An observational study of rotation and binarity of Galactic O-type runaway stars

¹ Departament de Física Quàntica i Astrofísica (FQA), Universitat de Barcelona (UB), c. Martí i Franquès 1 08028 Barcelona, Spain
² Institut de Ciències del Cosmos (ICCUB), Universitat de Barcelona (UB), c. Martí i Franquès 1 08028 Barcelona, Spain
³ Institut d’Estudis Espacials de Catalunya (IEEC), Edifici RDIT, Campus UPC 08860 Castelldefels (Barcelona), Spain
⁴ Instituto de Astrofísica de Canarias, c/Vía Láctea S/N 38205 La Laguna Tenerife, Spain
⁵ Departamento de Astrofísica, Universidad de La Laguna 38206 La Laguna Tenerife, Spain

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

Received: 29 July 2025
Accepted: 23 October 2025

Abstract

Context.Gaia Data Release 3 (DR3) has revealed new massive runaway stars and large spectroscopic surveys have now enable detailed characterization studies. However, the relative contributions of binary supernova (BSS) and dynamical ejection (DES) scenarios to explain their runaway origin remain poorly constrained, particularly in the Milky Way.

Aims. We aim to characterize the largest sample of Galactic O-type runaway stars ever investigated through their kinematics, rotation, and binarity with the ultimate objective of shedding light on their potential runaway origins.

Methods. We used the GOSC-Gaia DR3 catalog of normal and runaway stars, along with IACOB spectroscopic information to build a sample with 214 O-type stars with information on the projected rotational velocities (v sin i). We also built a subsample of 168 O-type stars with additional information about their likely single (LS) or single-lined (SB1) spectroscopic binary nature. We also considered an additional sample of 65 double-lined (SB2) spectroscopic binaries.

Results. We find that among our sample of Galactic O-type runaways, most (74%) have v sin i < 200 km s⁻¹, whereas for normal stars this fraction is slightly higher (82%). There are no fast-moving ($V_{\mathrm{PEC}}^{2\mathrm{D}}>85$ km s⁻¹) runaways that have been shown to be fast rotators (v sin i ≥ 200 km s⁻¹), except for HD 124 979. Runaways exhibit lower SB1 fractions than normal stars, with no runaway SB1 fast-rotating systems; on average, runaways rotate faster than normal stars; and their runaway fraction is higher among fast rotators (44%) versus the slow rotators (34%). This is consistent with BSS dominance for fast rotators. We also found that SB2 systems hardly reach runaway velocities with a low runaway fraction (10%). Runaways with $V_{\mathrm{PEC}}^{2\mathrm{D}}>60$ km s⁻¹ are mostly single and interpreted as DES products, while runaways with $V_{\mathrm{PEC}}^{2\mathrm{D}}>85$ km s⁻¹ are also interpreted as two-step products, with the binary V479 Sct/LS 5039 a likely example. Finally, we found that three of 12 runaway SB1 systems are high-mass X-ray binaries.

Conclusions. Our observational study reveals that Galactic O-type runaways are dominated by slow rotators. The study points to a dominance of BSS among fast-rotating runaways and of DES and the two-step scenario among the high-velocity ones. The observed trends provide valuable constraints on models on the origins of runaway stars.