Class W: Wolf–Rayet
Class W or WR represents the Wolf–Rayet stars, notably unusual since they have mostly helium in their atmospheres instead of hydrogen. They are thought to mostly be dying supergiants with their hydrogen layers blown away by stellar winds, thereby directly exposing their hot helium shells. Class W is further divided into subclasses according to the dominance of nitrogen and carbon emission lines in their spectra (and outer layers).
WR spectra range is listed below:
- WN, spectrum dominated by NitrogenIII-V and HeliumI-II lines.
- WNE (WN2 to WN5 with some WN6), hotter or "early".
- WNL (WN7 to WN9 with some WN6), cooler or "late".
- Extended WN classes WN10 and WN11 sometimes used for the Ofpe/WN9 stars.
- h tag used (e.g. WN9h) for WR with hydrogen emission and ha (e.g. WN6ha) for both hydrogen emission and absorption.
- WN/C, WN stars plus strong CarbonIV lines, intermediate between WN and WC stars.
- WC, spectrum with strong CarbonII-IV lines.
- WCE (WC4 to WC6), hotter or "early".
- WCL (WC7 to WC9), cooler or "late".
- WO (WO1 to WO4), strong OxygenVI lines, extremely rare.
- Example: R136a1 (WN5h)
- Example: Gamma2 Velorum A (WC8)
- Example: WR93B (WO3)
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... Class W or WR represents the Wolf–Rayet stars, notably unusual since they have mostly helium in their atmospheres instead of hydrogen ...