Mechanical luminosities of donor-star winds versus 5 keV/1 keV flux ratio assuming adiabatic shocks for the six binary models (cf. Table 2), during core helium burning of the donor star. The colour coding is the same as in Fig. 3. Also plotted (as stars) are observed X-ray luminosities and 5 keV/1 keV flux ratios of γ Cas stars versus their bolometric luminosities, according to Nazé & Motch (2018) (cf. Table 1).