The galactic supersoft X-ray binary RX J0925.7-4758 (MR Velorum)

New simultaneous photometric and spectroscopic observations of the supersof t X-ray binary RX J0925.7-4758 (MR Vel) have been obtained. These confirm t he unusually long orbital period near 3.8 days. An accurate period is deter mined based on several years of photometric observations. Short-term photom etric variability (similar to 0.25 days) is also present, but it does not a ppear to be strictly periodic. The spectroscopic behavior reveals large-amp litude He II and H velocity curves, indicating that the system is viewed fr om a moderately high inclination angle. Masses for the component stars are derived. Evidence of a high-velocity jet (outflow velocity of 5350 km s(-1) ) is present at H alpha. Its radial velocity curve is very similar to the d isk emission lines, suggesting the jet is formed near the compact star. A n ew model for the system is presented.