Name/Affiliation: Aren Heinze (Stony Brook University)
Brown Dwarfs with Dynamic, Rapidly Changing Clouds
As recently as two years ago, the existence of substantial aperiodic photometric variations in brown dwarfs was regarded with skepticism. This was warranted: difficult-to-quantify photometric systematics can easily mimic non-periodic variations, and theory did not necessarily predict the swift, global changes in brown dwarf cloud distributions that aperiodic data appeared to imply. However, new evidence shows that the photometric amplitude and phase of certain brown dwarfs (in particular Luhman 16B) can indeed change significantly on a rotational timescale. We present several new examples of brown dwarfs with confirmed aperiodic behavior, and we show that there is a wide range in the extent of aperiodicity among variable brown dwarfs. Some objects show perfectly periodic variations that remain coherent over many rotations, while for others the amplitude and phase change so rapidly that the true rotation period may be difficult to discern. The extent of a given brown dwarf's photometric aperiodicity should be determined mostly by the rapidity of its cloud evolution, and therefore aperiodicity constitutes a direct probe of the dynamics of brown dwarf atmospheres and an important new parameter in the analysis of brown dwarfs.