The Main-Sequence Turnoff of the Populous SMC Cluster Lindsay 1

A deep B, V color-magnitude diagram of the SMC cluster Lindsay 1 is derived from CTIO PFCCD frames. The main-sequence turnoff, giant and subgiant branches, and a stubby red horizontal branch or clump are all evident and well populated. The authors derive an age of 10 - 12 Gyr, consistent with the age estimate from carbon stars. They also include corrections for the proposed tilt of the SMC, which may place L1 0.3 mag more distant than the SMC center, and which yields a best fit with a 10 Gyr isochrone. The magnitude difference between the turnoff and clump giants, ΔV = 3.1, is consistent with these age estimates and shows L1 to be the second oldest SMC cluster, significantly younger than galactic globulars. The authors compare these results with those obtained from other SMC clusters and also discuss the fit to other CMDs, the dependence of the magnitude of the clump stars with age, and the probable absence of RR Lyraes in L1.