Wolf-Rayet Stars

Wolf-Rayet stars are hot (25-50,000+ degrees K), massive stars (20+ solar mass) with a high rate of mass loss. Strong, broad emission lines (with equivalent widths up to 1000Å!) arise from the winds of material being blown off the stars.
HST Close-up of WR124!

Credit: Yves Grosdidier, Anthony Moffat (Universitie de Montreal), Gilles Joncas (Universite Laval), Agnes Acker (Strasbourg), STScI, and NASA November, 1998

Wolf-Rayets stars are divided into 3 classes based on their spectra, the WN stars (nitrogen dominant, some carbon), WC stars (carbon dominant, no nitrogen), and the rare WO stars with C/O < 1. The WN stars optical spectra show emission lines from H, NIII (4640Å), NIV, NV, HeI, HeII, and from CIV at 5808Å. In the UV, there are strong emission features from NII, NIII, NIV, NV, CIII, CIV, HeII, OIV, OV, and SiV.

The WC stars optical spectra show emission lines from H, CII, CIII (5696Å), CIV (5805Å), OV (5592Å), HeI, and HeII. No nitrogen lines are seen in the WC stars. In the UV, there are strong emission features from CII, CIII, CIV, OIV, OV, SiIV, HeII, FeIII, FeIV, and FeV.

Wolf-Rayet galaxies are galaxies that contain a large population of Wolf-Rayet stars. These emission-line galaxies show a broad 4686 HeII emission feature due to the WR stars. About one-quarter of these galaxies also show broad NIII 4640 A emission. <<

Click here for a catalog of the northern WR stars.

WN Type Nitrogen Line Criteria Other Criteria
WN 9 NIII present; NIV weak or absent lower Balmer series; HeI
WN 8 NIII >> NIV NIII 4640Å <
WN 7 NIII > NIV NIII 4640Å <
WN 6 NIII = NIV; NV present but weak  
WN 5 NIII = NIV = NV  
WN 4.5 NIV > NV; NIII weak or absent  
WN 4 NIV = NV; NIII weak or absent  
WN 3 NIV <<  
WN 2 NV weak or absent Strong HeII

WC Type Carbon Line Criteria Carbon/Oxygen Criteria Other Criteria
WC 9 CIII > CIV OV weak or absent CII present
WC 8.5 CIII > CIV OV weak or absent CII not present
WC 8 CIII = CIV OV weak or absent  
WC 7 CIII < CIII >> OV  
WC 6 CIII << CIII > OV  
WC 5 CIII << CIII <  
WC 4 CIII <<< OV moderate  
From Smith(1968)

WC Series

WC5b WC5

WC6 WC6

WC7p WC7p

WC8 WC8+

WCn WC

WN Series

WN3

WN4 WN4

WN4+O WN4+OI

WN6 WN6+O

WN7+O WN9

HST Close-up of WR124!

Credit: Yves Grosdidier, Anthony Moffat (Universitie de Montreal), Gilles Joncas (Universite Laval), Agnes Acker (Strasbourg), STScI, and NASA
November, 1998