Dynamical masses for the Large Magellanic Cloud massive binary system [L72] LH 54-425

We present results from an optical spectroscopic investigation of the massive binary system [L72] LH 54-425 in the LH 54 OB association in the Large Magellanic Cloud. We revise the ephemeris of [L72] LH 54-425 and find an orbital period of 2.24741 +/- 0.00004 days. We find spectral types of O3 V for the primary and O5 V for the secondary. We made a combined solution of the radial velocities and previously published V-band photometry to determine the inclination for two system configurations, i = 52(-3)(+2) degrees for the configuration of the secondary star being more tidally distorted and i = 55 degrees +/- 1 degrees for the primary as the more tidally distorted star. We argue that the latter case is more probable, and this solution yields masses and radii of M-1 = 47 +/- 2 M-circle dot and R-1 = 11.4 +/- 0.1 R-circle dot for the primary, and M-2 = 28 +/- 1 M-circle dot and R-2 = 8.1 +/- 0.1 R-circle dot for the secondary. Our analysis places LH 54-425 among the most massive stars known. Based on the position of the two stars plotted on a theoretical HR diagram, we find the age of the system to be similar to 1.5 Myr.