Abstract
We present CCD Washington CT_1 photometry for 1162 stars in the field of the rich open cluster NGC 2236. These data were supplemented with photoelectric CMT_1T_2 photometry of 13 red giant candidates. The comparison of the cluster (T[1],C-T[1]) colour-magnitude diagram with theoretical isochrones computed for the Washington system yields E(C-T_1) = 1.10+/-0.10, equivalent to E(B - V) = 0.55+/-0.05, and T_1-M_{T_1} = 13.45+/-0.25 for log t=8.80 and Z=0.008. NGC 2236 is then located at 2.5+/-0.5 kpc from the Sun beyond the Perseus spiral arm. A cluster core radius of 1.2 pc and an annular corona of 2.2 pc were derived from the stellar density radial profile. A metal abundance [Fe/H] = -0.3+/-0.2 was estimated from 5 independent Washington abundance indices, which is not only in reasonably good agreement with the one obtained from the isochrone fit, but also compatible with the existence of a radial abundance gradient in the Galactic disc. We examined the properties of a sample of 20 known open clusters aligned along the line-of-sight to NGC 2236. Berkeley 27 appears as the farthest and oldest cluster of the studied sample (Clariá et al. 2007, MNRAS, 379, 159).
