Herschel far-infrared photometric monitoring of protostars in the Orion
  Nebula Cluster
  We have obtained time series observations of the Orion Nebula Cluster at 70
microns and 160 microns from the Herschel/PACS Photometer. This represents the
first wide-field far-infrared photometric monitoring of a young star forming
region. The acquired 35'x35' maps show complex extended structures, with
unprecedented details, that trace the interaction between the molecular gas and
the young hot stars. We detect 43 protostars, most of which are situated along
the integral-shaped filament extending from the Orion nebula, through OMC2 and
to OMC3. We present high-reliability light curves for some of these objects
using the first six epochs of our observing program spread over 6 weeks. We
find amplitude variations in excess of 20% for a fraction of the detected
protostars over periods as short as a few weeks. This is inconsistent with the
dynamical time-scales of cool far-IR emitting material that orbits at hundreds
of AU from the protostar, and it suggests that the mechanism(s) responsible for
the observed variability originates from the inner region of the protostars,
likely driven by variable mass accretion.
