  We have analyzed a Chandra HETGS spectrum of the Galactic black hole Cygnus
X-1, obtained at a source flux which is approximately twice that commonly
observed in its persistent low-intensity, spectrally-hard state. We find a
myriad of absorption lines in the spectrum, including Ly-alpha lines and
helium-like resonance lines from Ne, Na, Mg, and Si. We calculate a
flux-weighted mean red-shift of ~100 km/s and a flux-weighted mean velocity
width of 800 km/s (FWHM) for lines from these elements. We also detect a number
of transitions from Fe XVIII-XXIV and Ni XIX-XX in absorption; however, the
identification of these lines is less certain and a greater range of shifts and
breadth is measured. Our observation occurred at a binary phase of phi = 0.76;
the lines observed are consistent with absorption in an ionized region of the
supergiant O9.7 Iab companion wind. The spectrum is extremely complicated in
that a range of temperatures and densities are implied. Prior Chandra HETGS
spectra of Cygnus X-1 were obtained in a similar transition state (at phi =
0.93) and in the low/hard state (at phi= 0.84). Considered together, these
spectra provide evidence for a companion wind that is focused as it flows onto
the black hole primary in this system.
