Weather on the Nearest Brown Dwarfs: Resolved Simultaneous Multi-Wavelength Variability Monitoring of WISE J104915.57-531906.1AB

Abstract

We present two epochs of MPG/ESO 2.2m GROND simultaneous 6-band ($r^{\prime }{i}^{\prime }{z}^{\prime }JHK$) 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 hours of focused observations on the night of UT 2013-04-22, as well as 4 hours of defocused (unresolved) observations on the night of UT 2013-04-16. We note a number of robust trends in our light curves. The $r^{\prime }$ and $i^{\prime }$ light curves appear to be anticorrelated with $z^{\prime }$ and $H$ for the T0.5 component and in the unresolved lightcurve. In the defocused dataset, $J$ appears correlated with $z^{\prime }$ and $H$ and anticorrelated with $r^{\prime }$ and $i^{\prime }$, 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 lightcurve, the $K$ band lightcurve displays a significant phase offset relative to both $H$ and $z^{\prime }$. We argue that the measured phase offsets are correlated with atmospheric pressure probed at each band, as estimated from 1D atmospheric models. We also report low-amplitude variability in $i^{\prime }$ and $z^{\prime }$ intrinsic to the L7.5 component.

14 pages, 5 figures, accepted to ApJ Letters