Title:Multiplicity of spectroscopic binaries among massive stars: origin and implications for merger rates

Abstract:
A very high fraction of massive OB stars live in tight binary systems with orbital periods less than a week. 
The origin of these short-period systems will be discussed, as well as their fate during stellar evolution. In 
particular, very close binaries  among the most massive stars can lead to stellar mergers, which in turn 
could give rise to the rapidly rotating progenitors of long-duration gamma-ray-bursts.