Far-ultraviolet observations of the galactic supersoft binary RX J0019.8+2156 (QR Andromedae)

Far-Ultraviolet Spectroscopic Explorer spectra were obtained of the superso ft X-ray binary RX J0019.8+2156 (QR And) during 16 consecutive spacecraft o rbits, covering the binary orbit (P=15.85 hr) with about 0.2 phase overlap. The spectrum is dominated by strong H-2 absorption (column density similar to 10(20) g cm(-2)), which appears at the velocity different from other in terstellar absorption lines and may be partially circumbinary. This absorpt ion makes study of spectral features from the binary system difficult. The only well-detected emission lines are He II lambda 1085 and O VI lambda 103 2 (the other line of the O VI doublet, at 1037 Angstrom is largely obscured by strong H-2 absorption). The O VI shows a P Cygni profile that varies in velocity and strength with binary phase. We compare this with similar chan ges seen in Balmer line profiles. We extract the far-ultraviolet (FUV) ligh t curve and compare it with the optical light curve. There is an eclipse in both wavelength regions, but the FUV minimum lasts much longer, well beyon d the visible light egress. The FUV results are discussed in connection wit h the binary model and mass flows within the system.