The Eclipsing Supersoft X-Ray Binary CAL 87

摘要: We present and discuss 25 spectra obtained in 1996 November, covering all phases of the CAL 87 binary system. These are superior both signal-to-noise ratio wavelength coverage to previously published data, so additional spectral features can be measured. Photometry on same nights is used confirm ephemeris for comparison with light curves from previous years. Analysis color variation through orbital cycle has been carried out using archival MACHO data. When a barely resolved red field star accounted for, there no (V-R) variation, even eclipse. There have substantial changes depth minimum since 1988; it decreased more than 0.5 mag last several The radial velocities also found vary not only 0.44 day orbit but over timescales year or more. Possible interpretations these long-term discussed. contain phase-modulated Balmer absorption lines seen, apparently arising gas flowing region compact star. emission-line strengths phase indicate that azimuthal variations accretion disk structures. Radial give different amplitudes phasing, making determination stellar masses difficult. All solutions companion considerably less massive degenerate absorption-line correspond ~1.4 M☉ ~0.4 mass donor. However, strong He II emission much accreting star, MX > 4 M☉.