Shepherding Tidal Debris with the Galactic Bar: The Ophiuchus Stream
  The dynamics of stellar streams in rotating barred potentials is explained
for the first time. Naturally, neighbouring stream stars reach pericentre at
slightly different times. In the presence of a rotating bar, these neighbouring
stream stars experience different bar orientations during pericentric passage
and hence each star receives a different torque from the bar. These differing
torques reshape the angular momentum and energy distribution of stars in the
stream, which in turn changes the growth rate of the stream. For a progenitor
orbiting in the same sense as the bar's rotation and satisfying a resonance
condition, the resultant stream can be substantially shorter or longer than
expected, depending on whether the pericentric passages of the progenitor occur
along the bar's minor or major axis respectively. We present a full discussion
of this phenomenon focusing mainly on streams confined to the Galactic plane.
In stark contrast with the evolution in static potentials, which give rise to
streams that grow steadily in time, rotating barred potentials can produce
dynamically old, short streams. This challenges the traditional viewpoint that
the inner halo consists of well phase-mixed material whilst the
tidally-disrupted structures in the outer halo are more spatially coherent. We
argue that this mechanism plays an important role in explaining the
mysteriously short Ophiuchus stream that was recently discovered near the bulge
region of the Milky Way.
