Predicting Gaia's Parallax Distance to the Cygnus OB2 Association with
  Eclipsing Binaries
  The Cygnus OB2 Association is one of the nearest and largest collections of
massive stars in the Galaxy. Situated at the heart of the "Cygnus X" complex of
star-forming regions and molecular clouds, its distance has proven elusive
owing to the ambiguous nature of kinematic distances along this $\ell\simeq80$
degree sightline and the heavy, patchy extinction. In an effort to refine the
three-dimensional geometry of key Cygnus~X constituents, we have measured
distances to four eclipsing double-lined OB-type spectroscopic binaries that
are probable members of Cyg~OB2. We find distances of $1.33\pm0.17$,
$1.32\pm0.07$, $1.44\pm0.18$, and $1.32\pm0.13$ kpc toward MT91~372, MT91~696,
CPR2002~A36, and Schulte~3 respectively. We adopt a weighted average distance
of 1.33$\pm$0.06~kpc. This agrees well with spectrophotometric estimates for
the Association as a whole and with parallax measurements of protostellar
masers in the surrounding interstellar clouds, thereby linking the ongoing star
formation in these clouds with Cyg~OB2. We also identify Schulte 3C (O9.5V), a
4" visual companion to the 4.75 day binary Schulte~3(A+B), as a previously
unrecognized Association member.
