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The Galactic WN stars

Spectral analyses with line-blanketed model atmospheres versus stellar evolution models with and without rotation

Lehrstuhl Astrophysik der Universität Potsdam, Am Neuen Palais 10, 14469 Potsdam, Germany e-mail: wrh@astro.physik.uni-potsdam.de

Received: 20 February 2006
Accepted: 6 June 2006

Abstract

Context.Very massive stars pass through the Wolf-Rayet (WR)stage before they finally explode. Details of their evolution have notyet been safely established, and their physics are not well understood. Theirspectral analysis requires adequate model atmospheres, which have beendeveloped step by step during the past decades and account in theirrecent version for line blanketing by the millions of lines from ironand iron-group elements. However, only very few WN stars have beenre-analyzed by means of line-blanketed models yet.

Aims.The quantitative spectral analysis of a large sample of Galactic WN stars with the most advanced generation of model atmospheres should provide an empirical basis for various studies about the origin,evolution, and physics of the Wolf-Rayet stars and their powerful winds.

Methods.We analyze a large sample of Galactic WN stars bymeans of the Potsdam Wolf-Rayet (PoWR) model atmospheres, which accountfor iron line blanketing and clumping. The results arecompared with a synthetic population, generated from theGeneva tracks for massive star evolution.

Results.We obtain a homogeneous set ofstellar and atmospheric parameters for the Galactic WN stars, partly revising earlier results.

Conclusions.Comparing the results of our spectral analysesof the Galactic WN stars with the predictions of the Geneva evolutionarycalculations, we conclude that there is rough qualitative agreement.However, the quantitative discrepancies are still severe, and there isno preference for the tracks that account for the effects of rotation.It seems that the evolution of massive stars is still not satisfactorilyunderstood.