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Physical properties of W-R stars


Quantitative studies of W-R and related objects has only become possible in recent years since their stellar winds are so dense that their photospheres are invisible. The usual assumptions of plane parallel geometry and local thermodynamic equilibrium (LTE) are totally inadequate. W-R winds are well known to be highly stratified (Schulte-Ladbeck et al. 1995a), thus a minimum requirement is to consider non-LTE in an extended, expanding atmosphere for multi-level atoms. Two atmospheric codes, developed independently by Hamann & Schmutz (1987) and Hillier (1987), have been used successfully for spectroscopic modelling of W-R stars, utilising diagnostic (UV, optical and IR) line profiles and continuum fits to observed energy distributions. The so-called Standard Model is currently our best attempt to analyse the observed spectra of such objects.

In recent years, Standard Model analyses have allowed reliable physical properties and chemistries of W-R to be determined. Schmutz et al. (1989) developed a technique whereby large samples of stars can be analysed with minimal computational expense, using measured equivalent widths of selected HeI and HeII lines and a single continuum band absolute flux. This technique has been applied to a large sample of Galactic WN stars by Hamann et al. (1995), to LMC WN stars by Koesterke et al. (1991) and to Galactic WC stars by Koesterke & Hamann (1995). Detailed, tailored analyses of W-R stars, though time-consuming and computationally demanding, has the advantage of determining accurate abundances and identifying current model inadequacies (e.g. Crowther et al. 1995b). The latest generation of models now account for metal line blanketing and clumping (Schmutz 1996).

Paul Crowther
Mon Feb 12 13:51:35 GMT 1996