The black hole high-mass X-ray binary Cygnus X-1 is powered by accretion
of the stellar wind of its supergiant companion star HDE 226868.
As the donor is close to filling its Roche lobe,
its wind is therefore not symmetric,
but strongly focused towards the black hole.
Chandra-HETGS observations allow for an investigation of this wind's properties. In the hard state, absorption lines of H- and He-like atoms reveal a highly photoionized wind. As different parts of the wind can be probed at different orbital phases of the binary system, we investigate the structure and dynamics of the wind by comparing observations at the prominent orbital phases phi=0, 0.2, 0.5, and 0.75.
In addition, we study transient dips. During these absorption events, caused by density inhomogeneities in the wind, lower ionization stages are detected.