DAAD-Projekt A

»Spectra and feedback from young stellar clusters «

Prof. Dr. Wolf-Rainer Hamann (UP, advisor) and Dr. Adriane Liermann (AIP, co-advisor)


Background: Young stellar populations are dominated by massive stars which evolve on relatively short time-scales. With their high luminosity and powerful stellar winds they have a strong impact on their immediate environment. They provide ionizing UV photons, momentum and chemically processed material before they explode as supernova. With this feedback, massive stars are key players in the evolution of young stellar clusters and whole starburst galaxies. Massive or super-massive stars are even considered as source of the re-ionization of the Universe.

Aims: The goal of this PhD project is to provide synthetic spectra, ionizing radiation, mechanical feedback and chemical yields of young stellar populations for specific metallicity ranges, ages, and star-formation histories. Model predictions then form the basis for comparisons with observations, e.g., with the summed-up spectra of stars in resolved clusters, unresolved cluster spectra of distinct starburst galaxies, or ionizing fluxes as reconstructed from a cluster’s diffuse emission.

Methods: The project will exploit the Potsdam Wolf-Rayet (PoWR) model atmospheres, which have been extensively used so far for analyzing individual high-mass stars (spectral types O, B, WR, LBV) [1]. Stellar populations will be constructed, based on available stellar evolution models for massive stars at different metallicities [2]. The student has to critically assess the compatibility of these models regarding observations and characterize the dominant stellar feedback processes in comparison to observed resolved starburst clusters [3]. PoWR models will be employed to synthesize individual spectra of the stellar population, to derive stellar feedback parameters. Finally, from the individual PoWR models the integrated cluster spectrum is produced, to be compared to observations of unresolved stellar clusters, e.g., in starburst galaxies. The student will retrieve archival observations, publicly available for example from the European Southern Observatory (ESO) archive, and apply for supplementary observing time, e.g., at ESO’s Very Large Telescope, Chile, and the Large Binocular Telescope at Mt. Graham, Arizona. In the course of this project, the student will become deeply involved with different key fields of modern astrophysics: modelling of expanding stellar atmospheres; stellar evolution; cosmic circuit of matter; spectroscopic observations and data reduction.




  1. W.-R. Hamann, G. Gräfener, 2004: Grids of Model Spectra for WN Stars, Ready for Use. Astronomy and Astrophysics, 427, 697
  2. S. Ekström, C. Georgy, P. Eggenberger, et al. 2012: Grids of Stellar Models with Rotation. I. Models from 0.8 to 120M at Solar Metallicity (Z = 0.014). Astronomy and Astrophysics, 537, 146
  3. W.-R. Hamann, G. Gräfener, A. Liermann, 2006: The Galactic WN Stars. Spectral Analyses with Line-Blanketed Model Atmospheres Versus Stellar Evolution models with and without Rotation. Astronomy and Astrophysics, 457, 1015