591 High Velocity Star Candidates from the Large Sky Area Multi-object Spectroscopic Telescope and the Second Gaia Data Release
591 high velocity stars in the Galactic halo selected from LAMOST DR7 and Gaia DR2
We report 591 high velocity star candidates (hivelscs) selected from over 10 million spectra of the data release seven (dr7) of the large sky area multi-object fiber spectroscopic telescope and the second gaiadata release, with three-dimensional velocities in the galactic rest-frame larger than 445 km/s.
To investigate the origin of hivelscs, we perform orbit integrations and divide them into four types, i.e., hypervelocity stars, hyper-runaway stars, runaway stars and fast halo stars.
We show that at least 43 hivelscs are unbound to the galaxy with escape probabilities larger than 50%, and this number decreases to eight if the possible parallax zero-point error is corrected.
Most of these hivelscs are metal-poor and slightly alpha-enhanced inner halo stars with [fe/h] > -1, which may be the metal-rich"in situ''stars in halo formed in the initial collapse of the galaxy or metal-rich stars formed in the disk or bulge but kinematically heated but kinematically heated.