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arXiv · 1905.09296

The Wolf-Rayet binaries of the nitrogen sequence in the Large Magellanic Cloud: spectroscopy, orbital analysis, formation, and evolution

T. Shenar·D. P. Sablowski·R. Hainich·H Todt·A. F. J. Moffat·L. M. Oskinova·V. Ramachandran·H. Sana·A. A. C Sander·O. Schnurr·N. St-Louis·D. Vanbeveren·Y. Goetberg·W. -R. Hamann
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Abstract

Massive Wolf-Rayet (WR) stars dominate the radiative and mechanical energy budget of galaxies and probe a critical phase in the evolution of massive stars prior to core-collapse. It is not known whether core He-burning WR stars (classical WR, cWR) form predominantly through wind-stripping (w-WR) or binary stripping (b-WR). With spectroscopy of WR binaries so-far largely avoided due to its complexity, our study focuses on the 44 WR binaries / binary candidates of the Large Magellanic Cloud (LMC, metallicity Z~0.5 Zsun), identified on the basis of radial velocity variations, composite spectra, or high X-ray luminosities. Relying on a diverse spectroscopic database, we aim to derive the physical and orbital parameters of our targets, confronting evolution models of evolved massive stars at sub-solar metallicity, and constraining the impact of binary interaction in forming them. Spectroscopy is performed using the Potsdam Wolf-Rayet (PoWR) code and cross-correlation techniques. Disentanglement is performed using the code Spectangular or the shift-and-add algorithm. Evolutionary status is interpreted using the Binary Population and Spectral Synthesis (BPASS) code, exploring binary interaction and chemically-homogeneous evolution. No obvious dichotomy in the locations of apparently-single and binary WN stars on the Hertzsprung-Russell diagram is apparent. According to commonly used stellar evolution models (BPASS, Geneva), most apparently-single WN stars could not have formed as single stars, implying that they were stripped by an undetected companion. Otherwise, it must follow that pre-WR mass-loss/mixing (e.g., during the red supergiant phase) are strongly underestimated in standard stellar evolution models.

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T. Shenar, D. P. Sablowski, R. Hainich, H Todt, A. F. J. Moffat, L. M. Oskinova, V. Ramachandran, H. Sana, A. A. C Sander, O. Schnurr, N. St-Louis, D. Vanbeveren, Y. Goetberg, W. -R. Hamann. 2019-05-22. The Wolf-Rayet binaries of the nitrogen sequence in the Large Magellanic Cloud: spectroscopy, orbital analysis, formation, and evolution. https://doi.org/10.1051/0004-6361/201935684e

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