Order and Chaos in the Local Disc Stellar Kinematics

The effects of the Galactic bar on the velocity distribution of old disc stars in the Solar neighbourhood are investigated using high-resolution 2D test particle simulations. A detailed orbital analysis reveals that the structure of the U − V distribution in these simulations is closely related to the phase-space extent of regular and chaotic orbits. At low angular momentum and for a sufficiently strong bar, stars mainly follow chaotic orbits which may cross the corotation radius and the U − V contours follow lines of constant Jacobi's integral except near the regions occupied by weakly populated eccentric regular orbits. These properties can naturally account for the observed outward motion of the local high asymmetric drift stars.