The carbon and nitrogen abundances in WN and WC Wolf-rayet stars.

Abstract

New ultraviolet spectroscopy obtained with the IUE satellite of helium, carbon and nitrogen lines in six WN and four WC stars have been analysed using non-LTE Escape Probability techniques to derive the stellar atmospheric C/N, C/He and N/He ratios. The derived C/N ratio is found to lie in the range: 0.02-0.06 for WNE stars; 0.006-0.04 for WNL stars and 60 or greater for WC stars. These results are in fair agreement with recent predicted values from stellar evolutionary models in which mass ion reveals nuclear processed CNO products and He-burning products. This agreement strengthens the scenario that the WR stars are chemically evolved objects at different stages of H-burning and He-burning in massive hot stars.