Variability of the lowest mass objects in the AB Doradus moving group

We present the detection of [3.6 μm] photometric variability in two young, L/T transition brown dwarfs, WISE J004701.06+680352.1 (W0047) and 2MASS J2244316+204343 (2M2244) using the Spitzer Space Telescope. We find a period of 16.4 ±0.2 h and a peak-to-peak amplitude of 1.07 ± 0.04 per cent forW0047, and a period of 11±2 h and amplitude of 0.8 ± 0.2 per cent for 2M2244. This period is significantly longer than that measured previously during a shorter observation. We additionally detect significant J-band variability in 2M2244 using the Wide- Field Camera on UKIRT. We determine the radial and rotational velocities of both objects using Keck NIRSPEC data. We find a radial velocity of -16.0 _-0.9^+0.8 km s^-1 for 2M2244, and confirm it as a bona fide member of the AB Doradus moving group. We find rotational velocities of v sin i = 9.8 ± 0.3 and 14.3 _-1.5^+1.4 km s^-1 for W0047 and 2M2244, respectively. With inclination angles of 85_-9 ^+5° and 76 _-20+^14° W0047 and 2M2244 are viewed roughly equator-on. Their remarkably similar colours, spectra and inclinations are consistent with the possibility that viewing angle may influence atmospheric appearance. We additionally present Spitzer [4.5 μm] monitoring of the young, T5.5 object SDSS111010+011613 (SDSS1110) where we detect no variability. For periods < 18 h, we place an upper limit of 1.25 per cent on the peak-to-peak variability amplitude of SDSS1110.