Wolf-Rayet stars in the Magellanic clouds. VI. Spectroscopic orbits of WC binaries and implications for W-R evolution
Spectroscopic orbits are obtained for the first time for the three brightest WC + O binary systems in the LMC. An improved orbit is obtained for the bright WO + O system in the SMC. In one of the LMC systems the observed O companion is stationary; the remaining three systems show antiphased orbits o...
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1990
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| Acceso en línea: | https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_0004637X_v348_n1_p232_Moffat http://hdl.handle.net/20.500.12110/paper_0004637X_v348_n1_p232_Moffat |
| Aporte de: |
| Sumario: | Spectroscopic orbits are obtained for the first time for the three brightest WC + O binary systems in the LMC. An improved orbit is obtained for the bright WO + O system in the SMC. In one of the LMC systems the observed O companion is stationary; the remaining three systems show antiphased orbits of both components. Two of the LMC binary systems have very short periods (1.9 and 3.0 d), similar to the lower limit for periods of known WN + O and O + O binary systems in general. This means that orbital angular momentum must have been lost from the system in addition to that associated with the extreme mass loss of the present WC components, but not necessarily via mass transfer. On the basis of the double-line orbits for 10 known WC + O binaries in the Galaxy and the Magellanic Clouds, there emerges a continuous decrease of mass ratio M(WC)/M(O) with WC subtype, from 0.5 for WC8 to 0.2 for WC4, WO. Assuming that the initial mass ratio was ≳1, this implies that WC stars can evolve from WN stars and from cooler to hotter subtypes within the WC sequence, with mean mass-loss rate ∼4 × 10-5 M⊙ yr-1. It is noted that in WC + O binaries it is the mass ratio, not the mass, which probably best reflects the degree of evolution of the WC component to hotter subtypes, regardless of the initial mass. |
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