  The continuous temporal coverage and high photometric precision afforded by
space observatories has opened up new opportunities for the study of
variability processes in young stellar cluster members. Of particular interest
is the phenomenon of deuterium-burning pulsation in brown dwarfs and
very-low-mass stars, whose existence on 1-4 hours timescales has been proposed
but not yet borne out by observations. To investigate short-timescale
variability in young, low-mass objects, we carried out high-precision,
high-cadence time series monitoring with the Warm Spitzer mission on 14 low
mass stars and brown dwarfs in the ~3 Myr Sigma Orionis cluster. The flux in
many of our raw light curves is strongly correlated with sub-pixel position and
can vary systematically as much as 10%. We present a new approach to
disentangle true stellar variability from this "pixel-phase effect," which is
more pronounced in Warm Spitzer observations as compared to the cryogenic
mission. The light curves after correction reveal that most of the sample is
devoid of variability down to the few-millimagnitude level, on the minute to
day timescales probed. However, one exceptional brown dwarf displays erratic
brightness changes at the 10-15% level, suggestive of variable obscuration by
dusty material. The uninterrupted 24-hour datastream and sub-1% photometric
precision enables limits on pulsation in the near-infrared. If this phenomenon
is present in our light curves, then its amplitude must lie below 2-3
millimagnitudes. In addition, we present three field eclipsing binaries and one
pulsator for which optical ground-based data is also available.
