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Wolf-Rainer Hamann

Massive stars, winds, feedback, gravitational wave progenitors
When Feb 22, 2018 from 02:30 PM to 03:30 PM
  • Colloquium
Where SH Lecture Hall
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Luminous, massive stars play an important role in the cosmic evolution. With their stellar winds and strong ionizing radiation, they have a large impact on their environment. The spectral analysis of hot-star spectra requires adequate stellar atmosphere models. We have developed the Potsdam Wolf-Rayet (PoWR) model atmosphere code for this purpose, and have performed comprehensive analyses for massive stars of various types (Wolf-Rayet, O- and B-type stars) in our and other, nearby galaxies. The evolution of massive stars is not yet well understood. One uncertain factor is the mass loss in the different evolutionary stages. With our spectral analyses we constrain the mass-loss rates of massive stars empirically. In addition, we are developing self-consistent hydrodynamical models. From the results of the spetral analyses we can quantify the feedback in dependence from the stellar parameters. At low metallicities, as in the SMC, very massive stars are obviously internally mixed and hence evolve chemically homogeneous. We studied young, star-forming clusters and found that a handful of their most massive stars dominates the ionizing radiation and mechanical feedback. The mass loss during a stellar life also determines how much mass is left at gravitaional collapse. Under which conditions a black hole, or even a close pair of black holes, can form with such high masses as observed in the gravitational wave events?