2022AJ....164...86K

OB stars powering stellar bowshock nebulae (SBNe) have been presumed to have large peculiar velocities. We measured peculiar velocities of SBN central stars to assess their kinematics relative to the general O-star population using Gaia EDR3 data for 267 SBN central stars and a sample of 455 Galactic O stars to derive projected velocities v_2D. For a subset of each sample, we obtained new optical spectroscopy to measure radial velocities and identify multiple-star systems. We find a minimum multiplicity fraction of 36% ± 6% among SBN central stars, consistent with >28% among runaway Galactic O stars. The large multiplicity fraction among runaways implicates very efficient dynamical ejection rather than binary-supernova origins. The median v_2D of SBN central stars is v_2D = 14.6 km s^–1, larger than the median v_2D = 11.4 km s^–1 for non-bowshock O stars. Central stars of SBNe have a runaway (v_2D > 25 km s^–1) fraction of 24${}_{-7}^{+9}$%, consistent with the ${22}_{-3}^{+3}$% for control-sample O stars. Most (76%) SBNe central stars are not runaways. Our analysis of alignment (Δ_PA) between the nebular morphological and v_2D kinematic position angles reveals two populations: a highly aligned (σ_PA = 25°) population that includes stars with the largest v_2D (31% of the sample) and a random (nonaligned) population (69%). SBNe that lie within or near H II regions comprise a larger fraction of this latter component than SBNe in isolated environments, implicating localized ISM flows as a factor shaping their orientations and morphologies. We outline a new conceptual approach to computing the solar local standard of rest motion, yielding [U_⊙, V_⊙, W_⊙] = [5.5, 7.5,4.5] km s^–1.