uvbyCaHbeta CCD Photometry of Clusters. V. The Metal-Deficient Open Cluster NGC 2243

Abstract

CCD photometry on the intermediate-band uvbyCaHbeta system is presented for the metal-deficient open cluster, NGC 2243. Restricting the data to probable single members of the cluster using the CMD and the photometric indices alone generates a sample of 100 stars at the cluster turnoff. The average E(b-y) = 0.039 (0.003 s.e.m.) or E(B-V) = 0.055 (0.004 s.e.m.), where the errors refer to internal errors alone. With this reddening, [Fe/H] is derived from both m_1 and hk, using b-y and Hbeta as the temperature index. The agreement among the four approaches is excellent, leading to a final weighted average of [Fe/H] = -0.57 (0.03 s.e.m.) for the cluster, on a scale where the Hyades has [Fe/H] = +0.12. Using a combination of photometric and spectroscopic data, 27 probable cluster members are identified and used to delineate the red giant branch and a well-defined clump at V = 13.70, while eliminating the so-called second clump at V = 14.1. Interpolation between isochrones of appropriate [Fe/H] leads to an apparent modulus of (m-M) = 13.15 +/- 0.1 and an age of 3.8 +/- 0.2 Gyr. A differential CMD comparison with Berkeley 29, a cluster with a galactocentric distance almost twice that of NGC 2243, constrains Berkeley 29 to be at least as young and as metal-rich as NGC 2243.