Massive binary stars may constitute a substantial fraction of progenitors to supernovae and \gamma -ray bursts , and the distribution of their orbital characteristics holds clues to the formation process of massive stars .
As a contribution to securing statistics on OB-type binaries , we report the discovery and orbital parameters for five new systems as part of the Cygnus OB2 Radial Velocity Survey .
Four of the new systems ( MT070 , MT174 , MT267 , and MT734 \equiv VI Cygni # 11 ) are single-lined spectroscopic binaries while one ( MT103 ) is a double-lined system ( B1V+B2V ) .
MT070 is noteworthy as the longest period system yet measured in Cyg OB2 , with P =6.2 yr .
The other four systems have periods ranging between 4 and 73 days .
MT174 is noteworthy for having a probable mass ratio q < 0.1 , making it a candidate progenitor to a low-mass X-ray binary .
These measurements bring the total number of massive binaries in Cyg OB2 to 25 , the most currently known in any single cluster or association .