The relatively young, metal-poor and distant open cluster NGC 2324

PIATTI, ANDRÉS E.; CLARIA OLMEDO, JUAN JOSÉ; AHUMADA, A.V.

ASTRONOMY AND ASTROPHYSICS

Año: 2004 vol. 418 p. 979 - 988

0004-6361

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 arcmin × 13.6 arcmin. The comparison of the cluster colour-magnitude diagrams with isochrones of the Geneva group yield E(V-I) = 0.33 ± 0.07 and V-MV = 13.70 ± 0.15 for log t = 8.65 (t = 440 Myr) and Z = 0.008 ([Fe/H] = -0.40), and E(C-T1) = 0.40 ± 0.10 and T1-MT1 = 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 arcmin ± 0.3 arcmin (5.9 pc). When using the E(B-V) reddening value here derived and the original Washington photometric data of \citet{gcm91} 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 -0.07 dex kpc-1 in the Galactic disc.