WFPC2 Observations of Star Clusters in the Magellanic Clouds. II. The Oldest Star Clusters in the Small Magellanic Cloud

摘要

We present our analysis of archival Hubble Space Telescope Wide FieldPlanetary Camera 2 (WFPC2) observations in F450W (~B) and F555W (~V) of theintermediate- age populous star clusters NGC 121, NGC 339, NGC 361, NGC 416,and Kron 3 in the Small Magellanic Cloud. We use published photometry of twoother SMC populous star clusters, Lindsay 1 and Lindsay 113, to investigate theage sequence of these seven populous star clusters in order to improve ourunderstanding of the formation chronology of the SMC. We analyzed the V vs(B-V) and M_V vs (B-V)_0 color-magnitude diagrams of these populous SmallMagellanic Cloud star clusters using a variety of techniques and determinedtheir ages, metallicities, and reddenings. These new data enable us to improvethe age-metallicity relation of star clusters in the Small Magellanic Cloud. Inparticular, we find that a closed-box continuous star-formation model does notreproduce the age-metallicity relation adequately. However, a theoretical modelpunctuated by bursts of star formation is in better agreement with theobservational data presented herein.