Wolf--Rayet binaries in the Magellanic Clouds and implications for massive-star evolution -- II. Large Magellanic Cloud

Abstract

We present in this second paper the results of our intensive spectroscopic campaign to search for binaries via periodic radial-velocity (RV) variations among Wolf—Rayet (WR) stars for the Large Magellanic Cloud (LMC). We observed 61 nitrogen-rich WNE stars in the LMC. Along with the results of Bartzakos, Moffat & Niemela on the carbon/oxygen-rich WR stars, 2/3 of the WR population of the LMC (134 stars in total) has now been investigated for periodic RV variability. We have also retrieved time-dependent photometric data in the public domain from the OGLE and MACHO projects, as well as X-ray data from ROSAT and Chandra satellites, to provide additional constraints on the binary character. For each of our sample stars, we discuss its observational properties: RV variations, (periodic) photometric variability, X-ray luminosity, spectral classification, abundance of hydrogen, runaway status and line-profile variations (LPVs). For the binaries we discuss additional properties, such as wind—wind collision (WWC) effects, and the orbital parameters. With this large sample, we discuss the global properties of the WNE population, which is expected to be the most sensitive to binary evolution with respect to the influence of metallicity. To emphasize the relevance of the binary frequency test for the stellar evolution of massive stars in the LMC, we review their observational properties and provide new and meaningful evolutionary classes, which reconcile observational and theoretical definitions. Finally, we draw an overall evolutionary scheme for massive-star evolution, with respect to the three main ingredients of stellar evolution: mass, metallicity and rotation.