W. Schmutz

An exceptional population of late-type WC stars in the metal-rich spiral galaxy M 83 ⋆

We have surveyed the metal-rich spiral galaxy M 83 (NGC 5236) for its Wolf-Rayet population using VLT-FORS2 narrow-band imaging and follow-up spectroscopy. From a total of 280 candidates identified using He  λ4686 imaging, Multi Object Spectroscopy of 198 sources was carried out, revealing 132 objects containing bona-fide Wolf-Rayet features. From this sample, an exceptional W-R content of ∼1030 is inferred, with N(WC)/N(WN) ∼ 1.3, continuing the trend to larger values at higher metallicity amongst Local Group galaxies. More dramatic is the dominance of late-type WC stars in M 83 with N(WC8−9)/N(WC4−7) = 9 which we attribute to the sensitivity of the classification line C  λ5696 to mass-loss, providing the strength of WC winds scale with metallicity. One young massive compact cluster, #74 in our catalogue, hosts 20% of the entire galactic population, namely ∼180 late WC stars and ∼50 late WN stars.

Analyses of Wolf-Rayet stars in Local Group galaxies

We have started a project to observe and analyze Wolf-Rayet stars in the galaxies of the Local Group. The first observing run was marred with disastrous weather and therefore, we do not yet have any results to report. Instead, we briefly summarize the motivation of our project.

Complete Stellar Models: Interior and Spectral Evolution of Massive Stars

We present the first models of massive stars, where the interior structure is coupled to a spherically extended, metal line blanketed non-LTE atmosphere with a wind. This is accomplished with the Geneva stellar evolution code and the non-LTE atmosphere code of de Koter et al. (1993). The method described in Schaerer & Schmutz (1994) is used to treat line blanketing. A first account of this work is published in Schaerer et al. (1994).

Complete Stellar Models for Massive Stars

We present a first step towards complete stellar models for massive stars that treat the entire star including its wind. Our models are based on state-of-the art non-LTE atmospheric and interior modelling. The models yield the stellar evolution under the constraint of realistic atmospheres as well as line-blanketed continuum fluxes and H and He line profiles. We follow the evolution from OB to LBV, Ofpe/WN, and WR stars. We investigate the effect of line-blanketing during MS evolution. We adress the effect of an the extended atmosphere on the evolution and discuss the first results for WR stars.

Calculations of non-LTE radiative transfer in extended outflowing atmospheres using the Sobolev approximation for line transfer

The code that we are developing for the empirical modelling of LBVs using the Sobolev approximation ] for the line transfer, yields accurate results that compare well with those obtained using the co-moving frame method. By including absorption by the continuum in the resonance region in addition to escape from the resonance region we get a much more accurate result for the hydrogen ground level population. The following properties make the code extremely fast: • the Sobolev approximation for the line transfer • the choice of the local approximate lambda operator A*, which yields the exact local contributions to the continuum radiation field • the method of preconditioning the set of statistical equilibrium equations, which makes computationally expensive linearization unnecessary.