  Stellar photometry derived from the INT/WFC Photometric H$\alpha$ Survey of
the Northern Galactic Plane (IPHAS) can be used to identify large, reliable
samples of A0-A5 dwarfs. For every A star, so identified, it is also possible
to derive individual reddening and distance estimates, under the assumption
that most selected objects are on or near the main sequence, at a mean absolute
r' magnitude of 1.5 -- 1.6. This study presents the method for obtaining such
samples and shows that the known reddenings and distances to the open clusters
NGC 7510 and NGC 7790 are successfully recovered. A sample of over 1000 A stars
is then obtained from IPHAS data in the magnitude range 13.5 < r' < 20 from the
region of sky including the massive northern OB association Cyg OB2. Analysis
of these data reveals a concentration of ~200 A stars over an area about a
degree across, offset mainly to the south of the known 1--3 Myr old OB stars in
Cyg OB2: their dereddened r' magnitudes fall in the range 11.8 to 12.5. These
are consistent with a ~7 Myr old stellar population at DM = 10.8, or with an
age of ~5 Myr at DM = 11.2. The number of A stars found in this clustering
alone is consistent with a lower limit to the cluster mass of ~10000 M-sun.
