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The accretion onto the black hole in the system HDE 226868/Cygnus X-1 ispowered by the strong line driven stellar wind of the O-type donor star. Westudy the X-ray properties of the stellar wind in the hard state of Cyg X-1 asdetermined with data from the Chandra High Energy Transmission Gratings. Largedensity and temperature inhomogeneities are present in the wind, with afraction of the wind consisting of clumps of matter with higher density andlower temperature embedded in a photoionized gas. Absorption dips observed inthe light curve are believed to be caused by these clumps. This workconcentrates on the non-dip spectra as a function of orbital phase. The spectrashow lines of H-like and He-like ions of S, Si, Na, Mg, Al and highly ionizedFe (Fe xvii-Fe xxiv). We measure velocity shifts, column densities, and thermalbroadening of the line series. The excellent quality of these five observationsallows us to investigate the orbital phase dependence of these parameters. Weshow that the absorber is located close to the black hole. Doppler shiftedlines point at a complex wind structure in this region, while emission linesseen in some observations are from a denser medium than the absorber. Theobserved line profiles are phase dependent. Their shapes vary from pure,symmetric absorption at the superior conjunction to P Cygni profiles at theinferior conjunction of the black hole.

astronomy and astrophysics

Chandra X-Ray Spectroscopy of the Focused Wind in the Cygnus X-1 System.  II. The Nondip Spectrum in the Low/Hard State - Modulations with Orbital  Phase