Wolf-Rayet spectra: how to tell binaries from singles
W.-R. Hamann and G. Gräfener
Many Wolf-Rayet stars are suspected to be binaries because their spectra
are considered as looking composite. Corresponding criteria are the
weakness of the lines ("diluted emission lines, d.e.l."), or the
presence of absorption features. However, single WR stars can provide an
amazing variety of spectra, depending on their parameters. Many of the
"composite" spectra can be reproduced with single-star models. Synthetic
spectra from the Potsdam Wolf-Rayet (PoWR) code have been employed to test
the Galactic WN stars. It turns out that neither the weakness of emission
lines (d.e.l.) nor the presence of absorption features give unique
evidence for binarity. However, the spectral energy distribution over a
wide range (UV, optical, IR) should reveal the spectral contamination from
a companion. We checked eight d.e.l. suspects and 29 further WN stars,
but found significant UV/optical contamination only in one case of a
well-known binary. Thus the fraction of Galactic WN binaries might have
been over-estimated so far.
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