  A detailed analysis of simultaneous photometric and spectroscopic
observations of the optical counterpart of the LMC "supersoft" X-ray source RX
J0513.9-6951 (identified with HV 5682) is presented. The spectrum is dominated
by He II emission lines and H + He II blends; no He I is observed but several
higher ionization emission features, especially O VI (3811, 3834, and 5290A)
are prominent. Radial velocity measurements suggest a binary period of 0.76
days. If the small velocity amplitude, K~11 km/s, is interpreted as orbital
motion, this implies that the binary system contains a somewhat evolved star
plus a relatively massive compact object, viewed nearly pole-on. No orbital
photometric variations were found, although irregular brightness changes of
~0.3 mag occurred. Unusual emission lines are observed which cannot be
identified except as high velocity (4000 km/s) bipolar outflows or jets. These
outflows are seen in H and He II at the same positive and negative velocities.
They were relatively stable for periods of ~5 days, but their velocities appear
to have been ~250 km/s smaller in 1992 than in 1993 or 1994.
