Astronomy and Astrophysics – Astronomy
Scientific paper
Jun 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001mnras.324...18b&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 324, Issue 1, pp. 18-32.
Astronomy and Astrophysics
Astronomy
24
Atlases, Binaries: Spectroscopic, Stars: Wolf-Rayet, Magellanic Clouds
Scientific paper
A nearly complete sample of 24 Magellanic Cloud WC/WO subclass Wolf-Rayet stars is studied spectroscopically and photometrically to determine its binary frequency. Theory predicts the Roche lobe overflow produced Wolf-Rayet binary frequency to be 52+/-14 per cent in the Large Magellanic Cloud and 100 per cent in the Small Magellanic Cloud, not counting non-Roche lobe overflow Wolf-Rayet binaries. Lower ambient metallicity (Z) leads to lower opacity, preventing all but the most massive (hence luminous) single stars from reaching the Wolf-Rayet stage. However, theory predicts that Roche lobe overflow even in binaries of modest mass will lead to Wolf-Rayet stars in binaries with periods below approximately 200d, for initial periods below approximately 1000d, independent of Z. By examining their absolute continuum magnitudes, radial velocity variations, emission-line equivalent widths and full widths at half-maximum, a WC/WO binary frequency of only 13 per cent, significantly lower than the prediction, is found in the Large Magellanic Cloud. In the unlikely event that all of the cases with a less certain binary status actually turn out to be binary, current theory and observation would agree. (The Small Magellanic Cloud contains only one WC/WO star, which happens to be a binary.) The three WC+O binaries in the Large Magellanic Cloud all have periods well below 1000d. The large majority of WC/WO stars in such environments apparently can form without the aid of a binary companion. Current evolutionary scenarios appear to have difficulty explaining either the relatively large number of Wolf-Rayet stars in the Magellanic Clouds, or the formation of Wolf-Rayet stars in general.
Bartzakos Peter
Moffat Anthony F. J.
Niemela Virpi S.
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