Multi-Epoch VLBA Observations of the Compact Wind-Collision Region in
  the Quadruple System Cyg OB2 #5
  We present multi--epoch VLBA observations of the compact wind collision
region in the Cyg OB2 #5 system. These observation confirm the arc-shaped
morphology of the emission reported earlier. The total flux as a function of
time is roughly constant when the source is "on", but falls below the detection
limit as the wind collision region approaches periastron in its orbit around
the 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 that
this apparent variation could result from the inhomogeneity of the wind that
hides part of the flux rather than from an intrinsic variation. We measured a
trigonometrical 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, in
agreement with recent trigonometrical parallaxes measured for objects in the
Cygnus X complex. Using constraints on the total mass of the system and orbital
parameters previously reported in the literature, we obtain two independent
indirect measurements of the distance to the Cyg OB2 #5 system, both consistent
with 1.3--1.4 kpc. Finally, we suggest that the companion star responsible for
the wind interaction, yet undetected, is of spectral type between B0.5 to O8.
