The origin of high velocity stars from Gaia and LAMOST
  Based on the second Gaia data (Gaia DR2) and spectroscopy from the LAMOST
Data Release 5, we defined the high-velocity (HiVel) stars sample as those
stars with $v_{\mathrm{gc}} > 0.85 v_{\mathrm{esc}}$, and derived the final
sample of 24 HiVel stars with stellar astrometric parameters and radial
velocities. Most of the HiVel stars are metal-poor and $\alpha$-enhanced. In
order to further explore the origin of these HiVel stars, we traced the
backwards orbits of each HiVel star in the Galactic potential to derive
probability parameters which are used to classify these HiVel stars. Of these,
5 stars are from the tidal debris of disrupted dwarf galaxy and 19 stars are
runaway-star candidates which originate from the stellar disk.
