Current knowledge suggests that the dust-driven wind scenario provides arealistic framework for understanding mass loss from C-rich AGB stars. ForM-type objects, however, recent detailed models demonstrate that radiationpressure on silicate grains is not sufficient to drive the observed winds,contrary to previous expectations. In this paper, we suggest an alternativemechanism for the mass-loss of M-type AGB stars, involving the formation ofboth carbon and silicate grains due to non-equilibrium effects, and we studythe viability of this scenario. We model the dynamical atmospheres and winds ofAGB stars by solving the coupled system of frequency-dependent radiationhydrodynamics and time-dependent dust formation, using a parameterizeddescription of non-equilibrium effects in the gas phase. This approach allowsus to assess under which circumstances it is possible to drive winds with smallamounts of carbon dust and to get silicate grains forming in these outflows atthe same time. The properties of the resulting wind models, such as mass lossrates and outflow velocities, are well within the observed limits for M-typeAGB stars. Furthermore, according to our results, it is quite unlikely thatsignificant amounts of silicate grains will condense in a wind driven by aforce totally unrelated to dust formation, as the conditions in the upperatmosphere and wind acceleration region put strong constraints on grain growth.The proposed scenario provides a natural explanation for the observedsimilarities in wind properties of M-type and C-type AGB stars and implies asmooth transition for stars with increasing carbon abundance, fromsolar-composition to C-rich AGB stars, possibly solving the long-standingproblem of the driving mechanism for stars with C/O close to one.
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