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 5290 Å), are prominent. Radial velocity measurements suggest a binary period of 0.76 days. If the small velocity amplitude, K ∼ 11 km s⁻¹1, 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 that cannot be identified except as high-velocity (4000 km s⁻¹) 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 about 5 days, but their velocities appear to have been about 250 km s⁻¹ smaller in 1992 than in 1993 or 1994.
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Crampton et al. (1996) studied this question.