Melnick 33Na: a very massive colliding-wind binary system in 30 Doradus

We present spectroscopic analysis of the luminous X-ray source Melnick 33Na (Mk 33Na, HSH95 16) in the Large Magellanic Cloud (LMC) 30 Doradus region (Tarantula Nebula), utilizing new time-series Very Large Telescope/Ultraviolet and Visual Echelle Spectrograph spectroscopy. We confirm Mk 33Na as a double-lined O-type spectroscopic binary with a mass ratio q = 0.63 +/- 0.02, e = 0.33 +/- 0.01, and orbital period of 18.3 +/- 0.1 d, supporting the favoured period from X-ray observations obtained via the Tarantula - Revealed by X-rays survey. Disentangled spectra of each component provide spectral types of OC2.5 If* and O4 V for the primary and secondary, respectively. Unusually for an O supergiant the primary exhibits strong C iv 4658 emission and weak N v 4603-20, justifying the OC classification. Spectroscopic analysis favours extreme physical properties for the primary (T-eff = 50 kK, log L/L-circle dot = 6.15) with system components of M-1 = 83 +/- 19 M-circle dot and M-2 = 48 +/- 11 M-circle dot obtained from evolutionary models, which can be reconciled with results from our orbital analysis (e.g. M(1)sin (3)i = 20.0 +/- 1.2 M-circle dot) if the system inclination is similar to 38 degrees and it has an age of 0.9-1.6 Myr. This establishes Mk 33Na as one of the highest mass binary systems in the LMC, alongside other X-ray luminous early-type binaries Mk34 (WN5h+WN5h), R144 (WN5/6h+WN6/7h), and especially R139 (O6.5 Iafc + O6 Iaf).

Automated summary

In this study, spectroscopic analysis was conducted on the luminous X-ray source Mk 33Na in the Large Magellanic Cloud using new time-series spectroscopy. The analysis confirmed that Mk 33Na is a double-lined O-type spectroscopic binary with extreme physical properties, making it one of the highest mass binary systems in the LMC.