On the nature of extreme Of supergiants

Details On the nature of extreme Of supergiants On the nature of extreme Of supergiants

Jan 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997aas...18912003c&link_type=abstract

American Astronomical Society, 189th AAS Meeting, late abstracts, #120.03; Bulletin of the American Astronomical, Vol. 29, p. 73

Physics

Optics

Scientific paper

Astrophysically there is a clear distinction between extreme Of supergiants and WNL-type Wolf-Rayet stars, though the morphological distinction is often in the eye of the beholder, even for the most discriminating practitioner. Our spectroscopic analysis of the two extreme O supergiants, HD152408 and HD152386, and the morphologically related stars, HD151804 (O8Iaf), HDE313846 (WN9a), NS4 (WN9) and HD177230 (WN8) indicates that the astrophysical discrimination between Of and WNL is the surface mass flux (dotM /4pi R_{*}(2) ), with stellar temperature and surface helium abundance secondary effects. Above a surface mass flux of ~ 10(-8.8) Msunyr(-1) Rsun(-2) stars are classified as Wolf-Rayet. We conclude that OIafpe stars should be re-classified as WN9a stars from their overall spectral appearance, blue shifted absorption lines (e.g. Heii lambda 5412), their highly helium enriched atmospheres, and we suggest an evolutionary sequence between OIaf and WNLa stars, without direct observational evidence in favour of an intermediate Luminous Blue Variable phase (no ejecta nebulae, different morphologies, spatial locations). From new, high-resolution CTIO--IRS line profiles we find that given sufficient spectral resolution (R>=1000) over a suitable range in wavelength, the near-IR is a excellent region for quantatitive studies. We find good agreement between wind velocities derived from Hei 1.0830mu m and the usual ultraviolet P Cyg profiles. Overall our model analyses indicate good consistency between stellar parameters (mass-loss rates, luminosities, surface abundances) based on either near-IR or optical diagnostics, a question of importance to investigating stars obscured by interstellar dust (e.g. in the Galactic Center) or in crowded regions where IR spectroscopy and low-order adaptive optics provides spatial discrimination (e.g. stars in Local Group galaxies).

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