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The History and Evolution of the Milky Way

Means, Methods and Projects

The solar spectrum

In several projects we trace the evolution of the stellar content (through the star formation history and the build-up of chemical elements) in our Milky Way galaxy by combining knowledge of chemical composition, ages and kinematic properties of individual stars. For this we perform accurate and consistent determinations of abundances of chemical elements in stars.

This is achieved by making spectroscopic observations of high quality with high S/N and high spectral resolution using ground-based and space-telescope observations. It is important to match these observations with high quality analysis. We use methods of accurate analysis of stellar spectra, based on locally developed detailed physical modelling of stellar atmospheres. From the models we compute synthetic spectra which are directly compared to the observed ones. If e.g. the oxygen lines are too weak in the synthetic spectrum, we add more oxygen until the observations are fitted. We can obtain accuracies of between 10% and 25% in such studies.

Recently I attended the 4th Russbach workshop on Nuclear Astrophysics to learn more about the nucleosynthesis of chemical elements, and also to give a presentation of the methods and uncertainties used in the analysis of stellar spectra and abundance determinations. A commented pdf version of my presentation can be found here.

Our large study of 189 galactic-disk stars, Edvardsson et al. (1993, A&A 275, 101-152) traced the build-up of the abundancesof 13 chemical elements with time and position in the galactic disk, and suggested possible interpretations in terms of the history of the galactic disk. The paper has since become a standard reference for studies of the galactic disk, and is even being used for the interpretation of abundances in objects at cosmological distances.

The findings of this study have motivated a number of deeper studies in different directions, such as the properties of the most metal rich disk stars, the build-up of carbon, nitrogen and r-process elements, and studies of the galactic halo.

Some of my projects are described here if you click on the links to the left

A rectified piece of cool-star spectrum

Latest update: March 15, 2007