Quantitative classification of WC and WO stars

Abstract

We present a quantitative classification scheme for carbon and oxygen sequence Wolf-Rayet stars. Our scheme uses new high-quality optical AAT and INT observations of 20 stars for which we provide narrow-band photometry and estimates of interstellar reddenings. In increasing order of excitation, our spectral classes range from WC11 to WC4 for WolfRayet stars with a dominant carbon line visual spectrum, and subsequently from WO4 to WO1 for those with predominantly oxygen lines. We refine existing WC and WO schemes to incorporate stars with higher and lower excitation spectral features. Both massive stars and central stars of 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 X5808) values are observed from WO-type CSPNe than from massive WO stars.For WC4-11 stars, our primary diagnostic is the equivalent width or line flux ratio C Iv XX5801-12/C iii X5696. We extend the use of this as the principal criterion throughout the WC sequence, with few reclassifications necessary relative to Smith, Shara & Moffat. For WO stars, C iii is absent and our new criteria, using primarily oxygen lines, take over smoothly. We define subclasses W04-1, using 0 vi XX3811-34/O v X5590 as our primary diagnostic. The continuation in spectral sequence from WC to WO is used to indicate that the sequence is a result primarily of excitation effects, rather than significant abundance differences.Our scheme allows us to confirm that massive stars and CSPNe are differently distributed over the subclasses. Around 3/5 of massive WC stars lie within the range WC5-8, while -1/5 of CSPNe are found within these spectral types. Stars within both the highest (WO 1) 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 X5696 and C iv X5808 are absent in its optical spectrum. Additional criteria allow us to distinguish between WC-type, 'weak emission line' CSPNe, and 0 stars, allowing us to reclassify the central star of IRAS 21282+5050 (previously [WC11]) as an 0 star.

Gemini GMOS spectroscopy of HeII nebulae in M 33

“…We base our classification of WN stars on the line ratios proposed by Smith et al (1996) (e.g., HeIIλ5411/HeIλ5875; NVλ4604/NIIIλ4640; NIVλ4057/NV-IIIλ4604-40). The two WC stars in our sample were classified using the CIIIλ5696/CIVλ5808 line ratio (Crowther et al 1998). We also confirm the luminous blue variable (LBV)-like spectrum of the M 33 star J013416.07+303642.1 classified previously as a P Cyg LBV candidate by Massey et al (2007).…”

A spectroscopic search for the non-nuclear Wolf-Rayet population of the metal-rich spiral galaxy M 83

“…Data for WC7-9 stars in four Local Group galaxies are included, along with subtype boundaries as derived by Crowther et al (1998 for WCL stars in M 83 and Local Group galaxies (identical dataset as presented in Fig. 8).…”

Spatially Resolved STIS Spectra of WR + OB Binaries with Colliding Winds

“…6 ; Table 3) conÐrms the WC 6 classiÐcation. We measure a line equivalent width ratio IV III 5696)^1.03, log W j (C 5801)/log W j (C consistent with subtype WC 6 in the quantitative classiÐcation system of Crowther et al (1998). The lines in this star are especially broad, indicating a large wind terminal FIG.…”