Rapid mass loss from cool giants and supergiants via supersonic stellar winds is considered. It is proposed that when a star evolves to a state in which its wind, driven by hydrodynamic expansion, becomes supersonic at the base of the corona, the rate of mass loss from the star should increase essentially discontinuously by an amount equal to the ratio of gas densities at the top of the chromosphere and the base of the corona. Empirically determined chromospheric gas pressures are combined with the minimum-flux coronal model of Hearn (1975) in order to derive the locus in the H-R diagram along which stellar winds undergo a transition from transonic (fed by purely coronal material) to supersonic (fed by chromospheric material). This locus is found to agree well with the boundary of the domain occupied by circumstellar-shell stars (in which rapid mass loss is known to occur). An estimate of the mass-loss rate under supersonic conditions is made and shown to be consistent with observed rates.
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D. J. Mullan (1978) studied this question.