Astronomy and Astrophysics – Astronomy
Scientific paper
May 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995aas...186.2204m&link_type=abstract
American Astronomical Society, 186th AAS Meeting, #22.04; Bulletin of the American Astronomical Society, Vol. 27, p.841
Astronomy and Astrophysics
Astronomy
Scientific paper
The one-dimensional WN classification defined by Smith (1968, MNRAS 138, 109), based primarily on the relative strengths of Nsiii -- Nsv lines, has been described as unsuccessful because it fails to define a unique luminosity and temperature for a given spectral type (e.g. Conti ea 1983, ApJ 268, 228). Part of the problem lies in the lumping of ``weak'' and ``strong'' lined stars (Hiltner & Schild 1966, ApJ 143,770 ``A'' and ``B'' types) into the same spectral bins. Recently Hamann, Koesterke, & Wessolowski (1993, AA 274, 397) (HKW) have determined the luminosities and temperatures for 60% of the 71 apparently single WN stars in the updated Sixth Galactic WR Catalog of van der Hucht ea (1988, AA 199, 217), from the equivalent widths (EW) of Hesiilam 5412 and Hesilam 5876. I use their data to plot the EW_{lambda 5412} as a function of the ratio EW_{lambda 5412} / EW_{lambda 5876}. This plot shows a clear separation between ``weak'' lined and ``strong'' lined WN stars with a dividing line at EW_{lambda 5412} = --35 Angstroms. Both the strong and weak line sequences follow the N ionization classification along their respective curves. There is also a hint of a further bifurcation in the weak line sequence. I argue that this is an empirical HR diagram for the WN stars because for each sequence (weak and strong); there is a linear correlation between temperature and the equivalent width ratio, and an inverse linear correlation between the absolute visual magnitude and the EW_{lambda 5412}. (This second correlation is just the ``Baldwin Effect'' for WR stars; noted by Morris ea 1993, ApJ 414, L25). I will discuss a similar classification system by Smith, Shara, & Moffat (1995, IAUSymp 163, 48) who have suggested using the FWHM of Hesiilam 4686 in place of EW_{lambda 5412} and an additional third dimension measuring the H/He abundance ratio. I will also discuss the use of alternate luminosity (EW_{lambda 4686}) and temperature (EW_{lambda 4686} / EW_{lambda 10830}) indicators. This work has been supported by NAG5-619.
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