QUANTITATIVE CLASSIFICATION OF WC AND WO STARS

We present a quantitative classification scheme for carbon and oxygen sequence Wolf-Rayet stars. Our scheme uses new high-quality optical AA T and INT observations of 20 stars for which we provide narrow-band ph otometry and estimates of interstellar reddenings. In increasing order of excitation, our spectral classes range from WC11 to WC4 for Wolf-R ayet stars with a dominant carbon line visual spectrum, and subsequent ly from WO4 to WO1 for those with predominantly oxygen lines. We refin e existing WC and WO schemes to incorporate stars with higher and lowe r excitation spectral features. Both massive stars and central stars o f planetary nebulae (CSPNe) can be classified with the unified system. We have found no criterion that cleanly separates spectra of the two types of star, including elemental abundances (C/O or C/He). However, CSPNe show a wider range of line strength and width than massive stars in the same ionization subclass. Systematically lower FWHM(C IV lambd a 5808) values are observed from WO-type CSPNe than from massive WO st ars. For WC4-11 stars, our primary diagnostic is the equivalent width or line flux ratio Cry lambda lambda 5801-12/C III lambda 5696. We ext end the use of this as the principal criterion throughout the WC seque nce, with few reclassifications necessary relative to Smith, Shara & M offat. For WO stars, C III is absent and our new criteria, using prima rily oxygen lines, take over smoothly. We define subclasses WO4-1, usi ng O VI lambda lambda 3811-34/O V lambda 5590 as our primary diagnosti c. The continuation in spectral sequence from WC to WO is used to indi cate that the sequence is a result primarily of excitation effects, ra ther than significant abundance differences. Our scheme allows us to c onfirm that massive stars and CSPNe are differently distributed over t he subclasses. Around 3/5 of massive WC stars lie within the range WC5 -8, while less than or equal to 1/5 of CSPNe are found within these sp ectral types. Stars within both the highest (WO1) and lowest (WC10-11) excitation spectral classes are unique to CSPNe. A WC classification for the hot R CrB star V348 Sgr is excluded (previously [WC12]) since both C III lambda 5696 and C IV lambda 5808 are absent in its optical spectrum. Additional criteria allow us to distinguish between WC-type, 'weak emission line' CSPNe, and O stars, allowing us to reclassify th e central star of IRAS 21282+5050 (previously [WC11]) as an O star.