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Certain RS CVn binaries show ‘mass inversion’ (i. e. the more evolved star being the less massive) before Roche lobe overflow (RLOF) has taken place. We find that the mass loss rates of ordinary giants are too small by a large factor to produce the observed masses of Z Her, the best example of this phenomenon. We postulate that the originally less massive secondary has tidally enhanced the rate of mass loss by stellar wind from the primary and investigate a simple model of this enhancement over a wide range of initial mass ratios and periods. We find that the period/mass ratio space divides into three regions: (i) no Roche lobe overflow occurs before a white dwarf is produced leading to systems like FF Aqr and AY Cet; (ii) RLOF occurs after the mass ratio q has been reduced from |q₀ 1| to |q0. 7| after which slow (nuclear time-scale) mass transfer takes place allowing Algols to be formed from late Case B systems without drastic mass transfer; (iii) RLOF occurs while |q0. 7| resulting in rapid (hydrodynamic time-scale) mass transfer probably leading to common envelope evolution and possibly to coalescence.
Tout et al. (Fri,) studied this question.