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 LMC 30 Doradus region (Tarantula Nebula), utilising new time-series VLT/UVES spectroscopy. confirm Mk as a double-lined O-type binary with mass ratio $q = 0.63 \pm 0.02$, $e 0.33 0.01$ and orbital period $18.3 0.1$ days, supporting favoured from observations obtained via Tarantula -- Revealed by X-rays (T-ReX) survey. Disentangled spectra each component provide spectral types OC2.5 If* O4 V for primary secondary respectively - unusually an O supergiant exhibits strong CIV 4658 emission weak NV 4603-20, justifying OC classification. Spectroscopic favours extreme physical properties ($T_{\rm eff} 50$ kK, $\log L/L_{\odot} 6.15$) system components $M_{1} 83 19 M_{\odot}$ $M_{2} 48 11 evolutionary models, which can be reconciled results our (e.g. \sin^3 i 20.0 1.2 M_{\odot}$) if inclination is $\sim 38^{\circ}$ it has age 0.9 to 1.6 Myr. This establishes one highest systems LMC, alongside other early-type binaries Mk34 (WN5h+WN5h), R144 (WN5/6h+WN6/7h) especially R139 (O6.5\,Iafc+O6\,Iaf).