A Radial Velocity Survey of the Cyg OB2 Association

We conducted a radial velocity survey of the Cygnus OB2 Association over a 6year (1999 - 2005) time interval to search for massive close binaries. Duringthis time we obtained 1139 spectra on 146 OB stars to measure mean systemicradial velocities and radial velocity variations. We spectroscopically identify73 new OB stars for the first time, the majority of which are likely to beAssociation members. Spectroscopic evidence is also presented for a B3Iaeclassification and temperature class variation (B3 - B8) on the order of 1 yearfor Cygnus OB2 No. 12. Calculations of the intial mass function with thecurrent spectroscopic sample yield Gamma = -2.2 +/- 0.1. Of the 120 stars withthe most reliable data, 36 are probable and 9 are possible single-linedspectroscopic binaries. We also identify 3 new and 8 candidate double-linedspectroscopic binaries. These data imply a lower limit on the massive binaryfraction of 30% - 42%. The calculated velocity dispersion for Cygnus OB2 is2.44 +/- km/s, which is typical of open clusters. No runaway OB stars werefound.Comment: 56 pages, 23 figures, 5 tables, accepted for publication in the Astrophysical Journa