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We present multi--epoch VLBA observations of the compact wind collisionregion in the Cyg OB2 #5 system. These observation confirm the arc-shapedmorphology of the emission reported earlier. The total flux as a function oftime is roughly constant when the source is "on", but falls below the detectionlimit as the wind collision region approaches periastron in its orbit aroundthe contact binary at the center of the system. In addition, at one of the "on"epochs, the flux drops to about a fifth of its average value. We suggest thatthis apparent variation could result from the inhomogeneity of the wind thathides part of the flux rather than from an intrinsic variation. We measured atrigonometrical parallax, for the most compact radio emission of 0.61 $\pm$0.22 mas, corresponding to a distance of 1.65 $^{+0.96}_{-0.44}$ kpc, inagreement with recent trigonometrical parallaxes measured for objects in theCygnus X complex. Using constraints on the total mass of the system and orbitalparameters previously reported in the literature, we obtain two independentindirect measurements of the distance to the Cyg OB2 #5 system, both consistentwith 1.3--1.4 kpc. Finally, we suggest that the companion star responsible forthe wind interaction, yet undetected, is of spectral type between B0.5 to O8.

Multi-Epoch VLBA Observations of the Compact Wind-Collision Region in the Quadruple System Cyg OB2 #5