Tracing the Hercules stream around the Galaxy
  It has been proposed that the Hercules stream, a group of co-moving stars in
the Solar neighborhood offset from the bulk of the velocity distribution, is
the result of resonant interactions between stars in the outer disk and the
Galactic bar. So far it has only been seen in the immediate Solar neighborhood,
but the resonance model makes a prediction over a large fraction of the
Galactic disk. I predict the distribution of stellar velocities and the
changing Hercules feature in this distribution as a function of location in the
Galactic disk in a simple model for the Galaxy and the bar that produces the
observed Hercules stream. The Hercules feature is expected to be strong enough
to be unambiguously detected in the distribution of line-of-sight velocities in
selected directions. I identify quantitatively the most promising lines of
sight for detection in line-of-sight velocities using the Kullback-Leibler
divergence between the predictions of the resonance model and an axisymmetric
model; these directions are at 250 deg <~ l <~ 290 deg. The predictions
presented here are only weakly affected by distance uncertainties, assumptions
about the distribution function in the stellar disk, and the details of the
Galactic potential including the effect of spiral structure. Gaia and future
spectroscopic surveys of the Galactic disk such as APOGEE and HERMES will be
able to robustly test the origin of the Hercules stream and constrain the
properties of the Galactic bar.
