Kinematics of Highly R-Process-Enhanced Field Stars: Evidence for an Accretion Origin and Detection of Several Groups from Disrupted Satellites

Understand

We present kinematics of 35 highly r-process-enhanced ([Eu/Fe] >= +0.7) metal-poor (-3.8 < [Fe/H] < -1.4) field stars.

• We calculate six-dimensional positions and velocities, evaluate energies and integrals of motion, and compute orbits for each of these stars using parallaxes and proper motions from the second Gaia data release and published radial velocities.
• All of these stars have halo kinematics.
• Most stars (66%) remain in the inner regions of the halo (< 13 kpc), and many (51%) have orbits that pass within 2.6 kpc of the Galactic center.