FUSE observations were obtained in July 2003 during 1.2 cycles of the
0.76-day binary orbit of RX J0513.9-6951. Radial velocity measurements of the
broad O VI emission profile show a semiamplitude of K~26 km/sec, which is much
smaller than the value of 117 km/sec measured from 2001 FUSE data. Narrow O VI
emissions show no measurable velocity variation. The mean velocity of the broad
O VI emission is red-shifted by ~500 km/sec with respect to both the systemic
and narrow emission-line velocities. Spectral difference plots show
phase-related changes in the broad emission profile. Other phase-related
changes such as line and continuum variations are also smaller than in the 2001
spectra. We describe a moving broad absorption feature near 1020A as possible O
VI outflow associated with a precessing jet. We discuss the implications for
the stellar masses if the 2003 broad O VI velocities outline the compact star's
orbital motion.Comment: 16 pages, including 7 figures. To appear in A