Massive runaway stars in the Small Magellanic Cloud

TL;DR

This study used Spitzer data to identify and analyze a dozen runaway OB stars in the Small Magellanic Cloud via their bow shocks, revealing their origins, motions, and interactions with the interstellar medium.

Contribution

First detection of runaway OB stars in the SMC through bow shocks, providing insights into their origins and the dynamics of young stellar populations.

Findings

Identified a dozen runaway OB stars in the SMC.

Inferred star motions and possible parent clusters from bow shock geometry.

Discovered a nebula linked to a WN-type star, indicating stellar wind interactions.

Abstract

Using archival Spitzer Space Telescope data, we identified for the first time a dozen runaway OB stars in the Small Magellanic Cloud (SMC) through the detection of their bow shocks. The geometry of detected bow shocks allows us to infer the direction of motion of the associated stars and to determine their possible parent clusters and associations. One of the identified runaway stars, AzV 471, was already known as a high-velocity star on the basis of its high peculiar radial velocity, which is offset by ~40 km/s from the local systemic velocity. We discuss implications of our findings for the problem of the origin of field OB stars. Several of the bow shock-producing stars are found in the confines of associations, suggesting that these may be "alien" stars contributing to the age spread observed for some young stellar systems. We also report the discovery of a kidney-shaped nebula attached to the early WN-type star SMC-WR3 (AzV 60a). We interpreted this nebula as an interstellar structure created owing to the interaction between the stellar wind and the ambient interstellar medium.