NGC 2204 - OLD OPEN CLUSTER IN HALO

Photographie BV and photoelectric UBV photometry of stars in the open cluster NGC 2204 is presented. The cluster has a long giant branch reaching (B-V)0 ∼ Im·8 which probably includes a red variable of substantial ampli-tude. The giants appear to have a range in colour reminiscent of their counter- parts in NGC 188. There is a prominent giant clump at V = I3m·82 and the upper main sequence has a gap about Om·4 below its brightest point. Several blue stragglers are present, strongly concentrated towards the cluster centre. The reddening E(B-V) = Om·08 and an ultraviolet excess (U-B)0.6 = Om·095 ± Om·024 are derived from the two-colour diagram of probable cluster members. The cluster appears to be distinctly poor in heavy elements. The turn-off colour indicates an age of about 3 × 109 yr and the adopted distance modulus, (m-M)0 = 13m·25 ±Om·2 (estimated uncertainty) implies that the cluster lies about 1250 pc from the galactic plane, an exceptional distance for a Population I system. © 1976 Royal Astronomical Society. Provided by the NASA Astrophysics Data System.