Study of color-magnitude diagram of star cluster SL 506

We report a study of the color-magnitude diagram (CMD) of globular cluster SL 506, which shows extended main sequence turn-off (eMSTO). The CMD is derived from deep F450W (B) and F555W (V) images of Hubble Space Telescope/Wide Field Planetary Camera 2 (HST/WFPC2). We reproduce the CMD via simple stellar population including the combination of rotational stars and binaries, and composite stellar population of non-rotating single stars. We derive the parameters of the star cluster, including age, age spread, metallicity, color excess, distance modulus, binary fraction, and rotating star fraction, by comparing the observed and synthetic CMDs. The results show that the eMSTO region of the cluster can be reproduced by both age spread and a combination of rotating and binary stars, but the blue stragglers, color and magnitude distributions can not be reproduced well by age spread. This implies that SL 506 is a simple population with rotating, single and binary stars.