SiO maser survey off the Galactic Plane

To study this motion on a much larger scale in the Galaxy, we newly surveyed 134 evolved stars off the Galactic plane by SiO maser lines, obtaining accurate radial velocities of 84 detected stars. Together with the past data of SiO maser sources, we analyzed the radial-velocity data of a large sample of sources distributed in a distance range of about 0.3-6kpc in the first Galactic quadrant.

At Galactic longitudes between 20{deg} and 40{deg}, we found a group of stars with large negative radial velocities, which deviate by more than 100km/s from the Galactic rotation. We show that these deviant motions of maser stars are created by periodic gravitational perturbation of the Bulge bar, and that the effect appears most strongly at radii between corotation and outer Lindblad resonances. The resonance effect can explain the displacement of positions from the Galactic plane as well.