Effective temperature, rotational velocity, and surface helium abundance of our stripped core helium burning models at time of minimum radius (only systems with an initial donor mass below 10 M_⊙ are shown). The values measured for the sdOB stars in the known sdOB+Be stars (references in Table 3) are also shown. The rotational velocity of QY Gem (102 ± 4 km s⁻¹, green) lies beyond the figure’s limit.