The late stages in the evolution of intermediate-mass stars (Asymptotic Giant Branch - AGB and post-AGB) are of the greatest importance for the chemical evolution of galaxies. Pulsations, dust formation, and mass loss through massive stellar winds are characteristic phenomena of AGB stars. Stellar pulsations cause waves, which travel into the outer layers of the atmosphere and develop shocks, compressing matter to such a high density that dust formation occurs and mass loss is triggered. However, the nature of the mass loss is still not well understood. The chemistry of gas and dust lost by AGB stars depends heavily on dredge-up processes that bring the products of stellar nucleosynthesis to the stellar surface. The ejected material, enriched in heavy elements, is later incorporated into new generations of stars and planets.
We propose a comprehensive study of the physical properties of evolved stars, their atmospheres and environments. Radial velocities and brightness variations will be monitored for selected stars and a time series of high resolution spectra in the optical region will be obtained to better understand the dynamical phenomena and abundance transformations in the stellar atmospheres. Comprehensive modeling of photospheric and circumstellar chemistry, radiative transfer in molecular lines, and self-consistent treatment of hydrodynamics and chemistry will be carried out. The unique capabilities of the Herschel Space observatory will be used to probe the inner regions of circumstellar envelopes around evolved stars.
We plan to expand the existing Torun catalogue of Galactic post-AGB and related objects and create a new catalogue for post-AGB objects in the Large Magellanic Cloud. These will facilitate research on unsolved problems of stellar evolution, such as the mechanism that triggers the departure from AGB to post-AGB and post-AGB evolution in environments with different metallicities and will be available to the entire community.
Fields of science
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