A VLBA Survey of radio stars in the Orion Nebula Cluster: I. The
  nonthermal radio population
  We present first results of a four-epoch VLBA survey for nonthermal emission
toward all 556 compact radio sources previously identified in a deep VLA survey
of the Orion Nebula Cluster (ONC). We identify VLBA counterparts toward an
unprecedented 123 sources. Of these, 41 do not have X-ray counterparts, of
which 34 also do not display near-infrared counterparts. Since these cannot be
explained by extragalactic background sources, this suggests a component of the
ONC population of young stellar objects that are too deeply embedded for even
X-rays to be detectable. We find pervasive variability and detect even most of
the highest-S/N sources in only one out of four epochs. Neither a negative
spectral index nor extreme variability in the VLA data is a good predictor of a
VLBA detection.
