We present the detection of [ 3.6 ~ { } \mu m ] 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 \pm 0.2 ~ { } hr and a peak-to-peak amplitude of 1.07 \pm 0.04 \% for W0047 , and a period of 11 \pm 2 ~ { } hr and amplitude of 0.8 \pm 0.2 \% 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 \pm 0.3 ~ { } km s ^ { -1 } and 14.3 ^ { +1.4 } _ { -1.5 } ~ { } km s ^ { -1 } for W0047 and 2M2244 , respectively .
With inclination angles of 85 ^ { +5 \circ } _ { -9 } and 76 ^ { +14 \circ } _ { -20 } , 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 ~ { } \mu \mathrm { m } ] monitoring of the young , T5.5 object SDSS111010+011613 ( SDSS1110 ) where we detect no variability .
For periods < 18 ~ { } hr , we place an upper limit of 1.25 \% on the peak-to-peak variability amplitude of SDSS1110 .