We present the results of an adaptive optics survey for faint companions among Galactic O-type star systems (with V 8) using the Advanced Electro-Optical System (AEOS) 3.6 m telescope on Haleakala. We surveyed these O-star systems in the I-band, typically being able to detect a companion with a magnitude difference of ?mI 6 in the projected separation range 05 ρ 10, and ?mI 9.5 in the range 10 ρ 50. In the course of the survey, we discovered 40 new companions among 31 of the 116 objects examined and made astrometric and differential magnitude measurements of 24 additional known pairs, several of them being confirmation detections. We present new astrometric orbits for two binaries, BU 1032AB (WDS 05387–0236; σ Ori AB) and SEE 322 (WDS 17158–3344; HD 155889AB). We lack magnitude differences for other filter bands, so it is difficult to determine physical from line-of-sight companions, but we present empirical arguments for the limiting magnitude difference where field contamination is significant.
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