Weather on the nearest brown dwarfs: Resolved simultaneous multi-wavelength variability monitoring of wise J104915.57-531906.1AB

We present two epochs of MPG/ESO 2.2 m GROND simultaneous six-band (r′i′z′ JHK) photometric monitoring of the closest known L/T transition brown dwarf binary WISE J104915.57-531906.1AB. We report here the first resolved variability monitoring of both the T0.5 and L7.5 components. We obtained 4 hr of focused observations on the night of 2013 April 22 (UT), as well as 4 hr of defocused (unresolved) observations on the night of 2013 April 16 (UT). We note a number of robust trends in our light curves. The r′ and i′ light curves appear to be anti-correlated with z′ and H for the T0.5 component and in the unresolved light curve. In the defocused dataset, J appears correlated with z′ and H and anti-correlated with r′ and i′, while in the focused dataset we measure no variability for J at the level of our photometric precision, likely due to evolving weather phenomena. In our focused T0.5 component light curve, the K band light curve displays a significant phase offset relative to both H and z′. We argue that the measured phase offsets are correlated with atmospheric pressure probed at each band, as estimated from one-dimensional atmospheric models. We also report low-amplitude variability in i′ and z′ intrinsic to the L7.5 component.