IN SEARCH OF DUST CLOUDS: PHOTOMETRIC MONITORING OF A SAMPLE OF LATE L AND T DWARFS

Theoretical models indicate that L dwarf atmospheres are dominated by dust clouds made up of refractory elements; these clouds gradually disappear below the photosphere at the L/T transition. With the presence of dust-bearing clouds close to the photosphere, one expects weather-like features to appear on the brown dwarf surface, due to the presence of gaps in the cloud cover. We cannot hope to spatially resolve the disk of nearby brown dwarfs and directly explore the diversity of weather-like patterns on their surfaces with existing observational tools; therefore, indirect methods have to be used to probe these features, including rotation-induced flux modulation. In order to increase the sample of late L and T dwarfs probed for photometric variability, we observed a sample of nine brown dwarfs near the L/T transition. One target, SDSS J1052+4422 (T0.5), shows periodic flux variations with an evolving light curve and peak-to-peak amplitudes of ∼0.06 mag over a period of 3.0 hr, adding to the short list of early T dwarfs with semi-periodic photometric variability. The periodogram search also puts upper limits of ∼0.015 mag on the periodic variability of the remaining eight targets.