The Galactic WN stars: Spectral analyses with line-blanketed model atmospheres versus stellar evolution models with and without rotation

摘要

CONTEXT: Very massive stars pass through the Wolf-Rayet (WR) stage beforethey finally explode. Details of their evolution have not yet been safelyestablished, and their physics are not well understood. Their spectral analysisrequires adequate model atmospheres, which have been developed step by stepduring the past decades and account in their recent version for line blanketingby the millions of lines from iron and iron-group elements. However, only veryfew WN stars have been re-analyzed by means of line-blanketed models yet. AIMS: The quantitative spectral analysis of a large sample of Galactic WNstars with the most advanced generation of model atmospheres should provide anempirical basis for various studies about the origin, evolution, and physics ofthe Wolf-Rayet stars and their powerful winds. METHODS: We analyze a large sample of Galactic WN stars by means of thePotsdam Wolf-Rayet (PoWR) model atmospheres, which account for iron lineblanketing and clumping. The results are compared with a synthetic population,generated from the Geneva tracks for massive star evolution. RESULTS: We obtaina homogeneous set of stellar and atmospheric parameters for the Galactic WNstars, partly revising earlier results. CONCLUSIONS: Comparing the results of our spectral analyses of the GalacticWN stars with the predictions of the Geneva evolutionary calculations, weconclude that there is rough qualitative agreement. However, the quantitativediscrepancies are still severe, and there is no preference for the tracks thataccount for the effects of rotation. It seems that the evolution of massivestars is still not satisfactorily understood.