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Title: Temperature fluctuations as a source of brown dwarf variability

A number of brown dwarfs are now known to be variable with observed amplitudes as large as 10%-30% at some wavelengths. While spatial inhomogeneities in cloud coverage and thickness are likely responsible for much of the observed variability, it is possible that some of the variations arise from atmospheric temperature fluctuations instead of, or in addition to, clouds. To better understand the role that thermal variability might play we present a case study of brown dwarf variability using a newly developed one-dimensional, time-stepping model of atmospheric thermal structure. We focus on the effects of thermal perturbations, intentionally simplifying the problem through omission of clouds and atmospheric circulation. Model results demonstrate that thermal perturbations occurring deep in the atmosphere (at pressures greater than 10 bar) of a model T-dwarf can be communicated to the upper atmosphere through radiative heating via the windows in near-infrared water opacity. The response time depends on where in the atmosphere a thermal perturbation is introduced. We show that, for certain periodic perturbations, the emission spectrum can have complex time- and wavelength-dependent behaviors, including phase shifts in times of maximum flux observed at different wavelengths. Since different wavelengths probe different levels in the atmosphere, these variations trackmore » a wavelength-dependent set of radiative exchanges happening between different atmospheric levels as a perturbation evolves in time. We conclude that thermal—as well as cloud—fluctuations must be considered as possible contributors to the observed brown dwarf variability.« less
Authors:
;  [1]
  1. NASA Ames Research Center, MS 245-3, Moffett Field, CA 94035 (United States)
Publication Date:
OSTI Identifier:
22357058
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 785; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMBIENT TEMPERATURE; AMPLITUDES; ATMOSPHERES; ATMOSPHERIC CIRCULATION; DISTURBANCES; DWARF STARS; EMISSION SPECTRA; FLUCTUATIONS; ONE-DIMENSIONAL CALCULATIONS; OPACITY; PERIODICITY; PERTURBATION THEORY; PHASE SHIFT; SPACE; STAR EVOLUTION; STARS; THICKNESS; WATER; WAVELENGTHS