Thèse de doctorat en Sciences de l'univers
Soutenue en 2005
Low and intermediate mass stars on the main sequence evolves across the AGB phase. The luminous frequently pulsating and heavily mass-lossing AGB stars are enshrouded by dust, displaying high flux in the infrared. Dust shells around AGB stars are known to be spherically symmetric, whereas objects in the subsequent evolutionary stages, for example the planetary nebulae, appear to have axisymmetric geometries. The mechanisms responsible for such mass-loss are not fully understood yet. We have observed a sample of evolved stars in the thermal infrared. These observations which fort some stars of our sample are the first made in this wavelength range, led us to a better understanding of the morphologies of their envelope. A model, based on an inversion technique, has been achieved in order to study quantitatively the dusty envelopes by determining, from mid-infrared observations, some key parameters such as the density and temperature profiles of these envelopes, as well as their mass-loss rates. This method was applied to V~Hya, IRC~+10216 and the Red Rectangle nebula. A detailed study of the young planetary nebula Hen~2-113 was carried out thanks to imaging observations with the VLT. These observations give a new insight on this object, which presents characteristics observed for the first time as, for example, the presence of warm dust close to the central star.
Contribution of infrared observations to the study of mass-loss from evolved stars
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