: The CO5BOLD code described in this article is designed for so-called ''realistic'' simulations that take into account the detailed microphysics under the conditions in solar or stellar surface layers (equation-of-state and optical properties of the matter).
References
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