  Massive, eclipsing, double-lined, spectroscopic binaries are not common but
are necessary to understand the evolution of massive stars as they are the only
direct way to determine stellar masses. They are also the progenitors of
energetic phenomena such as X-ray binaries and gamma-ray bursts. We present a
photometric and spectroscopic analysis of the candidate binary system Cyg
OB2-B17 to show that it is indeed a massive evolved binary. We utilise V band
and white-light photometry to obtain a light curve and period of the system,
and spectra at different resolutions to calculate preliminary orbital
parameters and spectral classes for the components. Our results suggest that
B17 is an eclipsing, double-lined, spectroscopic binary with a period of
4.0217+/-0.0004 days, with two massive evolved components with preliminary
classifications of O7 and O9 supergiants. The radial velocity and light curves
are consistent with a massive binary containing components with similar
luminosities, and in turn with the preliminary spectral types and age of the
association.
