  The microquasar SS 433 is an interacting massive binary consisting of an
evolved mass donor and a compact companion that ejects relativistic jets. The
mass donor was previously identified through spectroscopic observations of
absorption lines in the blue part of the spectrum that showed Doppler shifts
associated with orbital motion and strength variations related to the orbital
modulation of the star-to-disk flux ratio and to disk obscuration. However,
subsequent observations revealed other absorption features that lacked these
properties and that were probably formed in the disk gas outflow. We present
here follow-up observations of SS 433 at orbital and precession phases
identical to those from several previous studies with the goals of confirming
the detection of the mass donor spectrum and providing more reliable masses for
the two system components. We show that the absorption features present as well
as those previously observed almost certainly belong to the mass donor star,
and we find revised masses of 12.3 +/- 3.3 and 4.3 +/- 0.8 M(sun) for the mass
donor and compact object, respectively.
