Departament d'Astronomia i Astrofísica
Universitat de València

    Infrared spectro-interferometry of AGB stars

Markus Wittkowski

European Southern Observatory, Garching bei M√ľnchen, Alemanya

Seminari del departament d'Astronomia i Astrofísica

Dimecres 23 novembre 2011



Mass loss from asymptotic giant branch (AGB) stars is the most important driver for the evolution of evolved low to intermediate mass stars toward planetary nebulae. It is also one of the most important sources of the chemical enrichment of the interstellar medium. The mass-loss process originates in the extended atmospheres, whose structure is affected by stellar pulsations, and where molecular and dusty layers are formed. Optical interferometry resolves the extended atmospheres of AGB stars and thereby enables us to obtain measurements of the intensity profile across this region. I will present recent near- and mid-infrared spectro-interferometric observations of AGB stars. These observations indicate a stellar intensity profile consistent with predictions of the latest dynamic model atmospheres based on self-excited pulsation models, and allow us to characterize the inner circumstellar dust shell. The AMBER data also show non-zero closure phases, which are indicative of deviations from point symmetry at all wavelengths, thus a complex non-spherical stratification of the extended atmosphere. We interpret these inhomogeneities as the result of pulsation- and shock-induced chaotic motion in the extended atmosphere. During this talk I will also describe the current status of the ESO VLT Interferometer and future plans.