The Tarantula Massive Binary Monitoring

II. First SB2 orbital and spectroscopic analysis for the Wolf-Rayet binary R145 ^⋆

¹ Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany
e-mail: shtomer@astro.physik.uni-potsdam.de
² Ritter Observatory, Department of Physics and Astronomy, The University of Toledo, Toledo, OH 43606-3390, USA
³ Leibniz-Institut für Astrophysik Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁴ Institute of Astrophysics, KU Leuven, Celestijnenlaan 200 D, 3001 Leuven, Belgium
⁵ Département de physique and Centre de Recherche en Astrophysique du Québec (CRAQ), Université de Montréal, CP 6128, Succ. Centre-Ville, Montréal, Québec, H3C 3J7, Canada
⁶ European Space Astronomy Centre (ESA/ESAC), PO Box 78, 28691 Villanueva de la Cañada, Madrid, Spain
⁷ Argelander-Institut für Astronomie der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁸ IAASARS, National Observatory of Athens, 15236 Penteli, Greece
⁹ Anton Pannenkoek Astronomical Institute, University of Amsterdam, 1090 GE Amsterdam, The Netherlands
¹⁰ Armagh Observatory, College Hill, Armagh, BT61 9DG, UK
¹¹ Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH, UK
¹² Instituto de Astronomia, Geofísica e Ciências, Rua do Matão 1226, Cidade Universitária São Paulo, SP, Brasil
¹³ Dep. of Physics & Astronomy, Johns Hopkins University, Bloomberg Center for Physics and Astronomy, 3400N Charles St, USA
¹⁴ Departamento de Física y Astronomía, Universidad de la Serena, Av. Juan Cisternas 1200 Norte, La Serena, Chile
¹⁵ Instituto de Astrofísica, Universidad de La Laguna, Avda. Astrofísico Francisco Sánchez s/n, 38071 La Laguna, Tenerife, Spain
¹⁶ Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland

Received: 30 August 2016
Accepted: 20 October 2016

Abstract

We present the first SB2 orbital solution and disentanglement of the massive Wolf-Rayet binary R145 (P = 159 d) located in the Large Magellanic Cloud. The primary was claimed to have a stellar mass greater than 300 M_⊙, making it a candidate for being the most massive star known to date. While the primary is a known late-type, H-rich Wolf-Rayet star (WN6h), the secondary has so far not been unambiguously detected. Using moderate-resolution spectra, we are able to derive accurate radial velocities for both components. By performing simultaneous orbital and polarimetric analyses, we derive the complete set of orbital parameters, including the inclination. The spectra are disentangled and spectroscopically analyzed, and an analysis of the wind-wind collision zone is conducted. The disentangled spectra and our models are consistent with a WN6h type for the primary and suggest that the secondary is an O3.5 If*/WN7 type star. We derive a high eccentricity of e = 0.78 and minimum masses of M₁sin³i ≈ M₂sin³i = 13 ± 2 M_⊙, with q = M₂/M₁ = 1.01 ± 0.07. An analysis of emission excess stemming from a wind-wind collision yields an inclination similar to that obtained from polarimetry (i = 39 ± 6°). Our analysis thus implies M₁ = 53⁺⁴⁰_-20 and M₂ = 54⁺⁴⁰_-20 M_⊙, excluding M₁ > 300 M_⊙. A detailed comparison with evolution tracks calculated for single and binary stars together with the high eccentricity suggests that the components of the system underwent quasi-homogeneous evolution and avoided mass-transfer. This scenario would suggest current masses of ≈ 80 M_⊙ and initial masses of M_i,1 ≈ 105 and M_i,2 ≈ 90 M_⊙, consistent with the upper limits of our derived orbital masses, and would imply an age of ≈ 2.2 Myr.