2011/05/24 by Paul A. Crowther, P. A. Crowther, Paul Crowther +3 · 124 citations
Physics and Astronomy · #Astronomy #Astronomy and Astrophysical Research #Astrophysics #Astrophysics and Star Formation Studies #Classification scheme #Herbig Ae/Be star #K-type main-sequence star #O-type star #Physics #Stars #Stellar classification #Stellar, planetary, and galactic studies #T Tauri star #astro-ph.SR
paper · pdf · doi:10.1111/j.1365-2966.2011.19129.x
published in Monthly Notices of the Royal Astronomical Society 416(2), 1311-1323 (Oxford University Press) · 16 pages, 8 figures, accepted for MNRAS
arxiv created 2011/05/24 · openalex publication_date 2011/07/25 · arxiv updated 2015/05/28 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
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 to the usual diagnostics from Smith et al. We also discuss approximate criteria to discriminate between these subtypes from near-infrared spectroscopy. The physical and wind properties of such stars are qualitatively discussed together with their evolutionary significance. We suggest that the majority of O2–3.5 If*/WN5–7 stars are young, very massive hydrogen-burning stars, genuinely intermediate between O2–3.5 If* and WN5–7 subtypes, although a minority are apparently core helium-burning stars evolving blueward towards the classical WN sequence. Finally, we reassess classifications for stars exhibiting lower ionization spectral features plus Hβ emission.