The origin of B-type runaway stars based on kinematics

¹ Yunnan observatories, Chinese Academy of Sciences P.O. Box 110 Kunming 650011, China
² International Centre of Supernovae, Yunnan Key Laboratory Kunming 650216, China
³ CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences Beijing 100101, People’s Republic of China
⁴ Department of Physics, Hebei Normal University Shijiazhuang 050024, People’s Republic of China
⁵ Shanghai NanHui High School Shanghai 200135, People’s Republic of China
⁶ Department of Astronomy, China West Normal University Nanchong 637002, People’s Republic of China

^★ Corresponding authors: This email address is being protected from spambots. You need JavaScript enabled to view it. ; This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 26 September 2025
Accepted: 20 November 2025

Abstract

Context. Runaway stars depart their birthplaces with high peculiar velocities. Two mechanisms are commonly invoked to explain their origin, the binary supernova scenario and the dynamical ejection scenario. Investigating the kinematic properties of runaway stars is key to understanding their origins.

Aims. We investigated the origins of 39 B-type runaway stars from LAMOST using orbital traceback analysis.

Methods. From the LAMOST catalog, we selected 39 B-type runaway stars and determined their spectral subtypes from key absorption lines. We then derived atmospheric parameters for each star using the Stellar Label Machine, which is trained on TLUSTY synthetic spectra computed under the nonlocal thermodynamic equilibrium assumption. Using the derived atmospheric parameters as input, we estimated stellar masses and ages with a machine learning model trained on PARSEC evolutionary tracks. We finally performed orbital traceback with GALPY to analyze their origins.

Results. Through orbital traceback, we find that 29 stars have trajectories entirely within the Galactic disk, whereas 10are disk-passing yet still trace back to the disk. Two stars have trajectories that intersect those of known clusters. Their orbits show similar morphologies in both the X − Y and R − Z planes, and their [M/H] values are comparable, suggesting possible cluster origins. However, definitive confirmation will require additional evidence. In addition, the V_Sp − v sin i plane shows that runaway stars with low peculiar space velocities but high v sin i remain on the Galactic disk, whereas those with high peculiar space velocities but low v sin ipass through the disk, possibly reflecting two distinct origins.