Hertzsprung–Russell diagram of models with helium cores and various hydrogen profiles displayed. The slope of the hydrogen profile has a value d X∕d Q= 2.3 (which is the typical value we infer for the SMC WR stars in binaries) for all models. The surface hydrogen mass fraction X_s is indicated by the colors of the dashed lines. Green diamonds indicate observed values for binary SMC WR stars, blue circles indicate apparently singles stars. The arrows point to models with the same log L and X_s as the observed objects. The peculiar SMC AB6 is displayed with a smaller symbol and arrow.