HR diagram of the evolution of the sdB progenitor for different values of the initial period. The location of the He ignition is indicated with a red square. Panel A) P = 600 d, the donor star loses too much mass to ignite He and ends up as a cooling white dwarf (M_d = 0.448 M_⊙). Panel B) P = 650 d, a late He flasher (M_d = 0.456 M_⊙). Panel C) P = 750 d, an early He flasher (M_d = 0.466 M_⊙). Panel D) P = 800 d, The core is too massive, and the donor ignites He on the tip of the RGB (M_d = 0.929 M_⊙). See Sect. 6 for discussion.