Projekt D

Early Enrichment History of the Milky Way Unveiled by the Bulge

Prof. Dr. Matthias Steinmetz (AIP, advisor) and Dr. Cristina Chiappini (AIP, co-advisor)


Background: The chemical abundance patterns of the oldest stars in the Milky Way (MW) and its satellites offer the most promising way of probing the early chemical enrichment of the Universe [14]. Most observational efforts to find the chemical imprints left by the »First Stars« focused on the most metal-poor stars, both in the MW halo and in the recently discovered ultra-faint dwarf galaxies [15]. Remarkably, the Galactic Bulge has been largely unexplored so far, except for two recent dedicated spectroscopic surveys, which – involving quite moderate samples – have already shown this part of the Galaxy to be a complex system made of several components [16][17].

Aims: We want to use spectroscopic observations of metal-poor bulge stars to determine their detailed chemical abundances. By comparison with inhomogeneous chemical evolution models of the bulge we want to constrain the formation process of the Bulge, which will have a big impact on our understanding of galaxy formation in general. We will also gain crucial insights on the First Stars and the re-ionization of the Universe [18].

Methods: The student will analyze high-resolution spectra of bulge stars with [Fe/H] ~ –1, taken from two recently started surveys, in order to extract detailed abundances: (1) The SDSS-III/APOGEE survey will yield NIR spectra of ~8000 bulge stars, providing more than 15 chemical elements. (2) The Gaia-ESO Survey (using UVES on the ESO VLT) will target bright K-giants and provide precise kinematic parameters and individual abundances of more than 10 chemical elements for up to 14,000 stars. In addition, we have already two approved projects of bulge observations with UVES. After extracting the abundances, ages, and kinematic constraints from the spectra, the student will use the new data to constrain the numerous bulge formation models in the literature, computed with the most up-do-date stellar yields (standard ones, as well as non-standard fast rotating stars).