19 low mass hyper-velocity star candidates from the first data release of LAMOST survey

TL;DR

This study identifies 19 low-mass hyper-velocity star candidates from LAMOST data, analyzing their probabilities of being unbound and suggesting their likely origin in the Galactic bulge or disk.

Contribution

First identification of low-mass hyper-velocity star candidates from LAMOST survey data, with probabilistic analysis of their unbound status and potential Galactic origin.

Findings

All candidates have over 50% probability of being unbound.

One candidate exceeds escape velocity with over 90% probability.

Candidates likely originate from the Galactic bulge or disk.

Abstract

Hyper-velocity stars are believed to be ejected out from the Galactic center through dynamical interactions between (binary) stars and the central massive black hole(s). In this paper, we report 19 low mass F/G/K type hyper-velocity star candidates from over one mil- lion stars of the first data release of the LAMOST general survey. We determine the unbound probability for each candidate using a Monte-Carlo simulation by assuming a non-Gaussian proper-motion error distribution, Gaussian heliocentric distance and radial velocity error dis- tributions. The simulation results show that all the candidates have unbound possibilities over 50% as expected, and one of them may even exceed escape velocity with over 90% probabili- ty. In addition, we compare the metallicities of our candidates with the metallicity distribution functions of the Galactic bulge, disk, halo and globular cluster, and conclude that the Galactic bulge or disk is likely the birth place for our candidates.