Author:

Abstract:

The detected variety in chemistry and circumstellar shell morphology of the limited sample of Galactic post-AGB stars is so large that there is no consensus yet on how the different objects are linked by evolutionary channels. An extra complication comes from the fact that the distance, and hence luminosity and initial mass, is badly determined. Thanks to recent infrared surveys, these Galactic limitations can be overcome by studying the post-AGB population in other galaxies where the distance can be assumed to be similar for all objects. In this thesis, we focus on the LMC. We discuss our selection process to develop a catalogue of 1407 candidate, optically bright post-AGB stars in the LMC. The objects in the catalogue were selected by cross-correlating the IR Spitzer SAGE catalogue with optical catalogues, and only retaining those objects that have far-IR colours indicative of circumstellar dust and a luminosity in the range predicted for post-AGB stars. Based on low-resolution, optical spectra, we selected a subcatalogue of about 70 high probability, post-AGB candidates with spectral types conform with their post-AGB status. Additionally, we observed a subsample of twelve spectroscopically confirmed post-AGB stars at high resolution with UVES at the VLT (ESO), and performed an abundance analysis for four of these. All objects were C-rich, and enhanced in s-process elements, which confirmed their post third dredge-up status. We confirmed the correlation between the efficiency of the third-dredge up and the neutron exposure that is present in the Galactic sample of post-AGB objects. The non-existence of a correlation between metallicity and neutron irradiation is also further corroborated. This thesis is to be seen as the first step in the systematic construction of a homogeneous and complete list of the optically bright post-AGB stars in the LMC. Because their distance, and therefore luminosity and initial mass, are well constrained, the objects in it form an ideal testbed for the predictions of stellar evolution theory for the final phases of stars of low- and intermediate mass. The ultimate goal of this project is to make significant progress in our understanding of the dredge-up processes and the associated s-process nucleosynthesis, and to better comprehend the evolution of binary post-AGB stars.