The high velocity stars in the Local Stellar Halo from Gaia and LAMOST

TL;DR

This study uses Gaia and LAMOST data to analyze the kinematics and chemistry of local halo stars, identifying high velocity stars and exploring their origins within the Galaxy.

Contribution

It presents a new catalog of 436 halo stars including 16 high velocity stars, and investigates their chemical properties and possible origins.

Findings

Most high velocity stars are metal-poor.

Some high velocity stars may originate from the Galactic center.

Others are likely kicked from the Galactic disk.

Abstract

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.