Spitzer/IRAC monitoring of WISE J085510.83-071442.5

To detect and characterize inhomogeneities in its atmosphere (e.g., patchy clouds, hot spots), we have performed time-series photometric monitoring of WISE 0855-0714 at 3.6 and 4.5{mu}m with the Spitzer Space Telescope during two 23hr periods that were separated by several months.

For both bands, we have detected variability with peak-to-peak amplitudes of 4%-5% and 3%-4% in the first and second epochs, respectively. The light curves are semiperiodic in the first epoch for both bands, but they are more irregular in the second epoch. Models of patchy clouds have predicted a large increase in mid-infrared (mid-IR) variability amplitudes (for a given cloud covering fraction) with the appearance of water ice clouds at T_eff_<375K, so if such clouds are responsible for the variability of WISE 0855-0714, then its small amplitudes of variability indicate a very small deviation in cloud coverage between hemispheres.