Variability at the Edge: Optical Near/IR Rapid Cadence Monitoring of
  Newly Outbursting FU Orionis Object HBC 722
  We present the detection of day-timescale periodic variability in the r-band
lightcurve of newly outbursting FU Orionis-type object HBC 722, taken from > 42
nights of observation with the CQUEAN instrument on the McDonald Observatory
2.1m telescope. The optical/near-IR lightcurve of HBC 722 shows a complex array
of periodic variability, clustering around 5.8 day (0.044 mag amplitude) and
1.28 day (0.016 mag amplitude) periods, after removal of overall baseline
variation. We attribute the unusual number of comparable strength signals to a
phenomenon related to the temporary increase in accretion rate associated with
FUors. We consider semi-random "flickering", magnetic braking/field compression
and rotational asymmetries in the disk instability region as potential sources
of variability. Assuming the 5.8 day period is due to stellar rotation and the
1.28 day period is indicative of Keplerian rotation at the inner radius of the
accretion disk (at 2 R(star)), we derive a B-field strength of 2.2-2.7 kG,
slightly larger than typical T Tauri stars. If instead the 5.8 day signal is
from a disk asymmetry, the instability region has an outer radius of 5.4
R(star), consistent with models of FUor disks. Further exploration of the time
domain in this complicated source and related objects will be key to
understanding accretion processes.
