It should be possible to calculate the masses of eclipsing binary stars with some accuracy, but in this case mass loss, changes in the orbital parameters, a disk obscuring the hot secondary, and doubt about the distance of the system have led to wildly varying estimates. The traditional model, from the spectroscopically derived orbit, has the masses of both stars around , which is typical for a luminous red supergiant and an early A main sequence star. An alternative model has been proposed based on the unexpected timing of the 1997 eclipse. Assuming that the change is due to mass transfer altering the orbit, dramatically lower mass values are required. In this model, the primary is a AGB star and the secondary is an B star. The spectroscopic radial velocities showing the secondary with equal mass to the primary is explained as being of a portion of the disc rather than the star itself.