A spectroscopic survey on the multiplicity of high-mass stars
  The formation of stars above about twenty solar masses and their apparently high multiplicity remain heavily debated subjects in astrophysics. We have performed a vast high-resolution radial velocity spectroscopic survey of about 250 O- and 540 B-type stars in the southern Milky Way which indicates that the majority of stars (> 82%) with masses above 16 solar masses form close binary systems while this fraction rapidly drops to 20% for stars of 3 solar masses. The binary fractions of O- type stars among different environment classes are: clusters (72 \pm 13%), associations (73 \pm 8%), field (43 \pm 13%), and runaways (69 \pm 11%). The high frequency of close pairs with components of similar mass argues in favour of a multiplicity originating from the formation process rather than from a tidal capture in a dense cluster. The high binary frequency of runaway O stars that we found in our survey (69% compared to 19-26% in previous surveys) points to the importance of ejection from young star clusters and thus supports the competitive accretion scenario. 
R. Chini, V.H. Hoffmeister, A. Nasseri, O. Stahl, and H. Zinnecker
astro-ph.SR