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Brown Dwarfs

Many brown dwarfs are known to have variable brightness, typically at the ~1% level, but with much larger variability observed in some instances.  Spectral observations of variability are currently rare, but one variable brown dwarf shows curious wavelength-dependent phase-lags in its spectrum (Buenzli et al. 2012).  Inspired by these data, a collaborator (M. Marley) and I set out to investigate how a column of gas in a brown dwarf atmosphere would respond to time-varying thermal perturbations (Robinson & Marley 2014).  We found that such perturbations can lead to a wealth of spectral behaviors, including wavelength-dependent phase-lags, depending on the period, strength, and location of the perturbation.  Our models don't fully explain the observations, though, which speaks to the complex nature of brown dwarfs---rotation, atmospheric circulation, clouds, and thermal variations are all at play!