The Galactic bulge shows a double red clump in sightlines at | b | ≳ 5° and −3° ≲ l ≲ 4°. This dump is interpreted as the signature of an X-shaped structure seen almost edge-on. We measure the proper motions of the stars belonging to the closer and the further arms of the X-shaped structure. The intrinsic kinematic properties of the two arms are found by incorporating information taken from the luminosity function. At b = −5°, we find that the proper motion difference between the two arms is a linear function of Galactic longitude for −0 1 < l < 0 5, which we interpret as a streaming motion of the stars within the X-shaped structure. A streaming motion was previously reported based on radial velocity data, not the proper motions. The proper motion difference in longitude is constant for −0 8 < l < −0 1, which provides an estimate of the bulge rotational speed of 87.9 ± 8.2 km s −1 kpc −1 .
No takes yet. Share an insight, caveat, or question.
A 2013 study studied this question.