C/He abundances in WC stars

The C/He abundances in 17 southern WC stars have been derived from spectra in the H and K bands using, for the most part, recombination theory with allowance for collision redistribution. As appropriate calculations for C III are not available, two extremes are considered; LTE treatment of C III gives C/He values that range from 0.04 to 0.3, by number. Maximum allowance for possible non-LTE effects gives values from 0.1 to 0.7, by number. C/He decreases from WC4 to WC7. C/He in WC8 and 9 stars is uncertain because of contributions from C2+ and possibly neutral helium, but may be as high as for WC5−7 stars. The ionization balance is lower than found in previous studies. He+/He2+ is approximately constant, 2.6−3.0, for WC5−8 stars, increasing to 7 for WC9 stars. C3+/C4+ increases from WC4 to WC9, the values are 0.6−3 for LTE treatment and 5–10 times higher if non-LTE effects are important. C2+ becomes important only for WC8 and 9 stars. Comparison with Torres indicates that in the IR region (observed by us) the photosphere is at a greater radius than in the optical range (observed by Torres), and that the ionization decreases outwards. Continuum slopes and corrections for the emission line contribution to the H and K magnitudes are derived.