SIMBAD references

We explore differences in Galactic halo kinematic properties derived from two commonly employed Galactic potentials: the Stackel potential and the default Milky Way-like potential used in the "Galpy" package (MWPotential2014), making use of stars with available metallicities, radial velocities, and proper motions from Sloan Digital Sky Survey Data Release 12. Adopting the Stackel potential, we find that the shape of the metallicity distribution function (MDF) and the distribution of orbital rotation abruptly change at Z_{max} = 15 kpc and r_{max} = 30 kpc (where Z_{max} and r_{max} are the maximum distances reached by a stellar orbit from the Galactic plane and from the Galactic center, respectively), indicating that the transition from dominance by the inner-halo stellar population to the outer-halo population occurs at those distances. Stars with Z_{max} > 15 kpc show an average retrograde motion of V_φ = -60 km s^–1, while stars with r_{max} > 30 kpc exhibit an even larger retrograde value, V_φ = -150 km s^–1. This retrograde signal is also confirmed using the sample of stars with radial velocities obtained by Gaia Data Release 2, assuming the Stackel potential. In comparison, when using the shallower Galpy potential, a noticeable change in the MDF occurs only at Z_{max} = 25 kpc, and a much less extreme retrograde motion is derived. This difference arises because stars with highly retrograde motions in the Stackel potential are unbound in the shallower Galpy potential, and stars with lower rotation velocities reach larger Z_{max} and r_{max}. The different kinematic characteristics derived from the two potentials suggest that the nature of the adopted Galactic potential can strongly influence interpretation of the properties of the Galactic halo.