Wolf-Rayet stars in the Magellanic Clouds. VII - Spectroscopic binary search among the WNL stars and the WN6/7-WN8/9 dichotomy

Details Wolf-Rayet stars in the Magellanic Clouds. VII - Spectroscopic binary search among the WNL stars and the WN6/7-WN8/9 dichotomy Wolf-Rayet stars in the Magellanic Clouds. VII - Spectroscopic binary search among the WNL stars and the WN6/7-WN8/9 dichotomy

Dec 1989

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989apj...347..373m&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 347, Dec. 1, 1989, p. 373-391. Research supported by NSERC.

Other

52

Binary Stars, Magellanic Clouds, Wolf-Rayet Stars, Emission Spectra, Radial Velocity, Spectral Line Width, Stellar Magnitude, Stellar Spectrophotometry, Stellar Temperature

Scientific paper

Late-type Wolf-Rayet (W-R) stars of the nitrogen sequence (WNL) can be sensibly divided into two groups: (1) WN6, WN7 and (2) the cooler WN8, WN9 stars. The latter generally have narrower emission lines and relatively strong He I P Cygni profiles. In either the LMC or the Galaxy, ˜¼ of all W-R stars are WNL; of these, ˜¼ are WN8,9. All massive stars that later become W-R stars, probably start as WNL.
None of the nine monitored WN8,9 stars in the LMC and the Galaxy shows W-R + O binary-related radial velocity variations. This is in stark contrast with the 58% W-R + O binary frequency among the 26 monitored WN6,7 stars. This fraction is the same in each galaxy. Orbital masses of WN6,7 stars lie in the range ˜30-60 Msun, with binary mass ratios M(WN6,7)/M(O) greater-than or equivalent to 1.
WN8,9 stars are much more dispersed in space than WN6,7 stars, which tend to be found in clusters. While WN8,9 stars have slightly fainter mean visual absolute magnitudes (Mv = -5.6 ± 0.3) than WN6,7 stars (Mv = - 6.1 ± 0.2), possibly a result of crowding and duplicity of the WN6,7 sample, both groups show similar, relatively large dispersion in absolute magnitude [σ(Mv) ˜ 0.8-0.9 mag]. However, WN8,9 stars are considerably more variable than WN6,7 (or any other W-R) stars. The basic reason for the often strong differences between these two groups is unknown.

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