Blue Supergiants as Probes of Stellar and Galactic Evolution in the Local Group

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Blue Supergiants are the visually brightest normal stars in star-forming galaxies. The present generation of large telescopes facilitates high-resolution spectroscopy of such objects within the Local Group of galaxies. Analyses of a statistically significant sample of objects in the two metal-rich giant spiral galaxies of the Local Group, the Milky Way and M 31, and in two metal-poor dwarf irregular galaxies, the Small Magellanic Cloud and NGC6822, will be performed. Recent developments in plasmaphysical stellar atmosphere modelling allow us to use blue supergiants as versatile tools for quantitative studies of stellar and galactochemical evolution. Precise stellar parameters and abundance determinations of the light elements will put tight observational constraints on evolution models for massive stars over a wide range of chemical composition. Galactic abundance patterns and gradients for numerous heavier elements will be probed to a far greater extent than possible by classical analyses of H II regions. These will provide a sound observational basis for the study of the cosmic cycle of matter and the chemical evolution of the four galaxies under study. The project will also allow to calibrate and establish blue supergiants as spectroscopic distance indicators on the first step of the cosmic distance ladder.