Evolutionary tracks of the produced sdB stars on the T_eff−log  g diagram. The star has an initial mass of 1 M_⊙ with a metallicity of Z = 0.004 (the dashed lines). The products crowd at the hottest end of EHB for the core mass M_c = 0.453−0.456 M_⊙ (located in the shaded narrow region of the lowest two lines), and spread throughout the canonical sdB region when M_c ≥ 0.466 M_⊙ (from bottom to top, M_c = 0.466,0.468,0.470, and 0.472 M_⊙). The solid lines show the results of Z = 0.02 for the star with the same initial mass. The age difference between adjacent crosses is 10⁷ yr. SdBs with short orbital periods from Maxted et al. (2001) and Kupfer et al. (2015) are presented in the figure for comparison. The grey lines are the tracks during helium flashes before stable He-core burning.