Discovery of two new hypervelocity stars from the LAMOST spectroscopic surveys

TL;DR

This paper reports the discovery of two new hypervelocity stars from LAMOST surveys, highlighting their properties and potential origins, and discusses how future Gaia data will clarify their ejection mechanisms.

Contribution

It presents the first identification of two unbound hypervelocity stars from LAMOST data, expanding the known sample and emphasizing the importance of future Gaia measurements.

Findings

Two new hypervelocity stars identified with high velocities

Their origins remain uncertain due to lack of proper motion data

Future Gaia data will help determine their ejection mechanisms

Abstract

We report the discovery of two new unbound hypervelocity stars (HVSs) from the LAMOST spectroscopic surveys. They are respectively a B2V type star of ~ 7 M$_{\rm \odot}$ with a Galactic rest-frame radial velocity of 502 km/s at a Galactocentric radius of ~ 21 kpc and a B7V type star of ~ 4 M$_{\rm \odot}$ with a Galactic rest-frame radial velocity of 408 km/s at a Galactocentric radius of ~ 30 kpc. The origins of the two HVSs are not clear given their currently poorly measured proper motions. However, the future data releases of Gaia should provide proper motion measurements accurate enough to solve this problem. The ongoing LAMOST spectroscopic surveys are expected to yield more HVSs to form a statistical sample, providing vital constraint on understanding the nature of HVSs and their ejection mechanisms.