We propose a novel explanation for the Hercules stream consistent with recent measurements of the extent and pattern speed of the Galactic bar .
We have adapted a made-to-measure dynamical model tailored for the Milky Way to investigate the kinematics of the solar neighborhood ( SNd ) .
The model matches the 3D density of the red clump giant stars ( RCGs ) in the bulge and bar as well as stellar kinematics in the inner Galaxy , with a pattern speed of 39 { km s ^ { -1 } kpc ^ { -1 } } .
Cross-matching this model with the Gaia DR1 TGAS data combined with RAVE and LAMOST radial velocities , we find that the model naturally predicts a bimodality in the U–V -velocity distribution for nearby stars which is in good agreement with the Hercules stream .
In the model , the Hercules stream is made of stars orbiting the Lagrange points of the bar which move outward from the bar ’ s corotation radius to visit the SNd .
While the model is not yet a quantitative fit of the velocity distribution , the new picture naturally predicts that the Hercules stream is more prominent inward from the Sun and nearly absent only a few 100 pc outward of the Sun , and plausibly explains that Hercules is prominent in old and metal-rich stars .