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Elemental abundances

Spectroscopic determinations of W-R atmospheres confirm that they are highly chemically evolved. Studies of Galactic (Hamann et al. 1995; Crowther et al. 1995b) and most recently LMC WN stars (Crowther & Smith 1996b) show most WN stars to be severely H-depleted, with the cool WN (WNL) stars exhibiting the largest values (H/He=0--4.5, by number), particular the WNLha stars (e.g. HD93162, Table 1). Studies of metal abundances for WN stars (e.g. Hillier 1988, Crowther et al. 1995d) provide evidence for CNO-cycle products.

A recent study by Crowther et al. (1995e) indicates that the properties and, crucially, chemical abundances of three composite WN/C stars lie between normal WN and WC stars (see HD62910 in Table 1). These results confirm that such objects represent intermediate WN/C stars rather than binary WN+WC systems.

Although detailed abundance determinations for WC stars remain scarce (e.g. Hillier 1989), the recent study by Koesterke & Hamann (1995) favours high carbon contents of C/He0.1--0.5 (by number) for WC5--8 stars, anticipated from evolutionary theory, although independent of spectral type (e.g. HD165763, Table 1). These abundances are broadly supported by results of recombination line analyses (Eenens & Williams 1992), while Kingsburgh et al. (1995) obtain C/He=0.8--2 for two WO stars.

Figure 2: A comparison of the synthetic 1.0--2.5m spectra (dotted-lines) of HD191765 (WN6) with UKIRT-CGS4 observations (solid) from Crowther & Smith (1996a). The resulting stellar parameters of WR134 (=53800K, log =5.3, log yr= -3.9, =2050 kms, H/He0.05) are in good agreement with previous optical analyses

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