Projekt E

Massive Stars in Binary Systems

Prof. Dr. Wolf-Rainer Hamann (UP, advisor) and Dr. Swetlana Hubrig (AIP, co-advisor)


Background: Stars that are initially much more massive than the sun play a fundamental role in the evolution of the Universe. They are a main source of ionizing photons and generate chemical elements which they distribute by mass loss. Finally they explode as supernova or gamma-ray burst. However, just because of their stellar winds, the massive stars are not well understood, especially with regard to their evolution and their feedback to the galactic ecology. Binaries are a potential key for massive-star research. Perhaps the majority of all massive stars form and evolve in close-binary systems. In such cases, their observed spectra are composed from two stars, which makes their analysis more difficult. However, as an advantage they provide additional information from the binary orbit, especially about the stellar masses. Strong global magnetic fields are found in a number of massive stars. Among the different scenarios for their origin is the possibility that such fields are generated by strong binary interactions in stellar mergers or during mass transfer.

Aims: The broad scientific goal of this project is to understand the massive stars and their contribution to the evolution of galaxies and to the cosmic circuit of matter. We suggest to study the about 50 binary systems containing a Wolf-Rayet star that are known in the Magellanic Clouds and the Galaxy, and combine the obtained results with the information from the binary properties. These three galaxies exhibit different concentrations of heavy elements, which makes a big difference for the evolution of massive stars. From such an investigation we expect important conclusions about the evolutionary fate of massive stars, concerning single stars as well as interacting binary systems.

Methods: The spectral analysis of early-type stars with winds requires especially laborious and complex model calculations, as we have developed in Potsdam over many years of work (the Potsdam Wolf-Rayet model atmospheres, PoWR). Spectroscopic observations of many massive binary systems are available to us, often for multiple epochs.

We suggest to:

  • analyze the known SB2 systems with a WR component in the SMC, LMC and the Galaxy, by calculating and applying PoWR models;
  • plan and perform further observational campaigns to complete the data if neccessary;
  • study the phase-dependent observations in order to improve the spectral decomposition and the orbital data;
  • fit and analyze the multi-wavelength light curves and spectral variability;
  • search and measure magnetic fields in spectrapolariometric observations of massive stars; and
  • discuss the results with respect to the evolution of massive stars as single stars and as binaries, and with regard to their feedback to the galactic ecology.