A follow-up study of the colliding wind binary Cyg OB2 8a

We propose to observe the colliding wind binary Cyg OB2 #8a (O6If + O5.5III(f))for 3 x 20 ksec near specific orbital phases. Previous XMMNewton observationsrevealed a modulation of the Xray flux of this system. At the same time, theradio emission of Cyg OB2 #8a also undergoes a phaselocked variation. The jointanalysis of the variations in the Xray and radio domains will provideunprecedented information on the interplay between colliding wind interactionsand the acceleration of relativistic particles that produce the nonthermalradio emission. The Cyg OB2 cluster further harbours a number of earlytypestars (two of them are nonthermal radio emitters) that are bright Xraysources, as well as a wealth of secondary sources (most of them being lowmass PMS stars). truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]