  Only a handful of late-T brown dwarfs have been monitored for
spectro-photometric variability, leaving incomplete the study of the
atmospheric cloud structures of the coldest brown dwarfs, that share
temperatures with some cold, directly-imaged exoplanets. 2MASSJ00501994-332240
is a T7.0 rapidly rotating, field brown dwarf that showed low-level photometric
variability in data obtained with the Spitzer Space telescope. We monitored
2MASSJ00501994-332240 during ~2.6 hr with MOSFIRE, installed at the Keck I
telescope, with the aim of constraining its near-infrared spectro-photometric
variability. We measured fluctuations with a peak-to-peak amplitude of
1.48+\-0.75% in the J-band photometric light curve, an amplitude of
0.62+/-0.18% in the J-band spectro-photometric light curve, and an amplitude of
1.26+/-0.93% in the H-band light curve, and an amplitude of 5.33+/-2.02% in the
CH_4-H_2O band light curve. Nevertheless, the Bayesian Information Criterion
does not detect significant variability in any of the light curves. Thus, given
the detection limitations due to the MOSFIRE sensitivity, we can only claim
tentative low-level variability for 2M0050-3322 in the best-case scenario. The
amplitudes of the peak-to-peak fluctuations measured for 2MASSJ00501994-332240
agree with the variability amplitude predictions of General Circulation Models
for a T7.0 brown dwarf for an edge on object. Radiative-transfer models predict
that the Na_2S and KCl clouds condense at pressures lower than that traced by
the CH_4-H_2O band, which might explain the higher peak-to-peak fluctuations
measured for this light curve. Finally, we provide a visual recreation of the
map provided by General Circulation Models and the vertical structure of
2MASSJ00501994-332240 provided by radiative-transfer models.
