Presentation #308.07 in the session “Stars III”.
The best measurements of stellar masses come from determination of orbits where we can measure the inclination to high precision. For evolved massive stars, it is even more difficult to measure the orbital inclination, and can usually only be done with long-baseline optical interferometry. Until recently, there were only two known Wolf-Rayet stars with visual orbits. As a result of a recent professional-amateur collaboration, we have measured the orbit of WR 140 to high precision, where we now have orbital elements with a precision of 1-2%. We also have measured the first visual orbit of a nitrogen-rich WR star, WR 133. With both of these systems measured, we have begun to test our measured orbits and stellar masses against spectroscopic models for the stars as well as evolutionary models. Our team has also been working on measuring the orbits of the dust-producing binary WR 137, and another nitrogen-rich system, WR 138.