SIMBAD references

We have obtained CCD photometry in the Johnson V, Kron-Cousins I and CT₁ Washington systems for NGC 2324, a rich open cluster located ∼35° from the Galactic anticentre direction. We measured V magnitudes and V-I colours for 2865 stars and T₁ magnitudes and C-T₁ colours for 1815 stars in an area of 13.6'x13.6'. The comparison of the cluster colour-magnitude diagrams with isochrones of the Geneva group yield E(V-I)=0.33±0.07 and V-M_V=13.70±0.15 for logt=8.65 (t=440Myr) and Z=0.008 ([Fe/H]=-0.40), and E(C-T₁)=0.40±0.10 and T₁-M_T1=13.65±0.15 for the same age and metallicity level. The resulting E(V-I) reddening value implies E(B-V)=0.25±0.05 and a distance from the Sun of (3.8±0.5)kpc. Star counts carried out within and outside the cluster region allowed us to estimate the cluster angular radius as 5.3'±0.3' (5.9pc). When using the E(B-V) reddening value here derived and the original Washington photometric data of Geisler et al. (1991AJ....102.1836G) for the stars confirmed as red cluster giants from Coravel radial velocities, we found [Fe/H]=-0.31±0.04, which is in good agreement with the best fits of isochrones. Therefore, NGC 2324 is found to be a relatively young, metal-poor and distant open cluster located beyond the Perseus spiral arm. A comparison of NGC 2324 with 10 well-known open clusters of nearly the same age shows that the cluster metal abundance and its position in the Galaxy are consistent with the existence of a radial abundance gradient of -0.07dex/kpc in the Galactic disc.