The Hercules stream as seen by APOGEE-2 South
  The Hercules stream is a group of co-moving stars in the Solar neighbourhood,
which can potentially be explained as a signature of either the outer Lindblad
resonance (OLR) of a fast Galactic bar or the corotation resonance of a slower
bar. In either case, the feature should be present over a large area of the
disc. With the recent commissioning of the APOGEE-2 Southern spectrograph we
can search for the Hercules stream at $(l,b)=(270^\circ,0)$, a direction in
which the Hercules stream, if caused by the bar's OLR, would be strong enough
to be detected using only the line-of-sight velocities. We clearly detect a
narrow, Hercules-like feature in the data that can be traced from the solar
neighbourhood to a distance of about 4 kpc. The detected feature matches well
the line-of-sight velocity distribution from the fast-bar (OLR) model.
Confronting the data with a model where the Hercules stream is caused by the
corotation resonance of a slower bar leads to a poorer match, as the corotation
model does not predict clearly separated modes, possibly because the slow-bar
model is too hot.
