Kinematics of bulge red clump stars

In this paper the authors measure the radial velocities and proper motions for a sample of 454 individual bulge giant stars, roughly equally distributed between the two red clumps to determine how such a structure could be formed from bar instabilities.

The radial velocity distribution of stars in the bright red clump, which traces the closer overdensity of bulge stars, shows an excess of stars moving towards the Sun. Similarly, an excess of stars receding from the Sun is seen in the more distant overdensity, which is traced by faint red clump stars. This can be explained by the presence of stars on elongated orbits, which are most likely streaming along the arms of the X-shaped bulge.