We present a high-precision I -band light curve for the Wolf-Rayet binary WR 20a , obtained as a sub-project of the Optical Gravitational Lensing Experiment .
Rauw et al .
have recently presented spectroscopy for this system , strongly suggesting extremely large minimum masses of 70.7 \pm 4.0 \mbox { M$ { } _ { \odot } $ } and 68.8 \pm 3.8 \mbox { M$ { } _ { \odot } $ } for the component stars of the system , with the exact values depending strongly on the period of the system .
We detect deep eclipses of about 0.4 mag in the light curve of WR 20a , confirming and refining the suspected period of P = 3.686 days and deriving an inclination angle of i = 74.5 \pm 2.0 \deg .
Using these photometric data and the radial velocity data of Rauw et al. , we derive the masses for the two components of WR 20a to be 83.0 \pm 5.0 \mbox { M$ { } _ { \odot } $ } and 82.0 \pm 5.0 \mbox { M$ { } _ { \odot } $ } .
Therefore , WR 20a is confirmed to consist of two extremely massive stars and to be the most massive binary known with an accurate mass determination .