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/He
0.1--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--2.5
m 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/He
0.05) are in
good agreement with previous optical analyses