The pattern speed of the Galactic bar

Most late-type stars in the solar neighborhood have velocities similar to t he local standard of rest (LSR), but there is a clearly separated secondary component corresponding to a slower rotation and a mean outward motion. De tailed simulations of the response of a stellar disk to a central bar show that such a bimodality is expected from outer Lindblad resonant scattering. When constraining the run of the rotation curve by the proper motion of Sa gittarius A* and the terminal gas velocities, the value observed for the ro tation velocity separating the two components results in a value of 53 +/- 3 km s(-1) kpc(-1) for the pattern speed of the bar, only weakly dependent on the precise values for R-0 and bar angle phi.