Chandra High Energy Transmission Grating Spectrometer ( HETGS ) observations of the extremely luminous and violent X-ray binary Cir X-1 reveal many X-ray emission lines showing broad P Cygni profiles .
These are from H-like and He-like ions of Ne , Mg , Si , S , Ar , and Fe .
The lines originate in a high-velocity ( up to 2000 km s ^ { -1 } ) outflow , which may be an accretion disk wind .
Cir X-1 has a radio jet , and during some periastron passages of the neutron star ( orbital phase = 0.0 ) , it flares at radio , infrared and X-ray wavelengths .
The X-ray P Cygni profiles were observed during this phase , where we also expect the strongest mass transfer from the companion star .
We present new results on the time variability of the P Cygni profiles and discuss their general importance .