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New spectroscopic observations of the LBV/WR multiple system HD5980 in theSmall Magellanic Cloud are used to address the question of the masses andevolutionary status of the two very luminous stars in the 19.3d eclipsingbinary system. Two distinct components of the N V 4944 A line are detected inemission and their radial velocity variations are used to derive masses of 61and 66 Mo, under the assumption that binary interaction effects on this atomictransition are negligible. We propose that this binary system is the product ofquasi-chemically homogeneous evolution with little or no mass transfer. Thus,both of these binary stars may be candidates for gamma-ray burst progenitors oreven pair instability supernovae. Analysis of the photospheric absorption linesbelonging to the third-light object in the system confirm that it consists ofan O-type star in a 96.56d eccentric orbit (e=0.82) around an unseen companion.The 5:1 period ratio and high eccentricities of the two binaries suggest thatthey may constitute a hierarchical quadruple system.

The HD5980 multiple system: Masses and evolutionary status