A New Hyper-runaway Star Discovered from LAMOST and Gaia: Ejected Almost in the Galactic Rotation Direction

摘要

In this paper, we report the discovery of a new late-B-type unbound hyper-runaway star (LAMOST-HVS4) fromthe LAMOST spectroscopic surveys. According to its atmospheric parameters, it is either a B-type main-sequence(MS) star or a blue horizontal branch (BHB) star. Its Galactocentric distance and velocity are 30.3?±?1.6 kpc and586?±?7kms ?1 if it is an MS star, and they are 13.2?±?3.7kpc and 590?±?7 km s ?1 if a BHB star. We track itstrajectories back and find that the trajectories intersect with the Galactic disk, and the Galactic center lies outside ofthe intersection region at the 3σ confidence level. We investigate a number of mechanisms that could beresponsible for the ejection of the star and find that it is probably ejected from the Galactic disk by supernovaexplosion or multiple-body interactions in dense young stellar clusters.