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Half of the energy emitted by late-T- and Y-type brown dwarfs emerges at 3.5 < lambda um < 5.5. We present new L (3.43 < lambda um < 4.11) photometry obtained at the Gemini North telescope for nine late-T and Y dwarfs, and synthesize L from spectra for an additional two dwarfs. The targets include two binary systems which were imaged at a resolution of 0.25. One of these, WISEP J045853.90+643452.6AB, shows significant motion, and we present an astrometric analysis of the binary using Hubble Space Telescope, Keck Adaptive Optics, and Gemini images. We compare lambda ~4um observations to models, and find that the model fluxes are too low for brown dwarfs cooler than ~700K. The discrepancy increases with decreasing temperature, and is a factor of ~2 at T_eff=500K and ~4 at T_eff=400K. Warming the upper layers of a model atmosphere generates a spectrum closer to what is observed. The thermal structure of cool brown dwarf atmospheres above the radiative-convective boundary may not be adequately modelled using pure radiative equilibrium; instead heat may be introduced by thermochemical instabilities (previously suggested for the L- to T-type transition) or by breaking gravity waves (previously suggested for the solar system giant planets). One-dimensional models may not capture these atmospheres, which likely have both horizontal and vertical pressure/temperature variations.
We present Spitzer 7.6-14.5um spectra of ULAS J003402.77-005206.7 and ULAS J133553.45+113005.2, two T9 dwarfs with the latest spectral types currently known. We fit synthetic spectra and photometry to the near- through mid-infrared energy distributio
The number of brown dwarfs (BDs) now identified tops 700. Yet our understanding of these cool objects is still lacking, and models are struggling to accurately reproduce observations. What is needed is a method of calibrating the models, BDs whose pr
In its all-sky survey, Gaia will monitor astrometrically and photometrically millions of main-sequence stars with sufficient sensitivity to brown dwarf companions within a few AUs from their host stars and to transiting brown dwarfs on very short per
In order to understand the atmospheres as well as the formation mechanism of giant planets formed outside our solar system, the next decade will require an investment in studies of isolated young brown dwarfs. In this white paper we summarize the opp
Beyond the main sequence solar type stars undergo extensive mass loss, providing an environment where planet and brown dwarf companions interact with the surrounding material. To examine the interaction of substellar mass objects embedded in the stel