CCD photometry of the northern open star cluster NGC 7790 has been carried
out in BVI photometric passbands down to V similar to 21 mag for 1150 stars
of which for similar to 700 stars, the data is obtained for the first time
. We derive the most reliable parameters for this cluster using all the ava
ilable photometric, spectroscopic and proper motion data. The interstellar
extinction over the cluster area is uniform and normal with E(B - V) = 0.51
+/- 0.03 mag. We determine a distance of 3.3 +/- 0.23 Kpc to the cluster.
The theoretical isochrone fittings to the Cepheid variables as well as the
evolved part of the main-sequence near turn-off point indicate that the clu
ster is 120 +/- 20 Myr old. We estimate the cluster radius to be 3.'7 using
radial stellar density profile. Both the distance and age determined using
period luminosity/age relations fog the Cepheid var variables are consiste
nt with their membership of the cluster. This unique opportunity has theref
ore been used to refine the zero-point of the period-luminosity relation fo
r the Galactic Cepheids.