OGLE-LMC-ECL-09937: The Most Massive Algol-Type Binary System with a Mass Measurement Accurate to 2%

This paper presents a detailed analysis of the light and radial velocity curves of the semi-detached eclipsing binary system OGLE-LMC-ECL-09937. The system is composed of a hot, massive and luminous primary star of a late-O spectral type, and a more evolved, but less massive and luminous secondary, implying an Algol-type system that underwent a mass transfer episode. We derive masses of 21.04±0.34 M<SUB>☉</SUB> and 7.61±0.09 M<SUB>☉</SUB> and radii of 9.93±0.06 R<SUB>☉</SUB> and 9.18±0.04 R<SUB>☉</SUB>, for the primary and the secondary component, respectively, which make it the most massive known Algol-type system with masses and radii of the components measured with <2% accuracy. Consequently, the parameters of OGLE-LMC-ECL-09937 provide an important contribution to the sparsely populated high-mass end of the stellar mass distribution, and an interesting object for stellar evolution studies, being a possible progenitor of a binary system composed of two neutron stars.