2025ApJ...988..183P

Stellar bow shock nebulae are arcuate shock fronts formed by the interaction of radiation-driven stellar winds and the relative motion of the ambient interstellar material. Stellar bow shock nebulae provide a promising means to measure wind-driven mass loss, independent of other established methods. In this work, we characterize the stellar sources at the center of bow shock nebulae drawn from all-sky catalogs of 24 μm-selected nebulae. We obtain new, low-resolution blue optical spectra for 104 stars and measure stellar parameters temperature T_eff, surface gravity ${\mathrm{log}}\,g$, and projected rotational broadening $v\sin i$. We perform additional photometric analysis to measure stellar radius R_*, luminosity L_*, and visual-band extinction A_V. All but one of our targets are O and early B stars, with temperatures ranging from T = 16.5 to 46.8 kK, gravities from ${\mathrm{log}}\,g=$2.57 to 4.60, and $v\sin i$ from <100 to 400 km s^–1. With the exception of rapid rotator ζ Oph, bow shock stars do not rotate at or near critical velocities. At least 60 of 103 (60%) OB bow shock stars are binaries, consistent with the multiplicity fraction of other OB samples. The sample shows a runaway fraction of 23%, with 19 stars having v_2D ≥ 25 km s^–1. Of the 19 runaways, at least 15 (≥79%) are binaries, favoring dynamical ejection over the binary supernova channel for producing runaways. We provide a comprehensive census of stellar parameters for bow shock stars, useful as a foundation for determining the mass-loss rates for OB-type stars-one of the single most critical factors in stellar evolution governing the production of neutron stars and black holes.