SiO Maser Survey off the Galactic Plane: A Signature of Streaming Motion

TL;DR

This study surveys SiO maser-emitting evolved stars off the Galactic plane to analyze their velocities, revealing streaming motions caused by the Galactic Bulge bar's gravitational perturbations, especially between corotation and Lindblad resonances.

Contribution

It provides new observational evidence of streaming motions in evolved stars caused by the Galactic bar, extending previous findings with a larger, more distant sample.

Findings

Identified stars with large negative radial velocities deviating from Galactic rotation.

Linked these deviations to gravitational effects of the Galactic Bulge bar.

Demonstrated resonance effects influence stellar positions and motions.

Abstract

A group of Mira variables in the solar neighborhood show unusual spatial motion in the Galaxy. To study this motion in 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 distributing in a distance range of about 0.3 -- 6 kpc in the first Galactic quadrant. At the Galactic longitudes between 20 and 40 deg, we found a group of stars with large negative radial velocities, which deviate by more than 100 km s^{-1} 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.