The Origin of High-velocity Stars from Gaia and LAMOST

Based on the second Gaia data release and spectroscopy from the Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST) Data Release 5, we define the high-velocity (HiVel) stars sample as those stars with vgc > 0.85vesc, 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 α-enhanced. In order to further explore the origin of these HiVel stars, we traced the backward orbits of each HiVel star in the Galactic potential to derive probability parameters that 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 originating from the stellar disk.