Tuesday 20 Feb 2018[Journal Club] Cloudless Atmospheres for Brown Dwarfs and Giant Exoplanets

Mark Phillips - University of Exeter

4th Floor Interaction Area 11:15-11:45

The presence of condensate clouds in the atmospheres of brown dwarfs and exoplanets is the generally accepted explanation or a wide range of observations, including the L-T brown dwarf spectral sequence and the extremely red near-infrared spectra of young planetary mass objects. However, issues still remain with this cloudy scenario. The physical process driving the inferred disappearance of clouds at the L-T transition is unclear, and reproducing the extremely red spectra of young objects with radii consistent with evolutionary models continues to be a challenge. This motivates our research into an alternative ‘cloud-free’ scenario. We suggest that brown dwarfs may be subject to a thermo-chemical instability induced by non-equilibrium chemistry, which can alter the temperature profile of the atmosphere and provide an alternative explanation for their spectral evolution. I will present new results from the development of a cloud-free grid of model atmospheres generated using our 1D forward model ATMO. I will show that our model can adequately reproduce the near-infrared spectra of benchmark objects throughout the L-T spectral sequence, suggesting that while clouds are present in brown dwarf atmospheres, they may not be driving the spectral evolution. These results highlight how processes other than clouds can have significant influence on the spectra of brown dwarfs and giant exoplanets.

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