Mon. Not. R. Astron. Soc., 484, 2692-2710 (2019/April-1)
Weighing Melnick 34: the most massive binary system known.
TEHRANI K.A., CROWTHER P.A., BESTENLEHNER J.M., LITTLEFAIR S.P., POLLOCK A.M.T., PARKER R.J. and SCHNURR O.
Abstract (from CDS):
Here, we confirm Melnick 34, an X-ray bright star in the 30 Dor region of the Large Magellanic Cloud, as an SB2 binary comprising WN5h + WN5h components. We present orbital solutions using 26 epochs of VLT/UVES spectra and 22 epochs of archival Gemini/GMOS spectra. Radial velocity monitoring and automated template-fitting methods both reveal a similar high-eccentricity system with a mass ratio close to unity, and an orbital period in agreement with the 155.1 ± 1 d X-ray light-curve period previously derived by Pollock et al. Our favoured solution derived an eccentricity of 0.68 ± 0.02 and mass ratio of 0.92 ± 0.07, giving minimum masses of MAsin3(i) = 65 ± 7 M☉ and MBsin3(i) = 60 ± 7 M☉. Spectral modelling using WN5h templates with CMFGEN reveals temperatures of T ∼ 53 kK for each component and luminosities of log(LA/L☉) = 6.43 ± 0.08 and log(LB/L☉) = 6.37 ± 0.08, from which BONNSAI evolutionary modelling gives masses of MA = 139+21–18 M☉ and MB = 127+17–17 M☉ and ages of ∼0.6 Myr. Spectroscopic and dynamic masses would agree if Mk34 has an inclination of i ∼ 50°, making Mk34 the most massive binary known and an excellent candidate for investigating the properties of colliding wind binaries. Within 2-3 Myr, both components of Mk34 are expected to evolve to stellar mass black holes, which, assuming the binary system survives, would make Mk34 a potential binary black hole merger progenitor and a gravitational wave source.
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
binaries: spectroscopic - stars: fundamental parameters - stars: individual: Melnick 34 - stars: massive - stars: Wolf-Rayet
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