Far-Ultraviolet Observations of the Galactic Supersoft Binary RX J0019.8+2156 (QR Andromedae)

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Abstract
Far-Ultraviolet Spectroscopic Explorer spectra were obtained of the supersoft X-ray binary RX J0019.8+2156 (QR And) during 16 consecutive spacecraft orbits, covering the binary orbit (P = 15.85 hr) with about 0.2 phase overlap. The spectrum is dominated by strong H2 absorption (column density ~1020 g cm-2), which appears at the velocity different from other interstellar absorption lines and may be partially circumbinary. This absorption makes study of spectral features from the binary system difficult. The only well-detected emission lines are He II λ1085 and O VI λ1032 (the other line of the O VI doublet, at 1037 Å, is largely obscured by strong H2 absorption). The O VI shows a P Cygni profile that varies in velocity and strength with binary phase. We compare this with similar changes seen in Balmer line profiles. We extract the far-ultraviolet (FUV) light 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 beyond the visible light egress. The FUV results are discussed in connection with the binary model and mass flows within the system.
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