Six supersoft X-ray binaries: System parameters and twin-jet outflows

A comparison is made between the properties of CAL 83, CAL 87, RX J0513.9-6 951, 1E 0035.4-7230 (SMC 13), RX 50019.8 + 2156, and RX J0925.7-4758, all s upersoft X-ray binaries. Spectra with the same resolution and wavelength co verage of these systems are compared and contrasted. Some new photometry is also presented. The equivalent widths of the principal emission lines of H and He II differ by more than an order of magnitude among these sources, a lthough those of the highest ionization lines (e.g., O VI) are very similar . In individual systems, the velocity curves derived from various ions ofte n differ in phasing and amplitude, but those whose phasing is consistent wi th the light curves (implying the Lines are formed near the compact star) g ive masses of similar to 1.2 M-. and similar to 0.5 M-. for the degenerate and mass-losing stars, respectively. This finding is in conflict with curre ntly prevailing theoretical models for supersoft binaries. The three highes t luminosity sources show evidence of "jet" outflows, with velocities of si milar to 1-4 x 10(3) km s(-1). In CAL 83 the shape of the He II lambda 4686 profile continues to show evidence that these jets may precess with a peri od of similar to 69 days.