OB runaway stars originating in the Vel OB1 association

¹ Byurakan Astrophysical Observatory, 0213, Aragatsotn prov., Armenia
² Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands

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

Received: 18 January 2026
Accepted: 7 April 2026

Abstract

Context. OB runaway stars are massive stars moving through interstellar space with a high velocity (up to 200 km s⁻¹). They are produced by dynamical ejections in young massive clusters or by supernova explosions in massive binaries. OB runaways can travel several hundred parsec before exploding as supernovae, affecting the dynamical and chemical evolution of the Galaxy.

Aims. The VelOB1 association is one of the largest OB associations, hosting about 20 O-type and more than 50 B-type stars. Our aim is to find OB runaway stars in this region. By quantifying their number and identifying their parent clusters, we seek to better understand their production channels and their impact on the surrounding medium.

Methods. We used Gaia DR3 coordinates, parallaxes, and proper motions of massive stars in the field centred on Vel OB1 to identify OB runaways by measuring their peculiar velocity. Under suitable physical conditions, OB runaways create observable bow shocks in the interstellar medium (ISM). We inspected infrared WISE images to identify wind bow shocks and their associated OB runaways. By reconstructing their path, we tried to locate their parent cluster and estimate their travel times.

Results. We identified six young stellar clusters hosting most of the massive-star population in Vel OB1 (distance 1.6–2.1 kpc; age 1–10 Myr). From the tangential velocity distribution of the members, we derived a threshold velocity of 15 km s⁻¹ to classify a star as a runaway. We identified 25 OB runaways (including the high-mass X-ray binary Vela X-1) and one F-type runaway. We detected 16 arc-like features, four for the first time, and six of the features are associated with OB runaways selected by peculiar velocity. Ten bow shocks are aligned with the proper motion of the runaways. Parent clusters are identified for seven runaways. Most likely, the majority of these runaways are produced by dynamical ejection.

Conclusions. The runaway fraction of the young stellar population in Vel OB1 is about 30%. Many OB runaways, even some far above the Galactic plane, produce wind bow shocks, which consequently reveal information on local ISM conditions.