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Paper: What Do We Really Know about Mass Loss on the AGB?
Volume: 378, Why Galaxies Care About AGB Stars: Their Importance as Actors and Probes
Page: 211
Authors: Wilson, L.A.
Abstract: Mass-loss rate formulae are derived from observations or from suites of models. For theoretical models, the following have all been identified as factors greatly influencing the atmospheric structure and mass-loss rates: pulsation with piston amplitude scaling appropriately with stellar L; dust nucleation and growth, with radiation pressure and grain-gas interactions and appropriate dependence on temperature and density; non-grey opacity with at least 51 frequency samples; non-LTE and departures from radiative equilibrium in the compressed and expanding flows; and non-equilibrium processes affecting the composition (grain formation; molecular chemistry). No one set of models yet includes all the factors known to be important. In fact, it is very difficult to construct a model that can simultaneously include these factors and be useful for computing spectra. Therefore, although theoretical model grids are needed to separate the effects of M,L,R and/or Teff or Z on the mass-loss rates, these models must be carefully checked against observations. Getting the right order of magnitude for the mass-loss rate is only the first step in such a comparison, and is not sufficient to determine whether the mass-loss formula is correct. However, there are observables that do test the validity of mass-loss formulae as they depend directly on d log (dM/dt) /d log L, d log (dM/dt) /d log R, or d log (dM/dt) /d log P.
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