CCD WASHINGTON PHOTOMETRY OF GALACTIC OPEN CLUSTERS: THE MODERATELY METAL-POOR CLUSTER NGC2236

J.J. CLARIÁ; A.E. PIATTI; M.C. PARISI; A.V. AHUMADA

Isla Margarita - Venezuela

Congreso; XII IAU Regional Latin American Meeting of Astronomy; 2007

We present CCD Washington CT1 photometry for 162 stars in the field of the rich open cluster NGC2236. These data were supplemented with photoelectric CMT1T2 photometry of 13 red giant candidates. The comparison of the cluster (T1,C-T1) colour-magnitude diagram with theoretical isochrones computed for the Washington system yields E(C-T1) = 1.10 ± 0.10, equivalent to E(B-V) = 0.55 ± 0.05, and T1 - MT1 = 13.45 ± 0.25 for log t = 8.80 and Z = 0.008. NGC2236 is then located at 2.5 ± 0.5 kpc from the Sun beyond the erseus 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 independentWashington 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 NGC2236. Berkeley 27 appears as the farthest and oldest cluster of the studied sample (Clariá et al. 2007, MNRAS, 379, 159).