Poster Abstracts

Name/Affiliation:  Jacqueline Radigan (STScI)

Title:  As the Dust Settles: continuous monitoring of L/T transition brown dwarfs with Spitzer

Recent observations of cool brown dwarfs in the time-domain have revealed large-amplitude variability at near-infrared wavelengths for a subset of objects spanning the transition between cloudy L-dwarf and clear T-dwarf spectral types. This quasi-periodic variability is indicative of patchy clouds and evolving weather patterns. We present the results of an intensive monitoring campaign where 5 highly variable L/T transition brown dwarfs were were followed up with Warm Spitzer. Light curves spanning several consecutive rotations were obtained, with our longest observation of the highly variable T1.5 dwarf 2MASS 2139+02, spanning 48 hours. Strong variability is confirmed in all targets, demonstrating persistence of variability over months and years. For all but one target, the dominant temporal component of the variability can be associated with rotation. Further changes in light curve shape are observed from rotation to rotation, demonstrating that cloud features evolve on timescales of hours. The observed amplitudes of variability are similar in the [3.6] and [4.5] Spitzer channels, but tend to be smaller on average than those found in the near-infrared. We present our attempt to model the observed light curves as a function of time and wavelength, and discuss possible interpretations based on current dynamical and spectral models of brown dwarf atmospheres.