A search for binaries and stellar winds among the O-type stars

Eighteen bright O-type stars were studied for the purpose of discovering low-amplitude (less than 30 km/sec) binary systems. The data suggest that only two of the 18 might be binaries (Alpha Cam and Zeta Ori), while five stars thought by Conti, Leep, and Lorre (1977) to be probable binaries are found to have constant velocities. A velocity gradient in the Balmer lines is observed in most O-type supergiants and Of stars but the gradient is found to be statistically significant in only three of six late O-type giants and main-sequence stars. The presence of photospheric mass motion complicates the search for spectroscopic binary systems. The possibility is considered that the lack of low-amplitude binaries represents a real absence of binary systems with unequal masses among the O-type stars.