A Lifetime of Influence: Abstracts, Talks, and Posters
 

Massive Stars as Tracers of Galactochemical Evolution

Norbert Przybilla
Dr. Remeis Observatory Bamberg

M. Fernanda Nieva
Max-Planck-Institute for Astrophysics

Markus Firnstein
Dr. Remeis Observatory Bamberg

Hot, massive stars are key drivers of the cosmic cycle of matter. As short-lived objects they determine the pace of galactic chemical evolution, as triggers of star formation and important sites of nucleosynthesis. Because of their high luminosities they can be used as powerful tracers of chemical composition over large distances, throughout the Milky Way, other star-forming galaxies of the Local Group, and even beyond. The most frequent massive stars, OB-type stars in the range from about 8 to 30 solar masses, are of particular interest to us. They are studied in a homogeneous way from the main sequence to the evolved stage as BA-type supergiants. Our improvements in analysis methodology and the construction of sophisticated non-LTE model atoms allow stellar parameters and elemental abundances to be determined with unprecedented accuracy, mainly due to a large reduction of systematic errors. We discuss here first results based on a sample of Galactic objects with high-resolution, high-S/N spectra. Early-type stars within ~1kpc around the Sun turn out to be more metal-rich on the mean than indicated in previous work and they show a high degree of chemical homogeneity, on the ~10% level. This facilitates a present-day "cosmic abundance standard" to be established as an alternative to solar values. Farther out, effects of the Galactic abundance gradient become apparent. Shallow gradients are found, with the individual objects showing a much lower scatter in abundances than indicated by previous work on stars and HII regions. Tight observational constraints on models of Galactochemical evolution are thus provided.