Spectroscopic evidence for photo-ionization wakes in Vela X-1 and 4U 1700-37

We present high-resolution, high signal-to-noise spectra of HD77581 and HD153919, the optical counterparts of the high-mass X-ray binaries Vela X-1 and 4U 1700-37, respectively. The spectral lines exhibit variations related to the presence of the X-ray source in unprecedented detail. For HD77581, at inferior conjunction of the neutron star (phi = 0.5), an extra absorption component appears in the blue wing of the absorption lines. This feature first increases in strength (up till binary phase phi = 0.6) whereafter it slowly fades; at the same time it shifts towards higher negative velocities. The observed velocities are low: from -50 km s(-1) at phi = 0.5 up to -250 km s(-1) at phi = 0.8. For HD 153919, the observed variations are similar in character, but stronger and more complicated. For both systems we find significant variations in the emission part of the P Cygni-type profiles. Based on the phase dependence of the velocity and strength of the absorption component, we show that it is unlikely that this component is related to an accretion wake, or to a gas stream through the inner Lagrangean point. These structures, although most likely present in the system, are not capable of providing sufficient obscuration of the supergiant, that would give the observed absorption. We suggest that this absorption component results from the presence of a photo-ionization wake in the system that trails the X-ray source. Furthermore, we predict that variations in X-ray luminosity will induce changes in the geometrical structure of the photo-ionization wake which might explain the observed orbit-to-orbit variations

Far Ultraviolet Observations of the High-Mass X-Ray Binary 4U1700-37/HD153919

The high-mass X-ray binary 4U1700-37/HD153919 has been observed with FUSE to study the effect of the X-ray source on the stellar wind of the primary. Phase-dependent changes in the wind lines have been observed, indicating the creation of an X-ray ionization zone in the stellar wind. The X-ray luminosity of 4U1700-37 ionizes much of the wind and leaves a Stromgren zone. This disrupts the resonance-line acceleration of the wind in portions of the orbit, quenches the wind and stalls the mass flow. This is the so-called Hatchett-McCray effect that had been predicted for 4U1700-37, but was not previously detected