The high velocity stars in the Local Stellar Halo from Gaia and LAMOST
  Based on the first Gaia data release and spectroscopy from the LAMOST Data
Release 4, we study the kinematics and chemistry of the local halo stars. The
halo stars are identified kinematically with a relative speed of at least 220
km s$^{-1}$ with respect to the local standard of rest. In total, 436 halo
stars are identified. From this halo sample, 16 high velocity (HiVel) stars are
identified. We studied the metallicity and [$\alpha$/Fe] distribution of these
HiVel stars. Though most of HiVel stars are metal-poor, there are several stars
that have metallicity above $-0.5$ dex. To understand the origin of high
velocity stars, we evolve the trajectory of the star backwards along the orbit
in our adopted Galaxy potential model to determine the orbital parameters and
assess whether the star could have originated in the Galactic center. We found
that some high velocity stars could have originated from the Galactic center,
but other stars were probably kicked up from the Galactic disk.
