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Wolf Rayet stars in galaxies and the role of binaries and hydrodynamics

Published online by Cambridge University Press:  07 August 2017

André Maeder
André Maeder*
Affiliation:
Geneva Observatory, CH-1290 Sauverny, Switzerland

Abstract

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WR stars obey M-L-·-Teff-R-chemistry relations, which are in general model independent (with the exception of chemistry). The processes of WR formation (stellar winds, hydrodynamical mixing, binary mass transfer etc.) influence, however, the domain of parameters occupied by WR stars. We specifically examine the distribution of luminosities and H-contents of WN stars, which both support heavy mass loss rates, or possibly mixing, in the main sequence and WNL phases. Detailed studies of the number ratios WR/O, WC/WN, WC/WR, etc. are made for galaxies at various metallicities Z which exhibit extremely different WR populations. Good agreement of models and observations is found. It is also shown that the data are better explained if a certain fraction Φ (less than 10%) of the O-stars become WR stars, preferentially of type WNE as a result of Roche lobe overflow (RLOF) in binaries. This result necessarily implies that the fraction of WR stars, owing their existence to RLOF, is variable with Z, being nearly 100% at low Z and much smaller at high Z. We also identify several hydrodynamical developments physically required in stellar models. Among them, we collect the available observational and theoretical arguments supporting an important role of mixing in massive star evolution.

Keywords

stars: Wolf-Rayetclose binariesmass-lossevolutionhydrodynamics
Type
Session V - Stellar winds and massive binary evolution
Information
Symposium - International Astronomical Union , Volume 163: Wolf-Rayet Stars: Binaries, Colliding Winds, Evolution , 1995 , pp. 280 - 290
Copyright
Copyright © Kluwer 1995 

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