OXYGEN AND CARBON ABUNDANCES FOR THE WO STARS

We present relative carbon and oxygen abundances derived via an optica lly thin recombination line analysis for five WO stars, and compare th e derived abundances to recent evolutionary models. New recombination coefficients for O4+, O5+ and O6+ ions have allowed total oxygen abund ances to be derived. The final C/He values range between 0.4 and 0.8 b y number, consistent with C/He ratios previously derived for WC stars. O/He values range between 0.1 - 0.4, with C/O ratios between 2.1 - 4. 8. A comparison of the derived abundances with the evolutionary models of Maeder (1990) and Schaller et al. (1992) shows promising agreement . We find reasonably tight agreement between the abundances derived fo r the WO stars. The degree of enhancement for the oxygen abundances in regions of low metallicity predicted by Maeder (1990) is not corrobor ated by our results. Additionally we present a revised, quantified cla ssification scheme for WO subtypes. We extend the class to lower excit ation, WO5, and place MS 4 (=WR 30a) in this class. Equivalent widths of the strongest lines of MS 4 are also presented. Finally, we present new observations of DR 1, a WO3 star located in the dwarf irregular g alaxy IC 1613.