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A Radial Velocity Survey of the Cyg OB2 Association
We conducted a radial velocity survey of the Cyg OB2 association over a6 yr (1999-2005) time interval to search for massive close binaries.During this time we obtained 1139 spectra on 146 OB stars to measuremean systemic radial velocities and radial velocity variations. Wespectroscopically identify 73 new OB stars for the first time, themajority of which are likely to be association members. Spectroscopicevidence is also presented for a B3 Iae classification and temperatureclass variation (B3-B8) on the order of 1 yr for Cyg OB2 No. 12.Calculations of the initial mass function with the current spectroscopicsample yield Γ=-2.2+/-0.1. Of the 120 stars with the most reliabledata, 36 are probable and 9 are possible single-lined spectroscopicbinaries. We also identify three new and eight candidate double-linedspectroscopic binaries. These data imply a lower limit on the massivebinary fraction of 30%-42%. The calculated velocity dispersion for CygOB2 is 2.44+/-0.07 km s-1, which is typical of open clusters.No runaway OB stars were found.
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