Oxygen-rich AGB stars with low mass-loss rate observed with Herschel

The work presented in this thesis contributes to our understanding of the wind-driving mechanism and the structure of the circumstellar environment of low mass-loss rate oxygen-rich AGB stars. We find that amorphous Al2O3 is likely present in large quantities in the extended atmospheres of these objects. This suggests that this is one of the first dust species to form, as expected from theoretical calculations. Their presence in a gravitationally bound shell suggests that by themselves they are insufficient to start the wind. The results obtained are consistent with translucent silicates driving the wind via scattering and we find ample evidence that translucent silicon-bearing species indeed exist in the circumstellar environment of these stars. The condensation of calcium, magnesium, and iron can also have an important impact on the dynamics of the wind, but that was not thoroughly explored by us. Particularly, the slow wind acceleration and the large inner radius for silicate emission of WHya might be an indication that the picture is still more complex, with the condensation of more opaque material and extra injection of momentum in the wind at larger distances from the star.