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The material lost through stellar winds of Asymptotic Giant Branch (AGB)stars is one of the main contributors to the chemical enrichment of galaxies.The general hypothesis of the mass loss mechanism of AGB winds is a combinationof stellar pulsations and radiative pressure on dust grains, yet current modelsstill suffer from limitations. Among others, they assume chemical equilibriumof the gas, which may not be justified due to rapid local dynamical changes inthe wind. This is important as it is the chemical composition that regulatesthe thermal structure of the wind, the creation of dust grains in the wind, andultimately the mass loss by the wind. Using a self-consistent hydrochemicalmodel, we investigated how non-equilibrium chemistry affects the dynamics ofthe wind. This paper compares a hydrodynamical and a hydrochemical dust-freewind, with focus on the chemical heating and cooling processes. No sustainablewind arises in a purely hydrodynamical model with physically reasonablepulsations. Moreover, temperatures are too high for dust formation to happen,rendering radiative pressure on grains impossible. A hydrochemical wind is evenharder to initiate due to efficient chemical cooling. However, temperatures aresufficiently low in dense regions for dust formation to take place. Theseregions occur close to the star, which is needed for radiation pressure on dustto sufficiently aid in creating a wind. Extending this model self-consistentlywith dust formation and evolution, and including radiation pressure, will helpto understand the mass loss by AGB winds.

Developing a self-consistent AGB wind model: I. Chemical, thermal, and dynamical coupling