Type WR star
Type WR, comprising several subtypes (all beginning with a W) are the naked cores of massive stars from which hot stellar winds have stripped off the overlying hydrogen layers. They are very luminous (105 to 106 L¤), extremely hot (up to ~50,000 K), with spectra characterised by strong emission bands of ionised elements, and dominated by helium rather than hydrogen. An example is Gamma 2 Velorum.
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Subtype WC
Intrinsically luminous, WR stars can be massive or mid-sized, but the most interesting stage is arguably the last 10% in the lifetime of the star, when hydrogen fuel is used up and the star survives by much hotter He-burning. Towards the end of this phase, the copious supply of carbon atoms head for the stellar surface and are ejected in the form of stellar winds. WR stars in this stage are known as WC stars. These amorphous dust grains range in size from a few to millions of atoms.
Subtype WN
- 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.
Subtype WO
- WO (WO1 to WO4), strong OxygenVI lines, extremely rare.
