# The origin of high velocity stars from Gaia and LAMOST

## TL;DR

This study identifies and classifies high-velocity stars from Gaia DR2 and LAMOST data, revealing their origins as either tidal debris from dwarf galaxies or runaway stars from the stellar disk.

## Contribution

It provides a detailed classification of high-velocity stars based on orbital tracing, distinguishing their origins with new methodology using combined Gaia and LAMOST data.

## Key findings

- 5 stars originate from disrupted dwarf galaxy debris
- 19 stars are runaway candidates from the stellar disk
- Most HiVel stars are metal-poor and alpha-enhanced

## Abstract

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.