COMBINED EFFECTS OF BINARIES AND STELLAR ROTATION ON THE COLOR-MAGNITUDE DIAGRAMS OF INTERMEDIATE-AGE STAR CLUSTERS

Abstract

About seventy percent of intermediate-age star clusters in the Large\nMagellanic Clouds have been confirmed to have broad main sequence, multiple or\nextended turn-offs and dual red giant clumps. The observed result seems against\nthe classical idea that such clusters are simple stellar populations. Although\nmany models have been used for explaining the results via factors such as\nprolonged star formation history, metallicity spread, differential redenning,\nselection effect, observational uncertainty, stellar rotation, and binary\ninteraction, the reason for the special color-magnitude diagrams is still\nuncertain. We revisit this question via the combination of stellar rotation and\nbinary effects. As a result, it shows "golf club" color-magnitude diagrams with\nbroad or multiple turn-offs, dual red clump, blue stragglers, red stragglers,\nand extended main sequences. Because both binaries and massive rotators are\ncommon, our result suggests that most color-magnitude diagrams including\nextended turn-off or multiple turn-offs can be explained using simple stellar\npopulations including both binary and stellar rotation effects, or composite\npopulations with two components.\n