Spectral classification of O2–3.5 If*/WN5–7 stars

@article{Crowther2011SpectralCO,
  title={Spectral classification of O2–3.5 If*/WN5–7 stars},
  author={Paul A. Crowther and Nolan R. Walborn},
  journal={Monthly Notices of the Royal Astronomical Society},
  year={2011},
  volume={416},
  pages={1311-1323}
}
An updated classification scheme for transition O2–3.5 If*/WN5–7 stars is presented, following recent revisions to the spectral classifications for O and WN stars. We propose that O2–3.5 If*, O2–3.5 If*/WN5–7 and WN5–7 stars may be discriminated using the morphology of Hβ to trace increasing wind density as follows: purely in absorption for O2–3.5 If* stars in addition to the usual diagnostics from Walborn et al.; P Cygni for O2–3.5 If*/WN5–7 stars; purely in emission for WN stars in addition… 

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